Alkali-activated fly ashes - A cement for the future

The alkali activation of waste materials (especially those coming from industrial and mining activities) has become an important area of research in many laboratories because it is possible to use these materials to synthesize inexpensive and ecologically sound cement-like construction materials. In the present paper, the mechanism of activation of a fly ash (no other solid material was used) with highly alkaline solutions is described. These solutions, made with NaOH, KOH, water glass, etc., have the common characteristic of having a very high OH- concentration. The product of the reaction is an amorphous aluminosilicate gel having a structure similar to that of zeolitic precursors. Temperature and time of curing of specimens together with the solution/fly ash ratio are some of the variables that were studied. These variables have been shown to notably influence the development of the mechanical strength of the final product. Mechanical strengths with values in the 60 MPa range were obtained after curing the fly ash at 85 degrees C for only 5 h. (C) 1999 Elsevier Science Ltd. All rights reserved.