Performance of Air-Lime Mortars Incorporating Locally Sourced DD3 Metakaolin for Sustainable Restoration of Neo-Moorish Heritage

Abstract

This study investigates the use of DD3 metakaolin (MK), derived from the Djebel Debbagh 3 deposit in Algeria, as a pozzolanic additive to improve the performance of air-lime mortars for the conservation of neo-Moorish heritage structures. The work addresses the inherent limitations of aerial lime, low mechanical strength and slow setting, while ensuring compatibility with historic materials. The formulation strategy is supported by the microstructural characterization of a mortar sample collected from the Meriem Azza Palace, a neo-Moorish building in Skikda. Air-lime mortars with MK substitution levels of 10–30% were investigated in terms of workability, setting time, mechanical strength, porosity, capillary absorption, carbonation, and microstructure (XRD and SEM). Results show that MK significantly enhances mortar performance. At constant consistency, water demand decreases (up to 2%), while setting times are drastically reduced (up to 99.1%). Mechanical properties improve markedly, with flexural and compressive strengths increasing by up to 336.3% and 323.5%, respectively, and the dynamic elastic modulus rising by 156%. Microstructural analyses reveal portlandite consumption and the formation of C-(A)-S-H type hydrates, leading to matrix densification. Based on the investigated properties, MK contents between 20% and 25% provided the best balance of performance.