764 KEPORT — 1891. 



6. On some of the Peculiarities to be ohserved in Portland Cements, and on 

 the most advanced methods for determining their Constructive Value. By 

 Henry Faija, M.Inst.C.E. 



After dealing with the manufacture of Portland Cement, and the materials 

 from which it is manufactured, the author proceeds to describe in detail the pro- 

 portions of lime, silica, and alumina which would constitute an ordinary Portland 

 •cement, and further explains that their degree of chemical affinity materially affects 

 the quality of the cement produced. The peculiarities appertaining to quick- and 

 slow-setting cements is exhaustively considered, and, after defining the ordinary 

 behaviour of cements when gauged with water, he says that any cement deviating 

 materially from these recognised laws, though it may be a perfectly good cement, 

 should be used with caution until its quality is absolutely determined by further 

 tests and experiments. 



The necessity of making tests for tensile strength at two dates, in order that 

 the growth or increase in strength of a cement may be ascertained, is explained, 

 and the author makes use of Professor Unwin's "formula for determining the 

 ultimate strength of a cement in order to compare the respective value of quick- 

 and slow-setting cements. 



With respect to the setting properties of a cement, the author explains that 

 there are two periods which may with advantage be noted when carrying out a 

 test ; the one being the ' initial set,' or, in other words, the time which elapses 

 between the addition of water to the cement and its commencing to set, and the 

 time when it is ' set hard ' ; tlie lime of ' initial set ' being considered the most 

 important, as it represents the commencement of an actual chemical process, and 

 that any disturbance of the cement after the .setting or crystallisation has com- 

 menced would detract from its ultimate strength, wliereas the time of ' set hard ' 

 is only a somewhat undefinable period, and really indicates no change in the 

 chemical process, being only one step towards the ultimate hardness and strength 

 which the cement will attain. 



The test, however, which the author considers the mo.st important is that by 

 which its ' soundness,' or freedom from expansion or contraction, is determined, 

 and he explains that no matter in what time the cement sets, to what fineness it is 

 ground, or what tensile strength it developes within the limited period of an ordi- 

 nary test, can possibly he of any value if the cement proves an unsound one, and 

 that in the course of time it will ' blow ' and destroy the work of which it is a 

 component. The causes which make a cement an unsound one are also considered, 

 and it is explained that a cement may ' blow ' within a day or two of its being 

 gauged, or it may not blow until several months afterwards.' 



The method of determining the soundness of a cement, which the author 

 devised some ten years ago, is then explained ; it consists in submitting a freshly- 

 made pat to a moist atmosphere of about 100° F., and when set hard immersing' it 

 for some hours in water at a temperature of 115° F. This treatment greatly 

 expedites the set and hardening of a cement, and in like manner developes any 

 blowing tendency which may exist in it, and consequently in the short time of 

 twenty-four hours the ' soundness ' or ' unsoundness ' of a cement may be abso- 

 lutely determined. 



The nature of aggregates used with cements in concretes and mortars is also 

 touched upon, and it is explained that they may in themselves, through being 

 unsuitable, cause a failure of the mass even when a perfectly good cement is used, 

 and that, therefore, the user should be as careful in his choice of aggregates as in 

 his choice of cements. 



Several peculiarities appertaining to old and new cements are also described, 

 and the author concludes with a reference to the Pontypridd Sewage Works, 

 which the members attending the meeting afterwards had an opportunity of 

 visiting under the guidance of Mr. Chatterton, the engineer of the works. 



