for shipbuilding, above 10 meters length, a reinforced concrete wall of 70 mm thickness is competitive in buoyancy to hull weight with wooden or metal construction. ('Les Bateaux en Ciment Armé', Charles Vireton; La Science & la Vie, 1917, an article in French; 'Concrete Boatbuilding', 1971. Gainor W. Jackson, W. Morley Sutherland; FAO fisheries documents, of open and free download, and much more...) Concrete made car: https://www4.uwm.edu/cbu/Concrete.Car.pdf
General data about materials appear in the Bosch: 'Manual of Automobile Technik'
Heat pipes were shown being able to keep satellite temperatures quite uniform and cold (Dornier), and a concrete hull would eliminate the need for silica tiles. About 'Heat Pipes', SAE held a webinar, by ACT (Advanced Cooling Technologies), focused mainly in electronics cooling. A classical text is: 'Heat Pipes. Theory, Design and Applications', 6th ed: David Reay, Ryan McGlen and Peter Kew. ISBN: 978-0-08-098266-3
When hearing that the construction of a 14.1 MeV neutron generating machine, in order of testing materials to be used in ITER, was just funded, I remembered the Dyna Soar case, that after expending lots of money in design, they realized temperatures from friction with air on re-entry would melt the machine. (this may not be 100% exact, pls search for Dyna Soar in the web)
Reinforced concrete columns in the Windsor building fire in Madrid, Spain, resisted without problems hours of temperatures above 900º and 1'000º C. 'Fire resistance of concrete structures', article in Spanish
Thus, a fully concrete made Space Shuttle won't need special isolation tiles.
Would the weight to volume ratio and the payload of such a concrete machine be acceptable for a Spaceship? Thanks, regards. Salut +
- CEMENTS Several familiar ceramic materials are classified as inorganic cements: cement, plaster of Paris, and lime, which as a group, are produced in extremely large quantities. The characteristic feature of these materials is that when mixed with water, it forms a paste that subsequently sets and hardens. This trait is especially useful in that solid and rigid structures having just about any shape may be expeditiously formed. Also, some of these materials act as a bonding phase that chemically binds particulate aggregates into a single cohesive structure. Under these circumstances, the role of the cement is similar to that of the glassy bonding phase that forms when clay products and some refractory bricks are fired. One important difference, however, is that the cementitious bond develops at room temperature. Of this group of materials, portland cement is consumed in the largest tonnages. It is produced by grinding and intimately mixing clay and lime-bearing minerals in the proper proportions, and the heating the mixture to about 1’400º C (2550º F), in a rotary kiln; this process, sometimes called calcination, produces physical and chemical changes in the raw materials. The resulting ‘clinker’ product is then ground into a very fine powder to which is added a small amount of gypsum (CaSO4-2H2O) to retard the setting process. This product is portland cement. The properties of portland cement, including setting time and final strength, to a large degree, depend on its composition. Several different constituents are found in Portland cement, the principal ones being tricalcium silicate (3CaO-SiO2), and dicalcium silicate (2CaO-SiO2). The setting and hardening of this material result from relatively complicated hydration reactions that occur between the various cement constituents and the water that is added. For example, one hydration reaction involving dicalcium silicate is as follows: 2CaO-SiO2 + xH2O = 2caO-Si>O2-xH2O where x is variable and depends on how much wáter is available. These hydrated products are in the form of complex gel or crystalline substances that form the cementitious bond. Hydration reactions begin just as soon as water is added to the cement. These are first manifested as setting (i.e, the stiffening of the once plastic paste), which takes place soon after mixing, usually within several hours. Hardening of the mass follows as a result of further hydration, a relatively slow process that may continue for as long as several years. It should be emphasized that the process by which cement hardens is not one of drying, but rather, of hydration in which water actually participates in a chemical bonding reaction. Portland cement is termed a hydraulic cement because its hardness develops by chemical reactions with water. It is used primarily in mortar and concrete to bind, into a cohesive mass, aggregates of inert particles (sand and/or gravel); these are considered to be composite materials (see section 16.2 in Particle reinforced composites: Large particle composites). Other cement materials, such as lime, are nonhydraulic; that is compounds other than water (e.g., CO2) are involved in the hardening reaction.
CONCRETE
Concrete is a common large-particle composite in which both matrix and dispersed phases are ceramic materials. Since the terms ‘concrete’ and ‘cement’ are sometimes incorrectly interchanged, perhaps it is appropriate to make a distinction between it. In a broad sense, concrete implies a composite material consisting of an aggregate of particles that are bound together in a solid body by some type of binding medium, that is, a cement. The two most familiar concretes are those made with Portland and asphaltic cements, where the aggregate is gravel and sand. Asphaltic concrete is widely used primarily as a paving material, whereas Portland cement concrete is employed extensively as a structural building material. Only the latter is treated in this discussion.
Portland cement concrete
The ingredients for this concrete are portland cement, a fine aggregate (sand), a coarse aggregate (gravel), and water. The process by which Portland cement is produced and the mechanism of setting and hardening were discussed very briefly in Section 13.6. The aggregate particles act as a filler material to reduce the overall cost of the concrete product because it is cheap, whereas cement is relatively expensive. To achieve the optimum strength and workability of a concrete mixture, the ingredients must be added in the correct proportions. Dense packing of the aggregate and good interfacial contact are achieved by having particles of two different sizes; the fine particles of sand should fill the void spaces between the gravel particles. Ordinarily, these aggregates comprise between 60% and 80% of the total volume. The amount of cement-water paste should be sufficient to coat all the sand and gravel particles, otherwise, the cementitious bond will be incomplete. Furthermore, all constituents should be thoroughly mixed. Complete bonding between cement and the aggregate particles is contingent upon the addition of the correct quantity of water. Too Little water leads to incomplete bonding, and too much results in excessive porosity; in either case, the final strength is less than the optimum.
The character of the aggregate particles is an important consideration. In particular, the size distribution of the aggregates influences the amount of the cement-water paste required. Also, the surfaces should be clean and free from clay and silt, which prevent the formation of a sound bond at the particle surface.
Portland cement concrete is a major material of construction, primarily because it can be poured in place and hardened at room temperature, and even when submerged in wáter. However, as a structural material, there are some limitations and disadvantages. Like most ceramics, portland cement concrete is relatively weak and extremely brittle; its tensile strength is approximately 10 to 15 times smaller than its compressive strength. Also, large concrete structures can experience considerable thermal expansion and contraction with temperature fluctuations. In addition, water penetrates into external pores, which can cause severe cracking in cold weather as a consequence of freeze-thaw cycles. Most of these inadequacies may be eliminated or at least improved by reinforcement and/or the incorporation of additives.
Reinforced concrete
The strength of Portland cement concrete may be increased by additional reinforcement. This is usually accomplished by means of Steel rods, wires, bars (rebar), or mesh, which are embedded into the fresh and uncured concrete. Thus, the reinforcement renders the hardened structure capable of supporting greater tensile, compressive, and shear stress. Even if cracks develop in the concrete, considerable reinforcement is maintained.
Steel serves as a suitable reinforcement material because its coefficient of thermal expansion is nearly the same as that of concrete. In addition, Steel is not rapidly corroded in the cement environment, and a relatively strong adhesive bond is formed between it and the cured concrete. This adhesion may be enhanced by the incorporation of contours into the Surface of Steel member, which permits a greater degree of mechanical interlocking.
Portland cement concrete may also be reinforced by mixing into the fresh concrete fibers of a high-modulus material such as glass, Steel, nylon, and polyethylene. Care must be exercised in utilizing this type of reinforcement, since some fiber materials experience rapid deterioration when exposed to the cement environment.
Still another reinforcement technique for strengthening concrete involves the introduction of residual compressive stresses into the structural member; the resulting material is called prestressed concrete. This method utilizes one characteristic of brittle ceramics, namely, that it is stronger in compression than in tension. Thus, to fracture a prestressed concrete member, the magnitude of the pre-compressive stress must be exceeded by an applied tensile stress.
In one such prestressing technique, high-strength Steel wires are positioned inside the empty molds and stretched with a high tensile force, which is maintained constant. After the concrete has been placed and allowed to harden, the tension is released. As the wires contract, it put the structure in a state of compression because the stress is transmitted to the concrete via the concrete-wire bond that is formed.
Another technique is also utilized in which stress are applied after the concrete hardens; it is appropriately called post-tensioning. Sheet metal or rubber tubes are situated inside and pass through the concrete forms, around which the concrete is cast. After the cement has hardened, Steel wires are fed through the resulting holes, and tension is applied to the wires by means of jacks attached and abutted to the faces of the structure. Again, a compressive stress is imposed on the concrete piece, this time by the jacks. Finally, the empty spaces inside the tubing are filled with a grout to protect the wire from corrosion.
Concrete that is prestressed should be of a high quality, with a low shrinkage and a low creep rate. Prestressed concretes, usually prefabricated, are commonly used for highway and railway bridges.
MATERIALS SCIENCE AND ENGINEERING. AN INTRODUCTION.
William D. Callister Jr. 6th edition, 2002. Wiley. ISBN 0-471-13576-3
