Natural talc as a promising candidate material to mitigate the strength deterioration of fly ash geopolymer cement cured in water

Fly ash (FA) geopolymer is widely used due to its friendly environmental and prospective properties in mechanical and durability issues. After initial heat curing, this system may be cured in air (which is most common) or in water. Unfortunately, there is a deterioration in its compressive strength when cured in water compared to air curing. In this article, for the first time, the authors tried to mitigate this strength deterioration by incorporating natural talc (NT) powder. For this reason, FA was partially substituted by NT powder at ratios in the range of 2.5–20 wt%. After preparation and initial heat curing for 24 h, half of the specimens were cured in air, whilst the remaining half were cured in water at room temperature for various ages. The compressive strength for each curing type was determined. For each curing age, the strength deterioration rate (SDR) caused by water curing was monitored. The results confirmed a negative effect of water curing on the strength development of specimens manufactured from neat FA. This deterioration can be mitigated with the inclusion of NT. As the amount of NT increased, the SDR decreased. Despite this positive effect of NT on mitigating the SDR, the incorporation of NT decreased the strength due to its high crystallinity. Similar crystalline phases were detected in the samples cured in water to those cured in air but with alteration in their intensities. The microstructure of the samples cured in water showed higher defects compared to those cured in air.