Cement and Iron Pipes.
In a recent number of The Genie Civil a description is given of the application of cement to the construction of pipes on the Bordenane system by sidero-cement. The general principle consists of embedding a framework of iron bars in cement mortar. Bars of I section are used, and these are made as long as possible, and are wound in helical form, the pitch of the helix being determined by the section employed and the pressure to be withstood. Dependence for structural strength to resist pressure is placed wholly on the metallic framework. The working stress is calculated at 9.8 tons per square inch, so that for a pipe of an inside diameter of 2 feet inches a bar .5 inch by .2 inch would have a pitch of 3.8 inches for a head of water of 33 feet. Cylindrical vessels are also made on this principle, the bottom being suitably constructed of radial and circumferential bars, with vertical bars also introduced in the walls. In this case the pitch of the helix is lessened toward the bottom, so as to withstand the increasing head. The principles set forth have been tested by use, an experimental line of four miles in length having been constructed. Fortunately the co-efficient of expansion of iron and cement are approximately equal ; otherwise, of course, the system would not be trustworthy. The metal is completely protected from wasting by the cement, which adheres closely to it. It is said that no vegetation or deposit of any kind will attach itself to the cement, and the danger from leakage is said to be less than in iron piping with lead joints, and, finally, it is claimed that there is a saving in cost over iron pipes of from fifteen to forty five per cent, according to circumstances, while the durability is said to be exceedingly good.