Activation of blast furnace slag by high-calcium fly ashes

High calcium fly ash generated at pulverized solid fuel combustion at thermal power plants in combination with sodium carbonate is an effective dry activator for hardening cementless mortar mixtures based on ground granulated blast furnace slag (GGBFS). The interaction
of Na2CO3  and components of high calcium fly ash provides an alkaline environment stimulating hydration of crystalline and amorphous ash and slag phases and emergence of a solid structure formed by close splicing of their hydration products - ettringite crystals and amorphous C-S-H gel. When 10-30 % of slag is
replaced with ash in the presence of 1-3 % Na2CO3 by weight of the binder, mixture of slag and ash, and the water-binder ratio of 0.30-0.45 the strength of slag-sand mortars reaches 10-30 and 30-45 MPa at 7 and 28 days under the conditions of wet curing at standard tempera-ture respectively.
Fly ash produced at low-temperature combustion using the technology of circulating fluidized bed has a high hydration activity and may have an independent value as a hardening activator for GGBFS, since the pres-
ence of Na2CO3 does not affect the strength of ash and slag samples. However, when using this type of ash, the strength of the resulting stone is limited by its high water demand.
The interest in clinker-free and low-clinker binders is increasing again everywhere in recent years. Development of new types of those can be a step towards solving environmental problems of the cement industry, metallurgy and coal energy (reduction of greenhouse gas emissions, recycling of man-made waste).
Author: A.S. Brykov, M.E. Voronkov

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