THE SPECIFIC GRAVITY OF PORTLAND CEMENT

D B BUTLER
1906 Minutes of the Proceedings of the Institution of Civil Engineers  
THE specific gravity of Portland cement has long been considered a test of its quality, and is specified as such in the recently-issued British Standard Specification. It is held to denote the degree of calcination to which the cement has been subjectecl in the course of manufacture, a high specific gravity indicating a thoroughly burned material, and ,&e aersrc ; it is also considered to indicate adulteration with materials of different specific gravity. It is well known that, owing to
more » ... on of water and carbonic acid (having specific gravities of 1 0 and 0 -88 respectively), the specific gravity of cement decrewes with age, or after aeration, but the Author WAS surprised to find that, after ignition at red heat to expel the water and carbonic acid and to reduce the material to practically the same condition as regards these substances as when it left the kiln, the specific gavities of various cements were so nearly identical as to render the test of little or no value as an indication of quality. The results of preliminary experiments with thirty different cements, having specific gravities varying between 3.026 and 3.138 (Le. a difference of 0-112), showed that after ignition the specific gmvities differed by only 0.016, which is well within the range of experimental error in ordinary technical determinations. I n order to test the generally accepted theory that specific gravity is an indication of the degree of calcination, twenty-eight samples of black well-burned and yellow under-burned clinker from the same kiln or charge were obtained from various works, and the specific gravity of each sample was ascertained (1) in the condition in which it was received, and (2) after ignition a t red heat. The results showed that all the yellow under-burned samples, when they had absorbed any appreciable amount of water and carbonic acid, had a much The complete Paper, with its accompanying Tables and Appendix, may be seen ~ ~ ~. _ _ _~ __ in the Library of the Institution. Downloaded by [ UNIVERSITY OF IOWA LIBRARIES] on [17/09/16].
doi:10.1680/imotp.1906.16743 fatcat:i6n6kaxypve4depeizt4drssja