CHAPTER XII. 



THE TESTING OF VITREOUS MATERIALS 

 AND TIMBER. 



PORTLAND CEMENT. 



170. Portland cement is by far the most important of the 

 cementing materials used in construction, and of which the 

 strength properties require to be determined by means of 

 systematic tests. 



Portland cement may be described as a product, con- 

 sisting for the most part of aluminates and silicates of 

 calcium, resulting from the calcination of materials con- 

 taining clay and lime. The process by which it is 

 produced may be summed up as follows : 



(a) Material containing clay in some form is intimately 

 mixed with other material containing lime as in chalk. 



British and American. Continental. 



FIG. 163. STANDARD FORMS OF BRIQUETTES. 



(6) The mixture so made, after being dried, is burnt 

 or calcined, during which calcination a chemical change 

 takes place, the silica and the alumina combining with the 

 lime to form the necessary silicates and aluminates. 



(c) The fine grinding of the resulting product to form 

 a cement which sets hard when mixed with water. 



