Issue 2

Mr. D.A.G. REID, in a few words supplementing Dr. Glanville’s presentation of the paper, said that he might try to express in another form what he felt to be the value of the wet mortar test. It amounted practically to this, that if one had a strength-age curve for the wet mortar, and then immediately one had also a strength-age curve for a 1:2:4 concrete with a water-cement ratio of 60 per cent., and, with the aid of a few general relationships, strength-age curves could be constructed for any other concrete made with that cement; and the strengths taken off from such strength-age curves would be correct to within about 10 per cent. If, however, any such operation were carried out with a dry mortar test, inevitably it seemed errors of 20 per cent. or more crept into the estimates. Of course, that could be got over if the mortar- concrete strength relationship were available for the particular batch of cement, but that contingency was not very likely. Dr. Glanville had mentioned the carrying out of preliminary tests before the commencement of the main programme. The results of these tests had proved very instructive, and had been of considerable value in assisting in the interpretation of the results of the main series. Mr. Reid felt that this portion of the work would be of great interest to anyone connected with the testing of cements and concretes.

Psychology. To appreciate the conditions of the problem which we are studying to-night it is necessary to visualise the circumstances which surround buildings at the present time, the conditions under which we live, and the constructional materials in common use. All these circumstances have very direct bearing, not only upon the amount of noise which exists, but upon the extent to which people using buildings and living in houses, are uncomfortably conscious of this noise; in fact, it may not be too much to say that consciousness of noise is very much more important than noise itself. T.P. Bennett

Revolutionary changes in structural design are so rare that particular interest attaches to occasional reports, principally from foreign countries, describing the manufacture in light aluminium alloys of structures which would normally be of steel. Clearly the choice of material is not dictated by some irresponsible whim, but by economic considerations, or other equally strong justification. For many years, the use of aluminium alloys has been standard practice for certain special types of structures, e.g., aircraft, and if proof were necessary of the suitability of aluminium alloys for withstanding stress, fatigue, corrosion, and other factors looked for in a structural material, it would be found in the behaviour of the delicate, complicated girderwork of a rigid airship, or the less intricate but equally elegant structure forming the fuselage and wings of an aeroplane. For such structures, however, the paramount importance of the stress-weight ratio reduces to a secondary consideration those questions of comparative cost which in general engineering are so important. The fact that the cost of duralumin may be 2s. 6d. per lb., whereas structural steel costs less than 2d., is of less importance than the fact that l-lb. of duralumin in the form of a bar of any given length will support nearly three times the load carried by l-lb. of structural steel of the same length. E.T. Painton

The rapid growth of aerial transportation during the last ten years so admirably illustrated by the activities of Imperial Airways Ltd., and particularly the wide interest shown in the spectacular flight of Scott and Black from Mildenhall Aerodrome to Melbourne in two and a half days, have focussed public attention on the urgent necessity for providing adequate landing fields and aerodromes in this country. It is noteworthy that H.R.H. The Prince of Wales remarked at the recent Airport Conference, “Take care of the wheels and the wings will take care of themselves.” The aeronautical engineer has indeed done his share, and such enormous strides have been made in aircraft design that the operational speed of machines is approaching 200 m.p.h. If, therefore, it is true that “time is money,” here is economy with a vengeance. H.E. Brooke-Bradley

It may be stated in a general way that, for a given nature of sand and a given quality of cement agglutinant the strength of the resulting concrete increases when its compactness increases. The lack of compactness may be due in part to bad granulometry, which is a question into which it is not proposed to enter specifically in this paper; assuming that the best granulometric composition of the inert, component has been attained, lack of compactness may still be due to the fact that full advantage is not taken of the possibilities presented by the composition of the mixture, that air cavities remain in the concrete, either through the presence of mechanically enclosed air bubbles, or through the gradual evaporation of superfluous water. T.J. Gueritte

The CHAIRMAY (Dr. Oscar Faber, O.B.E., M.Inst.C.E., Vice-president), who regarded the paper as one of the most interesting ever presented to the Institution, proposed a hearty vote of thanks to the author for the extraordinarily interesting collection of photographs he had shown, as well as for the paper itself, and for the admirable way in which he had presented it.