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UNDER this title, an endeavour will be made to give the ultimate results of practical experiments with concrete mixtures whiah have been carried out intermittently over a period of four years. The author has made his investigations as opportunities lent themselves, and found himself, after his first series of experiments, obliged to tear up the results of much labour, and persist later in a more thorough manner. This has happened several times, and this paper will be practically confined to the results of 1923, and as such, will be referred to here.
B. Price Davies
ALTHOUGH Portland cement was first, produced in England in 1824, the product of that date can hardly be considered as belonging to even the same class of material which to-day bears the name. The present era of Portland cement came into being with the development of the rotary kiln, and its beginning may be considered as contemporaneous with the opening of the twentieth century. The product of today is materially superior to that of twenty years ago, largely because it is manufactured under more definite supervision. The mechanical rocesses involved in its making have been highly developed and the regulation of the raw material at all stages, from the quarry to the finished cement, has, with the single exception of the control of tlhe kiln temperatures, been brought to a high state of perfection. Notwithstanding these great improvements and developments, there has, however, been no substantial change in the inherent characteristics of the cement itself. The product, of to-day is more uniform in quality, is ground more finely, and develops somewhat greater strength, but its essential properties have, with the passing of the years, remained unchanged. No new cements have been announced until quite recently, as in the case of those based on a high alumina content.
Increasing attention is being given, by engineers to this branch of civil engineering, principally in connection with the manufacture of the necessary steel reinforcement and in the selection, grading and mixture of the requisite concrete aggregates. That the latter question is of the utmost importance there can be no doubt; in fact, many of the successful reinforced concrete roads, for which the manufacturers of various
fabrics are taking no little credit upon themselves, are in reality due to the quality of the concrete rather than to the amount and arrangement of any embedded mesh.