PROPERTIES OF PORTLAND CEMENT. 



405 



Pig. 13. — Diagram showing variations in the effects of thorough aeration on the 

 volatile constituents of Portland cement. 



Of course, atmospheric conditions exert a marked influence upon the 

 amount of water and of carbon dioxide absorbed. In rainy weather, for 

 instance, cements frequently contain more than 2 per cent of moisture. 

 This tends to accelerate the hydration and to promote setting and caking. 

 Therefore, all of the recorded figures and curves are more or less subject 

 to variation. However, the information gained from these experiments 

 is applicable to practical considerations, as manufacturing conditions 

 also involve similar exposures and variations in atmospheric influences. 



• THE SEASONING OE PORTLAND CEMENT CLINKERS. 



The action of water and air on Portland cement clinker is radically 

 different from that on the ground commercial product. 



Tables XV and XVI show that ha»rd-burned 85 clinkers may produce 

 unsound cements containing a considerable amount of sintered free lime ; 

 and furthermore, that prolonged aeration of such clinkers may fail to 

 produce soundness, or to slake all of the free lime. On the other hand, 

 underburned clinkers from the same kiln and similar raw material acted 

 differently. Seasoned during the same time and in the same manner, 

 they produced sound cement. This is the opposite to the behavior of 



35 Well-burned and hard-burned designate clinkers which have undergone 

 incipient fusion and which have sintered into dense, hard, rock-like clinkers 

 which are very difficult to crush and grind and which do not disintegrate readily. 

 When such clinkers contain no free lime, they are regarded as being perfectly 

 sintered. 



