Effect of temperature of ashing of rice husk on the compressive strength of lime-rice husk silica mortar.

The content of silica in the rice husk was found to be 19.3% from TGA studies. The X-ray diffraction studies showed that highly amorphous silica was released by ashing rice husk at 700 degrees C and an increase in ashing temperature up to 900 degrees C led to increase in crystalline nature of silica. The test mortar cubes prepared using a mixture of hydrated lime, standard sand and rice husk ash silica obtained by ashing at different temperatures showed that, for both, 7 and 28 days curing, the compressive strength of the cubes increased as the ashing temperature is gradually increased from 500 to 700 degrees C. However, a further increase in ashing temperature up to 900 degrees C led to a decrease in the compressive strength, which is in conformity of the results obtained by X-ray studies. The SEM micrographs show rice husk silica ashed at 500 and 600 degrees C still contains significant quantity of carbonaceous matter and ashing at 700 degrees C lends to carbon free silica. The regular structure of silica skeleton in rice husk does not crumble even on heating at 900 degrees C.