Development of sustainable mortar and concrete by combined use of limestone calcined clay cement (LC3) and recycled aggregates

In recent years, high consumption of natural resources, environmental concerns about CO2 emissions from cement production, and improvements in mortar and concrete performance have driven the search for alternative materials. On one side, the generation of a tremendous amount of construction and demolition waste (C&D) has attracted widespread attention. C&D waste is often indiscriminately dumped or disposed of, resulting in landfill and ecosystems contamination. On the other hand, a major challenge facing cement industries in the 21st century is finding ways to reduce CO2 emissions and their environmental impact. Using recycled aggregates (RA) with Limestone-Calcined Clay Cement (LC3) is one of the low-carbon options for replacing ordinary mortar and concrete, leading to an eco-friendly and sustainable construction material while providing a solution for waste management. In this research study, a comprehensive investigation was carried out of the fresh-state, mechanical, durability and microstructural properties of LC3 mortar and concrete. The results highlight that LC3-70-2:1 binder with 17.55 wt % calcined clay, 8.77 wt % limestone, and 73.68 wt % CEM I show superior mechanical properties compared to CEM I with both natural and RA. The replacement of commercial cement with LC3 compensates for the negative impact of RA capillary water absorption and improves the pore size distribution and reduces the total porosity, contributing to the achievement of considerable mechanical resistance. Additionally, it significantly improves chloride resistance, long-term rheological properties, and negatively affects carbonation resistance. These results demonstrate that LC3-70-2:1 is a promising binder for producing mortar and concrete with RA, since it exhibits adequate durability and chloride resistance, and long-term rheological properties, particularly when RA, including fine and coarse recycled aggregate are used for concrete production. Thus, employing FRA and CRA with LC3 is a viable approach for minimizing Portland cement production, environmental impact, and disposal problems associated with C&D wastes.