. Annual report 1919. and bending testsup to their capacity. In addition to these a 500-pound capacity hand-driven anda 50-pound capacity motor-driven tension machine have been added for themechanical testing of tape, rubber, small wire, etc. Besides these testing machinesa Brinell meter for determining hardness of metals, a compressometer for obtainingthe modulus of elasticity of concrete, and a photomicrographic outfit for micro-scopical study of both metals and concrete are worthy of mention. The last twowere constructed in our Instrument Shop. The investigation upon the surface area theori
. Annual report 1919. and bending testsup to their capacity. In addition to these a 500-pound capacity hand-driven anda 50-pound capacity motor-driven tension machine have been added for themechanical testing of tape, rubber, small wire, etc. Besides these testing machinesa Brinell meter for determining hardness of metals, a compressometer for obtainingthe modulus of elasticity of concrete, and a photomicrographic outfit for micro-scopical study of both metals and concrete are worthy of mention. The last twowere constructed in our Instrument Shop. The investigation upon the surface area theories of proportioning concretemixtures has been carried on continuously throughout the year and to date hasinvolved some 4,000 tests. Important results are being obtained. As a result ofthis work a method of proportioning concrete mixtures which will give concreteof any desired quality and allows mixtures of various consistencies to be used asdesired, has been developed. This method has been used during the past summer. Sample of Frozen Concrete received from field work, showing frost marks causedby freezing before concrete had set. —Structural Materials Laboratory. on the High Falls Development and this fall on parts of the Niagara PowerDevelopment and has given very satisfactory results. Its use is to be extendedto other the coming year. Before applying the new method to any particular job it is necessary todetermine the quality and concrete making properties of the materials to be series of such tests have been carried out for the High Falls, Niagara Powerand Nipigon Developments. An interesting and important development arising out of this investigationalwork on concrete materials has been the relation discovered, that the change involume of a fine aggregate with change in its moisture content depends on thesurface area of the materials. Based on this, a method of obtaining the surfacearea of a material has been devised which does not require a screen ana
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