Performance of alkali-activated slag individually incorporated with two nanozinc sources

The role of nanozinc source (nanohydrozincite: nHZ; nanozinc oxide: nZO) on the performance of alkali-activated slag (AAS) was explored for the first time in the present work. The results showed that nHZ with different contents (0.5, 1.0, and 1.5 wt%) retards the early hydration rate of AAS, whereas nZO showed the lowest retardation effect. Zn(OH)₂ is the main retarder inside AAS-nZO and AAS-nHZ, which consumes the dissolved Ca²⁺ (responsible for the early hardening of AAS) from slag to yield calcium zincate hydrate (CZH). The high retardation rate of nHZ is originated from its high affinity to consume much Ca²⁺ through the formation of additional pirssonite (Na₂CO₃.CaCO₃.2H₂O) double salt. Although adding nHZ induced the drying shrinkage of AAS, it improved the later compressive strengths (28 to 365 days), especially at low nHZ content (0.5 wt%), via the formation of CASH with lower Ca/Si ratio and higher binding capacity compared to that formed inside AAS and AAS-nZO. A further research is needed to reduce the drying shrinkage and to accelerate the early strength of AAS containing nHZ.