Analysis of adobes from vernacular raw earth buildings in the Champagne region (France)

This study contributes to the understanding of the vernacular raw-earth heritage of the Champagne region in France, where such structures are currently being documented. The research investigates the mineral composition, grain size distribution, and physico-chemical, mechanical, thermal, and hydric properties of seven adobe types derived from soils with varying compositions (predominantly silicate or limestone-based soils). In particular, the influence of calcite content, which spans a wide range from 0 % to 84.9 %, was examined. The results indicate a strong dependency of peak compressive strength on calcite content: higher CaCO₃ levels correspond to lower peak compressive strength. Additionally, the study reveals that the metal oxide content of soils is a critical factor directly associated with mechanical performance. Interestingly, it was observed that historical builders often used weaker adobes for load-bearing purposes and stronger ones for filling, likely without adherence to formal construction standards. Rather than compressive strength, wall design appears to have played a more critical role in structural stability. Regarding thermal properties, calcite content showed minimal influence on diffusivity, specific heat capacity, and thermal conductivity across all adobe samples. Furthermore, all adobes demonstrated excellent to very good moisture regulation performance, with corresponding Moisture Buffer Values varying from 1.65 to 3.09 g/(m².%RH). The findings of this study underscore the potential of traditional raw-earth techniques in rediscovering and evaluating earthen architecture, with implications for promoting sustainable and environmentally friendly contemporary earthen construction and renovation practices. • Traditional raw-earth techniques may be employed in sustainable contemporary construction and renovation. • Seven different adobe types, with varying calcite content, are examined. • Mechanical properties are strongly affected by the calcite content, contrary to thermal characteristics. • Regardless of their origin, all adobe samples demonstrate excellent to very good moisture regulation capabilities.