The influence of alkalinity on activation and microstructure of fly ash

With the wide use of fly ash in cement and concrete construction, the function and hydration of fly ash, and the influence on the concrete properties are studied and emphasized more and more. The active mechanism, hydrates and microstructure of fly ash were studied by thermal gravity analysis (TGA), X-ray and SEM analysis. Results show that the reaction of fly ash was very low in the fly ash-cement, because Ca(OH)(2) had less activation capability on fly ash at room temperature. Only if the curing temperature is enhanced or the blended alkalinity and sulfate is added, does the breaking of glass structure of fly ash and the formation of stable hydrates occur. Results also show that in the action of NaOH, C-S-H and zeolite were present. When the gypsum is added, ettringite formation is related with the pH of the hydration system. (C) 2000 Elsevier Science Ltd. All rights reserved.