Effect of albite on shrinkage and carbonation resistance of alkali-activated slag

Abstract

Large shrinkage and poor carbonation resistance are important reasons that limit the widespread use of alkali-activated slag. The expansion pressure of albite due to alkali-activated silica reaction in alkaline environments and the sequestration of CO2 may solve the problems. In this paper, the effect of albite on shrinkage and carbonation resistance of alkali-activated slag were studied, and the mechanism of action between albite and alkali-activated slag was revealed. Firstly, alkali-activated slag slurry specimens with partial replacement of slag by albite were prepared with standard and carbonation curing. Then, the samples were tested for compressive and flexural strength as well as chemical shrinkage, autogenous shrinkage and drying shrinkage under standard and carbonation curing. Finally, the mechanism of interaction between albite and alkali-activated slag was analyzed by XRD, TG-DTG, FT-IR, SEM, MIP and 29Si MAS NMR. The results show that: 1) the influence of carbonation on the compressive strength and flexural strength of alkali-activated slag was reduced when mixed with albite. After carbonation curing for 28 days, the compressive strength of pure slag samples decreased by 50.67 %, while the strength of samples mixed with albite decreased by 34.51 %. 2) After adding albite, the chemical shrinkage, autogenous shrinkage and drying shrinkage of alkali-activated slag samples decreased by 33.33 %, 32.95 % and 46.76 %, respectively. 3) The amount of calcite due to carbonation curing was reduced. The content of calcite in the sample with albite was 65.49 % of that of pure slag sample under carbonation curing. 4) Albite can promote the degree of hydration and the generation of C-A-S-H gels of the alkali-activated slag.