Study on the interaction between limestone filler and rice husk ash on the rheological properties of cement composite pastes

Abstract

As an active supplementary cementitious material, rice husk ash (RHA) can improve several properties of cement paste. However, it has a significant negative impact on the flowability of cement pastes. This study aims to improve the rheological properties of cement-RHA paste by adding an additional admixture: limestone filler (LF). The rheological curve was measured using a rheometer, and the effects of LF and RHA on the rheological properties (dynamic and static yield stresses, consistency, and structural build-up) were investigated. The calculation and analysis of water film thickness (WFT) and the interaction forces between the particles in the paste were conducted to reveal the intrinsic mechanism. The results show that LF can effectively eliminate the adverse effect of RHA on rheological properties. When the RHA content is 10 %, the addition of 5 %, 10 %, and 20 % LF reduces the yield stress by 43.86 %, 69.64 %, and 87.11 %, respectively, and decreases the consistency by 28.17 %, 40.85 %, and 73.24 %, respectively. The high porosity of RHA leads to significant water absorption, which affects the WFT between paste particles much more than LF. The WFT decreases with RHA, resulting in a higher yield stress. The higher specific surface area (SSA) of RHA reduces the spacing between paste particles, and the enhanced interactions between particles significantly increase the initial yield stress (20 min). The addition of LF reduces the inter-particle forces and the structural build-up, lowering the yield stress, which results in a good complementary effect between LF and RHA on the rheological properties. This study can provide guidance for the design of mix proportions considering the workability of the cement-LF-RHA composite system.