The Influence of Biomass Fly Ash on the Plasticizing Effects in Cement Pastes

Abstract

The aim of this work is to determine the impact of biomass fly ash (BM-FA) on the plasticizing effects in cement pastes. The rheological properties of the cement pastes have been determined using rotational viscometer with coaxial cylinders Rheotest RN4.1. These tests, using rotational viscometer, have been conducted by making the assessment of cement paste flow curves, using Bingham rheological model. The rheological properties (yield stress, viscosity and thixotropy) of cement paste were determined at different times after paste mixing: 0 min, 30 min, 60 min, 90 min and 120 min. The cement pastes with same W/C ratio equal 0.35 were tested. 0%, 5%, 10%, 20% and 30% of cement were replaced by BM-FA. The rheological behavior of the cement pastes was also studied and compared to that of a reference BM-FA free production in order to evaluate the effect of BM-FA addition on rheological properties. Results showed that having replaced 10% of cement with BM-FA the paste exhibits better rheological properties: not only lower yield stress but also lower viscosity from mixing until 120 min after. Adequate amount of BM-FA (10%, in this case) not only improves rheological properties but also helps retaining plasticizing effect for the period of 120 min, which is important in long distance concrete mixtures transportation. It was observed that having replaced up to 10% of cement with BM-FA thixotropy was also improved and the fresh concrete mixtures produced can be transported, molded, consolidated, and finished within 90 minutes from mixing without losing good workability and rigidity.