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Rice husk ash (hereafter, this will be referred as RHA) is known to possess high potential of being utilized as a cementitious material for concrete because as high as 85 to 97% of the ash by weight is consisted of amorphous silica1>,2. Special interest has been given to the material in Asian countries mainly for three reasons, namely, abundance of rice husks, shortage of conventional Portland cement, and demand for low cost materials. During last 10 years, many workers worked on the material to increase the potential of its utilization both in the basic and applied fields, and there has been a worldwide race to devise better and cheaper ways of making quality RHA since 1974 when Mehta and Pitt3> published a paper which introduced a specially designed plant for mass producing active RHA. These efforts have confirmed that RHA, if produced properly, was a prospective silicious material not only for plastering but also for production of acid resistant high strength concrete,4,5>. Mehta states that he obtained patents on his discovery that active RHA could be produced by maintaining the combustion temperature for prolonged period below 500C under oxidizing conditions or, alternatively, combustion temperatures up to about 680C may be used provided the hold time is short, viz., less than 1 min4. However, as far as the authors know, none of his published papers includes any quantitative evidence to show how the discovery was made. In fact, lack of such information made many workers including Damers, Paul7> and Mallas fail to produce RHA of good quality although they burnt rice husks under very similar conditions to those suggested by Mehta. Ismail9 is another only worker who studied the optimum burning temperature of rice husks by means of differential thermal analysis and thermogravimetric curves and showed the results. But he could not use the results to explain the difference in activity of RHA actually obtained. Since useful RHA must be produced before its utilization, it is evident that factors involved for the

PRODUCTION AND UTILIZATION OF ACTIVE RICE HUSK ASH AS A SUBSTITUTE FOR CEMENT