The reaction between rice husk ash and Ca(OH)(2) solution and the nature of its product

In this study it was confirmed that, at temperatures around 40 degrees C an d in the presence of water, the amorphous silica contained in rice husk ash (RHA) can react with Ca(OH)(2) to form one kind of C-S-H gel (Ca1.5SiO3.5. xH(2)O). The C-S-H gel looks like flocs in morphology, with a porous struc ture and large specific surface. The average particle diameter of the react ion product, ranging from 4.8 to 7.9 mu m, varies slightly with the conditi on under which the reaction occurs. When the product is heated, it graduall y loses the water that exists in it, but it maintains an amorphous form up to 750 degrees C. Above 780 degrees C it begins to transform to crystalline CaSiO3. One of the main reasons for the improvement of concrete properties upon addition of RHA possibly may be attributed to the formation of more C -S-H gel and less portlandite in concrete due to the reaction occurring bet ween RHA and the Ca2+, OH- ions, or Ca(OH)(2) in hydrating cement. (C) 1999 Elsevier Science Ltd. All rights reserved.