Effect of alkali contents, moduli and curing time on engineering properties of alkali activated slag

Cement industry has become one of important sources of greenhouse gas emission. Compared with the cement, alkali activated slag (AAS) possesses comparable mechanical properties and lower carbon emission during its production. It can thus be employed as an alternative binder for low-carbon construction. This paper investigated the effect of alkali contents, moduli, and curing time on flexural strength, compressive strength, drying shrinkage, setting time, and resistance to chloride penetration of AAS. Alkali contents ranging from 2% to 6%, moduli of 0.6, 0.9, and 1.2, and curing time of 7, 28, 90 and 180 days were adopted in the test. Test results have shown that high alkali contents shorten setting and accelerate development of compressive strength, but cause large drying shrinkage, deterioration in flexural strength and resistance to chloride penetration of AAS. Alkali contents ranging from 3% to 4% in AAS can achieve the setting time, flexural and compressive strength comparable to cement. Increasing moduli can accelerate setting, improve compressive strength and lower chloride penetrability, but increase drying shrinkage and reduce flexural strength of AAS. Continuous curing after 28 days can significantly improve flexural strength, compressive strength and resistance to chloride penetration of AAS mortar with alkali contents of 2–3%. Using 28-day compressive strength as an index for classification will underestimate the AAS with low alkali contents. Analytical models considering effect of alkali contents and moduli are proposed to predict relationships between flexural strength and compressive strength of AAS mortar and achieve a good correlation with experimental results.