Mechanical and compositional characterization of ancient Yemeni Qadhad mortar for sustainable heritage conservation

Ancient Yemeni Qadhad is a lime-based traditional mortar used in water-retaining and masonry structures, yet quantitative data on its mechanical performance and original binder-to-aggregate proportions remain limited. This study extends multi-analytical characterization by quantifying compressive strength and mass-based binder-to-aggregate ratio of four archeological mortar groups from Aden Cisterns, Harawa Pool, Seera Fort, and Salama Pool. Compressive strength was measured on 22 non-standard specimens using an adapted ASTM C109/C109M procedure. Thermogravimetric analysis was performed on one representative sample per site; acid digestion and sieve analysis estimated insoluble and soluble fractions and aggregate grading. Mean compressive strength ranged from 2.77 to 4.39 MPa. Calculated binder-to-aggregate ratios ranged from 1:1.93 to 1:2.60 by mass. These findings, from four samples, establish a quantitative scientific basis for reproducing traditional Qadhad mortar for compatible repair materials in heritage conservation. It highlights Qadhad’s potential as durable, sustainable lime-pozzolan construction material for conservation and contemporary ecological building applications.