Innovative Utilization of Limestone Calcined Clay Cement from the Egyptian Desert: Enhancing the Physico-Mechanical Properties for Sustainable Construction

Abstract

Cement manufacturing is one of the industries that has a significant impact on climate pollution, contributing approximately 6-8% to global CO2 emissions and global warming. However, there has been a global shift towards more sustainable practices in various fields, including the cement industry. The aim of this study was to produce concrete binders based on calcined clays and limestone as a possible way to reduce the amount of clinker used in cement manufacturing. In order to produce limestone calcined clay cement, the study compared different concrete mixtures that included two different types of calcined clay (from the Egyptian deserts of Sinai and Zaafarana) in combination with limestone filler. The evaluation was based on compressive, indirect tensile and flexural strengths, and the degree of hydration. In this experiment, 9 cement-based concrete mixes, including a reference mix, were designed with fixed water content, sand, and basalt. Eight concrete mixes of limestone calcined clay cement (4 for each type of calcined clay) were produced, using 7.5%, 15%, 22.5%, and 30% of calcined clay, 10% of limestone filler, and 5% gypsum, with the remaining being clinker. The water consistency, setting times, Le Chatelier test, and compressive strengths of the concrete mixtures were evaluated. Furthermore, rapid chloride permeability test, XRD analysis and SEM study were conducted to investigate the kinetics of pore refinement and microstructure. The results showed that the binders exhibited a slight improvement in mechanical strengths compared to Ordinary Portland Cement, by 4.6%. Furthermore, the study revealed a significant pozzolanic activity and synergy between the calcined clay and limestone filler in the binder. Both limestone calcined clay cement concretes outperformed ordinary Portland cement, particularly in terms of workability and durability. The SEM images, processed using the MATLAB image processing toolbox, confirmed that the binder cement concretes have better pore refinement and microstructure compared to the Portland concrete, especially the Zaafarana mixture of 30% calcined clay at a curing age of 90 days. In conclusion, the development of limestone calcined clay cement concrete presents a promising approach for reducing the clinker content in cement production, thereby contributing to the global efforts towards more sustainable and environmentally-friendly construction materials.