Abstract
Two types of rice husk ash were used. One was produced by controlled field burning operations in Thailand, and the other was obtained by burning charred rice husks in a furnace at a laboratory. The ashes obtained were pulverized in a ball mill for 10 or 60 min and used as a partial cement replacement material in mortar and concrete. Several properties such as chemical compositions, specific surface areas, particle-size distributions and X-ray diffraction patterns of the ashes were determined. The longterm strength development of the concrete containing up to 40% rice husk ash by weight of the total cementing material and other properties such as the flow and bleeding of fresh mortar containing rice husk ash were also investigated. The following results were obtained.
(1) The rice husk ashes consisted of 90-92% silica.
(2) The 28-day and 91-day compressive strengths of the rice husk ash concrete were higher than those of the control concrete without rice husk ash.
(3) The bleeding capacity of the fresh mortars containing rice husk ash was significantly reduced compared with the control mortar. The fine rice husk ash pulverized for 60 min bled less than the coarser one pulverized for 10 min.
(4) The flow of the fresh mortars decreased as the ash content of the cementing material increased. The flow of the fresh mortars containing the fine rice husk ash was larger than that of the mortars containing the coarser one.
