Microstructure and Durability of Sustainable Concrete Incorporating Recycled Sand and Limestone Calcined Clay Cement

The use of recycled aggregates and Limestone Calcined Clay Cement (LC3) was shown to enable the production of green concrete as a promising and cost-effective solution to reduce the environmental impact of the building sector. This approach lowers CO2 emissions from cement production and offers a sustainable alternative to the depletion of natural resources. This study focuses on the performances of concrete composed of LC3, mixed in different proportions, and partial replacement of natural sand with recycled sand from construction and demolition waste. Fresh and hardened states were evaluated. The microstructural analysis of concrete incorporating recycled aggregates and low-carbon cement was carried out using Scanning Electron Microscopy (SEM) and 1H Time Domain Nuclear Magnetic Resonance (TD-NMR) techniques to assess material’s porosity and its impact on durability. The results showed that performances of concrete are enhanced when recycled sand is combined with LC3. Specifically, the combination of these sustainable materials allowed higher compressive strength and lower capillary absorption rate in comparison to concrete prepared with commercial cement and natural aggregate. The combination of SEM and NMR techniques provided a comprehensive evaluation of the microstructure and porosity evolution, which impact on the long-term performance of concrete. The study underscores the importance of microstructural properties in predicting the durability of concrete with recycled aggregates and low-carbon cement. These findings may contribute to paving the way for greener, more durable concrete solutions that reduce the environmental footprint of the building industry.