Hardening mechanisms of an alkaline-activated class F fly ash

The hardening mechanism of a paste composed of a low calcium fly ash and al kali was investigated. It was found that a fraction of fly ash reacted with water-glass and formed amorphous or low-ordered crystalline compounds of t he type of Na2O-Al2O3-SiO2, after the paste was cured at 60 degreesC for 24 h. For the water-glass with a modulus of 1.64, the strength of the paste i s mainly attributed to the gel-like reaction products that bind the particl es of fly ash together. When the modulus is decreased to 1.0, crystalline s odium silicate is formed in the matrix, which helps to achieve high strengt hs. (C) 2001 Elsevier Science Ltd. All rights reserved.