This paper reports the effect of elevated temperature exposures, up to 1200◦C, on the residual compressive
strengths of alkali-activated slag concrete (AASC) activated by sodium silicate and hydrated lime;
such temperatures can occur in a fire. The strength performance of AASC in the temperature range of
400–800◦C was similar to ordinary Portland cement concrete and blended slag cement concrete, despite
the finding that the AASC did not contain Ca(OH)2, which contributes to the strength deterioration at
elevated temperatures for Ordinary Portland Cement and blended slag cement concretes. Dilatometry
studies showed that the alkali-activated slag (AAS) paste had significantly higher thermal shrinkage than
the other pastes while the basalt aggregate gradually expanded. This led to a higher thermal incompatibility
between the AAS paste and aggregate compared with the other concretes. This is likely to be the
governing factor behind the strength loss of AASC at elevated temperatures.