1st January 1933
First published: 1st January 1933
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To the Editor of The Structural Engineer. Water-Cement Ratio. Sir,-In reference to Mr. C S Gray’s letter,Professor Duff A Abrams states that "Aggregates of equivalent concrete making qualities may be produced by an indefinite number of different gradings of a given material." "Aggregates of equivalent concrete qualities may be produced from materials of widely different size and grading." "In general, fine and coarse aggregates of widely different size or grading can be combined in such a manner as to produce similar results in concrete." The meaning seems to point clearly to the
fact that size or grading may vary widely in each aggregate, but not the different aggregates unless they have equivalent concrete qualities.
W D Williams
Dr Oscar Faber said the paper hardly lent itself to discussion in the ordinary manner, because it was such an excellent description of modern cement manufacture,and nobody could argue with anything that was said in the paper. That made it more difficult to arouse at any rate a very fierce discussion. The first years of his own college course were spent in a cement works, and he had been interested in cement ever since, and for that reason he had appreciated the paper very much. In referring to the universal practice of adding gypsum to make cement slow setting, the author said this is added to the extent of anywhere between 2 per cent, and 3 per cent., but the British Standard specification required that it should not exceed 2.75 per cent. This obviously meant that there was some objection to gypsum if it were introduced in
excessive quantities. The objection to gypsum was that an excess of it made a cement what was known as unsound, and it gave the cement certain properties which were deleterious to a permanent concrete.
The President, proposing a very hearty vote of thanks to Mr. Creswell for having put the matter so clearly before the members, said he was wondering when structural engineers would have the opportunity to acquire legal knowledge in addition to all the
scientific knowledge they must possess; perhaps the matter was one which might be placed before the Institution’s Board of Examiners. Mr W.C.Cocking(Past Member of Council) paid a tribute to Mr. Creswell in respect of his very happy knack of drawing the attention of professional men to various matters, often of very great importance, but which had previously escaped their attention, and said that the paper referred to many matters which professional men did not often consider.