Abstract
<title>Abstract</title> <p> Qadhad is a traditional Yemeni slaked-lime mortar renowned for its exceptional waterproofing properties, particularly in cisterns, reservoirs, and masonry structures that have remained functional for centuries. Despite its historical significance, the mechanical properties and precise mix proportions of the ancient Qadhad remain insufficiently quantified. This study investigates the mechanical properties and compositional characteristics of ancient Qadhad mortar samples collected from four archaeological sites in Yemen. Compressive strength testing, thermogravimetric analysis (TGA), and chemical analyses were conducted to determine the material’s performance and composition. Experimental results show that the compressive strength of the ancient mortars ranges from 2.77 to 4.39 <bold>MPa</bold> . Furthermore, the binder-to-aggregate ratio of the ancient mortars was determined to range between <bold>1:2 and 1:2.5 by weight</bold> . These findings establish a quantitative scientific basis for reproducing traditional Qadhad mortar for the development of compatible repair materials in heritage conservation. The study also highlights the potential of Qadhad as a durable and sustainable lime–pozzolan construction material suitable for both conservation and contemporary ecological building applications. </p>