Title:
Effect of Gypsum-Hemihydrate Ratio in Cement on Rheological Properties of Fresh Concrete
Author(s):
Jon Havard and Odd E. Gjorv
Publication:
Materials Journal
Volume:
94
Issue:
2
Appears on pages(s):
142-146
Keywords:
cement quality; concretes; gypsum; hemihydrate; slump tests;superplasticizers; workability;
DOI:
10.14359/295
Date:
3/1/1997
Abstract:
During production, storage, and transportation of cement, an uncontrolled variation in the gypsum-hemihydrate ratio may occur, which may cause an uncontrolled effect on the workability properties of the fresh concrete. In the present paper, the results of an experimental investigation on the effect of the gypsum-hemihydrate ratio in cement on the rheological properties of fresh concrete are presented. For the most reactive type of cement with a high content of both C3A and alkalies, a reduced gypsum-hemihydrate ratio from 80/20 to 20/80 reduced the yield stress, while the plastic viscosity was not much affected. For a less reactive type of cement, the effect of the gypsum-hemihydrate ratio was not so pronounced, but for the lowest ratio of 20/80 a false set was observed. In the presence of a melamine-based superplasticizer, an even more pronounced effect of the gypsum-hemihydrate ratio on the rheological properties of the fresh concrete was observed. However, for the most reactive type of clinker a reduced gypsum-hemihydrate ratio increased the yield stress, while for the less reactive type of clinker the effect was still less pronounced. An increased fineness of cement increased the effect of the gypsum-hemihydrate ratio, while a reduced total sulfate content reduced the observed yield stress.