172 The Philippine Journal of Science wu 



A mixture of the four cements in equal proportions aerated 

 for eighteen hours, molded into neat briquettes, and exposed to 

 the atmosphere in the laboratory gave the following average 

 tensile strength in pounds per square inch : 



7 days =138 pounds per square inch. 



28 days = 168 pounds per square inch. 



154 days= 85 pounds per square inch. 



The compressive strength, developed by 2-inch cubes of neat 

 and sand mortars of the same mixtures, is given in Table IX. 



Table IX. — Compressive strength of cements 1, 2, 3, and U, mixed. 



Age of 2-inch cubes. 



Compressive 



strength in pounds 



per square inch. 



1 



Neat 

 mortar. 



1:3 Otta- 

 wa-sand 

 mortar. 



1 



1,133 



28 days in air .. _ - _. 



1,989 





The strength developed by these cements far exceeds the 

 requirements of the standard specification for natural cements, 

 and there is little doubt but that a more thorough study would 

 secure still better results. 



Plate I, fig. 2, is a photograph of part of the Bureau of Science 

 exhibit of calcareous-siliceous resources at the 1914 Philippine 

 Exposition. It shows the Iwahig raw materials and the clinker, 

 cement, steamed soundness pats, and pressed concrete bricks 

 which they produced. 



CONCLUSIONS 



The Iwahig penal colony could convert its brick plant at 

 very little extra expense into a cement factory which could 

 produce a good grade of natural cement. The brick press at 

 the colony would serve to mold the cement mixture and the 

 kiln to burn the resulting bricks. It would be necessary to 

 install only pulverizers, and as both the raw materials and the 

 clinker require very little grinding this would not be expensive. 

 The cost of manufacture would be much less than for the 

 clay bricks. Neither the molding nor the burning requires 

 great care, and it is only necessary to maintain a temperature 

 of 1,000° C. in the kiln for from three to four hours, whereas 

 with the clay bricks a temperature of about 1,050°C. must be 

 maintained for twelve or more hours. 



