PROPERTIES OF PORTLAND CEMENT. PART III. 



243 



2.5 per cent mixture in a shallow pan until the microscopic test detected 

 only slaked lime. The results obtained are given in Table XXXIV: 



Table XXXIV. — The effects of aeration on the setting properties of non-seasoned 

 cement K -\- 2.5 per cent of plaster. 



Time 



aerated 



in 



days. 



Specific 

 gravity. 



Water 

 required 



in 

 per cent. 



Temperature 



of laboratory 



during the 



mixing and 



setting. 



Time of setting 

 in minutes. 



Initial. 



Final. 





 1 

 2 

 5 

 5 



3.11 

 3.10 

 3.09 

 3.06 

 3.06 



24.0 

 21.0 

 21.0 

 24.0 

 24.0 



27° -28° 

 27°. 5-29° 

 27° -30° 

 27° -29° 

 «31° -31°. 5 



30 

 35 

 40 

 35 

 10 



50 

 150 

 240 

 250 

 150 



» Obviously the activity of the setting compounds in cement K is greatly influenced by 

 thermal conditions. On the other hand the set of cement L remained practically constant 

 for temperatures varying from 26° to 32°. 



The figures in Table XXXIV show that this mixture remained too 

 quick setting and too susceptible to changes in heat to giiarantee a 

 normal initial set under all ordinary conditions of storage and use. 

 However, this same cement mixed with only 2.0 per cent of plaster and 

 aerated in the same manner soon became and remained slow setting. 



The cause of this apparent discrepancy is explained by the curves in 

 figure 22. (See also figure 19.) 



vi/ffO 



1 1 1 1 1 



1 





^ 









K 









< * 



1 t X \ 





- 



\ 



\ / \- 







^/oo 





' 



— 



K 



rv 7 V- 







kj 







<0 75 



" \ nV \^ 





- 



vj 

 X 









X 



- ^y \ 







1^ SO 





- 



\0 N. 







V. 





\ 





^ 25 



\> 



- 



Vi 



V, 



^\^ 



^ 







\^ 



>. 



, 





^>*- 



k 



1 1 1 1 1 



1 





0.5 to 2.5 2.0 2.5 



3.0 



5-0 





P£ff C£^r /=>IAST£/R ADDED 





102594- 



FlG. 22. 



