Effects of fly ash and silica fume on disintegration of alkali-activated slag at temperature exposure of 50°C

The compressive strength of alkali-activated slag (AAS) paste can be adversely affected by temperature. AAS paste loses its strength when exposed to 50°C for 24 hours. The objective of the current investigation is to evaluate two different mineral admixtures, i.e. fly ash and silica fume, in preventing AAS paste from strength loss. The effect of the above admixtures at various dosages on strength loss was assessed by measuring the retention of compressive strength of samples after exposed to 50°C. Results indicate that the admixtures reduced strength loss. Compared with the fly ash, the silica fume performs better at preventing AAS paste from strength loss. After exposure to 50°C, the use of silica fume to replace 15% of slag reduces the strength loss by 70%. The possible reason for this is discussed based on x-ray diffraction results.