"Grantville Gazette.Volume XIX" - читать интересную книгу автора (Flint Eric)

Better Foundations, Part 1: An Introduction to Concrete
Iver P. Cooper

Concrete-"Liquid Stone"-has made possible many innovations in architecture. Yet concrete is no Space Age wunderkind; it has its roots in antiquity. Concrete, albeit of a kind inferior to the modern product, was used by the Romans in the construction of the Pantheon, which has endured since the time of the Emperor Hadrian.

While the Roman concrete structures endured, concrete technology languished after the fall of Rome. The seventeenth century is still the Dark Ages so far as concrete is concerned. But the up-timers will bring about a "Concrete Renaissance" in short order.

What Is Concrete?

Concrete is a composite material, made by combining an aggregate (a hard particulate material) and a cement (a matrix forming material) with enough water to cause the cement to set and bind the aggregate together. The binding is the result of the chemical reaction of the cement with the water. The aggregate is a combination of fine aggregate (sand) and coarse aggregate (e.g., gravel).

Mortar is a paste-like mixture of sand, a binder (e.g., cement) and water. It doesn't contain coarse aggregate, but of course the mortar is used to bind together cut stones or bricks, and to fill in gaps between them. Those stones and bricks are much larger than the coarse aggregate of concrete.

Concrete and Cement in Canon

We know that when Grantville made its involuntary journey into seventeenth century Germany, some concrete construction came along for the ride. Mark Huston's "Gearhead" (Grantville Gazette, Volume9) mentions "a pair of concrete bridges." There is a concrete floor in the building which Chad Jenkins has converted to a shop for washboard manufacture, see Rittgers, "Von Grantville" (Grantville Gazette, Volume7). There is also a concrete floor at the farm where Harmon Manning suffered his ultimately fatal fall, see Ewing, "An Invisible War" (Grantville Gazette, Volume 2). Pam Miller has a concrete porch, see Vance, "Protected Species" (Grantville Gazette, Volume13). The high school has a concrete "awning" over the entrance, see Flint, 1632, Chapter 11. And there is at least a concrete slab in the Grantville city jail, see Weber, "The Company Men" (Grantville Gazette, Volume2).

Concrete was used in the displaced West Virginia mine featured in Mark Huston's "Twenty-eight Men" (Grantville Gazette, Volume10), in a wall separating the working and non-working sections of the mine. The wall was built out of concrete blocks, and thus, even if the wall was assembled after the Ring of Fire, the blocks themselves may have been cast up-time.

Since the Ring of Fire, there has been some new concrete work. Sometime before March 1632, Delia Higgins sold the remaining dolls in her collection, and used the proceeds for two projects. The first was building a warehouse. Her intent was to build a concrete warehouse, a "work of art", with "the best combination of up-time and down-time construction techniques possible." Gorg Huff, "Other People's Money" ( Grantville Gazette, Volume 3)(timeframe March-October 1632). What she got was, "if not exactly a work of art," a structure which "was functional, and very large." It was built with "fairly standard down-time construction techniques, with concrete pillars added for support."

In the process of trying to persuade the high school chemistry teacher, Alexandra Selluci, to help with the warehouse project, Delia got talked into becoming the "sugar grandma" for the Grantville High Tech Center's "brand new concrete research program, complete with structural engineering courses where the teachers were half a chapter ahead of the students, or sometimes half a chapter behind." In Delia's opinion, "the kids that had gone into concrete were phenomenal. They were about four to one down-timer to up-timer, about average for the high school. They wanted to build things. Great big things, dams, skyscrapers, and roads, and were willing to work at it."

Later in OPM, Delia reveals that she saw the warehouse as a stepping stone to a grander project, the Higgins Hotel. "The concrete program at the school was developing a group of young people who could make structural concrete, and form it into structures that would support tremendous weight. Hiring Michel Kappel was done both to get a down-time builder familiar with up-time building techniques, and as favor for Karl Schmidt. Claus Maurer was a master builder with more experience than Herr Kappel, but again, part of the reason for hiring him was to get him familiar with the available up-time tech. It wasn't her fault that they had fought with each other and with the teachers at the tech center and Carl over at Kelly Construction. Besides, materials were so expensive that the cheapest halfway decent material was quarried granite from the ring wall."

By December, 1631, the high schoolers are working on "some sort of concrete project," and mortar is available. See Huff and Goodlett, "Birdie's Village" (1634: The Ram Rebellion). In Cooper, "Stretching Out, Part One: Second Starts" (Grantville Gazette, Volume11), there is a passing reference to an equally mysterious "concrete project" which is apparently looking for venture capital in July 1633.

By July, 1633, the conservatory at the new hospital has "cement paths" (people often confuse cement and concrete, cement is a component of concrete). See Ewing, "An Invisible War" (Grantville Gazette, Volume2). I can't help but wonder whether the hospital itself, a three story building completed a year earlier, is of concrete construction.

The Higgins Hotel is at least partially built as of summer 1633, see Cooper, "Stretching Out Part 1" (Grantville Gazette, Volume 11) and "The Chase" (Ring of Fire II), but the stories don't say whether it used concrete.

Somewhat inconsistently, in the Friends' "Burgers, Fries, and Beer" (Grantville Gazette, Volume7), set in January 1634, Julio Sanabria wonders where he would get the cement, fire clay, and lime he needs in order to put his masonry tools to use. You can't make concrete without cement, and concrete was already being made.

The Grid lists a concrete company, started by William Roberts and his brother Ronald Chapman. Roberts is a managerial type and Chapman worked "for a company in Fairmont as a foreman of a team that built pre-fab metal buildings." The relationship of this company to the high school concrete research lab is unclear. It is possible that the company existed only on paper.

Concrete and Cement Knowhow

Grantville is in do-it-yourselfer territory. There are also going to be a fair number of "how-to" manuals (some even read by their owners), as well as homeowners with hands-on experience making (and repairing, especially those who didn't read the manuals) concrete flatwork (floors, driveways, patios, porches, walkways), foundations, walls and even outdoor furniture. But no pink concrete flamingos, I hope.

In addition, Grantville had at least two general contractors before the RoF, Happy Acres and Home Center (Grid). I doubt that either of them has built a skyscraper, and there isn't much concrete construction in Mannington, but chances are reasonable that they have employees who have worked with concrete.

There were also construction technology courses offered at the Marion County Technical Center. I have no idea which courses were offered in 1999-2000, but the current catalog includes "Basic Masonry and Landscaping," "Foundations and Framing," "Fundamentals of Building Construction," "Masonry and Plumbing," and "Construction Systems."

The up-timers with college engineering degrees are most likely to have attended either West Virginia University or Fairmont State. WVU offers a degree in civil engineering, with undergraduate elective courses in Civil Engineering Materials (CE310), Concrete and Aggregates (CE412), Construction Methods (CE413), Construction Engineering (CE414), Advanced Concrete Materials (CE416), and Reinforced Concrete Design (CE 462). While there is no guarantee that any particular civil engineer in Grantville has taken any of these courses, it is certainly possible.

In any event, there are going to be up-timers who know how to estimate how much concrete is needed for a job, prepare the forms to receive the concrete, put down the steel reinforcements, monitor the pour, and cure the concrete. A smaller number (those who didn't just use ready-mix) will know how to proportion concrete, that is, decide the proper ratios of cement, aggregates and water.

What is less certain is that the up-timers will know, firsthand, how to make cement. Cement is usually bought ready-made and even a building contractor needn't have firsthand knowledge of cement manufacture. If any up-timers do, it is probably because they worked in a cement plant outside Grantville. An EPA ranking of Portland cement plants, by size, listed Capitol Cement, in Martinsburg, in 29th place. That was the only West Virginia listing. (EPA) However, I have found a 1976 reference to the Marquette Cement Manufacturing Co. plant near Fairmont (PSC).

Grantville, according to canon, has pretty much every encyclopedia you can imagine. "Not just the great one, the 1911 Britannica, which they guarded so carefully, but all of them-the later Britannica editions, the World Book and Americana, Columbia, and Funk and Wagnalls, old and new, large and small." (Flint and DeMarce, 1635: The Bavarian Crisis, Chap. 5). My understanding is that the public library has the Encyclopedia Americana, and both the modern and the 1911 editions of the Encyclopedia Britannica. The high school has the World Book, and the junior high, the Collier's. There's also a nearly complete ninth edition of the Britannica, and, I suspect, several CDROM-based encyclopedias, most likely Compton's and Encarta. Besides having articles on concrete and cement, these encyclopedias have related tidbits scattered across their many volumes, which a sufficiently diligent researcher can uncover.

Grantville is modeled on Mannington, West Virginia, and I have checked the high school and public library holdings for more specific works. North Marion High School has the Time-Life Masonry (1977). It and the public library have Kicklighter's Modern Masonry: Brick, Block, Stone (1977).

There may also be other relevant books. For example, the high school has Trachtenberg's Brooklyn Bridge: Fact and Symbol (1979), and Stevens'

Dam: An American Adventure, and concrete was used in their construction.

There is no easy way of determining what books might be in private (home and work) libraries, or at the Voc-Ed Center. Bear in mind that any engineer almost certainly has kept all of his or her college engineering textbooks. Even a retired engineer would hesitate to part with them.

There is also a documented relationship between the North Marion High School of Mannington, WV and LaFarge, an Ohio cement company. LaFarge gave the high school a $300,000 atomic absorption spectrophotometer in 1997 (Zeller). Surely the student research projects developed using the AAS would have included ones dealing with cement. And perhaps the school got some cement technology texts along with the AAS.

Down-timers' Cement and Concrete Technology

Previously, I said that Roman concrete was inferior to modern concrete, and I should explain why. First, it had a compressive strength of only 2800-3000 psi (RomanConcrete. com; Spratt), comparable to the "low end" of the strength range of modern concrete. Secondly, it was not reinforced.

Many sources state that concrete technology was "lost" in the Middle Ages. But I very deliberately used the term "languished" in the introduction. The Normans used concrete in the construction of parts of Reading Abbey (1130), the White Tower of London, and other structures. (Davidovits, May, Ferguson). But Ferguson comments that "concrete in the hands of the Normans was a total failure," and lists a dozen Norman concrete towers which fell down.

Mukerji asserts that the Roman formula for "hydraulic cement" (that is, one which hardens in contact with water) wasn't lost, but rather remained "tacit knowledge" among masons and military engineers, at least in limited areas, so that it was known in, e.g., seventeenth century France. Idorn (38) says that use of hydraulic cement was monopolized by the authorities; e.g., Christian IV of Denmark imported trass (from Dutch merchants) for making hydraulic mortars for his palaces and castles.

In 1568, the French architect Philibrt de L'Orme taught preparing a mortar from burnt quicklime, river sand, pebbles and water, with the pebbles being "of all sizes." (Jackson 23).

A crude form of concrete was apparently used as ballast between the frames in the galleon Nuestra Senora de Atocha (1620)(Crisman).

The Advantages of Concrete

Concrete competes as a building material with steel, wood, and brick, and as a road pavement with asphalt. Concrete has numerous advantages as a structural material.

On-site Fabricability. The 1911 Encyclopedia Britannica (1911EB) says that concrete has "the immense advantage over natural stone that it can be easily molded while wet to any desired shape or size." It has similar advantages over steel and wood. Steel can be cast only at a high temperature and wood not at all. Steel can be bent but only through persistent application of great force, and wood can be bent only gingerly and slowly, to avoid breakage.

Convenience. "Its constituents can be obtained in almost any part of the world, and its manufacture is extremely simple." (1911EB).

Compressive strength. Like natural stone, it possesses great resistance to compression; its compressive strength is usually 4,000-15,000 pounds per square inch (psi), or higher, of cross-sectional area. (Levy/Down, 279). (In 2000, concrete with a strength of 8,000 psi or higher was considered "high strength"; Nilson 50.) The compressive strength of wood, parallel to the grain, is comparable, perhaps 6,000-7,500 psi, but perpendicular to the grain, wood is much weaker, perhaps 450-1050 (Green). As for natural stones, granites and marbles are stronger (up to 30,000 psi), and soft limestone weaker (700 psi)(Cowan 105).

Strength-to-Cost. The figure-of-merit (two-thirds power of strength, divided by cost per unit volume) is 80 for concrete, 60 reinforced concrete, 80 wood, 45 brick and stone and only 21 steel (Ashby 100).

Stiffness-to-Cost. The figure of merit (half power of Young's modulus of elasticity divided by unit cost) is 40 for concrete, 20 reinforced concrete and brick, 15 wood and stone, and only 3 steel.

Stiffness-to-Weight. For columns which fail by buckling, the figure of merit is the half power of Young's modulus, divided by the density. Steel is 59, but concrete is almost as good, 49 (Gordon 321). So by making the columns just a little thicker, you can use reinforced concrete instead of steel, saving perhaps 99% in steel consumption.

Fire resistance. Concrete itself is non-combustible, and has a thermal conductivity about 5% that of steel (PCA). However, it should be noted that with reinforced concrete, the reinforcing steel becomes ductile at high temperature, and since it presumably is there to provide tensile strength, the result may, ultimately, be structural failure.

Biological and chemical resistance. Wood rots, and is attacked by termites (or, at sea, teredo worms). Steel corrodes. Concrete isn't vulnerable to these threats, but it can be attacked by acids, sulfates and chlorides (from deicing salts). Special concretes are used for construction in the vicinity of high-sulfate soil (or groundwater). And of course the reinforcement in reinforced concrete can corrode if corrosive agents can reach it.

Temperature stability. A concrete wall or floor will absorb heat during the day and re-radiate it at night. That's true of any material, but concrete has a greater "thermal mass" than wood (HousingZone). (An interesting variation is a panel with a lightweight thermal insulating material sandwiched between layers of concrete.)

Soundproofing. The airborne sound insulation of a concrete first floor is 9-22 dB higher than that of a timber floor ("Going Up").

Disadvantages of Concrete

Low Tensile strength. Unfortunately, concrete's tensile strength (resistance to being pulled apart) is only about 10% of its compressive strength (Twelvetrees 41); Gordon (44) quotes a value of 600 psi (whereas commercial mild steel is 60,000 and high tensile engineering steel is 225,000). Because plain (unreinforced) concrete is strong in compression and weak in tension, it can be used in columns, arches and domes, but not in beams (horizontal structural members).

Low Compressive Strength-to-Weight Ratio. If we divide the compressive strength by the density (~2), we get values of about 2000-7500 psi/unit weight for unreinforced concrete. For steel, despite its greater density (~7.5), we get values of 4800-8000 (Twelvetrees 31).

Flexural strength. Concrete is not good at resisting failure from bending; its flexural strength is perhaps 12-20% compressive strength. (Cadman).

Brittleness. Concrete is also brittle, that is, once cracked it is easily fractured. The "fracture toughness" of concrete is 0.2-1.4, compared to 0.7-0.8 for soda lime glass and 50 for steel (Matt Gordon).

Shrinkage and Expansion. Freshly laid concrete shrinks as a result of the chemical reactions between its ingredients, the evaporation of water from the concrete, and the rising of air voids to its surface. Once hardened, concrete expands and shrinks in response to changes in temperature and moisture levels. Of course, all these dimensional changes stress the concrete, perhaps causing cracks.

Fortunately, if concrete is reinforced with a material, like steel, which is strong in tension, and ductile, it becomes an all-purpose structural material.

CONCRETE COMPOSITION

We start by reviewing the ingredients of concrete: cement, aggregate and water. Cement itself is a complex material. Once we know what goes into both concrete and cement, we can consider how concrete is mixed, laid, cured and tested.

Cement

Cement, in essence, is a binding agent. It can be used in mortar or in concrete. Cements are traditionally classified as being either hydraulic (those which, at least after setting, are resistant to water) or non-hydraulic (those which must be kept dry). The term "hydraulic" also has come to imply that when first mixed with water to make concrete, the cement reacts chemically with the water, forming hydrates which help bind the aggregate. (These hydrates are themselves insoluble in water, thus conferring the water resistance.)

The pozzolanic cements result from the mixture of a source of calcium (usually lime) and a source of silica (possibly also containing alumina). The lime is derived by heating chalk or limestone (calcium carbonate); the process is called calcination. The lime may be either the highly reactive quicklime (calcium oxide) or the somewhat less reactive slaked (hydrated) lime (calcium hydroxide), the latter being obtained by reacting quicklime with water.

Portland cements likewise are derived from a mixture of calciumand silica-rich materials, but this mixture is subjected to a further calcination at a high temperature.

The natural cements are prepared from a source material which naturally contains both lime and silica. Hence, no mixing step is needed. Like Portland cements, it is calcinated, but at a lower temperature than that typical in Portland cement production.

High-alumina cements are made from limestone and low-silica bauxite; they were invented in 1908.

In the twentieth century, the commercially dominant hydraulic cement was "Portland cement." However, we will first discuss the older pozzolanic cements.

Pozzolanic Cements

A pozzolan is a source of silica (silicon dioxide) which can react with lime to form a cement. A material can contain silica but not be useful as a pozzolan. For example, most sands contain silica, yet are unreactive. Moore says that this is because they have a tightly bound structure which frustrates the reaction. (Sands are used in concrete, but as aggregate.)

The ancient Roman cement, which is pozzolanic in nature, is described in Marcus Vitruvius Pollio's De Architectura, Book II. This classic text became available to Europeans, in Latin, Italian and German printed translations, in the fifteenth and sixteenth centuries. There is also Sir Henry Wotton's The Elements of Architecture (1624), which is derived from Vitruvius.

The first known post-Roman use of a pozzolanic cement was in Italy. The Venetians used the "black lime of Abetone" in the fifteenth century, and the Roman pozzolana was used by Fra Giocondo in the mortar of the pier of the Pont de Notre Dame in Paris (1499). (Giocondo published an edition of Vitruvius in 1511.)

Vitruvius refers to "rubble work," with stones mortared together. In chapters 4-5, Vitruvius says that one may mix sand (a silica source) with lime to make mortar. He recommends use of three parts sand to one of lime when the sand is from a pit, and a two to one ratio if the sand is from sea or river. According to Moore, Vitruvius' "pit sand" is actually volcanic ash, specifically, pozzolana.

Pozzolana. The eponymous pozzolana is a volcanic ash discovered at Pozzoli, near Vesuvius, but also found elsewhere in Italy (including near Rome). The 1911 Encyclopedia Britannica article on "cements" gives compositions for both Neapolitan (27.8% soluble silica, 5.68% lime) and Roman (32.64%; 4.06%) "Pozzuolana."

Vitruvius, in chapter 6, says: "There is a species of sand which, naturally, possesses extraordinary qualities. It is found about Baiae and the territory in the neighborhood of Mount Vesuvius; if mixed with lime and rubble, it hardens as well under water as in ordinary buildings." This "sand" is obviously a pozzolanic ash. Herring points out that this pozzolan could react with lime because it was already calcined by the volcano.

Santorin earth. This is really a volcanic tuff, which blankets the Greek island of Santorini (Thera). It is about 64% silica and 3.5% lime (USBM). It was used in ancient Greek mortar (Lea 3) and, millenia later, it was still exported for use in making pozzolanic cement (1911EB "Santorin").

Pottery shards were ground up, in antiquity, to produce a pozzolan. Pottery is made by heating (calcinating) clay, and clay is rich in silicate minerals. Brick could be recycled in a similar way. Vitruvius says that if mortar is made from river or sea sand, it is improved by addition of one-third part of ground potsherds.

A modern clay-derived pozzolan is metakaolin. It is obtained by calcinating the clay mineral kaolinite, an aluminosilicate clay mineral. Metakaolin is one of the most reactive pozzolans.

Pumice is a very light, highly porous igneous rock, with a silica content of 60-75%. In 1911, pumice was chiefly obtained for commercial use from the Lipari Islands north of eastern Sicily, and especially from Monte Pelato and Monte Chirica. The Lipari Islands have exported pumice since antiquity, and Canneto is the center of the pumice trade.

Trass, a Germanic pozzolan, is a tuff (rock derived from volcanic ash) found in the Eifel, a volcanic region of Germany lying between the Rhine and Moselle rivers (1911EB). The article on "Trass" specifically mentions the Brohl and Nette valleys, and the town of Andernach. Eckel (635) says that trass occurs along the Rhine, from Koln to Coblenz, and that the towns of Brohl, Kruft, Plaidt and Andernach near Coblenz are significant players in the trass industry. 1911EB characterizes it as 19% soluble, 50% insoluble silica. It is lacking in lime so it is less reactive than pozzolana. Nonetheless, the Romans recognized its resemblance to the Vesuvian material.

(Johnson, 387). In 1837, trass sold for $5.225 per cubic meter, whereas common sand cost $0.85. (Treussart 90).

Extinct volcanoes can also be found in the Vogelsberg (west of Fulda), the Roehn (east of Fulda), the Lausitz (north of Dresden), and in the Eschwege at the Werra, east of Kassel. (MB).

Kieselguhr (diatomaceous earth, diatomite), which is derived from the silica skeletons of fossil diatoms, is over 80% silica. In 1911, it was not an economical material for cement making, because it was in demand as an absorbent for the nitroglycerin in dynamite. The 1911EB mentions deposits of diatomite in Richmond, Virginia, in Aberdeenshire (between Logie Coldstone and Dinnet), in Wales (Llyn Arenig Bach), and on Skye. It is in fact found in Germany (e.g., Obrehole), but I don't know whether it was a known substance (e.g., for filtering beer) insofar as the down-timers are concerned.

Ground granulated blast furnace slag (GGBFS) is a product of steelmaking (1911EB). Slag cements were first used in 1774, in mortar (Prusinski).

While USE Steel in Grantville will no doubt be happy to sell its slag, King warns that the slag "requires a fair amount of processing to become a useful pozzolan." GGBFS is produced by rapidly quenching (cooling) molten iron blast furnace slag by immersing it in water or blowing air over it, in a "granulator," and then grinding it. The GGBFS is then combined with lime to make slag cement. (It should be noted that slag, processed differently, can be used to make an aggregate.)

Coal fly ash. When coal is burnt, it leaves behind both bottom ash and fly ash, the latter being the particles which are carried up into the smokestack. Fly ash was first used in a pozzolanic cement in the construction of the Hoover Dam (1929).

The silica content of the fly ash is dependent on the type of coal; 20-60% for bituminous, 40-60% for sub-bituminous, and 15-45% for lignite. The ash also contains lime; 1-12% for bituminous; 5-30% for sub-bituminous, and 15-40% for lignite. Fly ash is classified as being either Type C (calcium-rich) or Type F (calcium-poor). The type C ash is more reactive than the type F ash, and is even self-cementing. ("Fly Ash," Wikipedia).

Fly ash particles have diameters of 1-100 microns. The particles with sizes under 10 microns are the most pozzolanically active, and ASTM limits the concentration of particles larger than 45 microns to 38%. The particle size distribution varies depending on the coal deposit and also on the plant design and operating parameters.

By way of a bonus, since fly ash particles are almost perfect spheres, they act like microscopic ball bearings, improving the workability and pumpability of the concrete in which they are used (Copeland).

Grantville has a coal-burning power plant which may already be equipped with devices for filtering out fly ash to minimize air pollution. By the beginning of 1634: The Baltic War, there is a coal gas plant in Magdeburg. They are connected by rail and water, and the fly ash can therefore be shipped to any point along the line which is convenient for cement and concrete manufacture.

How much the up-timers know about this utility of fly ash? It is not mentioned in 1911EB. The Encyclopedia Americana notes that it can be removed from the smokestack gas by electrostatic precipitators ("Power, Electric") but doesn't mention its significance for cement-making.

On the other hand, the Allegheny Power Company (which presumably owns the Grantville power plant) reported to the SEC that its subsidiaries sold 131,000 tons of fly ash (and 168,000 tons of bottom ash) in 1996, and that the uses of the ash included "cement replacement."

So I am sure that at least the power plant manager, Bill Porter, knows about this possibility.

Talmy, USP 5521132 gives the composition of the fly ash from the Rivesville Power Plant, which was the model for the Grantville plant. It is 58.79% silica, 27.91% alumina, 8.41% iron oxide, and only 1.20% lime. Its LOI (loss on ignition), a measure of the unburnt carbon on the particles, is 28.3%. That's high, so it will have to be burnt off. ASTM C618 requires that the LOI be no more than 6% (King 5).

Rice husk ash. Traditionally, rice was milled just to remove the chaff (outer husk), leaving brown rice. The brown rice may be further milled to remove the bran (inner husk), leaving white rice. If the husks are burnt, about 20% of the husk weight remains as ash, and this ash is about 95% silica, and constitutes a highly reactive pozzolan (Allen, King). The difficulty in preparing the ash is burning the husk at a temperature low enough so that the silica doesn't form inactive crystals while burning it long enough to ensure that all the cellulose is consumed.

Americans don't think of rice as a European crop, but it was brought to Spain and Portugal by the Moors ("Rice," Wikipedia), and has been grown in Italy at least since the fifteenth century. Lombardy was the first major Italian producing region. By 1644, there was rice production in the Veneto, and in the nineteenth century canal construction made it possible to grow rice in the Piedmont. (Seed). Rice can also be grown in France and Greece.

Silica fume. Once the semiconductor industry is reestablished, there will be the possibility of using silica fume (0.1 micron silica particles, a byproduct of silicon production) as a high-activity pozzolan. Silica fume is expensive and difficult to work with, so it will probably be relegated to the same niche market it enjoys now (concrete with compressive strength exceeding 15,000 psi and with high chloride resistance). (King 7; SFA).

Portland Cement

"Portland cement" was patented by Joseph Aspdin in 1824, and improved by his son William in 1843. Aspdin's cement was made by heating together finely ground limestone and clay. He cooled the resulting "clinker" and pulverized it. This powder could be stored until it was ready to be activated by addition of water.

The Aspdins used too low a temperature (probably lower than 1400 deg. C) to achieve a true Portland cement. (Blezard 8). (EB11 specifies a "clinkering" temperature of 1500 deg. C (2732 deg. F) which is in accord with modern practice.)

There is a good description of the modern American cement-making process in "Cement," Encyclopedia Americana. Sources of lime (e.g., limestone, chalk, marl, marble, shells), and of silica (sand, sandstone, clay, slag, ash) and alumina (clay, shale, bauxite) are quarried and crushed, then mixed together and ground up some more. The grinding can be done wet (that is, in a water slurry) or dry. Wet grinding yields a more homogeneous blend, but the powder has to stay in the kiln longer. (Camp)

This "rawmix" flows into a continuously operated, inclined, rotating kiln. EA says that this is typically 300-400 feet long, inclined at one half inch to the foot, and rotated at 30-90 revolutions per hour. The kiln is hottest at the discharge end.

The material takes 2-4 hours to pass through the kiln, and reaches a temperature of 2600-2800 deg. F. First water is driven out, and then the carbonates decompose into oxides. Ultimately, some of the material liquefies, and the lime (calcium oxide) reacts with the silica to form calcium silicates, notably dicalcium silicate (belite) and tricalcium silicate (alite).

Shale and clay often have a high aluminum and iron content. Alumina (aluminum oxide) serves as a flux, that is, it reduces the melting point so that more of the charge is liquefied at the peak kiln processing temperature. Thanks to the flux, liquid appears at about 2400 deg. F, but even at the peak temperature, only 20-30% of the charge is in the liquid phase. When the charge is cooled, the alumina is converted into tricalcium aluminate.

The EA "Concrete" article explains that tricalcium aluminate "produces a very high heat of hydration" and "has poor durability because it reacts with sulfate alkalis found in soil and water." Overly high aluminate levels may be reduced by adding iron ore to the kiln.

Iron oxides also act as fluxes, and they react with aluminate to form tetracalcium aluminoferrate. This iron compound is responsible for the grey color of the cement; if cement is made from low-iron materials, it will be white in color. On the other hand, the iron improves the resistance of the concrete to sulfate water.

Tricalcium aluminate forms because a source (e.g., bauxite) of aluminum oxide (alumina) is added to the kiln when making Portland cement. It is provided to reduce the melting point of the composition so it is liquid at the peak kiln processing temperature, thereby favoring formation of alite and belite. Unfortunately, it has undesirable properties, Like tricalcium aluminate, the tetracalcium aluminoferrate acts as a flux.

The product of the calcination reaction in the kiln are black hard nodules with diameters of one-quarter to one inch diameter, called "clinker" because they make a clinking noise in the kiln. These are mixed with 4-5% gypsum (hydrous calcium sulfate). EA states that the purpose of the gypsum is to slow down the "setting" of cement, since otherwise a Portland cement concrete mix might set, and become unworkable, before pouring was complete.

On average, every thousand tons of cement requires roughly 1511 tons of various oxides (1315 tons calcium oxide, 71 tons silica, 108 tons alumina, 17 tons ferric oxide), and 53 tons gypsum. (Van Oss 22). To get those oxides probably means processing up to twice the weight in raw rock.

Vertical Kiln Development

Of course, the post-RoF cement industry is going to begin more humbly than with the monster rotary kilns described in EA. The first cement kilns were intermittent, vertical kilns. Such kilns are "old" technology, already used in pottery, lime and brick making, and so there will be a rapid adaptation.

The simplest kiln design is a pit kiln, in which the fire is allowed to burn downward. Unfortunately, most of the heat is wasted, because it escapes upward.

An improved design is a simple shaft kiln; this involved digging a horizontal tunnel into the side of a hill, and a vertical shaft down to meet it. An arch of limestone is built at the junction. The rawmix is piled on top of the arch, and the fuel goes below it ("separated feed"). The fuel is lit and the fire burns upward. (Lazell 24-30; Eckel 409-19).

In both pit and shaft kilns, earth acts as the insulator. The dome kiln is the free-standing equivalent, made of brick or perhaps brick-lined metal. The interior was egg- or bottle-shaped, with the top portion serving as a chimney. The arch was replaced with a grating, and the fuel (preferably coke, but sometimes firewood) and rawmix was piled above the grating in many alternating layers ("mixed feed"). A typical dome kiln was 15-20 feet high and perhaps six feet in diameter.

Normal operation was discontinuous. The kiln would be loaded with perhaps 50 tons slurry and 12 tons coke. It will take two days to fire up, two or three days to burn through, and additional time for cooling down, drawing out the clinker, and reloading the kiln. Dome kilns produced perhaps thirty tons clinker per batch, and one batch per week (EB11). According to Eckel, production is 0.5-1 ton clinker per cubic meter of burning space, and 23-30 pounds of fuel are needed per 100 pounds clinker.

Intermittent operation is wasteful of energy, since the kiln must be cooled down and then reheated for the next batch. But the new arrangement made it theoretically possible to operate the shaft or dome kiln continuously. One worker could (cautiously) collect clinker which has fallen through the grating, while another added new layers at the top. We then have a "running kiln."

In practice, the clinker tended to hang up, forcing a cool-down (Redgrave 158). Also, it was difficult to maintain a consistent burn in running lime kilns (Johnson) and I suspect that the same problem would have carried over to cement kilns. Lipowitz (32) said in 1868, "many attempts to establish a kiln on the perpetual system have been devised, but hitherto the desideratum of a perfectly unexceptionable running kiln is still unattained."

Chamber kilns were adapted from brickworks, and the basic concept was that excess heat from one chamber was transferred to another. They thus achieved a substantial fuel savings. Chamber kilns are an old technology, but they reached their pinnacle in 1858, when Hoffman invented the "continuous" chamber (ring) kiln, briefly described by EB11.

The first vertical kilns capable of sustained operation appeared in the 1880s. These were larger than dome kilns (the Coplay Cement Company's nine Schofer kilns, operated in Delaware 1893-1904, were ninety feet tall), with separate drawing, burning and loading floors for the workers, and multiple ports and chutes through which to regulate the supply of rawmix and fuel. They probably had better linings, too. However, my sources are maddeningly vague about just how they avoided the problems of the old "running" dome kilns.

The new kilns differed in terms of where exactly the fuel and rawmix were added, the fuel used (coke or small coal), and where the interior narrowed and widened. EB11 diagrams the Dietzsch type, in which the shaft is staggered to create a horizontal ledge to which the fuel was added. A pair was usually built back-to-back. The upper vertical shaft contains the unburnt rawmix and the lower shaft is the burning zone.

EB11 also mentions the Schneider kiln, which had a single vertical path. The Schofer (Aalborg) kiln was similar. Eckel says it produced 10-15 tons clinker daily, consuming 280 pounds coal per ton product.

Rotary Kiln Development

It took roughly ten years (1885-1895) to achieve a truly practical rotary kiln. There were "many practical difficulties" and "an immense amount of expensive experimenting" (Sabin 23; ER Chap. 20; Brown 39-42; Redgrave 167-176).

One problem with the early rotary kilns is that they were simply too short, Ransome's being twenty-six feet long and Navarro's, forty feet. Consequently, there was a lot of underburnt clinker, and also much heat was wasted. While our heroes will know that the modern rotary kilns are hundreds of feet long, without foreknowledge of the problems of the pioneers, the first post-RoF rotary kilns are likely to be short prototypes, of underwhelming performance.

Secondly, there were various problems with the kiln lining, both spalling of the lining and balling of clinker upon it.

And finally there were the issues of finding the right fuel and minimizing fuel consumption. The first fuel experimented with was gas. Next came a "jet of burning petroleum," because it allowed precise control of the temperature of the kiln. Indeed, a chemist asserted at the time that the "rotary kiln can be successfully operated only in localities where crude oil is abundant and cheap." (Prentice) However, in most places oil was expensive, and the rotary kiln didn't really catch on until it was adapted (1895) to use blown pulverized coal.

The great advantages of the rotary kiln, once perfected, were its low labor cost (20-30% that of continuous shaft kilns) and high production rate (over double) (ER 188). Its bugbear was fuel consumption.

For several decades, the standard dry-process kiln was sixty feet long and six feet diameter, and the wet-process cousin could be up to eighty feet. The dry-process kiln produced 160-180 barrels (each 376 pounds) of clinker daily, consuming 110-150 pounds coal per barrel. (Eckel 424; Sabin says 175-250 barrels for 95-120 pounds coal/barrel.) The wet process was even more wasteful of fuel (ER 17).

It took Edison from 1899 to 1902 (Vanderbilt) to build the first "long" (150 foot) kiln, despite his study of the "short" kiln technology. The Edison kiln tube, nine feet in diameter, was made from ten-foot sections of cast iron, bolted together. It was suspended on fifteen rollers, rotated by an electric motor, and there were ten thousand bearings, lubricated with an automatic oiling system. The kiln had a pitch of eighteen inches and powdered coal was forced in by pressurized air to create a forty foot combustion zone at the lower end. Only two men were needed per shift.

Edison shocked the industry by producing 350-375 barrels daily, while consuming only 65 pounds coal per barrel (Eckel 424). Edison ultimately increased production to 1100 barrels/day (Vanderbilt 185). The "light bulbs came on," and by 1918 there were kilns over 200 feet long.

In the standard sixty footer, the combustion zone, in which clinker was formed, was near the lower end, and about ten feet long, and the heated gases which rose from it had only the upper forty feet in which to decompose the rawmix. Much of the heat of the gases was wasted, and the processing path was so short that the rock still retained much of its carbon dioxide, releasing it when it reached the combustion zone. (Dyer)

By increasing the length, the cylinder could be fed faster, tilted more steeply and rotated more quickly, and still burn the stone properly, without the produced carbon dioxide interfering with the combustion. Eckel (429) estimates that the output (barrels/day) will be between one-eight and one-twelfth of the product of the length (feet) and the square of the internal diameter (feet) at the discharge end.

In re-inventing the rotary kiln, our heroes will need to solve problems relating to forming the giant metal cylinder, developing a proper lining (early 20c usage was alumina brick), providing the mechanisms for turning the cylinder, and assuring proper heating.

Comparison

In general, the fuel-efficient vertical kilns long remained popular in Europe, where labor was cheap and fuel was expensive. In America, where the reverse was true, by 1900, the rotary kiln accounted for 90% of production.

Grinding

The clinker is ground down, to a very fine powder. How fine? EB11 says, enough so most passes through 0.005 inch sieve holes. In modern practice, to an average of ten microns, which makes baby's talcum powder seem coarse in comparison. Cement plants will need to be able to measure particle size in order to ensure a consistently high quality product.

Grinding of clinker was done originally with millstones (EB11). However, by the late nineteenth century, ball mills were available. In a ball mill, the material to be ground enters one end of a rotating cylinder, and leaves at the other. The cylinder contains balls made of a hard material, such as steel, rock or ceramic, and the clinker is ground down by friction and impact. The mill can be powered by animals, wind, water or electricity.

Cement powder must be kept dry until use since cement reacts with water ("sets"). Cement also gradually loses strength when stored.

Types

There were five basic types of Portland cement in use in 2000:

Type I: General purpose.

Type II: Moderate sulfate resistance.

Type III: High early strength (gains strength faster than type I, which allows earlier removal of the forms which the concrete is poured into. According to Arnold 32, type III cures about twice as fast as Type I)

Type IV: Low heat of hydration (for use in massive structures, like dams, where it is difficult for the heat to escape because of a low surface-to-volume ratio)

Type V: High sulfate resistance.

There were also "air-entrained" variants of types I-III (IA-IIIA) so you could say that there are actually eight basic types.

Domestic production in 2000 was over 90% types I/II, with the balance split primarily between types III and V. Type IV was less than 1% of production. (USGS).

Type III is used mostly for precast concrete manufacture (so the molds can be reused more quickly) and for emergency repairs. Commercially, types IV and IV have been largely superseded by Portland-pozzolan blended cements (see below). What that all means is that, as a practical matter, the up-timers probably have experience only with types I and II.

The typical chemical composition of the five types of Portland cement is given in the Encyclopedia Americana "Cement" article. The chart lists the proportions of tricalcium silicate, dicalcium silicate, tricalcium aluminate, tetracalcium aluminoferrate, calcium sulfate, magnesium oxide, and free calcium oxide for each. EA notes that it isn't desirable for free calcium oxide to exceed 2-3%.

While this may make it seem that the chemical composition is critical, the ASTM specifications are "not very strict since cements with different chemical compounds can have similar physical behavior" (Camp). But Camp also says that "high quality cements require adequate and uniform raw materials." How do we reconcile these two statements?

What it comes down to is that the physical properties of the cement (and corresponding concrete) have to be predictable (so that, say, the concrete in the third floor is just as strong as the concrete in the lower floors). So once you determine that a particular combination of raw cement-making materials makes a physically desirable cement, you want to make sure that all of the cement produced will continue to manifest those desirable properties.

It is also worth noting that both chemical and physical properties of Portland cement have changed over the years, with post-1930 cements being more finely ground and containing more belite than older cements. The concrete made with post-1930 cements strengthens more quickly (so construction is faster) but is less durable (Mehta).

Quality Control

The quarried stone can vary from day to day in its content of the various oxides. Quality control-measuring the chemical composition of the stone and the clinker, and adjusting the proportions of limestone, clay etc. appropriately-began in the 1870s (Blezard 17).

In modern practice, the chemical composition of the rawmix is tightly controlled-within 0.1% or better! This accuracy is achieved by hourly X-ray fluorescence or, every three minutes, gamma neutron activation analysis. ("Portland Cement," Wikipedia).

Obviously, we are not going to achieve that kind of control in the early post-RoF period. Nor is such control critical, as long as one periodically tests the efficacy of the cement. After all, nineteenth century rawmix certainly wasn't monitored by X-ray fluorescence. EB11 says that "the silica may range from 19 to 27%, the alumina and ferric oxide jointly from 7 to 14%, the lime from 60 to 67%."

I would imagine that there would be an attempt to perform daily chemical analyses on the rawmix, and that these analyses would be correlated with tests of the cement emerging at the other end of the kiln. The latter will include both chemical tests (see below for the desired constituents of different types of cement) and physical ones, i.e., using the cement to make a concrete and then testing the concrete for strength. In addition, there would probably be at least daily chemical testing on the raw materials (e.g., limestone). Even this crude quality control is going to be new to the seventeenth century.

Grantville chemists will have to dredge up their old quantitative chemical analysis course textbooks and figure out how to assay for silica, alumina, iron oxide, lime, magnesia, etc. (Waterbury, Appendix III). Once they have an oxide analysis, the proportions of the four main reaction products can be predicted using what is called the Bogue calculation. Classical chemical analysis can require hours or even a few days to complete (Blezard 22), so adjustments will be sluggish by modern standards.

Natural Cement

So-called "natural cement" is a cement, similar to Portland cement, which was produced by calcination of a naturally occurring mixture of lime and clay, such as the "dolostone" (magnesium-rich limestone) of Rosendale, New York. It was used to make concrete for the Brooklyn Bridge and Grand Central station in New York City. EA "Cement" distinguishes between "hydraulic limes" (with a silica-alumina content of 10-20%) and "natural cements" (20-35%).

1911EB acknowledges the existence of natural-cement deposits near Chittenango, in Madison County, New York, as well as in Kentucky (Louisville), Indiana (Clark county), Illinois, Oregon (Rogue river), Pennsylvania (Williamsport, Lycoming County). EA mentions Rosendale and Fayettesville, NY.

Natural cements do occur in Europe, notably in Belgium (Tournai district) and England (septarian nodules found in southern England) (Eckel1905, 214-8). However, this will have to be discovered the hard way.

According to EA, natural cements can be made by processing the rock in "small, upright, wood-burning kilns… fired for about a week", and then grinding the resulting "clinker" between millstones, using waterpower. Firing temperatures are similar to those of lime kilns (1000-1200њF) (ER 21).

In any event, users of "natural cement" were at the mercy of nature; they had to be content with the particular mixture of lime and clay which the formation produced, whether it gave the cement and concrete the correct characteristics or not. The clinker must be sorted, and the under and over burnt material tossed away. Losses will probably be on the order of 25%. (Reid 9). The strength of natural cement is perhaps half that of Portland cement (Mills 41).

High Alumina Cement

This is made by heating a mixture of limestone and aluminum ore (bauxite). According to EA "Cement," it's resistant to sulfates and chlorides, and it hardens faster than Portland cement (and hence is useful for emergency road repair). Hot, moist conditions can cause it to suffer a catastrophic change in its microstructure-which is why the Europeans ban its use in structural concrete (Camp 6).

For sources of bauxite, see Cooper, "Aluminum: Will O' The Wisp?" (Grantville Gazette, Volume8).

Blended Cement

In the twentieth century, this referred to a combination of Portland cement with a pozzolanic cement. EB11 says that adding trass can increase strength.

Blended cements were first used in underground and underwater structures because they imparted increased durability. Later, they were used in massive concrete works because of their reduced heat evolution (compare type IV Portland cement) and in weather-exposed concrete to reduce expansion (and cracking) as a result of the alkali-aggregate reaction. Ultimately, they came into general use. (Lea 424-5).

In general, the blended cements have a lower short-term (28 day) strength and a higher long-term (1-5 years) strength. (Lea 436, 473).

Aggregates

The aggregates form about 60-80% of the concrete (Ahrens 17). You may think of the aggregates are the "bones" of concrete, and the cement as the "sinews." Most of the weight of concrete, and also most of the structural strength, is attributable to the aggregate.

A concrete mix will usually include both fine (under one-quarter inch) and coarse aggregates. The maximum size for the aggregate is usually an inch or two. (Roman concrete used much larger pieces, see Cowan 120.) The purpose of the fine aggregate is to fill in the spaces between the larger chunks, and it's usually sand. (Arnold 27)

The proper shape of the aggregate pieces is going to be a matter of study and debate. EB11 "Concrete" teaches that "spherical pebbles are to be avoided," and that the grains of sand should be of "an angular shape." However, modern concrete technologists are of the opinion that "the ideal aggregate would be spherical and smooth." (Camp, Chap. 6).

In the nineteenth century, aggregates were haphazardly collected from the pit or crusher. (Bauer 54). But ideally, the coarse aggregate is not a single size but rather exhibits a spectrum of sizes. An example of a desired grading curve, Fuller's "ideal curve" (1907) specifies that the fraction of aggregate smaller than a particular size is the square root of the ratio of that size to the maximum size of the aggregate.

Use of a well-graded aggregate permits more economical use of cement, but this is balanced somewhat by the greater amount of work which may be involved in achieving that degree of grading for the available aggregate. A sieve analysis is used to determine whether the aggregate approximates the desired grading curve.

Normal density aggregates include crushed limestone, sand, river gravel, and crushed recycled concrete. The density of concrete made from such aggregates would be perhaps 150 pounds/cubic foot.

Low density aggregates might be expanded clay, shale, slate, slag, or crushed recycled brick. They bring concrete density down to 100-130 pounds/cubic foot (Ahrens 23).

Very low density aggregates include expanded mica, vermiculite, perlite, pumice, and glass or ceramic spheres. Concrete density can be as low as 20 pounds/cubic foot, which is lighter than water. The concretes used in the annual "concrete boat" races make considerable use of these aggregates.

Sand and gravel. Sand and gravel may be deposited by glaciers, water, or wind. In general, wind deposits (dunes and loess) are not useful in concrete-making.

If you look at a map of Europe during the last ice age, you can see that the terminus of the continental glacier was along a gentle NE to SW curve, falling a little north of Hamburg and Dresden. In southern Germany, there are likely to be deposits left by alpine glaciers. However, since these glaciers were advancing during the seventeenth century (remember the Little Ice Age), I am not sure that they will be accessible.

Water deposits can be left by rivers or the sea, and in general river sand is more useful. The problem with sea sand is that it encrusted with sea salts. Twentieth century facilities can desalinate sea sand but this isn't likely to be a practical option for our protagonists.

You can find river sand (or gravel), not only in the beds and banks of existing waterways, but also in ancient channels. In the mountains, gravel may be found in alluvial fans.

Julio Sanabria may have exaggerated a bit when he assumed that "sand is everywhere," but there shouldn't be a problem finding some sand in the vicinity of Grantville and Magdeburg.

Crushed stone. In the United States (1989), the preferred rocks for crushing are, in descending order, limestone, then granite, traprock, dolomite, sandstone/quartz/quartzite, and marble, and finally volcanic cinder/scoria, slate, and marl (USGS). Quarrying is likely to occur where the rock outcrops or at least the soil overburden is thin. It might also be done as a byproduct of roadbuilding.

The choice of stone is dictated by a combination of its engineering properties, availability and cost. The rocks vary in mechanical strength, density, durability, chemical stability, surface characteristics, content of undesirable impurities, and the suitability of the shape of the crushed fragments (Waddell 2.6-. 19).

Air-cooled blast furnace slag. This can be obtained wherever pig iron is produced. Slag concrete is actually stronger than that made from gravel.(Ramachandran).

Bottom Ash. This is similar to fly ash, but unfortunately higher in alkalis and sulfates. Ramachandran suggests that it be used as a lightweight aggregate in concrete block production.

Red Mud. This is a waste product of the production of alumina from bauxite. It can be formed into balls and then fired, like clay pottery, to produce an aggregate. A fairly high temperature (1260-1310 deg. C) is required to melt it.

Sawdust. Sawdust can be used as an aggregate (as in "woodcrete"), but sawdust concrete has reduced strength and, if the sawdust content is high, is flammable. The best wood sources are spruce and Norway pine. (Ramachandran).

Waste glass. Glass refuse can be used as a lightweight aggregate, but it reduces strength, and also renders the concrete susceptible to certain chemical attacks.

Water

The key is to use water which doesn't contain significant levels of impurities that adversely alter the properties of the concrete. For example, seawater has a high content of dissolved salts, including sulfates and chlorides, which can cause a variety of problems.

According to EA "Concrete," if the water is good enough to drink, it is good enough to make concrete. However, drinkable water isn't strictly necessary.

In the seventeenth century, water quality cannot be taken for granted. The ASTM standard method of deciding whether water is acceptable for concrete mixing is "if the setting time does not differ by more than 30 minutes and the strength is not reduced by more than 20% when compared with a sample [made] using distilled water." (Camp).

In cold weather, it can be advantageous to use hot water, thereby speeding up the setting of the concrete (Arnold 32).

Admixtures (Additives)

The Romans experimented with animal fat, milk and blood as additives (UIUC).

Air. It is possible to entrain air into concrete, either when mixing the concrete, or by use of an air-entrained cement. Why is this good, when concrete layers are taught a variety of techniques to prevent voids? The difference is that these "good" air bubbles are small (one to three thousandth of an inch), numerous (400-600 billion per cubic yard), and well-distributed. The air content may be 3-7%, rather than the usual 1-2%.

Air-entrained concrete is more resistant to freeze-thaw cycles. In ordinary concrete, when temperatures drop below freezing, the residual water expands, and stresses the concrete, possibly cracking it. But in air-entrained concrete, all those air spaces can compress if the concrete nearby is stressed. Air-entrained concrete is also more workable. The mix must be adjusted to avoid loss of compressive strength.

Air-entrainment was developed in the 1930s. It is achieved by adding a surfactant to the concrete. The conventional air-entrainment agents include "Vinsol resin" (the "petroleum-hydrocarbon, insoluble fraction of a coal-tar, hydrocarbon extract of pine wood") and "Darex-AEA ("a triethanolamine salt of a sulfonated hydrocarbon")(Bauer 47). Vinsol resin is mentioned in the CRC Handbook of Mechanical Engineering, a reference book reasonably likely to have been in Grantville.

No doubt people will think about using ordinary household detergents, but use of the wrong one could reduce strength and not achieve the desired effect. So any candidate surfactant has to be tested for its effect on the concrete (CCN).

Accelerants. Agents, e.g., calcium chloride (CRC), can be added to reduce the setting time.

Retardants. Other agents, e.g. sugar (CRC), can be used to cause the concrete to set more slowly. They are typically used during hot weather.

Water-reducers. These reduce the amount of water needed for the mix to have the desired level of workability. Decreasing the water: cement ratio increases strength.

Superplasticizers are "second-generation" water-reducers; they were introduced in the 1980s. They include sulfonated melamine (or napthalene) formaldehyde condensates and ligonsulfonates (CRC).

Pigments. You can imagine an early architect telling a client, "you can have any color concrete wall you like, as long as it's grey." In the late twentieth century we had the choices of blue (cobalt oxide), brown (iron oxide), buff (another iron oxide), green (chromium oxide), and red (yet other iron oxide). Pigments can be expensive, and tend to weaken concrete, so they are used sparingly. (Chen 30).

Lightweight Concrete

Plain concrete weights 150-160 pounds/cubic foot. Lightweight concrete weighs 35-120 pounds/cubic foot. There are two basic methods of lightening concrete. Either you use a lightweight aggregate (see above), or you add a foaming agent (e.g. aluminum powder) to put gas bubbles into the concrete. In our time, concrete using a lightweight aggregate costs 30-50% more than ordinary concrete. (Merrill).

Structural lightweight concrete, made with expanded shale or clay aggregate, has a strength of 2,500-6,000 psi. It was used in constructing the 52 story One Shell Plaza in Houston. Intermediate lightweight concrete, made with pumice, scoria or herculite aggregate, has a strength of 1000-2500 psi. Extra-lightweight concrete, made with perlite, vermiculite and polystyrene bead aggregate, has a strength of only 100-1000 psi. (Ali).

Pumice and scoria are considered volcanic glass. Concrete made with them weighs 90-100 pounds/cubic foot. (Lewel).

Perlite is a volcanic rock which expands dramatically when heated, somewhat like popped popcorn. Encyclopedia Americana says that it is found in New Mexico, Greece, Hungary and Italy. Concrete made with expanded perlite weights 35-75 pounds/cubic foot.

Vermiculite is a clayey mineral (think "kitty litter") which, in the crude state, has a density about twice that of water. When heated, it "expands explosively," perhaps 20-30 fold. Encyclopedia Americana notes that it is mined in Montana (near Libby), North Carolina, South Carolina and Wyoming. It is doubtful that any up-time information is available on where it can be found in Europe. Concrete made with expanded vermiculite weights 35-75 pounds/cubic foot.

Heavyweight Concrete

High density aggregates, such as barite, limonite, magnetite and steel balls, have been used to increase the strength of a concrete structure, especially fortifications.

Reinforced Concrete

Steel. Reinforcement of concrete was proposed by Joseph-Louis Lambot in 1848. Reinforcing concrete with steel means that you take advantages of the strengths of both materials. The steel provides tensile strength, while the concrete provides compressive strength and also protects the steel from the environment. It can be provided in the form of individual bars, welded wire fabric, and cable (strands twisted together).

The steel is placed where it will carry the tensile loads of the structure. This is possible only because the concrete adheres to the steel, so tensions are transferred from one material to the other. The force of adhesion is dependent on the surface area of the reinforcing bar ("rebar"), and the bar must be long enough so that the strength of the bond is greater than the strength of the bar itself.

Most materials expand when it is hot and contract when it is cold. The dimensional change with temperature is measured by the "coefficient of expansion." If the coefficients for steel and concrete were dissimilar, then changes in temperature would disrupt the adhesion needed for the composite material to behave as a single unit. However, they are in fact quite similar, Twelvetrees (47) giving values of 0.0000066 and 0.0000055, per degree Fahrenheit, respectively. Still, a change of temperature will cause some stress; the steel bears it better because it is about 100 times as elastic as concrete.

Besides resisting tensile stress, the rebar also helps distribute strain throughout the concrete, and hence reduces the chance of rupture at a point of concentration.

Obviously, our ability to use steel-reinforced concrete is dependent to some degree on steel production. However, it is equally clear that it is more economical of our precious steel production capacity to build with steel-reinforced concrete than with steel alone. For a reinforced concrete beam, if the relative cross-sectional area of the rebar was 1% ("Reinforced Concrete," Wikipedia), the rebar might add just 3.6% to the weight of the beam. That 1% corresponds to 132 pounds of steel of per cubic yard concrete. (Taylor 536).

During the first decade post-RoF, I expect that reinforcement practice will be similar to that of the early twentieth century. Figure 50-200 pounds of steel reinforcement per cubic yard of concrete, depending on the use. (Taylor, 14-32).

The advantages of reinforcement aren't limited to poured concrete. Precast blocks usually have two or three vertical holes; steel bars may be placed through the holes for increased strength.

Prestressed concrete. This is a variation on ordinary reinforced concrete. The idea is that a tensile stress applied to steel tendons generates a compressive stress in the surrounding concrete. The tendons are placed so that the compressive force offsets tensile forces which are imposed on the concrete by the overall structure in service. In other words, prestressing permits the concrete to match its strength (resistance to compression) against what would otherwise be a foe to which it is especially vulnerable (a tensile structural load). (Waddell, Chap. 41). Prestressed concrete is used to make the floors of many high-rise buildings.

In pre-tensioning, the "tendons" are tensed in a "stressing bed" by hydraulic jacks. The ends are anchored by reinforced concrete or structural steel abutments which extend deep into the ground. The concrete is poured into the bed and, once it cures to a desired compressive strength, the tendons are cut loose at the ends, which causes the transfer of the stress from the steel to the concrete ("detensioning"). Typically, pre-tensioning is done when the concrete members are manufactured in a central casting yard for transport to building sites.

In post-tensioning, the concrete is cast so that it contains ducts (by using thin-walled steel forms), and, once the concrete has gained sufficient strength, the "tendons" are run through the ducts and tensed and grouted. Post-tensioning is more likely to be carried out on-site.

It is fairly common for prestressed concrete to also be precast.

Cast or Wrought Iron. Traditional cast iron has a tensile strength of 10,000-20,000 psi, and wrought iron, 20,000-40,000 psi (Gordon 44). While inferior to steel in strength, and quicker to rust, they can be used in reinforcements if steel supplies are inadequate.

Non-Ferrous Metals. The common ones (copper, zinc, brass, bronze, aluminum) won't work. While their strength is at least equal to that of cast iron, their coefficient of thermal expansion is significantly higher than that of concrete. There's also the problem of corrosion by caustic alkalis in the concrete. Tin has a good coefficient, but is weaker than cast iron.

Wood Reinforced Concrete. Mass production of steel was unknown in the seventeenth century prior to the Ring of Fire. Hence, the steel industry in the early post-RoF years has a lot of catching up to do in order to be on par with what it was in the mid-nineteenth century, when steel-reinforced concrete was invented. This led me to wonder whether one might, as an expedient, use large wooden beams in place of steel bars as reinforcements for the less demanding concrete structures. While the tensile strength of wood is inferior to that of iron, it is still far superior to that of concrete-at least if the tensile forces act along the grain of the wood.

That said, it doesn't seem likely that wooden rebar (as opposed to wood fibers, see below) is practical. With regard to posts, Radford (154) said "no form of wooden reinforcement, either on the surface or within the post, can be recommended. If on the surface, the wood will decay; and if a wooden core is used, it will in all probability swell by the absorption of moisture, and crack the post." So the problem of moisture must be addressed by applying some kind of waterproof coating to the wood.

Another issue is whether the concrete will adhere to the wood, which is critical for the transfer of tensile stress from the concrete to the reinforcement. Cobleigh says, " A wooden reinforcement in the center of a concrete fence post is worse than useless. It does not make a bond with the concrete, and thus weakens, instead of strengthens, the post. Of course, the same is true of wooden reinforcement of any concrete work."

Finally, there is the issue of whether the wood and concrete would expand or contract the same amount if the temperature changed. From what I can tell, the coefficient of thermal expansion of wood is about half that of concrete (Luebkeman).

Bamboo can be used as rebar, but it isn't bound well by cement, and the bamboo must be treated so that water absorption doesn't become a problem. (Swamy, 141, 157).

Fiber Reinforced Concrete. "And Pharaoh commanded the same day the taskmasters of the people, and their officers, saying, 'Ye shall no more give the people straw to make brick, as heretofore: let them go and gather straw for themselves." (Exodus 5:6). Clearly, fibers have been used to reinforce brittle materials since antiquity. For example, straw and horsehair were baked into mud bricks (Mohr 113). Cement and concrete have been reinforced with a variety of fibers, including steel, wood, asbestos, glass, textile, plastic, and carbon.

Fibers tend to be used in two different ways. First, they can be directly incorporated into the cement of conventionally reinforced concrete to reduce local cracking. Secondly, they can be incorporated into a matrix of some kind, and the resulting composite fabricated into rebar used in lieu of steel reinforcement, to increase tensile strength (while adding less weight).

Direct incorporation of glass or hemp fibers can actually reduce tensile strength (Materschlager). Steel fibers do increase tensile strength by 30-40%, and flexural strength (resistance to first cracking) by 50-150% (Frank). Of course, the tensile strength of unreinforced concrete is abyssmal, so 30-40% isn't much of an improvement.

In the case of direct incorporation, it is critical that the cement adhere to the fibers, or the fibers create weak spots. It may be possible to overcome adhesion problems with suitable coatings.

Straw was used to reinforce bricks in ancient Mesopotamia. The Finns added asbestos fibers to clay pots as early as 2500 BC. They were added to cement in 1898, but given the health concerns with asbestos, this history isn't likely to be repeated in the new time line.

Steel fiber reinforcement has been studied since the 1950s. Steel fibers are usually 0.5-2.5 inches long, and are added at a concentration of 0.25-2% by volume. (R amp;T).

Plastic (acrylic, nylon, polyester, polypropylene, rayon) fibers are also popular, but of course to make plastics, we need a variety of reagents and organic chemical feedstocks. So plastic fibers are going to be a relatively late introduction to the new time line concrete industry.

Wood fibers are the subject of current experimentation. They are added to cement shingles to increase ductility. Cement shingles have advantages in areas susceptible to wildfires. (Muhollem). Wood fibers have also been used in fiber-cement sidings (Mohr).

There are other natural fibers, too. The vegetable fibers include bast (flax, hemp, jute, kenaf, akwara, bamboo), leaf (sisal, henequen, pineapple, banana, elephant grass), and seed or fruit fibers (cotton, kapok, coconut husk "coir"). There are also animal fibers like wool. Obviously, the tropical fibers aren't going to be readily available in seventeenth century Germany, at least at a low enough cost.

Direct incorporation of glass fibers is possible only if alkali-resistant glass is used; ordinary glass fibers don't tolerate the highly alkaline environment of concrete.

Combination of fibers of different lengths or compositions can have synergistic effects (Banthia).

Composite Rebar-Reinforced Concrete

It is possible to fabricate rebar out of a composite material, a fiber-reinforced plastic ("FRP"). The purpose of the plastic matrix is to protect the fiber from abrasion and chemical attack, and to transfer loads to it. Hence it has to be able to bind to both the cement and the fiber.

The properties of FRPs are strongly influenced by the length, diameter, arrangement and composition of the fibers, and the composition of the matrix.

Matrix. The FRP has to be readily fabricatable into rods, which means the plastic (resin) is usually either thermosetting or thermoplastic (which can be recast). It is desirable that the rods be bendable on-site. The resins in commercial use are synthetic; the thermosets include polyester, epoxy, and phenolics, and the thermoplastics, polycarbonate, polysulfone, and polphenylene oxide. In order to explore these possibilities, we first have to reconstruct the plastics industry to the point at which we have fine control over the mechanical and chemical properties of the plastic.

There are a number of natural resins which might be tested as potential matrixes. But Humphreys warns that natural resins "generally lack the processing and performance characteristics sought after in a matrix resin." (For desired characteristics of matrix resins, see Hale

Casein, a milk protein, can be precipitated from milk with heat and acid, and hardened with formaldehyde to make a semi-synthetic plastic. According to canon, it was made by the winter of 1631-32 (see Offord, "Bootstrapping," Grantville Gazette, Volume11, and DeMarce, "Songs and Ballads," Grantville Gazette, Volume14). It is probably too soft, and too vulnerable to water absorption and biological degradation to be a good FRP matrix.

Most of the research I have seen on natural resins has focused on their combination with natural fibers to make a biodegradable material. Biodegradability is great for bottles, but not what one wants in a skyscraper, bridge or dam.

Glass ("GFRP") and Carbon ("CFRP") composite rebars are commercially available nowadays. There is some information about glass and carbon fibers available in the Encyclopedia Americana.

Glass Fibers. A glass fiber-reinforced plastic ("GFRP") is often called, somewhat misleadingly, "fiberglass". The latter term actually refers to the "bundle" (cloth, tape, etc.) of glass fibers used to make the GFRP.

A GFRP rod has a higher tensile strength than one made of steel, and it is lightweight and corrosion-resistant. However, its mechanical properties are different enough from those of steel (they vary by direction, and it isn't as stiff) that direct substitution of GFRP bars for steel bars is not possible. (CPPI).

Glass fibers are intriguing, because there is a down-time glass industry-we aren't starting from scratch. Coarse glass fibers have been used for decoration since antiquity (Cooper, "In Vitro Veritas" ( Grantville Gazette, Volume 5), and they are mentioned in Antonio Neri's L'Arte Vetraria (Florence, 1612).

When glass is drawn into a fiber, it deforms, wiping out most of the weakening surface defects. The tensile strength of glass fibers with a diameter of 1/2000th inch is perhaps ten times that of bulk glass, and comparable to high tensile engineering steel. Glass fibers of those dimensions were first drawn by Griffith in 1920.

However, he was just testing the strength of individual fibers, not trying to produce them en masse. To make glass fibers (preferably, 5-20 micron diameter) on a commercial scale, we need to be able to produce a homogeneous glass (to control viscosity during drawing, and so the final product will have consistent mechanical properties), and we need glass drawing machinery which can reliably produce fibers of the correct dimensions. The Encyclopedia Americana "Fiberglass" article says to draw the glass through a platinum orifice plate, but platinum is not available immediately after RoF (it was considered a "waste" metal).

Moreover, the new fibers tend to stick to (and weaken) each other. Hence you also need to integrate, into the drawing operation, treatment of the fiber with a protective film (and in turn we need to identify a suitable chemical for that purpose). (Gordon, 74-76, 183-4). And once we have the glass fibers, we still have to find the right matrix.

I would have expected it to take some years to solve these problems. However, canon (Huff and Goodlett, "The Monster," Grantville Gazette, Volume 12) says that sometime between June and November 1633, "fiberglass" is available, albeit at a high price. Georg Markgraf 's second airplane, the "Jupiter," has an GFRP skin "made of a composite of fiberglass and resin." Perhaps the "fiberglass" was hand-drawn?

Unlike the composite rebars discussed here, Georg's aircraft body doesn't have to have a lot of strength. It is "semi-monocoque" construction, meaning only part of the stress is borne by the body itself.

Carbon Fibers. Alternatively, it is possible to carbonize certain artificial and natural fibers. The first carbon fibers were made, by Edison (1879), from cotton or bamboo, for use as incandescent light bulb filaments. They were "extremely brittle" (Lee, II147).

High-performance carbon fibers were first made commercially available in 1959, at a price of over $500/pound (Jacobs 544). The usual starting materials were polacrylonitrile or rayon. Of course, we have to make these synthetic fibers before we can carbonize them.

The most interesting potential source for carbon fibers is pitch, which can be derived from oil or coal. Fibers can be pulled, like taffy, from the pitch, and these carbonized. In fact, if a high enough temperature is used, they can be converted to a particular form of carbon, graphite, with especially desirable properties (ACS; U. Kentucky).

Bear in mind that carbon fibers were leading-edge materials even in 2000 (Hegde; ACS), so even entertaining the notion of carbon fiber-reinforcement is going to give some readers apoplexy. But at least there is no doubt that the raw materials are available. The trick is going to be working out the manufacturing technology.

Hale 47 quotes 1998 fiber prices per pound as follows: E-glass ($1), S-glass ($5), aramid (e.g., KevlarR) ($15-50), standard graphite ($17-35), high strength ($40), high stiffness ($65), and ultra-high stiffness ($275-650).

The great advantage of FRPs over steel is their high ratio of tensile strength to weight. This is especially important for vehicles, many parts of which can be made completely out of composites.

Unfortunately, FRPs suffer from a relatively high price and relatively low stiffness. Even with today's production technology, these composites are much more expensive than steel ($3-4/pound for GFRP, and more for CFRP, compared to $0.32 for epoxy-coated steel. (Purdue).

In part, the high prices are because GFRPs and CFRPs are still produced in relatively low volumes (MIT). Arguably, they will have a better chance in the new time line, because steel itself is a specialty product in the seventeenth century. On the other hand, steel will probably be needed for the very machinery used to manufacture GFRPs and CFRPs. And the availability of concrete as a building material should reduce the demand for wood, which could in turn bring down the price of iron and steel (because in 1630, charcoal was over three-quarters of the cost of smelting iron; Sass, 162).

Moreover, civil engineers need a material which not only has high tensile strength, but which is also stiff. GFRPs are quite inferior to steel in terms of stiffness, and CFRPs can only be made stiff with substantial difficulty and expense. CFRPs also fail at a lower strain than steel. (Humphreys).

Hence, I think it may be more than a decade before we see substantial building use of GFRPs or CFRPs. However, their weight advantages are of particular moment to the aircraft industry, and that industry is likely to fund research which will eventually benefit builders, too.

Macro-Defect Free Cement

It doubtful that anyone in Grantville will know about it, and even less likely that they will know how to make it, but in the 1980s it was shown that one could essentially eliminate pores by use of the combination of a Portland (calcium silicate) or better, a calcium aluminate cement, a water-soluble polymer (e.g. polyvinyl alcohol-acetate copolymer), water and glycerine. Compressive and flexural strength increase ten-fold, toughness more so, and stiffness doubles. (Ghosh, 352-3).

Concrete-Related Materials

Ferrocement. This material is similar to reinforced concrete, but there is no coarse aggregate in the concrete (so it is really reinforced mortar), and the reinforcement is closely spaced layers of small-diameter wire mesh and bars. The wire was originally steel, but other materials (e.g., bamboo) have been used. (Haussler; Robles-Austriaco). A crude form, with a single mesh layer, was invented by Lambot in 1855 (Jackson 28). Experimentation revealed that the weight of steel should be about 27 to 37 pounds per cubic foot.

"Micro-Reinforced Concrete" has been touted for blast resistance (Hoffman; Hauser; Chusid; Excendinc). From what I can tell, it is just ferrocement "on steroids"-supplemental cementitious materials, superplasticizers used to reduce the water-cement ratio, etc. I suspect there has also been some optimization of the mesh.

Seacrete. This was a highly experimental, concrete-like material as of the time of writing. Calcium carbonate, from seawater, is electrodeposited on a wire mesh which carries the necessary electrical current (Hibbert, USP 4246075). Seacrete is potentially as strong as concrete. There are a few catches. One is to get high strength, you have to use low currents so the rate of deposit is slow-you have to grow seacrete for a year or more to get a strength of 8000 psi. Another is that all the electricity needed is expensive (see "Seacrete," Wikipedia). And third, there is no moving Seacrete, you grow it where you want the wall (or whatever) to be. So its use is likely to be limited to underwater or coastal structures.

Pykrete. This is a composite material made of 14% sawdust (or wood pulp) and 86% water. It is frozen to produce a concrete-like material. In World War II, there was a proposal to use it to make aircraft carriers (Project Habbakuk). A sixty foot experimental structure was constructed and floated at Patricia Lake, Alberta.

Concrete Cloth. This is a recent (2003) development, a dry concrete mix-impregnated fabric, usually bonded to the outer surface of an inflatable plastic (PVC). The theory is that the plastic is inflated, the concrete is hydrated, and the concrete cloth hardens into a dome shape, for use as an emergency shelter. (ConcreteCanvas)

Polymer concrete. A concrete-like material in which part or all of the cement is replaced with a polymer (e.g., polyester or vinyl ester resin, or latex). The polymer inhibits water absorption. It is often used for emergency repairs because it can obtain useable strength in minutes. Unfortunately, the polymer is expensive (and not immediately available post-RoF).

In Part II of this article, I will explain how concrete is produced, laid and tested, and what sort of structures it could be used to build.

To be continued in Grantville Gazette, Volume 20

Plausibility Denial or Truth is Stranger Than Fiction

Written by Gorg Huff

Predictions and Reality

Some years ago the barflies who frequent the 1632 Tech Manual, after much debate, came up with the number of computers in Mannington, West Virginia. Which was also the number of computers in Grantville. At the most recent 1632 con, we discovered that that estimate was off. As of the year 2000, there were more computers in Mannington than we thought.

Based in large part on library usage, we estimated the number of books in Mannington. Then we found out about a couple of large private libraries. Turns out there are more books in Mannington than we thought.

Estimates were made about the amount of heavy machinery. There was more heavy construction equipment than we thought.

Estimates were made about the precision with which the down-timers could produce products by hand. When checks were made about what they had actually done it turned out that: The down-timers were capable of more precision than we thought.

Is anyone starting to notice a pattern here? I haven't been involved in 1632 Tech from the beginning, but I have been around for a while. And one thing has shown itself to be amazingly consistent throughout: every learned estimate that has been checked against the facts on the ground-at least all those that I'm aware of-have been off, and all in the same direction. That direction is "less." Less equipment, less knowledge, less craftsmanship, less everything. Up-timer, down-timer, it doesn't matter. It's still always "less."

Thought Experiment

Let's take a break for a bit and try a thought experiment. To do this experiment, go to your local movie rental place and rent The African Queen. Now comes the hard part. Watch the movie, but try not to be distracted by the story or the excellent acting of Bogart and Hepburn. Instead, I want you to pay fairly close attention to the boat, and especially the little steam engine it uses for propulsion. Pause the tape, take notes, try to remember everything you've learned about steam engines from grade school on. Then, sit down and, using the movie and what you remember, try to design a small steam engine of comparable power.

Some of you will be able to do this, some won't. If one of ten of you can do so, then steam-powered barges on the Elbe and the lower Saale rivers will become fairly common, fairly quickly. Perhaps as important, small steam mills and shops will come into use in the towns around Grantville, to run things like lathes and small mills.

Now, in your minds eye, consult with some down-time craftsmen. Show them your drawings, tell them about how it's important that the steam be contained in the piston or pistons, then released at the right point in the stroke. Ask your pretend down-timer how he would go about making the pistons and cylinders, the rods, the valves, the crankshaft, and so on. Talk it over with friends from work, get their opinion. The percentage of those who can design a steam engine, compared to those that can't, goes up as errors get caught and concepts get added. One person doesn't have to be able to do it. Five, or six, or a dozen-each knowing different parts of how to do it-can get together and work it out.

Now, do the same thing with airframes, internal combustion engines, suspension systems, and so on. I think you'll be surprised at how often you come up with something that will actually work. It might not work really well, but it'll be an airplane that will fly or a suspension system that's better than they had on the stagecoaches of the old West. It has been said that all technology goes through three phases:

1 – Simple invention that doesn't work really well, like the first steam engine or the first screw on a ship.

2 – Gradual improvement and increasing complexity, like better carburetors, improved ignition systems, timing controls, gearing. In the case of screws/propellers improved tuning for speed, to avoid cavitation, reduce drag and a direct the greatest amount of water rearward. Here the increasing complexity is not in the screws themselves so much as in the design of the screws.

3 – Abandoning an invention for the next. Going from paddle wheels to screws is a good example of this one. Because even a pretty cruddy screw/propeller has one vast improvement over the best possible paddlewheel. Weight. Screws, even the most perfectly designed, are not nearly as efficient as a paddlewheel in direct terms. However, a paddlewheel weighs so much more than a screw that the improved performance is not worth the excess weight. Not even if it's a pretty crappy screw.

Cost Versus Benefit

In the simplest terms, the value of any product can be measured as the sum of material cost and production cost. The benefit in terms of industrial equipment can be measured in reduction of production cost. So the questions facing any person thinking of investing their time and money in a new production device are:

Will it work?

How much will it benefit us if it does?

In determining-well, guessing about-the answers to those two questions. the potential investor of the seventeenth century had to consider how much they were spending to produce the final product without the innovations. In the seventeenth century, before the Ring of Fire, that involved a couple of very basic problems for people who were considering, or willing to consider, investing in new production techniques. The first of those problems was, to great extent, that they did not really have a means of accurately measuring how much it cost them to make stuff without the new technique. And labor costs were dirt cheap. Together, those factors meant that they were buying a very expensive pig in a poke.

It is mentioned in 1632 that businesses are cropping up all over the place within only months of the Ring of Fire. By September of 1631, you cannot hire people without offering stock options, at least in the opinion of one of the people starting up the chemical plant. So why is that?

Not having so many people shooting at them might have had something to do with it. So did improved roads that meant that goods could be shipped by the wagon load rather than by mule load. The machines and electrical power that the up-timers brought with them must also have been a big help, both in making the production of production machines much cheaper and in facilitating the transport of goods.

However, to my mind the most important change was one of information. The question "will it work" changed to "can we make it work." And the answers, in general, became much more positive.

Cheap labor becomes less of a factor when you add in the amount of time labor takes. The craftsmen of the seventeenth century were often very skilled. They could produce products of exact measurements and fine quality, but doing so with the tools they had before the Ring of Fire took an incredible amount of time. And they had to be paid, at least a little bit, for all that time. If one semiskilled laborer and a machine could make the same number of products in a day as five highly skilled master craftsmen in a week, the savings are considerable, even when you include the cost of the machine. And with the spreadsheets and amortization calculations available, the estimations of those savings became a lot more solid.

How much time in inventing is spent inventing? What part of the years from first try to successful commercial production is spent actually figuring out how to make a product work? How much time does the inventor spend on the day job? How much time in interesting backers in the concept? More importantly, how much time is spent failing to interest backers in a particular product? In the sixteenth, seventeenth and eighteenth centuries, the amount of time spent on that last factor was measured in decades-and sometimes centuries. In large part, this was because the skills needed to invent something are not necessarily the same as the skills necessary to make a go of the company that will produce the product. And it can be really hard to tell whether a product failed because it just wasn't commercially viable or because the inventor was a lousy business person. Absent evidence to the contrary, the general assumption in the Early Modern period was that the product wasn't viable.

The Wietze Oil Fields

Did they drill for oil or mine oil? Who cares? The reason I don't care is because, whatever they did in our time line, it probably wasn't what Quentin Underwood did in the 1632 time line. Mr. Underwood had access to up-time equipment used for drilling water wells, parts fabricated in the up-timer shops, and certain preconceived notions about how you get oil out of the ground. Once he got to Wietze, he would have learned that the locals had been mining the oil sands and using the tar to pave the local roads and as a patent medicine. It is fairly unlikely that Quentin would have forbidden the local down-timers from continuing their mining operation. In fact, he probably started buying oil sands from them. He would also have started drilling oil wells, because that's the way you get oil out of the ground up-time. After consulting the closest thing the up-timers had to a geologist and the down-timers, he would have had a pretty decent idea of where to drill. He might well have drilled a couple of dry holes. If he was unlucky, he'd have drilled five or six dry holes. This is not by any means a disaster, it's more along the lines of an irritation. Sooner or later, and not much later, he was going to hit oil. The precise details about how all this happened would probably make a really good Gazette story. But it doesn't really matter that much in terms of the larger story arc.

What does matter in terms of the larger story arc, is the simple fact that there's oil at Wietze. Quite a lot of oil, certainly enough to run every machine brought back by the Ring of Fire. Plus all the machines that can be built in the USE until the mid-sixteen forties. It also matters that there is lots of oil in lots of places around the world. Places that are at least generally known. They know where to look.

Other nations will be slower… but not that much

Why hasn't Africa become an industrial power house? What about South America? There are, of course, any number of factors, many of them political, but one of them will tend to swamp the rest. Competition. By the mid-twentieth century, large and powerful industrial complexes had been established. To establish an auto factory in Uganda, you would need to make it impractical for the auto manufacturers in the US, Europe and Japan to sell to you and, at the same time, provide enough market to support mass production. The countries you're competing with already have the factories to make the car parts and the cars they build. Their heavy initial investment is already made, and paid for by their sales in other places.

That is not the case in Grantville, the SoTF, or the USE. It will take decades before they can even approach market saturation. Build a sewing machine factory, fine, great. But you're not going to make enough machines to get more than a small percentage of the market. So, six months later-two years at the outside-someone in another part of the USE or in France, Britain, Poland-or all of the above-will start a sewing machine factory. Start a typewriter factory: same thing. Drill an oil well: same thing. Most of the "how to" is in the library and preventing industrial espionage for the little bit left falls somewhere between impractical and impossible. But even if you pass a miracle and manage it, that won't keep your competitors from figuring out the missing bits on their own. Besides, what do you care? You have more customers than you can feed as it is.

An almost effective alternative to the hog-in-the-manger attitude of "We must keep it all" is the notion of franchises. Where the first, or one of the first, to do something makes up a set-up kit which they either sell outright or offer for a percentage of the new business. I say "almost effective" because it still won't keep people from going out on their own to do the same thing. It will just mean that the easiest route to successfully making widgets is to buy the widget franchise package. It's not a new idea or one that the up-timers can fail to be aware of, not with the ubiquitous McDonalds and Pizza Hut franchises. It might seem a bit strange to apply it to manufacturing shoes or sanitary products, but the down-timers were already doing something fairly similar with the spinsters working as jobbers for the cloth makers.

And what does this mean?

1632 Europe is an open market with lots of consumers and room for lots of people getting filthy rich by making lots of new products and old products faster and cheaper. So what does all this have to do with writing stories in the 1632 universe? Well, a couple of things.

One: it's not that important whether or not there is a book telling precisely how to make widget X. If there is, great. But even if there ain't, you can still probably make it a lot faster than it happened in our time line because, if for no other reason, it's going to be a lot easier to find investors. You may not find quite the same way to make it as they did in our time line, in fact you probably won't. You'll skip steps that were needed in our time line which can be replaced by something that wasn't available in 1816 or whenever the widget you're after was first produced. You'll have to find workarounds for stuff that didn't come back with the Ring of Fire or came back incomplete. You don't actually need a blueprint of a Fresno scraper or a life-size model of the Hindenburg. You can build a Grantville scraper or a lighter-than-air crane support without them. It doesn't hurt to have them, but it doesn't kill your story if you don't.

Two: you don't need up-timers. Like the books, they are convenient but not really necessary. Senor Carlos De Vega in Portugal can-and often should-be your hero, perhaps loyal to the Spanish crown or perhaps seeking an independent Portugal. In either case, working to make himself richer and the world a better place at the same time. Or Lue Chin, who just this morning got hold of a packet of plans from Grantville on how to make a Jacquard loom and realized that with it he can weave complex designs in to his silks and sell them to Japan for twice what he could before. Assuming that whoever is Emperor this week doesn't have him executed for western corruption or steal the factory for taxes.

By now it's out there, folks. The crate load of lamps and bottles are cascading down the hill and genies are popping up like weeds in a poorly tended garden. Air conditioners in Mexico? Sure, why not. After all, by now someone has gone though the books and magazines in Grantville, put together a cheat sheet and published it. It doesn't matter whether the design comes from the 1911 Encyclopedia Britannica, from one of the air conditioners in Grantville, or from down-time experimentation that was given just a few clues. What matters is that Chechiwa, the maid of the Spanish noble that owns the air conditioner, gets a chance to examine it and figure out that with a bit more work it could be used to freeze things and keep them fresh.

So go forth and write stories, tell tall, really tall, tales. Don't worry too much whether the book you read that told you how to build a can opener was in Grantville. By now, it doesn't matter that much. There's a good chance some of those busy researchers at the National Library have put together fairly decent specs and they are being published in German and Latin all over the USE. Don't try to have a Huey sitting in a forgotten valley in Grantville. Have your character build himself a rocket-powered air plane.

And be a bit cautious about telling your fellow barflies they can't build X because the vital bit didn't come though the Ring of Fire. A lot more stuff came though than was noticed at first glance. And even if the vital bit didn't make it through, there is probably a workaround.

Go find it.

Wingless Wonders

Written by Kevin H. Evans

Lighter-than-air technology is a lot like the game Go. It is easy to learn, but very hard to master. Many countries tried the technology, but only a few managed to master it. By far the largest number of rigid airships were built by Germany. On the other hand, the United States was the country which built the most non-rigid airships. Both countries expended large amounts of resources and effort in perfecting the technology. Other countries, in an effort to keep pace in the lighter-than-air race, created airships that were both technologically inferior and poorly operated. Many of these efforts represent some of the worst accidents in lighter-than-air history.

This technology, although considered by many to be obsolete, is actually quite useful and is coming back into use in modern technology. The following article is mostly about what we would need to do to use this technology in the post-Ring of Fire time frame.

Glossary

Normally I put the definition list at the end of the article, but I have seen such a large variation in terminology, that I want to put the list up front.

Dirigible – any aircraft that is controllable as it flies through the air.

Rigid Airship – any aircraft that has a framework inside the skin which provides shape and support for the aircraft.

Non-rigid Airship – an aircraft that depends on pressurization to maintain it's shape.

Semi-rigid Airship – an aircraft that has a keel and framework in the ends to support the load and provide shape to the airship.

Balloon – a non-powered aircraft that depends on lifting gas to make it fly.

Aerostat – any aircraft that depends on lift generated by an internal gas.

Ballonet – an internal balloon used to provide pressure and shape to a non rigid airship.

Gas cell – a container to hold lifting gas in a rigid airship.

Lift – the force that holds the aircraft in the air.

Drag – the force that impedes the aircraft as it moves through the air.

Thrust – the force that propels the aircraft through the air.

Control surface – devices that allow changes in attitude of the aircraft.

Density – the weight of a gas as measured in pounds per cubic inch.

Gross weight – the total weight of the aircraft including cargo and crew.

Tech Work-Arounds

Certainly many of the currently used materials and techniques are not available post-ROF and so work-arounds need to be developed for those items. Further, some items are very expensive and a cheaper item needs to be developed to use it its place. Throughout the text suitable workarounds will be mentioned where possible.

How Lift Works

Lift can be generated dynamically, as in a heaver-than-air aircraft, by moving the aircraft through the air. Indeed many modern aircraft when un-powered, have the flight characteristics of a brick, and depend on a continuous application of thrust to keep the craft in the air.

Lift can also be generated statically, as in aerostats, by using a lifting gas. This gas provides lift by displacing the atmosphere, which is denser and heavy, causing the container of lighter gas to float on top of the thicker air. The lighter the gas, the more it can lift. How much a gas will lift will be described later on.

Captive Balloons

These are balloons that are attached to the ground with an anchor. Such balloons are useful as observation platforms, entertainment devices, advertising, and as a "skyhook" for use as a crane. Captive balloons used as observation points have the advantage of allowing a communication wire to be attached to the tether, making telegraph or voice communications possible.

Balloons can be used for entertainment (rides) or advertising icons. Both are effective as a result of their size, eye catching colors, position overhead, and sense of fantastic unreality.

Balloon cranes have been used in to modern times as efficient transportation devices. One of the biggest advantages is the ability to transport bulky items (like logs or large stone blocks) across distances without the need for cutting roads or obtaining access through congested urban areas. This transport is achieved via the use of a cable affixed to a mast or hill top and using a traveling block and tackle mounted on a pulley. The use of a sufficiently large balloon allows lifts of weights in the tens of tons.

Free Balloons

This is the category of balloons that are inflated and released. Such balloons are subject to the wind and go where the wind pushes them. This does not mean that they are uncontrolled or un-guidable. They can be flown to locations by picking the wind layer going in the direction desired.

Free balloons can not "tack" like a ship because they have no counter-drag. A ship has the water it floats through to provide drag or resistance. This drag acts as a modification to the thrust of the wind allowing progress against the wind. Balloons are so large that the size of the envelope makes any secondary sail drag streamer or other passive device irrelevant. The closest a free balloon comes to tacking is when a pilot can balance the balloon on the interface between two wind layers and go in a third direction. This maneuver requires great skill and the existence suitable wind layers.

Airships

What we know as airships are aerostats that have the ability to be guided to a desired point regardless of the direction of the wind. The ability to guide an airship depends on the addition of thrust and control surfaces to the airship. This thrust is generally provided by propellers powered by engines attached to the airship. Also of note is the need for the airship to have a means of maintaining its shape. Moving a large object through the air faster than the air is moving causes stress on the object, and as the stress increases the object distorts in shape causing increased drag and unstable movement. Shape distortion can be severe enough to cause the venting of the lifting gasses and loss of lift.

Rigid Airships

Airships that have a system of internal stiffening are known as Rigid Airships. The internal structure provides shape to the airship and support for its equipment. Normally the frame is covered by a skin which is hardened by a "dope" that colors the skin and increases the skin's durability. Lifting gasses are contained in gas cells which are attached to the frame. Power plants, holds, cabins, control cars, and control surfaces are also attached to the frame. This class of airship also tends to be larger as the weight of the frame increases the dead weight which in turn makes the size needed to lift the gross weight larger.

Semi-rigid Airships

These airships are much like their rigid cousins. That is, they have a keel to support equipment. Often this includes a nose-cone frame to resist the forces created by forward movement and a tail cone to support the control surfaces. A semi-rigid design saves much of the weight attached to a rigid design but can make non inflated storage complicated. Semi-rigid designs often include elements of non-rigid designs, notably ballonets to aid in maintaining the shape of the envelope.

Non-rigid Airships

In a non-rigid airship, the skin is the gas-containing device. Shape of the skin is maintained by the use of a ballonet. A ballonet is a cell within the skin that is pressurized to create induced pressure on the skin and so maintain the shape of the airship. It is usually only about five percent of the total envelope capacity, and is only necessary to maintain the desired shape of the airship. It is notable that the ballonet is normally filled with air pumped in from the outside of the skin and thus can be regulated without loss of the lifting gasses. Equipment is usually mounted on the control car, which is hung from a cantenary curtain attached to the top inside of the skin.

Other Classes of Airship

In our time line, near the end of the airship age, (in the 1940s and 50s) developers were experimenting with airships called metal-clads. Metal-clads were airships that had a skin composed of aluminum and had elements of rigid and non-rigid design. The greatest advantage was that the metal skin almost completely stopped leakage of the lifting gasses. The best known of these was the US ZMC-2 called the "Tin Bubble." The Tin Bubble was perhaps the most successful of the U.S. Navy's airships. This airship was so reliable that it used up two sets of engines before it was retired from service.

In addition were classes where a significant portion of the lift was provided by the shape of the airship, and acted much like more standard aircraft.

Lifting Gasses

Flight in LTA (lighter than air) is a result of static lift. That is lift that exists whether the aircraft is moving or not. This lift is generated by the difference in weight of the contained gas compared to the atmospheric gas the aircraft is immersed in. By and large there are three gasses in use for lift and a few more gasses that can work but are marginal in application. In our time line, we use hydrogen, helium, and hot air as lifting gasses. Some commercial city gasses such as natural gas and ammonia are also lighter than air and have been used as lifting gasses. But they are not a lot lighter than air and require a much larger volume to be effective. Of the big three, hydrogen is the lightest and provides the most lift, approximately 66 lb per 1000 cubic feet. Helium will lift around 44 lb per 1000 cubic feet. And hot air will lift around 20 lb per 1000 cubic feet.

Each of these gasses have advantages and disadvantages. Hydrogen will burn, helium is extremely hard to find, and lift from hot air varies depends on the air pressure, temperature and humidity present during its use. On the other hand, hydrogen can lift a lot, helium is non-flammable, and hot air is easy to get and can be used with minimal crews and facilities. For example, to lift one ton hydrogen needs 30,304 cubic feet of gas, with a sphere of 39 feet in diameter. Helium needs a sphere 44 feet in diameter with a volume of 45,454.4 cubic feet. Hot air varies (18-24 lb per 1000 cubic feet) but for design purposes is centered at 20 lb per 1000 cubic feet. This results in a sphere of 57 feet in diameter with a volume of 100,000 cubic feet.

Of the lifting gasses now used, helium is right out for the Ring of Fire. The only known source of helium in usable quantities is a set of gas wells in the western half of the North American continent. Both the location and the technology needed will make this gas impractical.

This leaves hydrogen and hot air as usable alternatives. Hydrogen will lift 30% more than helium and is much easier to get. Hot air will lift just less than half of helium, but is even more simple to get. The disadvantages are that hydrogen burns with great enthusiasm, and hot air needs the frequent application of heat to keep its lift.

Hydrogen has had a bad reputation since the 1930s, but has become much more favored in the last ten or so years. Much of the reputation was due to a number of accidents caused by an imperfect understanding of the gas and electricity. New practices and designs have significantly lowered the hazards of hydrogen. Long distance gas balloon racing has switched more and more to hydrogen due to it's substantially lower cost and greater lifting capacity.

Most important among the new practices for hydrogen use is that the aircraft must be a single entity in relation to conducting electricity. This oneness of structure prevents arcing from one section to another section of the aircraft and denies any ambient hydrogen an ignition source. Also the envelope must be adequately vented so as to allow any leakage of gas to immediately exit the aircraft. And finally the gas cells must be frequently emptied and refilled with pure hydrogen, as oxygen has a tendency to migrate in to the gas cell, creating what is called a rotten cell. That is a cell that is easily combustible due to the availability of oxygen in the mix.

Hot air has a lower lifting capacity and requires an aircraft of roughly three times the size for an equivalent amount of lift. Also significant allowance must be made for fuel to maintain the heat in the air, this fuel is in addition to the fuel for used for motive power if any. Currently in our timeline, fuel requirements have been going down with the use of redesigned materials. A standard hot air balloon usually gets about an hour and a half of flight time from twenty gallons of fuel. New materials have allowed as much as thirty hours of flight from the same amount of fuel. Surprisingly the biggest modification has been a multiple layer approach that reduces the heat transfer out of the envelope. Hot air also has another great advantage, because the typical balloon or airship is non-rigid it stores in a much smaller space and can be handled and crewed by significantly smaller numbers of people.

Power Plants

Many types of aerostats need power plants. Airships need them to move through the air and hot air balloons need them to heat the air inside to provide lift. A power plant should be light. That is, they need to have a good power-to-weight ratio and should be dependable. Traditionally, diesel and gasoline have been the fuels of choice, but kerosene and propane have also been used. Due to the ability of an airship to provide static lift, lower horsepower engines are usable. Lower horsepower engines provide economy in fuel and cost of the engines. Additionally, other types of power plants have been used, with steam and hot air (Carnot cycle) engines being the most common. The lifting gas used also affects the power plant, with the power being mounted inside the envelope when using nonflammable gasses (allowing easy engine maintenance) and mounting the plants outboard when flammable gasses are used. Power plants for hot air balloons are the burners used to heat the air inside the balloon. Such burners normally provide 2 to 6 million BTUs to the air inside the envelope depending on the size of the air mass to be heated.

Modern airships are powered by a variety of means, most commonly the internal combustion engine. Such engines are in limited supply in the immediately post-ROF world, but will become more common as knowledge and tooling spread out from Grantville. Many internal combustion engines need tight tolerances and advanced lubricants, however there are large numbers of engines possible at a lower technical expertise.

In 1900 the "gnome rotary" (an engine where the cylinder block spun and the pistons were attached to the frame) was invented. This engine was a single valve (per cylinder) with the fuel fed from the center crankshaft along with the lubrication, all of which was exhausted from the cylinder each rotation of the block. This is the engine that made all early airplanes possible. Their major disadvantage was that they were a single-pass lubrication. That is, the oil is used once, and ejected from the engine. This oil was castor oil, and the engine moved in a constant cloud of oil vapor.

By the way, this accounts for the drinking tradition of fighter pilots. Since the pilot was bathed in a cloud of castor oil, they ingested large amounts of it. In an effort to absorb some kind of food value that was not "cleansed away" by the qualities of castor oil, they took in vast quantities of wine and beer as the alcohol metabolized quickly, before the colonic took everything else away. At least, that was the excuse. If this sort of engine is used in an airship, since it would be mounted below or behind the cabin, airship pilots would be "beyond" this sort of problem.

In 1903 the Wright brothers made their engine in a bicycle shop. This was a standard internal combustion engine of four cylinders using the Otto cycle. Such engines are not high compression, efficient, or even very powerful. But they work, dependably and every time (mostly). Further, such engines can be made with low tolerances and primitive machine tools.

Steam power is also an option. A steam generator (a flash boiler), a light weight engine, and a condensing coil can be made well within the weight limits available.

Last, a Carnot cycle engine removes even the need for water as a working fluid, but does so at a need for much higher tolerances. So much so that the internal combustion engine, with it's low tolerances claimed the position of first choice among engines, and so received almost all the research and development in our culture.

Envelope Construction

Envelopes are constructed from materials that are impervious or resistant to passage of the lifting gas. Of note is that the rigid frame airship has gas-containing cells inside the frame with a cloth covering over the frame that provides a smooth surface to the outside environment.

Traditionally the great airships of the 1930s used a material called goldbeaters skin to form the gas-containing area. Goldbeaters skin is made from the lining of an ox stomach and had the dual properties of being impervious to hydrogen gas and of making gas-tight seals when the edges are properly treated and placed together. The problem with this material is that the total amount of "skin" per oxen is very small (not much larger than a sheet of paper), and thus needs a lot of dead oxen, with over 200,000 used for a ship like the Hindenburg.

Currently most airships use a layered fabric made from cloth treated with latex or Mylar. Mylar is also used solo as a gas-containing material in some airships. Gas balloons are made from treated nylon, because the lifting gas is vented in flight as part of the control process. Hot air balloons are normally made from treated rip stop nylon. It is important to note that the use of the nylon imposes a maximum usable temperature, as too much heat will melt the envelope.

Physically the envelopes are normally made from a set of segments called gores. The gores are sewn together using "French seams" which are double sewn and leave no loose ends. Additionally some seams may have a load-bearing tape or wire enclosed to provide strength to the envelope and give places where the load can be attached.

The best envelope ever constructed was that of the ZMC-2, a semi-rigid airship called by its crew the "Tin Bubble." This envelope was a three layer sandwich of aluminum that allowed gas leakage only at the valves and outlasted two sets of engines. Alas, large quantities of aluminum are probably out of reach for the near- and mid-future in the 1630s.

By far, the largest number of envelopes were made from latex-impregnated fabric. Over 150 such aircraft envelopes were made for the US Navy alone. Nylon, polyester, and rayon are also popular materials for envelopes. Of all of these, the cotton and latex fabric is the most feasible for the ROF. Cotton cloth is available in large quantities from India, and latex is found in usable quantities in a number of common plants notably dandelions, ragweed, and milkweed. And so the manufacture of this fabric is possible in the post ROF time line.

Structure

The material of choice for airships is aluminum. As previously mentioned, aluminum will not be available in large quantities for some time. Rigid airships will need something else. A substitute, actually used by the German navy in World War I, was wood. Split and laminated spruce is light, strong, and provides many of the properties of aluminum. The downfall of wood is its slightly greater weight by volume for the same strength, and its tendency to absorb moisture. Moisture makes the wood heavy and can cause degradation of the lamination in the frame. One of the cures is to coat the frame in varnish. This excludes the moisture but adds to the overall weight.

Applications

Aerostats have both civil and military uses. Almost any conceivable activity can be customized for either use. At first glance the military would seem to be a higher priority, but commercial uses may greatly outstrip military uses in value.

The most immediate use would be transportation. Properly constructed, an airship can move large cargos to remote areas with little or no infrastructure on the receiving end. An airship of 1.5 million cubic feet (440' X 70') would carry 50 tons gross weight. Assuming fifteen tons of vehicle and crew, that gives thirty-five tons of cargo delivered anywhere.

Power requirements for an airship are significantly lower than aircraft of the same capacity due to static lift of the gas. Handling and storage can be greatly simplified with proper terminal design and vectored thrust engines (Mount them on pivots to allow maneuvering against the wind.)

Militarily this would allow the delivery of high priority cargos to the battlefield. Commercially, an airship could pick up a cargo from the factory and deliver it directly to the customer, even position the cargo in the case of a large item like a generator rotor for a large hydraulic plant. A company, "Cargolifter" had built a prototype and had obtained terminal facilities to begin operations in 2002. It lost funding in the stock market crash of that year, and so never built beyond the prototype.

The ability of an airship to hang in one spot makes it an unsurpassed observation platform. Combined with a radio, and a telescope, airships can provide search and rescue, survey, and battlefield reconnaissance. Tether balloons also have great utility as an observation platform and gave significant advantages to the forces using them in the American Civil War. Convoys escorted by blimps used by the US Navy suffered no losses to submarines in WWII due primarily to the airship's ability to maintain station on the convoy and look directly down into the water for the submarines. Also the Navy had a number of rigid airships that were used as scouting elements for the fleet allowing a very large area to be surveyed in combat conditions. These airships were also aircraft carriers and could launch and recover aircraft while in flight to further expand their coverage.

Another use is to lift really large loads with a minimal infrastructure. "Sky Cranes" were used in the logging industry to reduce the need for cutting roads and make transportation fast and easy. Tethered balloons can lift and position large loads in crowded urban environments. Militarily, a cargo lifting balloon can speed cargo load-on in forward areas without the need for heavy cranes or large scale ground stabilization for lifts and loaders.

The last area that I will mention is recreation, including passenger transport. The Graf Zeppelin (LZ127) logged more than a million miles of passenger transport. All these miles were without accident and using hydrogen as a lifting medium. The Graf also made the first non-stop flight across the Pacific in 1929. In the 20's and 30's numerous point-to-point air routes were in use as fast luxury travel in Germany. While the Queen Elizabeth could make twenty knots, the Graf averaged eighty. So an Atlantic crossing would take the ship an average of twelve days. The airship could make the trip in three. The most common run for Graf Zeppelin was Berlin to Buenos Aires nonstop. It was not until after World War II that any commercial airplane could attempt the same trip.

Weather

Another item that needs to be specifically covered is the handling of the airship in rough weather conditions. Like fixed-wing aircraft, airships have conditions where they cannot fly. High wind conditions, and thunderheads are the two biggest killers of airships. In a high wind, that is 60 miles an hour or more, airships have great difficulty in flying against the wind. One early proto-type aerostat was scheduled for a trip into Germany, but was delayed several days, because no progress can be made against the wind. While this was not fatal for the airship, it did cause the airship to have a delay in its service.

The other big weather problem are extreme thunderstorms. The Shenandoah, an airship flown by the U.S. Army, was lost when its captain decided to fly through a line squall of thunderheads. This resulted in the airship being broken into three pieces and the death of over half of the crew. However, these weather conditions also affect fixed-wing aircraft in very much the same manner. Even at our level of technology, the weather still is king. Therefore an airship needs special facilities to keep it safe from the weather when not in use.

This is usually a hangar large enough to contain the whole airship and strong enough to resist any wind that hits it. An alternative to a hangar, is to have a tower with a pivot connector that hooks to the bow of the airship, and a track that circles the tower, so that the back of the airship can be connected to a cart that runs on the track. This allows the airship to change its orientation much like a weathervane so that wind resistance is minimized. Certainly the most important means of safe flight in bad weather is knowing when not to fly.

Sample Aerostats

In describing sample aerostats the following criteria will be used:

Purpose, gross lift, weight, useful lift, cubic capacity, shape, dimensions, speed, power plant, lifting gas used, and rough cost.

First a small thermal airship.

This is a recreation and sport aircraft designed for local use buy a hobbyist.

The cubic capacity is 150,000 feet.

The gross lift is 3000 lb @ 20 lb per 1000 cubic feet.

The weight of the airship is roughly 1500 lb (600 lb envelope, 400 lb basket, 500 lb fuel and power plant).

The airship is an ellipsoid (cigar shaped).

The airship is roughly 160 feet long by 40 feet in diameter.

In still air the airship can attain 30 mph.

The airship is powered by two 40 hp air-cooled engines with ducted fan propellers.

Lift is provided by hot air created by burners internal to the envelope.

The rough cost is 80,000 to 95,000 $USE primarily due to the cost of the fabric.

This airship is a recreational vehicle for a hobbyist. The design is based around the thermal airships in current use in our time line for competition and light advertising. It is a pressurized envelope with internal burners. Pressure in the envelope is maintained by a fan forcing air in to the envelope and controlled by a pressure relief valve in the nose. Landing and emergency venting of the envelope is by means of "parachute" valve in the top front of the envelope. This allows the venting of hot air for rapid descent or emergency deflation on landing if needed.

The construction is basically non-rigid, with the load of the "car" carried on cantenary wires from the crown of the envelope. Control surfaces are mounted on the car, and consist of an inverted "V" tail placed in the slipstream of the engines.

Operation of the control surfaces is by means of cables between a yoke in the pilot's position and the tail planes. The engines are mounted on the rear sides of the car and can be pivoted 270 degrees for climb and dive. Control of the engines is also by cables and include speed and pivot position. Instrumentation includes an altimeter, a vertical sink indicator, fuel gauge, an internal temperature readout for the envelope, and a sight ring for estimating speed.

A flight would proceed as follows. With the car and envelope unloaded from storage, the car would be oriented with the long dimension of the envelope parallel to the wind (bow upwind). The envelope would be spread out in preparation for the cold inflate. The bow line is attached to an anchor strong enough to hold the airship against any wind present.

The envelope pressure valve is tested, the burners are mounted to the car outside of the envelope (which is displaced to the side for the test) and hooked up to the propane supply tanks. The burners are then test fired for a preflight check. After the burners cool they are mounted inside the envelope and the envelope is sealed.

Cold inflation is by the fan used to maintain pressure in the envelope. Unlike a hot air balloon, the cold inflation causes the envelope to fill and stand above the car even without the hot air. During cold inflation the control surfaces and engine tilt are operated to insure that they are functioning. Once cold inflation is complete, the burner pilot-lights are lit and the burners are operated to put hot air in the envelope. The crown vent is checked to insure that the control rope is free and functioning.

As the lift increases, crew and passengers are boarded. The engines are started and run through their power range then set to idle. The burners are run until positive lift is achieved. The engines are run up until the bow rope is slack, then the anchor is cast off and some tilt is given to the engines to lift off.

During flight attention is focused on maintaining level flight via the VSI and burner control. The pilot also maintains the desired course. Maximum recommended altitude is 18,000 feet. There are serious oxygen issues over 15,000 feet. Typical endurances for this type of airship is two and a half to three hours. Recommended flight times should not exceed two hours, allowing a reserve of air time for emergencies.

Landing is begun by approaching the desired landing site from downwind, and flying against the wind up to the landing site. The airship loses altitude by allowing the air in the envelope to cool, venting air, and engine tilt as needed. The ground crew captures the bow rope and attaches it to the anchor. The air is allowed to cool (or is vented) until negative buoyancy is achieved. Any ground operations are carried out such as ground crew holding lines, or maneuvering the basket. Also, more fuel and passengers or cargo could be loaded, and so start another flight.

Shut down of the airship requires that the burners are extinguished, and allowed to cool. Then the pressure fan is stopped, and the crown vent is opened. The tanks are removed and the envelope is rolled up and placed in the car, and the airship is placed in storage.

Next, a rigid cargo airship

This is a medium-sized ridge airship primarily used to transport cargo.

Gross lift is 50 tons (100,000 lb)

The airship weighs about 15 tons (with fuel and crew)

Useful lift is around 35 tons.

The envelope holds 1,500,000 cubic feet.

The airship is an ellipsoid (cigar shaped) with external control car, control surfaces, and engines.

The envelope is about 440 feet long and 70 feet in diameter, cargo is slung below the keel.

As equipped the airship can travel 65-70 mph at full power.

Power is provided by six nine-cylinder steam engines, with 300 hp generated when running at full speed. (2200 rpm, 400 psi). Engines are rotary, with bash valve steam admission, composed of nine single-acting pistons each. Exhausted steam is recovered and condensed. Steam is made by mono-tube "flash" boilers, with a boiler, condenser, and engine all housed in each "pod."

Lifting gas is hydrogen, with an average lift of 66 lb per 1000 cubic feet. This is a SWAG but cost should be in the neighborhood of 1.5 to 3 million $USE.

This airship is a cargo hauler. The airship has a frame with a skin on the outside and gas cells inside for lift. Control car engines and cargo are mounted outside the envelope. The cargo is carried in a container slung below the keel of the airship below the center of gravity. Further the container should be standardized to also fit truck and railcars, making it a true intermodal system. (Note that anything that can be balanced and slung could also be carried.) All the engine pods are powering ducted fans, and are mounted so as to be rotated for vectored thrust, allowing the airship to be "parked" while loading and unloading the container or cargo.

Such airships could pick up and deliver cargo almost anywhere. When not in use more elaborate basing systems are needed. Best is enclosed hanger space, allowing the airship to be stored in "flight," or filled with lifting gasses. Next best is a central tower with a ring of track around it, this allows the airship to be docked to the tower by the nose and rotate around the tower in accordance with the wind. The ring track allows the rear of the airship to be tethered to a rail car, allowing control of the whole airship on the ground.

Air crew would include enough bridge crew to stand twenty four hour watches, (Helm and watch officer x 3) and a chief engineer, and enough engine crew to stand watch on each engine pod, (1+(6*3)), and a cargo officer. This gives a crew of at least 15.

Off duty crew are accommodated inside the envelope at the keel of the airship. Since the gas cells of this ship are smaller than the skin of the ship, there is sufficient room for crew quarters a small living space. It would be not much more than a space to sling hammocks when not on duty. Food preparation would be without flame, so would probably be cold prepared foods in flight. While this ship is capable of longer flights, it would be most used for one or two day trips.

Such an airship should also have enough fuel for ten days cruise, giving a sustained cruise of 12,000 miles at fifty mph. Such a speed would allow easy one day trips to any part of Europe. A typical day would be, at the main base, fuel and preflight, load ballast, launch, fly to intermodal yard and pick up outbound container, (20,000 lb of cane crushing widgets, and 40,000lb of mixed cargo), drop ballast, fly to Amsterdam intermodal yard, drop container, pick up 60,000 lb container of new world Rum, return to Magdeburg intermodal yard, drop cargo, pick up ballast, return to base, moor to handling equipment, move to hanger, rinse and repeat. Bulk cargos could make lots of money. In 1657, England averaged 400 ships a year, with 150 tons of cargo each, just of sugar.

Last, a sky crane.

The aerostat is a tethered balloon, used as a construction crane.

Balloon gross lift is four tons. (8,000 lb)

The weight of the flying tackle (balloon, lift harness, ropes and pulleys, etc) is 3,000.

Max free lift is 5,000 lb, working lift is 4,000 lb.

Cubic capacity of the aerostat is just under 121,300 cubic feet. (hydrogen at 66 lb per 1000 cubic feet)

The aerostat is a sphere, roughly 28.7 feet in diameter. 2588 square feet surface area.

Aerostat is tethered, no power plant or on board crew.

This aerostat is a stationary lifting device. It's purpose is to pick up heavy things and put them, precisely, in an exact spot. The envelope is constructed of sealed cloth inside a net. The net supports the "flying tackle" that is, ropes, pulleys, and control systems. The balloon is tethered to the ground by three adjustable anchor ropes.

In use, the balloon would first be topped with off with gas for the day's work. The control tackle (the three tether ropes) are let out until the balloon is above the first load of the day. The flying tackle is attached to the load, and the control tackle is let out until the balloon is above the desired unloading position. The maneuvering of the balloon is by means of the three control tackles. The flying tackle is then let out until the load is in position. The load is removed from the flying tackle, and the balloon is repositioned for the next load.

System cost is the envelope and the tackles. The envelope is 2588 square feet of fabric, and the netting. The four tackles are a set of blocks and rope each strong enough to hold the max load (16,000 lb allowing safety factor). Total cost should be close to 150,000 $USE.

The Grantville Connection

In Grantville, purpose-built lifting and recreational aerostats will come in to existence as soon as the need is perceived. Some members of the community have prior experience with sport ballooning, and others may have a historic interest. Lifting balloons may be especially attractive when high-capacity cranes are found to be difficult to build, with movement of the crane systems being another large concern. Information sources to be found in Grantville are encyclopedias and personal libraries of the sport ballooning enthusiasts in town. Most notably, the Encyclopedia Americana, and the Encyclopedia Britannica. While the articles are not highly detailed, they do give enough information to get lighter-than-air technology started. The biggest factor in lighter-than-air development will be that the people know it is possible and will try stuff until they make it work.

The biggest concern however will be overcoming the "it's not modern enough" bias built in to the up-timer mentality. In our time line, airship travel was abandoned just as really efficient airships entered the market. This abandonment has been attributed to the dangers of flammable lifting gasses, but is probably more due to the outbreak of World War II.

Post war, the facilities and technologies created during the war lead the aviation industry in a different direction. Airplanes were available from army surplus, air bases were located around the world, and we had gotten used to the idea of large airplanes with internal combustion engines. With such momentum, research and development of airships did not recommence until the 1980s.

The Rest of the World

Airships will be very attractive to down-time political units. Static lift provides flight with much lower horsepower demands. Also, airships give a limited technology plant a lot of "bang for its buck" when large numbers of complex engines are difficult or impossible to make. Large lifters will allow comparable cargo amounts to be shifted, and will allow the "We fly too" for the polity. As with many other concepts, just the knowledge that it is possible will spur development.

In regard to those hostile to Grantville or the USE, having something that flies will allow them to gain some equality on the field of conflict. The benefits from scouting alone make any kind of aerial vehicle well worth the effort. This is not exclusively limited to powered airships. Tethered balloons with some type of signaling apparatus, either a wired teletype, or even signal flags, can be invaluable on the battlefield. Having timely pertinent information as to what is really going on and can be an enormous force multiplier. Said information can be the difference between winning or losing the battle especially in this time period.

Another use that may be of interest to the world is to have a small airship as part of the equipment of a naval warship. The small airship is not intended to do any combat, but it is to be used as a scout to increase the amount of area that the warship can see and therefore control. Having such a scout will allow fewer numbers of ships to control larger amounts of space, thus making each ship much more flexible in allowing the use of fewer ships for the same amount of work.

Conclusion

Lighter-than-air vehicles will have a window of utility where they can be the best alternative for a developing aeronautical program, especially outside the Ring of Fire. As has been stated, lighter than air vehicles will allow nations who are developing new technology, to maximize the amount of aerial capacity for the material they expend in their flight programs. Well-developed airships will be able to carry more weight sooner than comparable aircraft, especially as ground facilities will have to be developed for those aircraft. Nevertheless, heavier-than-air aircraft will dominate where air speed is more important than capacity. To say it another way, if you want to go in comfort take an airship but, if you want to get there right now take the plane.