The Role of Built Heritage in the Decarbonization Roadway: Air Lime Mortars

Society is urging the public and private sectors to adopt sustainable measures to mitigate global warming. In response, the construction industry is exploring alternative binders to reduce its carbon footprint. Yet, durability concerns and regulatory gaps remain unresolved for this new generation of binders. In contrast, another potential path to decarbonization may lie in the built heritage. Standing the weathering of time, Egyptians, Phoenicians, and Romans relied on lime-based binders to create future-proof buildings before Portland cement was invented. However, as most lime applications were empirical and undocumented, the current bottleneck lies in the limited availability of scientific data—needed to establish lime as a sustainable and structurally viable material. Thus, this study investigated four mortar mixtures commonly used in masonry structures, monitoring key properties such as mechanical strength, permeability, and carbon capture capacity for six months. Results indicate that mixtures with higher air lime content exhibited lower strength, primarily governed by carbonation. Permeability tests confirmed air lime’s breathability, which favored carbon capture, as demonstrated through phenolphthalein and thermogravimetric analysis. Within the monitoring period, lime-cement groups absorbed more carbon dioxide earlier than others, likely due to interactions between hydration, carbonation, and water evaporation, which led to faster carbonation rates. Finally, an extended monitoring is recommended for future studies.