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The Structural Engineer

A reply to J. Singleton-Green, Esq., B.SC., A.M.I.Struct.E. Sir,-If the discussion in your paper upon Concrete Roads is to be continued for the benefit of those really interested in this important branch of engineering it appears necessary to focus it upon those lines which lead to useful information.

The Structural Engineer

An hydraulic lime is one which will set and harden under water. This property is common to several well-known materials used for constructional purposes, notably Portland cement. The power of setting and hardening under water in the case of hydraulic lime is due to the formation during the burning of the lime of certain chemical compounds of silica, alumina and lime, of which tri-calcic silicate (3CaO.Si02) is the chief. Other compounds such as di-calcic aluminate (2Ca0.A1203) and certain ferrites of limes are also formed, but these act only as fluxes and aid in the combination of lime and silica, and in themselves do not increase the hydraulic properties of the lime. Henry Pooley, Junr.

The Structural Engineer

A FURTHER notable step in the long series of experiments carried on during the past twenty years in relation to heat transmission through heavy building materials has to be recorded in the publication of Special Report No. 7 of the Building Research Board.

The Structural Engineer

0NE of the problems of civilisation to-day is the prevention of waste, and most countries of the world, if they adopted scientific methods, could live on what they throw away. One good example of this is the fact that millions of tons of ash and clinker, from steam boiler, destructor and other furnaces, for example, together with blast furnace slag, are wasted every year, whereas all this material could be converted, at a handsome profit, into high grade bricks. A Correspondent

The Structural Engineer

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.

The Structural Engineer

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 Structural Engineer

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