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Effect of rheological parameters on rice husk ash blended pastes with various superplasticizers
(2017)
Rice husk ash (RHA) is a low-energy efficient material with high pozzolanic characteristics compared to other supplementary cementitious materials (SCMs). The replacement of cement with RHA has extensive improvement on the mechanical properties of concrete. However due to the porous nature of the RHA particles, it requires a higher water demand when replaced with Portland cement. Therefore, superplasticizers (SPs) are essential to reduce the water demand and improve the workability of the mixes. There is very little information about the effect of RHA with added SPs in its fresh state. Hence, this paper investigates the interaction of RHA pastes with three types of SPs, i.e. one polycarboxylate-based SP and two different types of lignosulphonates. This paper presents results of the investigation related to the flow behaviour of blended mixes with increasing percentage of RHA. The yield stress for the pastes with and without the addition of SPs is investigated over time as well as the plastic viscosity.
The paper presents rheometric results and hydration curves for cementitious systems based on cement mixed with different aqueous phases at solid volume fraction of = 0.45. The varied aqueous phases were deionized water, limewater, the filter residue of a cement paste mixed at w/c = 2.0, and the filtrate of cement paste at solid volume fraction of 0.45. Each cementitious system provided different amounts and sizes of particles formed in the aqueous phase. The pastes were observed with and without polycarboxylate ether based superplasticizer. It was observed that the presence of particles causes higher PCE saturation dosages to achieve a minimum value, but the minimum value is only affected in the case of large particles. In all cases with and without PCE, the presence of small particles causes increased plastic viscosity. In addition, with decreased number and size of hydrates in the aqueous phase the hydration was retarded, which was specifically pronounced in the presence of PCE