214 ANNALS NEW YORK ACADEMY OF SCIENCES 



constitution of the cement is the only way to prevent decomposition. In 

 concrete block construction, where the blocks may be made long before 

 they are actually put into the structure, it is found of great advantage to 

 allow them to harden in air or in damp sand, and so permit to a great 

 extent the carbonation of the lime compounds. Some investigators claim 

 excellent results from this method (41, 55). 



As to the modifications in the constitution of the cement that will 

 combat the action of saline solutions, there is a great disparity of opin- 

 ion, which possibly is based upon lack of standardization of experimental 

 conditions. It is generally conceded that high silica cements are best 

 suited for the purpose (7). The use of puzzolan cements, or of addi- 

 tions of puzzolan to the cement in use, is also well recommended (7, 37, 

 66) ; and the addition of clay, burnt or dehydrated, finds favor with 

 some (7, 75). As to the lime content of the cement, opinions are divided 

 whether it should be high (5, 41) or low (92). 



Cement of greater density (57) and cement ground to a greater fine- 

 ness than usual (72) are favorably commented upon. The subject, 

 because of its great complexity and because of the questionable value of 

 laboratory results, is at present in a chaotic state. The length of time 

 that must elapse before judgment may be passed upon the permanence 

 of a material under these conditions and the corresponding newness of 

 the field of Portland cement render present conclusions largely a matter 

 of speculation. 



Effect of storage in various saline solutions upon the strength of 

 mortar. In order to study the relative resistance to saline solutions 

 offered by cements varying in chemical composition and in fineness of 

 grinding, a series of 132 2-inch mortar cubes was made up, in the pro- 

 portion of 1:3, with standard Ottawa sand, the cements used being 



A. A high silica cement 



B. A low silica cement 



C. A cement of ordinary composition, sifted and remixed so that 



98.8 per cent passed the 100 mesh sieve and 88.6 per cent 

 passed the 200 mesh sieve 



D. The same cement as C sifted so that 92 per cent passed the 



100 sieve and 75 per cent passed the 200 sieve 



