KLEIN AND PHILLIPS! HYDRATION OF CEMENT 573 



PHYSICAL CHE:MISTRY.— r/ie hydration of Portland cement.' 

 A. A. Klein and A. J. Phillips. Bureau of Standards. 

 Communicated by the Bureau of Standards. 



The study of the hydration of Portland cement follows as a 

 natural sequence to the study of its constitution. The latter 

 has been determined by the work of the Geophysical Laboratory 

 on the ternary system lime-silica-alumina, and for that portion 

 of the ternary -field in which Portland cement is situated, these 

 compounds have been verified by the Pittsburgh laboratory of 

 the Bureau of Standards. 



In the present paper various hydration experiments were made 

 on mono-calcium aluminate (CaO.Al203), 5:3 calcium aluminate 

 (5Ca0.3Al203), tri-calcium aluminate (3CaO.Al203), mono-cal- 

 cium silicate (CaO.SiOo), beta-orthosilicate (2CaO.Si02), gamma- 

 orthosilicate (2CaO.Si02), tri-calcium silicate (3CaO.Si02), on 

 lime burned at different temperatures and ground to various 

 degrees of fineness, and on the following commercial cements, 

 a high silica, a low silica, a high iron, and a high magnesia cement. 



The tests consisted of (1) hydration on microscopic slides with 

 water, without access of air, (2) hydration with superheated 

 steam in a cylinder, according to the method proposed by Bied, 

 (3) hydration in an autoclave, and (4) moulding with limited 

 quantities of water, approximating those used in normal con- 

 sistency mixes. Lime water and plaster of Paris solution were 

 also used as hydrating media. Petrographic microscope methods 

 were employed to determine the hydration processes and the 

 final products. 



The only crystalline product observed in the hydration of the 

 aluminateswashydrated tri-calcium aluminate (3CaO.Al2O3.xH2O) 

 and this is only formed with a large excess of water. It crys- 

 taUizes in hexagonal needles, plates, and spheruhtes, and is uni- 

 axial positive. The refractive indices are e = 1.552 ± .003 

 and CO = 1.535 ± .003. The 5:3 calcium aluminate and mono- 

 calcium aluminate split off amorphous hydrated alumina and 

 form the crystalhne hydrated tri-calcium aluminate. The 



^ Detailed paper to appear in the Bulletin of the Bureau of Standards. 



