Correpondence on Concrete Roads

VII-GENERAL DISCUSSION. Qualities of the Aggregates Nothing was brought out in the tests to show marked differences in strengths because of the differences in the nature of the surface of the grains and the effect of smoothness or of differences in the porosity of the grain on the adhesion of the cement to the grain. There was some indication that the smooth and non-porous grain of the Ottawa sand gave slightly lower strength results. J. Singleton-Green

With the gradual raising of concrete engineering into a definite branch of science, the need for accuracy in every detail and, therefore, for testing at each successive step, has brought about the introduction of quite a large number of appliances used in controlling operations. Such checking of operations is required not only in connection with the primary materials-cement, sand, the larger aggregates and water-but the secondary adjuncts, including reinforcements, waterproofing or other ingredients, and also the mixtures at various stages, as well as the completed work, whether this be in the form of mass construction or moulded units.

The following simple problem in Graphic Statics is sfbpplied by The Bennett College, Sheffield, the Governor of which will give a prize of 10s. for the best solution. In allotting points, neatness will receive the same consideration as accuracy.