PORTLAND CEMENT TESTING. 175 



Among other conclusions he states ^^ "that low specific gravity is usually 

 caused by seasoning of the cement or of the clinker, either of which 

 improves the j)rocluct. * * * Underburned cement is readily and 

 promptly detected by the soundness tests and no others are needed for 

 this purpose. * * * That the requirements of specific gravity should 

 be omitted." 



Underburning is readily detected by the soundness test, only when 

 the cement is fresh. Seasoning of underburned cement may eliminate 

 the causes of its unsoundness. Meade himself states in this same refer- 

 ence tliat an underburned cement which, when freshly made, failed to 

 stand a 5-hour steam test without complete disintegration, after one 

 month's seasoning stood 5-hour steam and boiling tests perfectly. The 

 greater piart of the cement received at this laboratory for commercial 

 testing has been seasoned lor a greater or less length of time, therefore 

 the soundness tests are not liable to detect underburning in most instances. 



Cement raw material, high in alumina, fuses so readily that it is 

 difficialt to control its burning, and as a result almost all high alumina 

 cements vary considerably. It is also very difficult to detect the relative 

 degrees of burning which the commercial, high-alumina cements have 

 undergone and it is only possible to do so by taking into consideration 

 many of the iDliysical p>roperties of the material. It has been observed 

 that a brown shade,^- a low specific gravity, ■'*■* a high loss on ignition, 

 the presence of blotches ■'* between the soundness pat and the glass plate, 

 a high, insoluble residue and a generally erratic behavior of a cement, 

 exist simultaneously with a relative increase in the rate of carbonic acid 

 and water absorption. These are all regarded as signs of rmderbuming, 

 and a study of all of them gives the only indications of the relative 

 degree of burning of seasoned, high-alumina cements that we have been 

 able to recogTiize. 



Meade's statement that seasoning of the clinker improves a cement is 

 also open to discussion. Some cements are improved by this pirocedure, 

 but many others are not. Instances are on record where seasoning 

 induced quick setting and low tensile strength, even when calcium 

 sulphate was present. Meade admits "that cements should contain at 

 least 3.5 times as much silica as alumina. Cements containing less than 

 this amount of silica are apt to be quick setting, or else to become quick 

 setting on exposure to air." 



It is hardly necessary to state that we do not think that the require- 

 ments of specific gravity should be omitted from specifications. This 



=i/6ic/., 6, 19. 



'- Sabin, Louis Carlton: Ibkl., 36. 

 '^Soc. Chem. Industry (1894), 13, 2.5.5. 

 =' Taylor and Thompson: Ibid., 101-107. 



