PROPERTIES OF PORTLAND CEMENT. 369 



tests ; compression determinations on concrete cubes, mortar cylinders and 

 the broken tensile-strength briquettes ; expansion bars ; air, moist-air, and 

 sea-water exposures; and acid and alkali treatments, were all utilized. 

 After working on the commercial product, we continued the investigation 

 on the nonaerated clinker received from manufacturers in Europe and 

 China. Finally, one of the authors visited a few cement mills, where 

 every courtesy and assistance were given to him and where he was enabled 

 to secure valuable information and collect special material for this work. 

 For the sake of brevity and clearness the work which we have clone 

 will be presented, as far as possible, as an abstract of the results. 



CHEMICAL ANALYSES. 



Table A (Appendix I) gives the chemical analyses and physical 

 characteristics of typical samples of various brands, the requirements and 

 methods of the American Society for Testing Materials being used. 



The chemical analyses of the same brand of cement taken from time to 

 time during the past five years usually have shown very little variation, 

 and the analytical work of this Bureau has been found to agree very closely 

 with similar records taken from factory reports on identical material. 

 Despite this uniformity in chemical composition, we have at times encoun- 

 tered much variability in physical properties. Even in the same shipment 

 we have met with sound and unsound, and slow and quick-setting cements, 

 as well as cements which developed both low and high seven-day tests, 

 accompanied by good increases, or slight decreases in later determinations 

 of strength. 



On the other hand, some brands of Portland cement have shown the 

 most remarkable uniformity in physical properties. The significance of 

 chemical composition and the relationship between chemical and physical 

 properties are given under the specific heads of the discussion. 



Paet I. 

 FREE LIME IN PORTLAND CEMENT. 



As our investigations progressed it became evident that the physical 

 properties of Portland cements were influenced to a marked degree not 

 only by the amount of free lime, but also by its condition, that is whether 

 this calcium was present as the hydroxide, oxide, or as the latter heated 

 to a degree of incipient fusion. 



The most diverse opinions have been expressed concerning the ques- 

 tion of the existence and importance of free lime in Portland cement. 



Alfred H. White * says : "It is rather generally, although by no means univer- 

 sally, assumed that the lime must be in a state of combination, but the evidence 

 for this belief is almost entirely indirect." 



*Journ. Ind. & Eng. Chem. (1909), 1, 5. 



