Using of Modified AlF3 Production Waste in Cement-Based Materials

Abstract

The paper deals with the investigations of impure silicagel AlF3⋅3.5H2O, obtained as a by-product of phosphatic fertilizers production, in hardened cement paste. It was determined that silicagel is a suitable additive in hardened cement paste only when thermally activated for 1 hour at 800 °C. An amorphous SiO2 of this additive reacts with Ca(OH)2 that was formed during cement hydration and composes hydrosilicates of (1.5–2.0)CaO·SiO2·nH2O type that add additional strength to the samples. With the optimal amount of additive of 10 % the compressive strength of hardened cement paste samples increases by (5–7) MPa compared to the samples without additive. By forming hardened cement paste samples with thermally activated SiO2 it is observed, that it form agglomerate structures. The plasticizer additive is used to destroy the agglomerates. It was established that the optimal amount of plasticizer is 1.2 % in examine conditions, because it obtained the increase in strength of samples and smooth hardened cement paste structure form.