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Mr. R. H. H. STANGER (Chairman of the Concrete Sectional Committee of the Institution), after congratulating the author upon the very great care he had taken with the preparation of the paper, said that the Concrete Sectional Committee had been awaiting the paper. One of the instructions to the Sectional Committee had been to look into the question of the compression testing of concrete, and they had hoped to persuade Professor Lea to take up the work, which was a big work, very complicated, and one which would require a lot of time. There were one or two points in the paper upon which he (Mr. Stanger) did not agree with the author. At the beginning of the paper the author said that he had tried to get a consistency which would give the greatest strength, but he (Mr. Stanger) was not sure whether testing officials, independent or otherwise, should try to get at the greatest strength which a concrete would give, because, after all, in actual practice we were not likely to get the greatest strength. Mr. Lloyd knew his opinion of the Boulogne test so far as the sand and cement was concerned, because the repraentatives of various testing laboratories had met to discuss and to carry out, this and other tests when the standard Portland Cement specification was being revised. The Boulogne test, one must admit, had given extraordinarily consistent and uniform results, but so had others. In his opinion, the use of the Boulogne ball test was rather a retrograde step, because too much depended upon the personal element, which was always a difficult matter to avoid in the testing of cement. Mr. Lloyd had thought out his paper and arranged his tests very carefully, but surely he could have thought out some centrifuge which would have saved them all these Swedish exercises. At the same time, he did not want anyone to think that various methods, because they happened to be new, were not necessarily the correct ones; it was only by trying various methods that we should arrive at, the correct method of carrying out what was really a very difficult operation. In a discussion on mass concrete, at Newcastle, there seemed to be a concensus of opinion that, of the sands to be used for concrete work, the coarser and the finer sands were really the useful ones, and that the sands which passed through the medium-size sieves were not
of great use. With regard to crashing tests, Mr. Lloyd had found that in ten tests the blocks in which there were no voids failed suddenly, whilst those containing voids crushed slowly. He agreed with this ahsolutelv as the resnlt of his own experience. Continuing, Mr. Stanger assured the author that the paper was really going to be useful in helping the Concrete Section to get out a scheme, and they could certainly take the paper as a good example of the care which was required in carrying out a series of comparative concrete tests, whether on cubes or on cylinders. The question of whether cubes or cylinders were the correct specimens to
This paper is the sequel to the previous one on " The Consistency of Portland Cement,
Mortar and Concrete," read by the Author at the Concrete Institute on April 22, 1920.
The object of that paper was "to describe a simple means of ascertaining the quantity
of water required when mixing mortar or concrete."
It is too often forgotten that England is a country of bridges, and has been so since Elizabethan times. There were about nine hundred of them by the middle of the seventeenth century. Are these nine hundred still with us? Alas, their numbers must by now be very sensibly reduced, and that not because of any inherent defects, but because we of the twentieth century insist that our roads and bridges shall carry burdens which eighty years ago would only have been entrusted to a specially constructed track of steel. As the volume of modern traffic swells, one bridge after another becomes inadequate both in size and strength; too narrow, that is, to contain it, and too weak to support it. What is to be done? Shall it be widened, or strengthened, or both, or neither? Such, in brief, is the choice open to those whose duty it is to provide smooth and ample roads and bridges for the thousands of internal combustion vehicles that daily troop forth from American and European factories. It is not an enviable task; to some it may seem a never-ending one comparable to that upon which poor Sisyphus was (and perhaps is still) engaged. What width must the widening add, what strength the strengthening? Is it enough if they serve the need of today, or must they be prepared for that of to-morrow, and perchance the day after, too? Roads and bridges that once were wide are already narrow, and will be narrower still in a few years' time.