Owner-Built Home & Homestead
(Page 14 of 15)
The utilization of waste iron and tin cans for concrete reinforcement dates back at least to 1927, when George Watson of England developed and patented a process of flattening and shredding waste iron. To the budgeted owner-builder every city dump or local junk yard can be a source of concrete reinforcement (bed frames, iron pipe, wire fencing, wire cable, etc., as well as the ubiquitous tin can).
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When integral reinforcing is used in cement materials, even if it is nothing more than shredded tin, much greater stresses can be withstood. Expensive iron rods are not always necessary; in some countries the absence of iron, or perhaps a scarcity caused by war demands, or a desire to use available natural materials, suggests that the possibility of using satisfactory substitutes for commercial iron rods should be explored.
One of the first to experiment with the use of wood for concrete reinforcement was H. K. Chow, a Chinese student at the Massachusetts Institute of Technology, in 1914. In Nanking, China, a few years later, a stretch of highway was laid down with bamboo as reinforcement. This successful experiment encouraged the Chinese to extend the uses of bamboo in concrete reinforcement.
Then in Italy, in 1935, as a result of iron shortages because of war preparation, a number of wood-reinforcement experiments were carried on and bamboo was found to be the most suitable. There is no chemical reaction between bamboo and cement mortar, the bond with concrete is much greater for bamboo than for any other wood, and bamboo has great tensile strength (about the same as concrete itself).
The Italian experiments showed that the modulus of elasticity in bamboo is about one-tenth that of steel; in other words, the cross section area of bamboo should be ten times that of steel to give the same results. Other researchers (notably those doing engineering research at Clemson, S. C.) point out that bamboo reinforcement increases the load-carrying capacity of a beam to four or five times that of an unreinforced member.
Even more significant than structural similarities is the cost differential between bamboo and steel. In tropical countries, bamboo cane will grow as much as three feet in one day, it grows without any special attention, and no particular problems complicate the harvest.
The Clemson research reports that greater loads are possible if the bamboo is unseasoned, split and treated with asphalt emulsion. (Ed. note: Asphalt emulsion is now available in low- or no-volatile organic compound versions.) Concrete has excellent compression resistance but its modulus of elasticity is negligible; bamboo can be economically substituted for steel to achieve this tensile strength.
In areas where bamboo is not available, timber can be employed to achieve similar results. Composite timber-concrete beams were built and tested in 1940 at the Talbot Laboratory, University of Illinois. The timber section was designed to withstand tensile forces and the concrete section to provide compressive rigidity. The Talbot investigators found that the major obstacle to such a structural system is the high horizontal shearing stress that exists at the junction between the two materials; some mechanical device is needed to key the two parts of a beam together. Of the wide variety of shear connections studied, it was found that triangular steel plate-units combined with iron spikes appeared to be most satisfactory in producing integral beam action.
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