The high autogenous shrinkage of alkali-activated fly ash/slag (AASF) poses a significant concern for the widespread application of AASF in structural engineering. The present study compares the efficacy of activator and mineral admixtures in mitigating the autogenous shrinkage of AASF, and discusses the underlying mechanism. The results show that the use of activators with a lower silicate modulus and a lower sodium content, as well as incorporating metakaolin (MK) or silica fume, can reduce the autogenous shrinkage of AAMs. These approaches delay the appearance of the second exothermic peak, which corresponds to the later formation of C-A-S-H gels and slower development of capillary pressure. The inclusion of MK not only retards the reaction but also facilitates the formation of N-A-S-H gels, resulting in a coarse pore structure and reduced water consumption. The use of the activator with a lower silicate modulus (reduced from 1.5 to 1.0) leads to a higher internal relative humidity and the reduced pore volume of silt-shaped and ink-bottle pores (2–50 nm) in AASF, thereby reducing the autogenous shrinkage without significant strength reduction.@en

Investigating the mechanism of multi-walled carbon nanotube (MWCNT) in the early cement hydration enables better utilization of the potential of MWCNT as reinforcing agents in cement composites. The interaction of MWCNT with ions and its effect on cement hydration were investigated. Zeta potential measurement was intended to discuss the interaction of the MWCNT surface with Ca2+. Then, the formation processes of C–S–H were observed with a scanning electron microscope (SEM). The influence of MWCNT on the early cement hydration was investigated using isothermal calorimetry. The results showed that MWCNT significantly accelerates early cement hydration. It is likely attributed to its high surface area and strong adsorption for Ca2+, which greatly promotes the migration of ions, especially Ca2+, and thus the precipitation of ions on the cement surface. This facilitates the C–S–H nucleation and growth process, thus the cement hydration. These results also indicated that the MWCNT would not provide a stable nucleation site for C–S–H, since the size of MWCNT is less than that of C–S–H.@en