238 



REIBLING AND REYES. 



woiild result. The further hydration of the lime would tend to retard the set 

 until finally, as shovm by the figures in Table XXIX; its rate would become 

 normal. A third change could be brought about by converting the slaked lime 

 into calcium carbonate, in which event the mixture would again become quick 

 setting and remain so until the cement itself was allowed to become so inert 

 as to set very slowly. 



It would also be predicted of this cement that if more than 1.0 per cent of 

 plaster were to be added, seasoning could only induce three radical changes in 

 its setting properties. One change only could be brought about by the slaking 

 of the free lime, as this would result in increasing the efficiency of the plaster 

 alone, thereby retarding the set. The data recorded in Table XXIX and figure 

 18 also indicate that if as much as 1.5 per cent of plaster is present, the slaking 

 of the lime would not cause the set of the cement to change beyond the normal, 

 but that if less than this amount is added, the set would change from abnormally 

 quick to normal. Two other changes could be induced to take place; the first 

 by converting the slaked lime into calcium carbonate, and the second by then 

 aerating the mixture until the cement itself became sufficiently inert so that 

 the rate of set would again become slow. Accordingly, the changes in set which 

 in reality took place when Oj cement was first plastered and then subjected to 

 thorough aeration were as shown by Table XXXI. 



Conditions of the experiment recorded in Table XXXI. — ^A sample of 30 kilo- 

 grams of Oi cement was divided into two equal parts to one of which 0.5 and 

 to the other 1.5 per cent of plaster were added. These two mixtures were then 

 thoroughly aerated side by side in shallow pans and from time to time subjected 

 to the tests as given in the table: 



Table XXXI. — Changes in the setting properties of plastered 0^ cement. 

 (Temperature of the laboratory during the mixing and setting = 27° to 29°.) 



Time 

 aerat- 

 ed in 

 days. 







cement+0. 5 per cent of plaster. 



0, cement-i-1. 5 per cent of plaster. 



Specific 

 grav- 

 ity. 



Free lime 



(microscopic 



test). 



Quantity 

 of water 

 required 

 to pro- 

 duce a 

 normal 

 consist- 

 ency 

 paste. 



Time 



of 

 initial 

 set in 

 min- 

 utes. 



Specific 

 grav- 

 ity. 



Free lime 



(microscopic 



test.) 



Quantity 

 of water 

 required 

 to pro- 

 duce a 

 normal 

 consist- 

 ency 

 paste. 



Time 



of 

 initial 

 set in 

 min- 

 utes. 







3 



7 

 13 

 18 

 28 

 37 

 48 

 90 



3.184 



3.153 

 3.130 

 3.107 

 3.100 

 3.063 

 3.050 



Mostly CaO. A 

 little Ca (OH),. 



CaO,Ca(OH)2 



Ca(OH)o 



Per cent. 

 28.0 



18.5 

 19.0 

 20.5 

 20.5 

 21.5 

 22.0 



»185 



15 



115 



110 



35 



5 



5 



3 180 



3.153 



3.122 



3.114 



3.107 



3.077 



3.063 



3.03 



2.928 



Mostly CaO. A 

 little Ca(OH)2. 



CaO,Ca(OH)2- 



Ca(OH)» 



Per cent. 

 21.0 



20.0 

 19.5 

 20.0 

 20.5 

 21.0 

 21.5 

 22.0 

 25. b 



45 



120 



165 



150 



140 



90 



30 



15 



170 



A little Ca (OH), - 



No Ca(OH), 



do 



AlitterCa(0H)2- 



No Ca(OH) 2 



do 





_. _ do 



do - 



do 



2. 920 



do 



25.5 



100 



,_ _.do 







Partially regauged. 



Pigui'e 21 diagramatically shows the changes in set and plasticity which 

 took place as the specific gravity of the cement gradually decreased. 



