Study on the hydration product and embodied CO2 of NHL-mineral admixture system based on thermodynamic simulation and experiments

The global cement industry is facing severe pressure to reduce emissions, it is of great importance for developing low-carbon cement-based materials. Natural hydraulic lime (NHL), as an environmentally friendly binder, can be used to prepare green concrete instead of cement. In this paper, a thermodynamic simulation method was employed to analyze the hydration products of the NHL-mineral admixture system. The strength of mortars with NHL-mineral admixtures was tested. The environmental impacts of different NHL-mineral admixtures were analyzed based on the embodied CO2 (EC) indicators. The relationships between the main hydration product (CSH gel) in the NHL-mineral admixture system, the mechanical strength, and EC were established. In addition, considering the best mechanical properties and low carbon emissions, the optimal composition of the system was discussed. The results showed that in the NHL-mineral admixture system, different composition ratios of mineral admixture and NHL had significant effects on CSH gel content and EC. The optimal compositions of binary and ternary systems of different NHL-mineral admixtures were analyzed. Among them, the NHL-GGBS-SF ternary system is the best, in which the CSH gel content is greater than 80%, and the EC is only one-third of Portland cement and one-half of pure NHL systems, respectively. This achievement will provide important technical support for the development of sustainable cement-based materials.