The mechanical and microstructural characteristics of low-energy calcined clay from a high-Egyptian gray clay with hydrated lime for rendering mortar applications

Abstract

Abstract The production of Portland cement has a significant global impact. Consequently, research into clinker replacement materials and alternative low-CO 2 cements is becoming increasingly important to minimize their carbon footprint. For this study, limestone and raw clay were sourced from various locations in Egypt. These materials were calcined in a kiln at temperatures of 950 °C and 750 °C for 2 h, respectively. The primary goal of this study is to prepare and render mortars based on calcined clay with lime as a low-energy binder. The research primarily focuses on the mechanical and microstructural properties of lime-clay mortars and lime-clay render mortars, specifically hydrated lime (HL) and calcined clay (CCL). The mechanical and physical properties of these mortars were tested according to EN 196-1, using a mixing ratio of 1:3 (binder to sand) with total weight proportions of 450:1350. Water was added to achieve the necessary consistency and workability for this type of mortar, with an amount of approximately 302 ± 5 g. The results suggest that the most recommended proportion for optimal mortar performance with the used binder (CCL-HL) is L40, mainly consisting of 60% CCL and 40% HL with a water-to-solid ratio of approximately 0.17. The compressive and flexural strengths for the CCL-HL mortar sample (L40) are 13.2 MPa and 3.2 MPa, respectively. Additionally, the preparation of render mortars using this binder (L40) demonstrates that the most cost-effective and environmentally friendly binder proportion is R35Y, which consists of 35% L40 and 2% Fe 2 O 3 as a yellow pigment, with a water-to-solid ratio of approximately 0.30. The compressive and flexural strengths of the R35Y render mortar are 5.2 and 2.1 MPa, respectively. The findings demonstrate that all prepared CCL-HL render mortars are suitable for rendering applications, meeting the requirements of EN998-1/2010 and offering a cost-effective, environmentally conscious solution for decorative and protective coatings, particularly in the preservation of historic structures.