Cement pastes of low water to solid ratio: An investigation of the polymerization of silicate anions in the presence of a superplasticizer and silica fume

Abstract

Polymerization of silicate anions was investigated by the molybdate method in cement pastes with water to solid ratio of 0.28. Two series of samples - with and without superplasticizer admixture - were prepared using ordinary portland cement (OPC) in which 0, 5, 10, and 15 percent by weight was replaced by condensed silica fume (CSF). During the hydration ranging from 4 hours up to 50 days, the free lime content and insoluble residue were also determined. The 28 day compressive strengths of the hardened composites were between 79 and 108 MPa. The results from the molybdate complex confirm that the presence of CSF in hydrating blends and its pozzolanic activity influences the size dispersity of silica anions by increasing the proportion of polymers. It is also suggested that in the cement pastes of w/s ratio of 0.28, the conversion level of CSF by pozzolanic reaction decreased. Finally, a comparison is made between the polymerization characteristics of the 0.28 w/s-ratio pastes and pastes of w/s = 0.68 which have been hydrated for 6.3 years.