Hydration and Microstructure of Cement Pastes Containing Limestone Powder and Rice Husk Ash

There has been a growing interest in the use of limestone powder (LP) and rice husk ash ( RHA) in concrete due to their low cost, high availability and environmental friendliness. The hydration and microstructure evolution of hardened cement pastes containing LP and RHA were investigated via different characterization methods in this paper. The results indicate that the additions of RHA alone as well as both RHA and LP retard the hydration degree, and the hydration of the sample containing RHA alone has a larger growth with the increase of ages, close to that of the controlled sample. The variation of hydration has a certain corresponding relationship with the variation of compressive strengths. RHA alone as well as both RHA and 10% LP improve the pore structures obviously at the later ages. RHA is helpful to increase the volume fractions of high-density calcium-silicate-hydrate (HD C-S-H), and LP in the presence of RHA shows the negative effect on the formation of HD C-S-H. An increase of 10% LP in the presence of RHA deteriorates the microstructure evolution all the time.