Compatibility of PC Superplasticizers with Slag-Blended Cements

摘要

The aim of the present study was to determine the adsorption isotherms of polycarboxylate (PC) superplasticizers with different structures on slag-blended cement pastes (with a slag content between 0-75%). Also, their effect on the rheological properties and hydration process has been evaluated.rnThe results indicate the adsorption of PCs decreases slightly as the slag content in the cement increases; however, their fluidizing properties are significantly higher in the slag-blended cement. This effect is mainly attributed to the content of C_3A (mineralogical phase with the highest affinity for the PCs) which decreases in slag-blended cement. Consequently, the amount of PCs consumed and adsorbed by this mineralogical phase also decreases. In this way, most of the PC admixtures are absorbed onto the silicate phases of the clinker and onto the slag particles, inducing an electrosteric repulsion and the concomitant reduction in yield stress. The rheological results show that the highest increase of the fluidity is caused by the admixture with highest molecular weight concluded to be due to the higher steric repulsion expected for thicker adsorbed layers. As a consequence of the adsorption of the PCs, a delay of the hydration process of the cement pastes has been observed.