In the world the up-timers left behind, the most widely consumed substance on Earth was water. What came second? Concrete. Indeed, concrete can be said to be, quite literally, the foundation of modern society. We depend upon it for shelter (concrete buildings), transportation (concrete highways), and energy (concrete dams providing hydroelectric power).
In Part I, we found out why the down-timers are going to rediscover the advantages of concrete as a structural material, and, by reinforcing it, take it—literally—to new heights.
In this part, we will first consider the nitty-gritty of proportioning, mixing, laying, curing and testing concrete, and then move on to the fun stuff—talking about what we can build with it.
Designing (proportioning) the concrete mix is an essay in the art of compromise. For plain concrete, we need to worry about the ratios of four ingredients: water, cement, coarse aggregate and fine aggregate. (For the moment, we will assume a Portland cement and no admixtures.)
An architect (or perhaps a building code) will have specified the minimum 28-day compressive strength of the concrete (“design strength”). The most important consideration is the ratio of water to cement (w/c). In 1919, Duff Abrams discovered that the strength (at a fixed age) increases as the w/c ratio decreases, provided the concrete can still be fully compacted (Camp; Cowan 128; Bauer 98). ACI figures that for plain concrete (non-air entrained), a 0.68 ratio yields a standard strength of 3000 psi, and 0.41, 6000 psi. (For air-entrained concrete, reduce the ratios by about 0.08-0.09.)
A lower w/c ratio also results in lower porosity of the cement paste. (Camp, Chap. 8). That correlates with lower permeability and hence higher durability (stops water from entering, bringing nasty chemicals in with it, or just freezing inside the concrete and stressing it).
Unfortunately, low w/c ratios (“stiff mixes”) are also less “workable,” because there is less water to act as lubricant between the particles. (It follows that high aggregate-to-water ratios also result in less workability.)
“Workability” refers to the ability to mix, place, compact and finish the concrete. Workability is usually measured by the “slump” test (see below). Slump is usually specified by the contract with the concrete supplier. The desired slump will depend on the type of construction, but it will usually be in the 1-4 inch range.
Typical w/c ratios are 0.4-0.7:1, and it is customary to prepare trial mixes and test whether, with the available cement and aggregates, they provide the desired strength and workability.
Another consideration is shrinkage. Shrinkage causes cracking. To reduce shrinkage, we need to reduce the amount of cement in the mix (sand and gravel doesn’t shrink). But you need enough cement to mostly fill up the voids between particles. So that means that you have to find the right “grading,” so the fine aggregate fills up the voids between the larger pieces.
Reducing the amount of cement is also economical; cement is typically the most expensive concrete ingredient.
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Several engineering handbooks contain extensive tables of trial mixes. Grantville’s encyclopedias contain a number of recommendations on mix design and even some specific “starter” mixes. 1911EB “Concrete” says that the ratio of sand to cement can vary from 1:1 to 4:1, and that of gravel to cement is in the range of 3:1 (for very strong work) to 2:1 (for “unimportant” work). It says that the combined volume of the sand and cement should be sufficient to fill the void volume of the gravel. (The void volume can be crudely determined by filling a can of known volume with the gravel, and then seeing what volume of water the can will hold.)
A sample proportion mentioned in the article is one part cement, two parts sand, and five parts gravel. (Note that this gives a gravel/cement ratio of 5:1 which is higher than the 3:1 stated previously. I suspect that the intent of the writer was to refer to the ratio of gravel/sand, or gravel/sand+cement, and not to gravel/cement.) Insofar as water is concerned, it says that the amount required for the chemical reaction is 16% by weight, but that in practice more is needed to compensate for evaporation and other losses.
The Columbia Encyclopedia gives a “typical proportion” of “one part of cement, two parts of sand, and five parts of broken stone or gravel, with the proper amount of water for a pouring consistency.” The Encyclopedia Americana “Concrete” article suggests, as a hand mix, one pound water, two pounds cement, four pounds sand, and five pounds coarse aggregate. And Time-Life’s Masonry (26) suggests one part cement, two parts sand, and four parts gravel, with a half part water.
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Because fly ash improves workability, blending it with Portland cement allows use of a lower water/cement issue and hence the concrete can be of higher strength. It is no accident that Chicago, which is well supplied with fly ash, has a large number of concrete skyscrapers (Camp).
A 94 pound (one cubic foot) bag of Portland cement might be combined with 188 pounds sand and 376 pounds gravel (ratio 1:2:4) . If the w/c ratio is 0.5:1, that calls for 47 pounds (5.64 gallons) of water. Air-free concrete with standard aggregate would weigh about 150 pounds per cubic foot. If the air content of the concrete is 4%, the density is 144 pounds/cubic foot, and you have about 715 pounds, or 4.95 cubic feet, of concrete per bag cement. If you know the volume of the slab, wall, column or beam you wish to pour, you can calculate how many bags of cement (and everything else) you need. One percent reinforcing steel would add about 4 pounds/cubic foot to the plain concrete.
In 2000, there were several choices for mixing concrete. The simplest from the contractor’s point of view was “ready-mix.” The concrete batch is placed in a mobile mixer, and mixed while en route to the job site. Or the concrete is mixed in a stationary mixer at the ready-mix plant, and then transferred to a truck, which merely keeps it sufficiently agitated so it doesn’t set.
While concrete was used in construction in the early nineteenth century (in a concrete bridge in Souillac, France in 1816), it was not until 1913 that ready-mixed concrete became available; it was hauled in a dump truck. That meant that the concrete had to be remixed upon arrival (Ali). Dedicated truck mixers were introduced in the 1920s. The earliest ones carried only one cubic yard of concrete; a modern truck mixer carries 10-12. The horizontal-axis revolving-drum mixer truck was introduced in 1930. (Kuhlman Corp.).
It remains to be seen how quickly ready-mix will be introduced in the new time line. The alternative in 2000 was to mix the ingredients at the job site. A contractor might have a portable mixer, mounted on skids, wheels or a tractor hitch. The ingredients (including as much as two bags of cement) are dumped into a hopper, and mixed in a revolving drum, which is powered by an electric motor, a small gasoline engine, or a tractor. In post-RoF Germany, one can imagine the drum being turned as a result of animals trudging in a turnstile, or even hand-cranking.
An even more primitive method of hand-mixing is to lay the sand, cement and gravel in a “mud box,” or a wheelbarrow, mix them up with a hoe-like instrument, and then slowly add water. (Ahrens 55).
In 2000, hand-mixing of concrete was facilitated by buying dry mix concrete, that is, a mix containing all of the ingredients except water. This isn’t available in the seventeenth century, of course, but it isn’t much of a step to go from bagging cement to bagging dry mix. The real problem with dry mix after RoF will be transportation costs; it will be cheaper to just have cement delivered to you, and mix it with local sand and gravel, then to pay for delivery of a much greater weight of dry mix.
For a big job, a mixing plant can be built on site. It may be possible to come up with a “set up, use, and knock down” plant design, primarily of lightweight (wood) construction, so that the plant can “hop” from one major construction site to another.
Formwork. The plasticity of newly formed concrete is both blessing and curse. Blessing, because that is what gives it its characteristic versatility of form. Curse, because it must be poured into a “form” (a kind of mold) to hold it until it has hardened enough to support its own weight. That typically takes 1-2 days in summer and 4-7 days in winter (Ahrens 62).
That means, in turn, that the preparation of the site includes building, erecting and bracing the forms, which can be made of wood, metal, or, when they become available, plastic or fiberglass. Handling formwork is probably the most time-consuming aspect of concrete construction in the modern age. (Of course, in the modern age, contractors don’t have to worry about making their own cement. )
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Placing. Once the forms are ready, the freshly mixed concrete is placed where it needs to go. Time is of the essence, since the initial set takes place in 30-60 minutes, and moving the concrete after it occurs will reduce strength. That means that the labor on hand for placing the concrete has to be adequate for the amount being handled.
Concrete is compacted to reduce air voids. If the mix is high in water, this should be done with a hand tool. But vibrators allow the use of “stiff” (relatively low water content) mixes that can’t be placed properly by hand. They can reduce the air content from, say, 1.5% to less than 0.5% in perhaps two minutes. (Used on a water-rich mix, they have the undesirable effect of segregating the water from the aggregate.)
Vibrators are gas- or electric-powered, and can be internal (placed inside the concrete), attached to the form, or placed on the surface. It is reasonable to expect the general contractors in Grantville to have a few concrete vibrators. (Ahrens 67-9).
An alternative is to formulate self-consolidating (self-compacting) concrete, which can be placed by its own weight, without vibration. This was introduced in the 1980s, and uses water-reducing and superplasticizing agents. We will have to rediscover the additives before we can make the concrete behave this way.
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Pumping was developed in the 1930s, if not earlier. Pumping comes in handy for reaching the upper floors of a building. There are piston, pneumatic and squeeze pump designs. Concrete can be pumped 500 feet vertically and more than 1500 feet horizontally. The concrete mix may need to be adjusted (e.g., restrict maximum aggregate size) to render it suitable for pumping. (Camp). A special concrete mix, “shotcrete,” may be sprayed onto the interior of a fabric balloon to make a thin shell monolithic dome.
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The old Roman concrete (really, a mortar) was not plastic; it had a very low (“zero slump”) water content. The Romans laid the coarse aggregate by hand and pounded the mortar into the gaps. The modern equivalent is roller-compacted concrete. It is placed with an asphalt paver and then compacted with a vibratory roller. (Moore). RCC is used mostly for low traffic pavement, and for dams (less heat generation).
Setting and Curing of Concrete
It is important to recognize that the setting (loss of plasticity) and curing (hardening and strengthening) of concrete is not the result of drying out by evaporation. Alite and belite react chemically with water (so-called “hydraulic reaction”) to form calcium silicate hydrates (C-S-H), which are the effective cementing agents. The more reactive alite contributes to early strength and belite to late strength. (If pozzolans are present, there is also the reaction of silica and lime to form C-S-H.)
Once concrete has dried out, it stops getting harder and stronger. Fresh concrete has, initially, enough water for the concrete to reach full strength, but unfortunately it will lose water as a result of evaporation. Hence it is customary to moist-cure it for a period of time, either by sealing the surface (e.g., covering it with plastic or waterproof paper sheets, or spraying it with a sealant), or by supplying additional water during the curing period. Water can be supplied by covering the surface with wet material (wet burlap, canvas, sand, shaving, straw) or by spraying, flooding or ponding. (Ahrens 83).
Ideally, the concrete is moist-cured for 28 days (the standard); the usual recommendation is at least five days if the temperature is at least 70 deg. F, and at least seven days if it is 50-70. Fully moist-cured Type I concrete will reach 50% of its 28-day strength about 5 days after it is laid, and 75% after perhaps 12 days. Between three and six months after it’s laid, its strength will be 125% of standard. In contrast, if the concrete is in air the entire time, its strength will plateau at a little over 50% of standard. If the concrete is moist-cured for 3 days and then air-cured, it will level off at about 80% of standard. And if it is moist-cured for 7 days before air-curing, it will reach the standard strength but not exceed it. (Ahrens 82).
Moist-curing not only improves strength, but also wearability and water-tightness. A 7-day moist-cure is sufficient for complete watertightness.
The curing reaction is slower if the temperature is lowered; it takes three times as long to reach a given strength at 33 deg. F. as at 70 deg. F. There is permanent damage if the concrete is frozen during the first 24 hours after it is laid. Hence, in modern practice, if the temperatures are near freezing; it is customary to heat the sand, gravel and water before they are mixed with the cement. Care must be taken not to heat the materials so much as to cause “flash” (rapid premature) setting of the concrete. The concrete, once placed, can be covered with insulating material such as canvas, straw or hay. The forms may need to be warmed up; it is probably better to use wood rather than steel. Another possible cold weather expedient is to build a temporary enclosure for the concreting area and heat it while the concrete is being laid and cured.
The danger in hot weather is that the heat causes greater evaporation of the water in the concrete. Evaporation at 90 deg. F. is quadruple that at 50 deg. F. and double that at 70 deg. F. There is also a further loss of strength at high temperatures, beyond that attributable to water loss. Often, the concrete will have a higher early strength but a lower ultimate strength.
The usual hot weather concreting expedient is to keep the aggregate cool by shading and sprinkling, and to cool the water by adding ice or refrigerating it. It is also possible to dampen the forms.
The rate of evaporation is also dependent on humidity; it increases five times when relative humidity decreases from 90% (Washington DC in the summer) to 50%. And on wind; the rate is four times higher in a 10 mph breeze than in a calm.
Because the raw materials used to make concrete are heavy, they usually are obtained locally. Consequently, concrete made in one area will not be quite the same as concrete made somewhere else even if they use the same nominal mix of cement, aggregate and water.
So, to be sure the concrete will perform as expected, you need to test it. Even a “how-to” manual will explain how to carry out a “slump” test, which measures the stiffness of the mix. Mixes with small slumps are difficult to work and those with big slumps won’t be particularly strong or durable.
Those manuals also talk about compression tests. Unfortunately, they just tell how to make the sample cylinder; it is then sent off-site to a testing lab. It is possible that the Tech Center has a test machine which can be used post-RoF. If not, then we will have to wait until the machine shops can create one. In essence, it hydraulically applies increasing pressure to the sample cylinder until it fails.
Compression tests are typically carried out 1, 3, 7 and 28 days after the concrete is laid. Unfortunately, the one and three day strengths are not necessarily well correlated with the 28 day strength, because they are sensitive to certain factors which are operative in the short term. To get a better idea of what the 28-day strength is going to be, we need to accelerate the curing time. In general, this is done by using warm or even boiling water to moist-cure the concrete. (Camp).
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Don’t expect that early post-RoF concrete will be the equal of modern concrete. For example, in spring 2000, students from Villanova University designed and constructed a reinforced concrete cross for a Catholic orphanage in Honduras. the Honduran-made concrete only had a compressive strength of 1800 psi, rather than the U.S. norm of 4,000 psi. (Dinehart). This was almost certainly attributable to want of quality control in a Third World country. We are likely to experience even more acute quality control problems in the seventeenth century.
The concrete doesn’t have to be cast and cured in place. Instead, concrete elements can be precast, and then assembled. While precasting can be done at a building site, it is more common for it to be done at a precasting plant. Such a plant will often use steel forms because they can be reused many times. At the building site, the precast elements are erected and joined.
A special case of a precast element is a concrete block. This is intended to be used like masonry; that is, the blocks are mortared together at the building site. Block mixes usually contain less cement and less water than the mixes used to make structural concrete, and often contain lightweight aggregate. The blocks are usually steam-cured, at normal or even high pressure, at the plant.
Precasting plants won’t be practical until the transportation network is capable of accommodating heavy traffic.
In Flint, 1633, Chapter 27, Jesse tells Jim, “Next time you’re in Magdeburg, go talk to Mr. Simpson. I understand he’s got plans for producing some sort of paving material. Find out what it is, concrete, macadam, whatever, and what it will take to get it down here to the field.”
Jesse, of course, is thinking about aircraft runways, but concrete provides an excellent road surface for land vehicles, too. Details are given in Cooper, “All Roads Lead . . .” (Grantville Gazette, Volume 10). Concrete is durable; the first concrete street in the United States was laid by George Bartholomew in Bellefontaine, Ohio in 1891, and is still in use (Snell).
It is worth noting that roads can be made either of reinforced or unreinforced concrete. Given the shortage of steel in the early post-RoF period, I expect that unreinforced concrete will be preferred.
Apartment and office buildings
The Romans built insulae (tenements), usually not higher than six stories, using masonry or unreinforced concrete. (Idorn 38).
The first reinforced concrete building (a two story servant’s cottage) was built by plasterer William Wilkinson in 1854. More upscale homes were built using reinforced concrete in the 1870s, but they were “made to resemble masonry to be socially acceptable.” The single most important reason for concrete construction was fear of fire. (Camp).
It is worth noting that while concrete itself is fire resistant, the furnishings of a building are likely to be flammable. Hence, as concrete buildings became taller, it became important to assure that one could easily escape the upper floors in case of a fire, and also that firefighters could direct water against an upper-story fire.
Edison wanted to mass-produce concrete houses for the betterment of the poor. The whole project proved to be a marketing disaster. While the first two-story homes were put on the market in 1917 for a mere $1,200 apiece, none sold in the first month. “No one wanted to live in a house that had been described as ‘the salvation of the slum dweller.'” (Peterson) So the fledgling concrete industry in Grantville should be careful how it markets its product.
The first concrete skyscraper (16 stories, 210 feet high, 50 x 100 feet base) was built in Cincinnati in 1904 (the Ingalls building). The columns were built first, then the walls, girders, joists and floor slabs.
Concrete ingredients were brought to the site and stored in the basement until needed. Mixing was done on-site, using a powered mixer (invented in the 1880s). One hundred cubic yards of concrete were produced on each 10-hour shift. The concrete was one part Portland cement, two parts sand, and four parts pebbles or crushed limestone. The compressive strength of the concrete isn’t stated, but I would expect it to have been at least 2,200 p.s.i. in that period (and the steel to have a tensile strength of 80,000 p.s.i.). The total consumption of concrete was about 4000 cubic yards (Newby 274).
The total staff of workmen dealing with the concrete were 28 men, of whom nine wheeled cement, sand and stone, one attended to the mixer and ground hoist, two more to the hoist on the upper floor, four wheeled concrete on the upper floor, and twelve placed the concrete.
Three sets of forms (molds) were used; that is, while concrete was poured into one set, previously poured concrete was curing in the other two. The “floor cycle” was nearly three stories a month, with ten days to erect the molds for each story and two days to place the concrete. Molds were kept in position for about fourteen days after the concrete set, and, after they were removed, temporary struts were used to provide partial support for another thirty days while the concrete increased further in strength. The Ingalls Building was completed in eight months.
The principal floor panels were five inches thick. Supporting columns were 30×34 inches for the first ten floors and 10×10 for the remaining ones. The principal girders were 32 feet long, column to column, 27 inches deep, and 16-20 inches wide. The cross girders were 16 feet long, 18 inches deep, 9-12 inches wide. The exterior walls were eight inches thick. After the second floor, the floor height was 12’6″, which was a foot less than what would have been required by steel girder construction and hence effectuated a saving in construction costs. (Ali, “Ingalls”; Twelvetrees Bldgs., 101, 312-37; Taylor 611-12) .
The height achievable with reinforced concrete is largely a function of the strength of the concrete. The stronger the concrete, the slenderer the supporting columns on the lowest floors can be. In the 1950s, 5000 psi was considered high strength. (Prairie Material) . With 6000 psi concrete, Place Victoria in Montreal reached a high of 624 feet, and in 1970, One Shell Plaza in Houston ascended to 714 feet. (Camp). By the 1960s, 7,500 psi was feasible; such concrete was used in 1968 to raise Lake Point Towers, in Chicago, to 645 feet (seventy stories).
In the early 1970s, builders had access to 9000 psi concrete. The 859 foot Water Tower Place, the tallest concrete building in the world from 1975-1990, used 3000 psi concrete for the slabs and 9000 psi for the columns (with some assist from superplasticizers) (ConcreteContractor.com).
The taller the building, the greater the lateral wind force which it must resist. The “structural system” must be suitable. The classic frame (column-beam) construction is good only to about twenty office stories. A shear wall construction (1940) is appropriate up to perhaps forty stories. And so on (Ali).
For early high-rises, the concrete was hoisted to the working floor in buckets. In the 1960s, it became possible to pump the concrete to some floors. However, the higher the floor, the greater the pumping pressure required, and so, once the building reaches a certain height, it’s back to buckets.
Bridges and Dams
In the United States, the first concrete bridge was built in New York in 1871, and the first reinforced concrete bridge was the Alvord Lake Bridge in California (1889). It survived the San Francisco Earthquake. The first concrete dam was built in 1887 in California, and the first reinforced concrete one in 1899 (Prentice 18).
The tallest unreinforced concrete structure in the world is an obelisk, the 351-foot Jefferson Davis Monument in Kentucky. It is 8.5 feet thick at the base and tapers to 2.5 feet at the apex. The Pantheon is still the largest unreinforced solid concrete dome in the world (43.4 meter diameter). It was constructed in seven years; the similar sized dome of St. Peter’s in Rome took fifty years to build with stone (Davidovits).
Reinforced concrete can be used in the construction of monumental public structures characterized by long, open spans suitable for large public gatherings. These are often based on thin shells with load resistant shapes, singly curved (cylinders, cones) or doubly curved (spheres, hyperbolic paraboloids). Special structures have been used as stadiums, performance and exhibition halls, churches and factories. (Bradshaw).
The first concrete fortification was probably the Aurelian Wall, 12.5 miles long, and built in 271-275 A.D. using brick-faced plain concrete. The walls were initially 11.5 feet thick and 26.2 feet high. (“Aurelian Walls,” Wikipedia). When concrete was rediscovered, and more particularly when reinforced concrete was invented, the world military powers took note.
Initially, any concrete fortifications we build will face just solid shot. However, the USE navy used explosive shells in the Baltic War, and this will inevitably be copied by other governments.
Gillette (185) reports that the amount of concrete required for two 12 inch gun emplacements at Staten Island, NY was 5609 cubic yards, and cost $5.50/cubic yard.
I have a bit of data on the ability of unreinforced concrete to resist artillery fire:
—In an 1881 experiment, a Woolworth rifled cannon, of ten inch caliber, fired a 408 pound projectile at a range of 145 yards. It struck unreinforced concrete at a velocity of 1424 feet/second, and penetrated 13-17 feet. Under essentially the same conditions, the penetration into earth was 34.5 feet. (Mahan’s Permanent Fortifications 163).
—One meter of concrete masonry is the equivalent of two meters of brick, or three of earth, when it comes to resisting a direct (flat) shot from a 1912 vintage field howitzer. (Fiebeger, A Textbook on Field Fortification ).
—Heavy guns (e.g., an 80-ton gun firing a 1700 pound cast iron projectile with a striking velocity of 1580 feet per second) could expect to penetrate 32 feet of Portland cement concrete or twelve inches of steel-faced wrought iron. (Abbot, Course of Lectures Upon the Defence of the Sea-coast of the U.S, 147 )
—In 1897, six feet of hard concrete resisted shells of the eight inch B.L. howitzer, and at Port Arthur, 4.5 feet concrete proved sufficient to resist single shells. (Sydenham, Fortification 128).
Reinforced concrete is of course capable of offering greater resistance. The German World War II “Verstärkt Feltmessig” (Vf) were bunkers with three foot thick walls and ceiling, intended to protect the troops from a 50 kg bomb or a 105 mm artillery shell. The next level up were the Ständige Anlage (St), and in the Baustarke B (build strength B), they used 6.5 feet of concrete to hold of a half-ton bomb or a 220 mm artillery shell. (Regelbau).
A USMC Staff Officer’s Manual (Hyperwar) compares the resistance of plain concrete, reinforced concrete and other materials to attacks by modern weapons ranging from small arms fire to 88-mm artillery. In general, you need 20-30% less thickness of plain concrete, or 20-50% less reinforced concrete, than brick masonry, to resist the fire. The difference is most pronounced for the less powerful attacks.
A material known as “very high strength concrete” (high silica content; low water/cement ratio, steel fiber reinforcement; steam cured), with compressive strength four times that of conventional plain concrete, and tensile strength almost three times, reduces penetration about 50% (Cargile).
Concrete fortifications can be used, not only to protect troops or guns, but also to channel the enemy. For example, there were the “dragon’s teeth” of World War II, three or four feet tall pyramids of reinforced concrete, spaced so that tanks couldn’t drive through.
Concrete Ships and Other Floating Structures
Yes, you can sail a concrete ship. This shouldn’t come as a surprise, since all metal ships ply the seas, and steel is more than three times denser than concrete. One secret is displacement; the ship displaces a volume of water whose weight is greater than the weight of the ship, creating buoyancy, and that is possible because the hull encloses a lot of empty space.
Displacement is not the only secret. Since the 1960s, engineering schools have raced concrete canoes in competition (NCCC). Formal regional competitions began in the 1970s, and the first national competition was held in 1988.
At the competition, the teams must swamp the canoe (fully submerge it) and then release it. To qualify, the canoe must float up and break the water surface. That means that the concrete itself must be able to float. The modern concrete canoes use concrete mixes which weigh 35-50 pounds/cubic foot, whereas the density of water is about 62 pounds/cubic foot(Bie).
The cement is usually a blend of Portland cement and a pozzolan (fly ash, metakaolin, slag, rice hull ash, silica fume). Latex polymers may be added. The concrete is usually reinforced with metal, carbon, fiberglass or plastic fiber. The lightweight coarse aggregates used in these concrete canoes include glass and ceramic beads, epoxy coated styrofoam beads, perlite, and vermiculite, The concrete must be air-entrained (at least 6%). The mix is usually low in water (maximum water cement ratio is 0.5:1), to keep strength high, and so superplasticizers are likely to be used to improve workability. (OSU, NCCC 2007 Rules).
Both West Virginia University and Fairmont State have participated in concrete canoe competitions since at least 1998 (their participation is mentioned in a 1998 issue of Mountaineer Spirit.) The American Society of Civil Engineers (ASCE) Virginias Conference (Virginia and West Virginia) was held at WVU on April 3-4, 1998, and WVU competed against teams from Old Dominion University, Virginia Polytechnic Institute, University of Virginia, Virginia Military Academy, and Fairmont State College. Virginia Tech won the regionals, but came in tied for last in the nationals, which were won by University of Alabama in Huntsville. Fairmont State has made it to the nationals four times, but all after RoF. So far as I know, WVU has never made it that far. The “winningest” team in the Virginias Regional Conference is certainly Virginia Tech, which made it to the nationals fourteen times (including 1988-95 and 1998-2000).
Which leads to the logical question: Are there any “Hokies” among Grantville’s civil engineers?
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The first known concrete ship was a small ferrocement boat built by Joseph Louis Lambot (1848) and exhibited at the 1855 World’s Fair. The first ocean-going concrete steamer, N.K. Fougner’s 84-foot, 600 ton Namsenfjord, was launched in August, 1917. Fougner went on to build two more, the Patent and the Concrete. There was also W. Leslie Comyn’s 5,000 ton Faith, launched in May 1918. Her first cargo was 4300 tons of salt and copper ore, which she carried from San Francisco to Vancouver. (Thomas; Bender)
During the First World War, steel scarcities prompted the construction of twelve other concrete ships under government auspices, at a total cost of $50 million. However, they didn’t see any wartime use. One of these ships, the 420 foot oil tanker S.S. Peralta (launched 1921), is still afloat (as part of a breakwater for a paper mill in British Columbia).
Steel was again hard to come by during the Second World War, and at least twenty more concrete ships were built. All weighed 4690 tons and were 102.5 meters long; they were typically used as storeships. Some still survive as wharves and breakwaters. The closest ones to Grantville are the nine used to form a breakwater for a ferry landing at Kiptopeke Beach, Virginia.
So far as I know, since World War II, there have been no large merchant ships constructed using concrete. However, there have been quite a few amateur built “ferro-cement” sailboats. In 1984, Peter Freeman circumnavigated the world in a 32 footer, in the process setting the then record for fastest singlehanded nonstop circumnavigation in a sailing craft (236 days, 10 hours, 45 minutes).
I find mixed reports as to the durability of concrete ships. Clearly, they were capable of handling ordinary seas and winds. S.S. Aspdin (1944) was “caught in a hurricane with 60 to 80 foot high waves, but survived with minimal damage.” Likewise, “in the course of a trip to Vancouver [the Faith] encountered an 80-mile gale and 35-foot waves. During this storm she made a speed of between 4 and 5 knots, considered an excellent performance under the circumstances.” On the other hand, the S.S. Cape Fear “shattered like a teacup” after colliding with the City of Atlanta in 1920. (Thomas)
Thomas contends that concrete merchant ships were unable to compete economically with steel ships because they couldn’t carry as much cargo relative to their own weight. Steel, of course, is more than three times as dense as concrete, but for a concrete hull to be as strong as a steel hull, it would have to be considerably more than three times as thick.
In the early post-RoF period, of course, concrete ships don’t have to compete with steel ships, but rather with wooden ones. The navy and the railroads will gobble up most of the available steel. So there may be a window of opportunity for civilian concrete ship construction.
Concrete ships have some other advantages worth mentioning. As compared with wooden ships, they aren’t vulnerable to marine borers, like the teredo worm. And they can be repaired easily (in fact, even steel ships sometimes carry ready-mix concrete for emergency repairs).
Kim Mackey has suggested to me, “for the Maghreb Regencies which consisted of a narrow green belt between the Mediterranean and the Sahara, making ships with a minimum of wood might be attractive.” To this, I will add that there are quite a few other powers which are suffering acute wood shortages, including the Ottoman Empire proper, Spain, the Netherlands, and the various Italian states.
I can also imagine using concrete “floating batteries” to protect harbors.
There is a “weird tech” proposal I floated on the Bar in 2006: might the Ottomans, or the Mughals, who at this time still use stone cannonballs, think it worthwhile to replace them with concrete cannonballs (or some other concrete projectile)?
A naval historian, Guilmartin (286) , says that while cast iron cannonballs had a greater maximum range than stone cannonballs (presumably with the same cannon and equal weight balls), the stone cannonball, because of its lesser sectional density (about one-third that of cast iron), created less internal pressure within the gun for a given muzzle velocity . . . so the cannon could be lighter and thinner for a given projectile weight. Guilmartin also says that a stone cannonball left a larger hole than an iron one of the same weight.
Guilmartin attributes the demise of the stone cannonball to the problem of finding cannon ball cutters who could cut a smooth, perfectly spherical ball. In other words, labor costs were the problem. Much the same thing is said by another military historian, Cowley (49). A concrete cannonball would not have to be cut, since the concrete is cast in a mold. The mold has to have a hole for pouring in the concrete, so the resulting sphere may need a little bit of work—but much less than for stone. A visitor to Grantville (like the pirate’s son in my story, “A Pirate’s Ken”) might even find some inspiration in one of those hollow or solid concrete garden spheres (Artistic Garden).
It is important to recognize that in the 1630s, the Ottomans and the Mughals, rightly or wrongly, thought that stone cannonballs better suited their tactical needs than cast iron ones. So, from their point of view, the issue is whether to replace stone with concrete, not whether iron is better than either.
It is difficult to say whether the concrete cannonball would be cheaper to make or not. On the one hand, you don’t need to quarry and ship the right kind of stone, and you don’t need skilled workers to carve it into spheres. On the other hand, if you use carved stone, you don’t have to learn to make cement and how to mix concrete.
If the only reason for developing a cement/concrete industry was to make concrete cannonballs, that probably would not be reason enough. But there are plenty of uses for concrete, and if concrete is of general interest, there isn’t much incremental effort necessary to develop concrete cannonballs.
There was some debate on the Bar as to whether my proposed concrete cannonballs would fragment inside the barrel (bad) or on impact (good or bad, depending on whether you want to kill personnel with shrapnel or do serious structural damage to a hull or wall).
Since stone cannonballs were still in use, at least by the Ottomans in the Mediterranean, the real issue is whether concrete would be more vulnerable to premature shattering than carved stone. And, if so, could you work around this in some way.
One solution is to use a fiber-reinforced concrete. Scrap cloth or rope would probably work well enough. Another possibility is a bit of a cheat; take a large rough stone which is a little smaller than the desired cannonball size, put it inside the mold, and then pour in enough concrete mix to fill the mold. (To get the stone in, you will probably need to use a two part mold; plop the stone into one hemisphere and then put the other hemisphere over it.) The concrete is then more of a surface treatment, so you don’t have to carve the stone to a sphere.
Another issue is whether the concrete balls would damage the gun barrel. Since the Ottoman pedreros (stone-throwers) work fine, I don’t see why concrete would be any worse. If it is, then it can be given a smooth finish in a number of ways.
Concrete Pointed Shot
There is a reason that modern rifles shoot bullets (which have an “ogive” shape, that is, a cylindrical shank with a streamlined tip) rather than balls: you can increase the mass (and therefore the damage potential) without increasing air resistance.
Which leads, logically, to an inquiry into whether the Ottomans might make ogive cannon projectiles out of concrete. Concrete, of course, can be cast into any desired shape. But there are a few practical problems to be solved. First, when the projectile isn’t spherical, if it is fired from a smoothbore barrel, it is going to tumble erratically, changing its aerodynamic profile as it does so. So, with an ogive projectile, you need a rifled barrel, and the projectile needs to be able to engage the rifling so it is spun (which gyroscopically stabilizes its flight).
A projectile with a cylindrical shape is going to have a greater surface area in contract with the barrel. While that means that the seal is better (less loss of gas generated by the combustion of the charge), it also means that there is more friction. So either the concrete must be finished so it is quite smooth (perhaps it could be glazed?), or it must be jacketed. There are modern concrete projectiles used in mining (see below) which are plastic-jacketed, but the Ottomans aren’t going to have access to plastic so their jackets are likely to be metal (perhaps copper or tin).
U.S. Patent 3963275 (1976) is directed to the use of concrete projectiles in mining. The idea is that the effect is more controlled than with explosives, and boulders can be fragmented from a distance of perhaps 150 feet. According to the patentee, if a one-caliber granite cylinder (~ten pounds, five inch diameter and length), fired from a cannon, strikes a free-standing boulder with an impact velocity of 4,000 feet/second, the impact stress is about 1,750,000 psi. The patentee found that a ten pound concrete projectile could fragment 10-30 ton boulders with one shot and a forty ton boulder with two shots. Against a solid cliff face, the projectile broke out a mass of 1000-1100 pounds, leaving a crater twelve inches deep and fifty inches diameter.
An earlier patent, 3695715 (1972), suggests firing (from a rapid fire breechloader) one kilogram, ten centimeter diameter concrete slugs, cast in a plastic casing, for rapid vertical excavation. Indeed, it even gives us a formula; crater volume (cubic inches) = 0.0005 * E ^ 1.25 (E, kinetic energy in foot pounds). So a one kilogram slug impacting at 1.5 kilometers/second would excavate 7.2 cubic feet (about 500 kilograms). The ‘715 patent says that stiff, dense projectiles, like concrete, are those most effective in breaking rock.
It is possible that the miners in Grantville have heard of this technique. But even if they haven’t, the important point is that it is clear that a concrete projectile can be fired from a cannon and can damage a target.
Concrete (non-explosive) bombs have been dropped upon military targets which are uncomfortably close to civilian ones. They have also been directed against military targets which you want to damage but not destroy; say, a bridge you might like to use yourself in a week or two.
These bombs might weigh 900 kilograms and strike the target at a speed of 200 m/s, which is faster than a rifle bullet. The energy release is proportional to the mass and to the square of the speed.
Concrete in Flight
Series production of the Blohm & Voss BV 246 glide bomb, featuring “die-cast” reinforced concrete wings, was authorized on Dev. 12, 1943. The bomb was suspended under the carrier aircraft, and the wings were bent so as to “spring” the bomb away when it was released.. The Germans used a “light” concrete obtained by a chemical additive which generated gas bubbles during the curing process, thereby increasing porosity. (BV 246; Bruner).
In 1949, Eugene Freysinnet, the inventor of prestressed concrete, helped Breguet Aircraft Company build wings, intended for a 4.8m long gliding bomb (Breguet-910), out of that material. The concrete was specially formulated, to a compressive strength of 14,000 psi, and had a density of 2.5. The prestressing, with aviation quality piano wires of tensile strength 280,000 psi, was intended to avoid surface cracking.
Each wing was made of two half wings, upper and lower, each with two matching spars, so the wing when assembled has three cavities. The thickness of concrete in the wing, which had a span of 4m, was 18mm at the root and 13 at the tip.
The normal load on the wings was 143 psf, and the breaking load was five times that. Presumably because of the relatively thick stressed walls, the prestressed concrete wings were 50% stiffer than comparable metal wings. Because the prestressed concrete wings didn’t require much in the way of stiffeners, they weighed only 10-15% more than a conventional metal wing.
(Bruner noted the possibility of using a “mixed structure” wing, with concrete where stresses are high, and a stiffened light-alloy sheet used elsewhere. )
The concrete wings were well suited to mass production. Bruner says it took only 0.5 hr/kg to cast and finish a concrete wing, as opposed to 10 hours for a metal one (a ratio of 20). APMRTEF says production times were reduced by a ratio of 3.4 for batches of fifty wings, and 5 for batches of 500. The discrepancy could be attributable to smoothing and painting operations, which Bruner stated could take longer than the building of the wing itself.
Four hundred bombs were produced. Launched from an altitude of 5000m, they had a range of 50 km. The bomb was capable of both normal and inverted flight. (Bruner; ICJ; APMRTEF 98).
A French patent (958272) on constructing aircraft (!) structural elements out of prestressed concrete was filed by Louis Breguet in 1949. In his US Patent 2787042 (1957), he argued that concrete wings were much cheaper than metal wings, they could be fabricated with a very high degree of accuracy, they had superior torsional rigidity (leading to reduced elastic interference and thus, hopefully, improved acrobatic flight under heavy loads), and greater temperature resistance (temperature elevation limited the maximum velocities attainable by metallic aircraft).
Breguet, in US Patent 2776100 (1957), says that he actually constructed a fighter craft wing from concrete, and that there was only a negligible difference in weight between it and an identically shaped wing of light metal construction. He explains that the relatively thick wall sections of the concrete ring prevented local buckling and sagging, and thus reduced the number of local reinforcing ribs needed.
Breguet ‘100 describes an improved wing in which the cross-sectional area of the concrete is reduced as you move out along the wing; so as to correspond to the outward diminution in the bending moments resulting from the aerodynamic load. The desired airfoil shape is maintained by filling it in with a lightweight material.
The problem isn’t with submerging concrete vessels, it’s getting them back to the surface! Just joking. In actuality, a reinforced concrete personal submarine was built and used (in a lake) by Willfried Ellmer in 1996. It weighed 14 tons before ballasting, and had a seven inch thick hull, made of Portland “cement” reinforced with 4mm and 6mm steel in a 10cm mesh. Its design operational depth was 300 meters, and crush depth 900 meters. (diseno-art.com; sub-log.com; concretesubmarine.com).
Kathleen Ann Goonan, speaking about her novel In War Times, says the Weber plant produced some concrete submarines in 1945. (Goonan).
By 1998, there were rumors that the Russians were designing six-man concrete submarines equipped with rocket-powered torpedoes. Concrete is not only cheap, it is strong in compression. Which means that a concrete submarine might be able to descend below the 1800 foot crush depth for steel. And a concrete submarine will be more difficult to detect by sonar. (Wilson)
The Concrete U-Plane
Ah, Karl Heinz Lipschutz’s U-Plane design of the late 1920s. No, it doesn’t actually fly. It is a submarine with wings to provide additional lift, somewhat like a modern hydrofoil. Well, if we can put prestressed concrete wings on a plane, and give a submarine a concrete hull, I suppose we could make a concrete U-Plane.
According to Lipowitz (32), the 1868 cost of erecting a large (30 ton/batch) dome kiln was 120-150 pounds sterling, and the annual maintenance cost 30. In 1632-34 pounds sterling, the cost would be about one-third that (adjusting for inflation based on London building laborer’s wages.)
The 1900 cost of construction for a rotary plant was $50,000 (1250 pounds in 1632) for a 125 barrel/day kiln, and $400/barrel capacity (with the possibility of reducing costs to $300/barrel capacity with certain economies). The cost of a Dietsch or Schofer kiln was only $200/barrel capacity but labor costs were much higher. (Ries/Clays 194-196). A 1903 USGS estimate (Davis) for a 300 barrel/day plant, with two rotary kilns, was $91,000 (2000 pounds in 1632).
The first consideration in siting a cement plant is to locate it where it can economically obtain limestone, clay and coal. Ideally it is right next to suitable quarries. If not, the source should be within a few miles of the plant, or at least the materials are transportable almost entirely by water or rail.
Concrete can be made from rock which isn’t directly useable as a building material because of cosmetic or structural flaws. Limestone with clayey intrusions is ideal “cement rock.” Other “inferior” rock can be crushed into aggregate. Clay can be leftover material from the brick and ceramics industries.
Limestone, sand, etc. are readily available worldwide, so if the price of concrete gets too high, more kilns are built. (theoildrum.com).In part because it can be made anywhere, it is not cost-effective to transport concrete over long distances. The density of normal concrete is about 2.4 times that of water (Elert). So it is heavy. But imported concrete needs to be priced to compete with imported natural rock, and locally made concrete, so the price per unit weight is low. Even with a twentieth century transportation infrastructure, that limits the trade in concrete.
The situation is similar for cement, which has a density of about 2.1 times that of water (Logicsphere). The decision in the CEMEX anti-dumping case remarked, “The price of cement is largely determined by the transportation costs involved in delivering the cement. . . . The majority of cement produced in the U.S. is sold within 200 miles of the plant or terminal of origin.”
This is not a new problem. Jamul Cement (California) found that it “cost about as much to haul cement by wagon the dozen or so miles to the railroad at Sweetwater Valley as it did to ship it [from Europe] around the Horn to the [San Diego] Bay.” ((Burkenroad).
Likewise, the cost of transporting limestone, clay and coal affects where a cement plant can be sited.
The introduction of the rotary kiln reduced the price of concrete from $2-2.50/barrel (380 pounds net) to around $1/barrel (1895). (Eckel 501) In twentieth century America, cement prices, in constant 1998 dollars, were $65-115/ton. The actual 1900 price was $4/ton (1998$78). (USGS).
Even in the early 1900s, concrete was cheaper than steel (Ali). In 1911 America, it was still more expensive to construct a house from concrete than with wood. But in 1902 Edison predicted to the press that concrete would become more economical as the forests shrunk (Peterson), and he was right. Western and Central Europe, in the seventeenth century, were already feeling the pinch when it came to lumber production, and in the new time line concrete may quite quickly acquire a cost advantage over wood.
Geography of Cement and Concrete Production
If one “data mines” the 1911EB, the following German towns can be identified as associated in some way with late nineteenth century cement production:
Central: Halle (has coal), Magdeburg, Eisenach (cement pipes).
Northeast: Chemnitz, Mittweida, Wittenberge, Bredow, Stettin, Dirschau, Oppeln, Hirschberg, Gleiwitz.
Northwest: Luneburg (near Hamburg—”owes its importance chiefly to the gypsum and lime quarries of the Kalkberg, which afford the materials for its cement works”), Wesel, Unna, Emden, Hoxter.
Southeast: Straubing, Heiligenstadt, Kitzingen, Weissenburg-am-Sand.
Southwest: Heidelberg, Karlsruhe, Heilbronn (also quarries for sandstone and gypsum), Biebrich, Ingelheim, Malstatt-Burbach (has coal), Kirchheim.
There is no guarantee that history will repeat itself, but whatever advantages these centers enjoyed in the old time line in terms of proximity to sources of raw materials, or to river transport, are likely to be reasserted in the new time line, too.
The first German cement works was in Stettin; other early ones were at Bonn and Mannheim. According to a 1900 cement industry survey, the largest operation in Germany was the Alsen Works, near Hamburg, which had plants at the clay deposit of Itzehoe and the chalk quarries of Laegerdorf. Marl, and clay below it, were exploited at Misburg, near Hanove, and at Luneburg. The Dyckerhoff plant on the Rhine, at Amoeneburg near Mainz, was situated near a limestone-and-marl quarry, and coal was brought in (and cement shipped out) by water. Across the Rhine, there were similar plants at Mannheim and Weisenau. Finally, the survey mentioned that there had been works at Heidelberg. (ER, Chap. XXII).
Carsten Edelberger, in “Railroading in Germany” (Grantville Gazette, Volume7), notes that Bernburg (near Stassfurt, thirty miles south of Magdeburg) has big deposits of limestone and therefore could become a center of lime and cement production. I would add that the nearby Stassfurt lignite could, when burnt, be used as a source of fly ash. Stassfurt also has gypsum, which is used in Portland cement. There is sand available from the banks of the Elbe. The oldest and largest clay mining region in Germany is the Westerwald, but there are clay deposits in Thuringia and Saxony (Meissen), too. Also note that there is limestone at Kamsdorf, and clay at Kahla, both within a few miles of Grantville.
I have tried to determine how quickly a Portland cement plant can be built, with only limited success. Bear in mind that a kiln by itself isn’t going to make any cement. You need limestone and clay quarries, rock crushers and fuel, grinding machinery, and transport facilities. In Jamul, twenty miles from San Diego, construction of a cement plant, with two kilns, was begun April 1890; the kilns were only fired up in March, 1891. Part of the problem was that materials not available on site, such as fireclay and coke, had to be brought in by rail and then wagon-freighted over a dozen miles to the plant. With the plant infrastructure in place, it was possible to add five small pot kilns and bring them on-line in July, 1891. (Burkenroad).
Beginning in the latter part of 1881, the Walkill Portland Cement Company (NY) built sixteen dome kilns, with a total capacity of 200-300 barrels/day, and put them into operation in 1883. (Ries, 854). In 1893 the Glens Falls Portland Cement Company (NY) commenced construction of six Schofer kilns, with a total capacity of 500 barrels/day, and began production in 1894 (866). Under the right circumstances, it might be possible to build a single dome kiln in a month or two.
As for short rotary kilns, in 1899, the Catskill Cement Company (NY) built a plant, with two kilns, total capacity 300 barrels/day, and was shipping cement by July 1900 (862). In 1900, Helderberg Cement Company (NY) built a new plant, with twelve kilns, and a total capacity of 1500 barrels/day. (868).
Natural cements (that is, cements made from rocks which could be burnt without admixture and then ground to make a crude cement) were in use in the early nineteenth century in England (1796), France (1796/1802), the United States (1818/1824) and probably also Belgium.
John Smeaton improvised an artificial hydraulic cement in the late eighteenth century. There was experimental work in France and England during the early nineteenth century, and Joseph Aspdin received a patent for “Portland Cement” in 1824. This was improved by Joseph Aspdin and Isaac Johnson in the 1830s and 1840s. Nonetheless, in 1850, there were only four Portland cement factories in England.
French Portland cement production began in 1846 or 1850. The first German plant opened in 1852, and Germany manufactured 30,000 barrels in 1855.
Even though the Europeans could witness firsthand the strength and durability of Roman concrete (and it was surely for marketing purposes that Parker called his natural cement, “Roman” cement), this didn’t lead them to rapidly adopt Portland cement for structural purposes.
The first large scale use of Portland cement was in the Thames Tunnel (1828), but it continued to be considered inferior to other cements until its use in the London Drainage Canal (1859). Portland cement was then used primarily for underground and underwater work until a shortage of structural steel in 1897-98 forced architects to place greater reliance on reinforced concrete. (Haber 21; Howe 10).
American Portland cement production began in 1872 and Canadian in 1890. The growth of the North American industries was retarded by the high cost of labor. In 1895, Americans consumed eight million barrels of natural cement (50 cents/265-pound barrel), almost two million of imported Portland cement (which traveled cheaply on ships as ballast), and only 335,500 barrels of domestic Portland (both $2-2.50/376-pound barrel). The labor-saving rotary kiln made it possible to sell domestic Portland cement at a price of 88 cents (1904). (Eckel 501)
Germany had relatively low labor costs in the nineteenth century, so it was well suited to become a leader in Portland cement production. Production rose as follows: 30,000 barrels (1855), 2,400,000 (1877), 5,700,000 (1886); 12,000,000 (1892), 13,000,000 (1895), 18,000,000 (1900). World (primarily US and Europe) Portland cement production was 1.7 million tons in 1880, 2.5 in 1886, 7.5 in 1904, 11 in 1906.
The following per capita consumption values may be useful for estimating the post-RoF demand for cement.
|Place||Year||All cement pounds /person||% Portland cement||Source|
|1880||11.3 13.9||~5%||(2) (3)|
|1890||43.5 50.2||~32%||(2) (3)|
|1900||83.5 80.8||~65%||(2) (3)|
|*annual average (1) Eckel 242 (2) Eno 22, Mills 88 (3) PanCanalHrg|
Population of USE in 1633 is about ten million. That of all Christian Europe (excluding Russia), ~75 million. (http://www.1632.org/1632tech/faqs/eur_pop.html).
Because concrete is primarily a building material, the demand for cement should increase as the population increases. But that of course isn’t the only factor. The private and public sector have to be able to afford new construction. Per capita GDP might be a good measure of economic prosperity .. but of course it isn’t easy to find GDP figures for the “old” seventeenth century, let alone the new one!
Jackson (25) gives the following chronology for the increases in the standard strength of Portland cement concrete, which I have annotated:
|Year||Strength (psi)||Related Tech|
|1800||400 (Parker’s “Roman” cement)||natural cement|
|1850||800 (William Aspdin)||higher clinkering temp|
|1875||1600 (“German”)||chemical analysis/QC|
|1887||2300||continuous vertical kilns|
|1905||2800||long rotary kilns, ball mills|
|1918||3600||Abrams analysis of water/cement ratios|
It’s head extrusion time. . . .
Please bear in mind that there are a variety of scenarios for the evolution of the cement and concrete industries after the Ring of Fire. There are several big questions:
1) will investors insist on seeing that buildings made with “post-RoF” cement-based concrete are standing up before investing in cement plants “back home”?
2) how quick will be the growth of the supply of skilled workers, especially chemical and engineering technicians who can do the periodic testing needed to assure a high-quality cement?
3) how quick will be the growth of the transportation infrastructure necessary to support the economical movement of raw materials and finished product?
4) when will there be an adequate supply of steel for use in reinforcing concrete?
5) how interested will builders be in using unreinforced concrete?
6) what will be the relative costs of labor and fuel?
7) What is the risk and profit potential of cement-making and concrete construction, compared to other industries?
8) What will be the rate of increase in new construction over the first decade after the RoF and what fraction of the new construction will be using concrete?
The scenario outlined below is based on one set of possible answers to those questions.
Late 1631-end 1632. A simple dome kiln is constructed at Kamsdorf for use by the Grantville Tech Center research lab. Adding clay from Kahla, a crude Portland cement is made. By year’s end, production is running four to six tons a day.
Fly ash from the power plant is tested as a possible pozzolan for blending with the Portland cement. Various fine and coarse aggregates from nearby (e.g., sand from the banks of the Saale?) are also tested.
Some of the dwindling supply of up-time cement is used in comparison testing, and some is used in demonstrations for down-time dignitaries so they can see how concrete is mixed and poured. The compressive strength of concrete made with only down-time cement is probably in the 1000-2000 psi range.
1633. Trass is imported and tested in blended cements. (Once the steel mill is in operation, blast furnace slag will be used as a pozzolan and as an aggregate.) Quality control on the rawmix improves, and concrete made using down-time cement achieves compressive strengths in the 2000-3000 psi range.
Unfortunately, steel is hard to obtain (at least in the USE), thanks to the ironclads and the railroad, so there is experimentation with other forms of reinforcement. Cement demand, and therefore production, is primarily limited to the Grantville area, as a result of both skepticism as to the utility of unreinforced concrete, and the limited transportation infrastructure.
New dome kilns are built at Kamsdorf, and total cement production capacity is probably 10-50 tons a day. Higgins Hotel built in Grantville to showcase the “new” technology and ramp up cement demand. (Bear in mind that to build an Ingalls Building equivalent, you will need something like 1000 tons of cement.)
1634. The railroad connects Grantville to Halle in spring 1634, and dome kilns are built there. The railroad is also being built southward from Magdeburg, and once it gets there (July 1634?), more dome kilns are built and concrete construction begins in Magdeburg. The end of the Baltic War in mid-1634 allows much more steel production to be devoted to rebar. In late 1634, kilns are constructed in the areas of Hamburg and Stettin, and perhaps somewhere on the Rhine.
European daily cement production jumps to perhaps 50-200 tons, and includes small-scale production outside the USE. That assumes per capita demand of about US 1860-1870 levels in the USE, and early 19c levels elsewhere.
1635. The completion of the Grantville-Magdeburg railroad line in mid or late 1634 facilitates movement of coal, clay, limestone, and cement, increasing supply and demand. Dome kilns pop up in many parts of Europe, wherever there is a reasonable convergence of raw materials, demand, and transport. It is difficult to predict where, since warfare will interfere with construction, but England, France, and Germany were leaders in the early European Portland cement industry. Outside the USE, cement plants are likely to be located near navigable rivers, to reduce transport costs and to provide power for crushing and grinding mills.
A cement plant with continuous vertical kilns is constructed, possibly near Stassfurt, to reduce fuel consumption.
Cement production could easily be expanded to the 1000-2000 ton/day range. The catch is that I don’t think the population and economic productivity levels will be high enough to support that level. Based on the relationship of cement production (see above) to historical American/European GDP and population (Maddison), I would guess that the economic and population level of Christian Europe and its colonies in 1600 would have supported production of something like 60,000-140,000 tons annually (had the technology existed back then!). Multiply that by however much you think makes sense as the economic impact of the RoF. Bear in mind that when China industrialized in 1990-2000, its annual growth rate in cement production was only about 12%.
1636-40. Hoffman ring kilns and continuous vertical kilns proliferate. By 1640, 3000 psi concrete is standard and specified for most building jobs.
Note the omission of any reference to rotary kilns. While the growth of the transportation infrastructure will facilitate shipment of raw materials and cement, and wages are going to be rising, fuel costs are likely to be high enough to discourage pre-1640 adoption of rotary kilns. At most, we might see some experimentation with prototypes.
Once the economic incentive is there, it will probably be possible to achieve the first workable rotary kiln in 1-3 years (significantly faster than in OTL).
The twentieth century has been called the Atomic Age, the Space Age and the Information Age, but with some justification it could be called the Concrete Age. Yes, concrete was used before the twentieth century, but more money is spent on concrete construction than on atomic reactors, space ships, or even computers. In 2005, six billion cubic meters of concrete were made. It remains to be seen whether, in the new time line, the seventeenth century will become the “New Age of Concrete.”
The bibliography for this article is extensive. Hence, it has been posted to the FAQ section of www.1632.org. <http://www.1632.org./>
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