Issue 2

WHEN our energetic Secretary suggested, I should read a paper before the Concrete Institute, it was with a certain amount of misgiving that I agreed to his suggestion, as I had not a vast amount of spare time in which to write anything, and I was inclined to think that many, if not most, of you know more about the subject of Economy in Reinforced Concrete than I do. Still there may be some, to whom some of the information is fresh, and the paper may help by discussion to bring forth from the members of the Institute points of economy which are unknown to all of us, and so I trust, that it will prove of some benefit to the Institute. T. A. Watson

STONE lime of great purity, and consequently nonhydraulic, is used largely in India and Burma, and engineers have learnt to place considerable confidence in the material. To enable it to set under water, it is mixed with "soorkhee," the homra of Egypt.* To the present day engineers in India do not know exactly how much soorkhee is required by each kind of lime, and this ignorance is due to the want of scientific laboratory tests, of the kind so frequently made in Europe. It seems no advantage to send lime and soorkhee to England to be tested, since the difference in climate, the sea voyage, and the lapse of time in transit might vitiate the results. Conservative Indian opinion, based on long experience, approves of a mixture of a half-part of under-burnt with a half-part of well-burnt soorkhee to one part of slaked lime and one part of sharp, clean sand, all measured in bulk, dry. The materials are thoroughly incorporated and ground in a mortar-mill, either under one wheel pulled round a circular trough by a bullock, or in a pan-machine under a pair of wheels. The mortar should be a thick reddish paste, in which the particles of lime cannot be distinguished by the naked eye. A mortar made in this way sets very well indeed in still water, but it sets comparatively very slowly, and some engineers (the author included) add, when necessary, a proportion of Portland cement to the mixture. The introduction markedly hastens the setting to an extent depending on the proportion of cement to lime. One part cement to one part lime by volume sets apparently as quickly as cement mortar. In the early stages of setting the strength of the concrete is much increased, admitting of early handling and removal of moulding boards. The addition of cement preserves soorkhee mortar in wet foundations from the evils of percolation, and the cement, besides, seems to have a chemical (?) effect on the lime, fixing the particles and aiding in a more solid set. * "Soorkhee" in India is finely powdered red brick. E. A. W. Phillips

The Concrete Institute had on April 30, 1915, 935 Members, 40 Associate Members, 8 Associates, 64 Students, 5 Special Subscribers, and 14 Honorary Members.

A WRITER in the Encyclopaedia Britannica states that wind pressure is "supposed to interest the engineer and the navigator"; if we drop the latter and substitute the architect we can say that it is supposed to interest this Institute. R. Graham Keevil

THIS paper is submitted with the view and the hope that a new Act will shortly be prepared embodying the existing Acts, By-laws, and Regulations. In 1894 our present London Building Act was passed, and thereby cancelled some thirteen existing Acts which had to be read together. Twenty-one years have elapsed Since then; many decisions have been given in the High Courts, some of which completely annul the intention of the Act; many amendments have been framed, some of which have become law; and it will soon be necessary to repeat the process of 1894 and pass a new Act embodying all the existing laws and regulations, with certain desired modifications and improvements. Such improvements should be the carefully considered results of the various authorities: the Royal Institute of British Architects, the London Society, the Town Planning Association, architects, surveyors, structural engineers, builders, and property-owners should now unite in preparing such improvements in the Acts as they consider essential in readiness for submission to the proper authority. The London County Council "fathered" the Act of 1894 through Parliament, and the writer believes they have already collected much material for a proposed new Act. Osborn C. Hills

IN spite of the large amount of experience which has been gained in the construction of quay walls, it is still one of the most difficult problems in engineering to design a wall on an earth foundation with confidence that it will be stable when completed. A warehouse or a bridge can now be designed, not only with the assurance that it will bear its load, but also, with a knowledge of its factor of safety sufficiently accurate to satisfy the designer that material has not been wasted. But the same can certainly not be said of a retaining wall on a soft bottom-at all events not of a wall, say, 40 to 80 ft. high, such as is commonly needed to sustain the quays of a modern dock. Even if the designer of such a wall is assured that it will stand, he cannot with any confidence tell you what factor of safety it possesses. The cause of his uncertainty is of course the difficulty of ascertaining the actual lateral pressure imposed by an earth backing and the actual resistance offered by an earth foundation. His difficulties are thus quite different from those of the engineer who has to design large masonry dams. The latter structures are invariably placed on a foundation of solid rock, and the designer's chief care is that the stresses in the masonry of which the dam is composed shall not exceed a safe limit. The dock engineer on the other hand has to be anxious that his wall shall not move as a whole on the comparatively soft material on which such structures have in general to be placed. F. E. Wentworth-Shields