Cement-free binders based on combined acid and high-basic fly ash and the problem of free CaO

The mixture of high- and low-calcium types of fly ash and activator, sodium carbonate, can serve as a low-grade clinker-free binder gaged with water. In the alkaline environment created as a result of interaction of binder components and water, the hydraulic and pozzolanic properties of the said types of fly ash are activated, resulting in a water resistant matrix with a strength of 10-20 MPa and more. The hardening process is stimulated by steam curing. Volumetric deformations accompanying the hydration of free CaO in the high-calcium fly ash and affecting the stability of samples and their strength depend on the composition of fly ash and its particle size distribution, composition of the binder and its curing mode. Using these factors, it is possible to control the development of deformations at the level of permissible limits or significantly lower them. Introduction of ultradisperse silica into the binder composition suppresses destructive processes even in case of coarse high-calcium fly ash with a high content of free CaO.
Author: A.S. Brykov, M.E. Voronkov

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