PROPERTIES OF PORTLAND CEMENT. PART III. 



229 



regauged. Therefore it also required only a minimum amount (31 

 per cent) of water. 



The use of 0.5 per cent of plaster was not sufficient entirely to retard 

 the rate of reaction of all the setting compounds to the normal but it 

 did so to a certain extent, because the temperature of the calorimeter 

 only rose 0°.8 above that of the lime factor. This normal consistency- 

 paste may therefore be considered as a partially regauged cement, a 

 conclusion which is corroborated by the corresponding requirement of 

 water (24 per cent) and time of initial set (80 minutes). More than 

 1 per cent of plaster only retarded the set, until finally from 2 to 3 per 

 cent produced a maximum result. Beyond this amount the natural 

 tendency of plaster of Paris to set very quickly manifested itself in the 

 combined results obtained, and the time of initial set again approached 

 a minimum. 



The general character of the plastic and set curves derived from 

 brand Oj and K cements can be accounted for by similar analytical 

 reasoning, the only difference being that cement K required 1.5 per 

 cent of plaster totally to retard the rate of its setting sufficiently to 

 permit the molding of a normal consistency-paste. 



Table XXVII gives a comparison of the quantitative effects of the 

 same amount of plaster on the different cements. It shows that the 

 setting properties of the normal consistency-pastes made from cement L 

 are more readily retarded than those from cement Oj. At the same time 

 it is seen that it is almost impossible to retard the set of cement K 

 sufficiently to pass the requirements of our standard specifications. 



Table XXVII. — The qtuintitative effects of plaster upon the initial set of non- 

 seasoned L, Oi and K cements. 





The per cent of plaster 









required— 



The 













To retard 





maxi- 







the ini- 





mum re- 







tial set 



To pro- 



tardation 



Brand. 





sufficient- 



duce a 



of the 



To pre- 



ly to pass 



maxi- 



time of 





vent 



the re- 



mum re- 



initial 





regaug- 



quire- 



tardation 



set, in 





ing. 



ments of 

 the A. S. 

 T. M. spe- 

 cifica- 



of the 



initial 



set. 



minutes. 



L 





tions. 







1.0 



1.0 



2.0 



100 



0, 



1.0 



1.5 



2.5 



85 



K 



1.5 



2.5 



2.5 



32 



THE EFFECT OF SEASONING ON NON-PLASTERED PORTLAND CEMENTS. 



We next studied the changes in the plastic and setting properties of 

 non-plastered Portland cements brought about by various methods of 

 seasoning. The condition of the free lime was noted in each test. 



