CONCRETE AND STEEL.
BY J. F. SPRINGER.
[New York author of articles in Applied Science.]
The life of properly made concrete is not known. However, specimens from the times of the Romans are yet in good condition. This material has very considerable ability to resist compression; it is practically fireproof and teredo proof; when properly protected it is probably but little deteriorated by weather changes; and, if properly made, it is probably inappreciably subject to chemical disintegration when submerged. But there is one palpable fault—it is weak when subjected to tensile stresses. On the other hand—steel has great tensile resistivity and is strong under transverse stress. These two materials—concrete and steel—supplement each other in valuable qualities. The possibility of using them in combination depends largely upon the fact that their co-efficients of expansion are practically the same for moderate thermal fluctuations. Steel is easily corroded. Nor is it strictly fireproof, as temperatures which are not excessive will induce bending and buckling. When it is surrounded by concrete, steel is protected against both fire and corrosion.