COMPARISON OF TWO MIXING METHODS FOR PRODUCING 100 MPa HIGH PERFORMANCE RICE HUSK ASH CONCRETE

摘要

Rice husk ash (RHA) was used as pozzolanic admixture for high performance concrete (HPC). This paper reports two mixing methods to achieve 100 MPa high performance rice husk ash concrete with low water binder ratio of 0.25, 550 kg binder and 15% replacement of cement with RHA. The water absorption of RHA is more than other pozzolanic materials due to the high specific surface area. Appropriate mixing method is required in order to get low mixing time, homogeneous mixing and good workability. The coarse aggregate used was granite of 19 mm maximum size and fine aggregate used was mining sand with fineness modulus of three. Amorphous RHA with 10 μm particle size was used. The conventional mixing and two step mixing methods were introduced to OPC and RHA concrete mixtures. The fresh and hardened properties of HPC were compared. Tests on hardened concrete included the determination of compressive strength and tensile strength. The effect of mixing methods on the refinement of the pore structure and hydration product in those concrete was confirmed through porosity test. Concrete produced with two step mixing method has better workability and higher compressive strength than that of conventional concrete.