AN AVERAGE-SIZE CEMENTPLANT
Cement Progress and Research R. W. CARLSON llassachusetts Institute of Technology, Cambridge, Rlass.
G
REAT as has been the progress in the cement industry, the greatest progress lies ahead. Past improvement has been largely toward economy of manufacture, increased production, and greater uniformity. Future progress will continue along these lines but will also comprise adapting cement to new uses and making it better suited to present uses. Research has added greatly to the knowledge of cement and concrete, especially during the last few years, but that knowledge has not yet been put to its most intelligent use. The improvement in the quality of concrete, as regards its ability t o perform its main purpose of supporting load, has not been great. Intrinsic strengths have been increased beyond all expectations, but structures must still be designed without full regard for this increased strength, as will be explained later. First, acknowledgment should be given to the progress which has been made.
cement was made which exhibited flash ?et, the c a u e sometimes being vaguely attributed to an “underlimed” mix. Impurities were often present in such large percentage that the specific gravity test was introduced to prevent too great an adulteration of the cement. A large percentage of the cost of manufacture was attributed to delays and expenses occasioned by the formation of huge rings in the clinkering zone of kilns. While these experiences are not unknown today, they are practically a thing of the past. Progress was made when it was learned that too coarse grinding of the raw mix produced a clinker containing an appreciable percentage of free lime which expanded on hydrating to make an unsound cement. A satisfactory method of determining the percentage of free lime in a clinker was gradually developed. Temperature control in the kiln helped to solve the “ring” problem, as did also chemical control of materials. Routine analyses finally included the separation of the oxides of iron and alumina, paving the way for the calculation of the actual compounds likely t o be present in a clinker. Probably the greatest forward step was the identification of the major compounds and the providing of simple equations for computation of the percentages present. The introduction of the wet process for grinding and blending the raw mix was a step both toward greater economy and greater uniformity, mhile the recovery and utilization of waste heat was purely economical. The recent development of the flotation process for separating minerals seems destined t o aid those manufacturers who are not so fortunate as to have pure raw materials, and the process should make possible generally a freer choice of chemical composition.
CTniformity Only those of long experience in the cement industry can appreciate the fight which has been fought and won to obtain uniformity in Portland cement. The producer has been kept in a state of perpetual alertness by the demands of standard specifications which have gradually grown and become more rigid. His goal has been to meet the requirements as to soundness, setting time, insoluble residue, loss on ignition, etc., and still show an operating profit. His research facilities have been almost entirely absorbed in avoiding cement likely to be rejected and a t the same time in striving for efficiency of production. He has solved his problems so well and has demonstrated that he can make cement so uniform that he is occasionally being called upon t o deliver a uniformity more Drecise than can be ascertained bv test. The manufacturer recalls early expeFiences of having made thousands of barrels of unsound cement without knowing a t the time the exact cause of the unsoundness. Likewise, much
Recent Progress in Manufacture The outstanding drifts in Portland cement have been toward greater uniformity, increased fineness, and economy of manufacture, but chemical composition has been almost 638
.*
