Ancient Yemeni Qadhad Mortar Decoded: Science Reveals Sustainable Building Secrets

Ancient Yemeni Qadhad, a traditional lime-based mortar integral to water-retaining and masonry structures, has long been recognized for its durability in historical architecture. However, quantitative data regarding its precise mechanical performance and the original proportions of its binder to aggregate components remained largely undocumented until a recent study. Researchers undertook a comprehensive multi-analytical characterization of four distinct archeological mortar groups sourced from significant Yemeni sites, including Aden Cisterns, Harawa Pool, Seera Fort, and Salama Pool, to establish a scientific basis for its use in modern heritage conservation efforts.

The study employed rigorous materials science methodologies to assess the physical properties of these ancient samples. Compressive strength measurements were conducted on 22 non-standard specimens, utilizing an adapted procedure based on the ASTM C109/C109M standard. Furthermore, detailed compositional analysis was performed on representative samples from each site. This involved thermogravimetric analysis, acid digestion, and sieve analysis to accurately estimate the insoluble and soluble fractions, thereby determining the aggregate grading and the overall chemical makeup of the historical material.

The findings revealed that the mean compressive strength of the analyzed Qadhad mortar ranged between 2.77 and 4.39 MPa. These values provide critical data points regarding the structural integrity of the traditional material. Beyond strength, the study calculated the mass-based binder-to-aggregate ratios for the four sampled groups. These ratios varied, ranging from 1:1.93 to 1:2.60 by mass, offering insight into the specific recipes employed by ancient builders across different regional sites.

These quantitative results are highly significant for the field of sustainable heritage conservation. By establishing a precise scientific framework for the composition and performance of Qadhad, the research provides a clear pathway for reproducing these traditional materials. This allows conservationists to formulate compatible repair materials that respect the original engineering and chemical characteristics of the historical structures.

The study ultimately highlights Qadhad’s potential as a highly durable and sustainable lime-pozzolan construction material. Its successful application in historical contexts, combined with the new quantitative data, positions it as a valuable resource not only for the preservation of Yemeni heritage but also for contemporary ecological building practices seeking low-impact, high-performance alternatives to modern cement-based materials.

Subject of Research: Characterization of traditional Yemeni lime-pozzolan mortar for conservation.

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

Article References: Algorafi, M. A., Alwathaf, A. H., Al-Gawi, S., & Al-Nono, A. M. (2026). Mechanical and compositional characterization of ancient Yemeni Qadhad mortar for sustainable heritage conservation. npj Heritage Science. https://doi.org/10.1038/s40494-026-03063-9

Image Credits: AI Generated

DOI: 10.1038/s40494-026-03063-9

Keywords: Heritage conservation, Qadhad, Lime mortar, Sustainable building, Material science, Yemeni architecture, Compressive strength, Pozzolan, Archaeology, Mechanical, compositional, characterization