IX, A, 1 West and Cox: Philippine Cement Raw Materials 83 



usual methods of testing commercial cements. However, the 

 establishment of the best working proportions of any particular 

 raw materials is usually an empirical procedure, and it is fre- 

 quently necessary to bum several mixtures in order to determine 

 the proper combining proportions and real efficiency of a given 

 material. 



If the raw materials have been combined in the most appro- 

 priate proportions and properly burned, the resulting clinker, 

 when properly ground, requires no treatment other than the 

 addition of a retarder. If these operations are carried out im- 

 properly, further treatment is necessary. The manner in which 

 the degree of pulverization, vitrification, seasoning, and plas- 

 tering affect the soundness, setting, hardening properties, etc. 

 of cements has been fully treated in the articles of Reibling and 

 Reyes,* and results obtained from ground clinker are apt to be 

 misleading unless these factors are taken into consideration. 

 It is necessary to study the cements as well as the raw materials 

 from which they are produced to secure satisfactory results. 



RAW MATERIALS 



Satisfactory raw materials yield a cement with a magnesia 

 content of less than 3 per cent; a silica to alumina (plus iron 

 oxide) ratio (hydraulic modulus) 



/ per cent silica (Si02) Si02 \ 



Vper cent alumina (Al203)+per cent iron oxide (Fe203) R2O3/ 



of between 2 and 3.5; a lime to silica, alumina, and iron oxide 

 ratio 



/ per cent lime (CaO) CaO \ 



\percentsilica(Si02)+alumina(Al203)+percentironoxide(Fe203) Si02+R203/ 



between 1.8 and 2.3 ; and a cementation index 



/(2.8Xp er cent silica) -|-(l.lXper cent alumina) + (0-7X per cent iron oxide) \ 

 \ (per cent lime) 4- (1.4Xper cent magnesia) / 



between 1.0 and 1.2. The time of setting and ultimate strength 

 of a Portland cement are in inverse proportion to the value of 

 the silica to alumina (plus iron oxide) ratio, and a high lime to 

 silica, alumina, and iron oxide ratio is an indication of a high 

 testing cement. 



Theoretically, it is possible to manufacture Portland cement 

 from many different materials which are available in the Phil- 

 ippines. However, the selection of the raw materials which 



'This Journal, Sec. A (1910), 5, 117-142; (1911), 6, 207-252; (1912), 

 7, 135-191; (1913), 8, 107-125. 



