Dangers of Concrete.

Progress, Volume III, Issue 4, 1 February 1908, Page 134

Dangers of Concrete.

A valuable paper was read recently before the Western Society of Engineers by Dr. Michaelis. After dealing sharply with the prevailing exaggerations of previous expectation and subsequent criticism, the author insisted that the best way to establish confidence in this .modern building material

would be to minimise thef~danger of failure by establishing proper building ordinances, which would compel the contractor to handle the material in the prescribed^way, and to make proper tests of it while the building is in course of construction. j|~ The principles governing modern concrete construction are thoroughly understood by comparative^ 7 few ; and this explains the divergence of opinion on many points pertaining to this branch of the building industry. While some engineers are careful to specify concrete of ample strength, others blame such " overcautious " builders foi making use of en excessive factor of safety. In reply to the statement frequently made by engineers that cement is not sufficiently uniform at present, and that if it could be so manufactured as to give as uniform results as steel, it would be possible for the engineer to reduce the larger factor of safety now demanded for concrete over that required for steel, the author of the paper answers that such a statement is entirely without foundation. Steel is a welldefined chemical compound rolled into the desired shape, while concrete is the sum of a number of factors. The calculation of a steel girder and that of a reinforced concrete girder can never be based on equal safety factors, no matter how much the properties of cement may be improved in the future ; and it will not be improved in the future for the reason that we have arrived at the limits of its good qualities. In the opinion of Dr. Michaelis, the author of the paper, failures of concrete steel can be materially lessened ,if not entirely prevented, by making it compulsory to use concrete of specified proportion of crushed stone, sand, and cement, and to use the proper kind of reinforcement in each case, and the necessary amount of it. Cert? in standard rules should