138 The Philippine Journal of Science isu 



Also, the addition of slaked lime in quantities up to 2 per cent 

 failed to retard the set. 



The object of adding slaked lime was to ascertain the possible 

 effects of free lime, small amounts of which are present even, 

 in the best burned commercial products. It is known that if 

 this lime remains unslaked until the cement is used the heat 

 generated when the water is added will tend to quicken the set. 

 Since, in this instance, small quantities of slaked lime did not 

 retard the set, the presence of free lime could only serve to 

 quicken the setting properties. Consequently, we believe that it 

 would be impossible to control the set of well-burned cements 

 made from the same mixture as cement 2a so that it would remain 

 within desirable limits until used. 



We believe that this change from normal to quick-setting 

 properties was due entirely to the reduction in the content of 

 calcareous materials. This conclusion is warranted to some 

 extent by the fact that the same raw materials were used in 

 both instances and by the normal setting properties of the 

 cements (3, 3a, 4, and 5), which were made with either similar 

 limestone or similar clay. However, it required additional data 

 either to verify this conclusion or to prove that good results 

 were dependent upon the conditions of manufacture which pro- 

 duced cement 2. Owing to this and the importance of the raw 

 materials under consideration, we prepared and tested a third 

 mixture (2b) which contained more of the calcareous material 

 than either 2 or 2a. 



Mixture 2b was calculated so that the resulting cement would 

 contain about 66 per cent of calcium oxide, thus increasing the 

 hydraulic modulus from 1.86 and 2.15 to 2.31. No difficulty 

 was experienced in burning this high-limed mixture properly, 

 and the well-sintered clinker, pulverized with 1 per cent of 

 plaster to about the same fineness as cements 2 and 2a, gave the 

 excellent results recorded in Table VIII. 



Table VIII. — Composition and setting properties of cement 2b. 



Material. 



Parte. 



Composition of mixture: 



Limestone, equal parte of Nos. 35, 37, and 39- 

 Clay 47 



100 

 7 



