from a rice mill factory in Chainat, Thailand. The chemical composition of the RHA mainly consisted of silicon oxide (SiO2) and minor oxides as shown in Table 2. The specific gravity of the RHA was 2.10 and fineness was in the range 2,900–3,200 cm2.g-1 after grinding for 60 min. The surface texture of the RHA particles was rough surfaced and the particles were nonuniformly shaped (Figure 1).