Effects of GGBFS on hydration and carbonation process, microstructure, and mechanical properties of NHL-based materials

Natural hydraulic lime (NHL) is an inorganic building material with hydraulic and air-hardening properties, having exceptional application in restoring ancient buildings compared to Portland cement and ancient air-hardening lime. However, the characteristic of slow performance development limits its application field. This study used ground granulated blast furnace slag (GGBFS) to replace parts of NHL. The hydration heat release, phase composition, micromorphology, pore structure, and physical and mechanical properties of GGBFS-NHL (S-NHL) based materials in the hardening process are investigated in-depth. The influence of GGBFS on the hardening process and performance development of NHL are systematically evaluated. The NHL is dominated by the hydration reaction of C2S to produce C–S–H in the early stage (less than 28 days). Moreover, C3AH6, CASH4, C4AĈH11, and C–S–H gel generated by the reaction of GGBFS with Ca(OH)2 changes the composition of hardened products, including the microstructure of the hardened paste. The higher the dosage of GGBFS, the more the hydration products in the NHL-based paste. The NHL-based paste gradually hardens with increasing age, mainly due to carbonation reaction. Moreover, its pore structure gradually densifies with curing age, and the average pore size and total pore volume of S-NHL decrease gradually with increasing GGBFS content. GGBFS significantly influences the mechanical properties and weight of the NHL-based mortar development. In addition, the S-NHL mortar's early and long-term mechanical strength increased significantly with increasing GGBFS. •GGBFS has an obvious influence on the hydration and carbonation of S-NHL paste.•C3AH6, C4AĈH11, CASH4 and C–S–H gel are generated by the hydration reaction of S-NHL paste.•The addition of GGBFS obviously changes the microstructure of hardened paste.•GGBFS has a positive effect on the mechanical strength of S-NHL mortar.