Sustainable Render Mortars Using Limestone Calcined Clay Cement (LC3): Mechanical, Microstructural, and Environmental Evaluation

The cement industry significantly contributes to global greenhouse gas emissions. Since their limestone calcination process releases substantial amounts of carbon dioxide, Portland cement (OPC) production is a major environmental concern. This study evaluated the potential of limestone calcined clay cement (LC3) as a sustainable alternative to ordinary Portland cement (OPC), specifically in its application for render mortars. Three LC3 formulations were developed, designated as A, B, and C, featuring different proportions of Egyptian raw materials, including clinker (CK), calcined clay (CCL), limestone (LS), and 5% gypsum. These formulations were tested for their physical, mechanical, and microstructural properties. Results show that the most efficient low-energy binder that reduces carbon emissions while maintaining good strength is LC3(C) (with 50% clinker replacement). At 28 days, its compressive and flexural strengths reached 48.7 MPa and 6.9 MPa, respectively. In render applications, the R25B mix (25% LC3 with black pigment) offered the best combination of low cost, performance, and environmental benefits. It met EN998 standards, achieved strong compressive and flexural strengths, and exhibited better adherence and thermal performance compared to traditional mortars. Additionally, black pigment showed better compatibility with LC3 than red, enhancing workability and aesthetics. The research highlights the potential of LC3, especially LC3(C), as an eco-friendly solution for reducing the cement industry's environmental footprint and offers a practical approach for adopting sustainable practices in construction and addressing climate change.