Effect of thermal treatment of rice husk ash on surface properties of hydrated portland cement-rice husk ash pastes

Portland cement was mixed with rice husk ash (RHA) fired at 450, 700 and 1000 degrees C, in ratios of 5, 15 and 25 \% of RHA by mass. Cement-RHA pastes were made by using a water/solid mixture ratio of 0.30 by mass and then cured for various hydration periods within the range 3 to 90 days. The surface properties of the hydrated samples were studied by means of the nitrogen adsorption technique. The results indicated that the hydrated cement-RHA samples made from rice husks fired at 450 and 700 degrees C gave higher values of surface area than that for the hydrated cement-RHA sample made from rice husks fired at 1000 degrees C. The surface area and pore volume results could be related to the pore structure of the silica produced in the RHA, as controlled by its predicted degree of crystallinity.