Biopolymers impact on hygrothermal properties of rammed earth: from material to building scale

Three biopolymers were tested as rammed earth (RE) stabilizers, evaluating their impact on the hygrothermal behavior from material to building scale. Hygrothermal characterization included the determination of sorption isotherm, water vapor permeability, thermal conductivity at different moisture content, and specific heat ca-pacity. The hygrothermal data were used as input for the simulation at whole-building scale considering com-bined heat and moisture transfer. The results were evaluated by comparing heating demand, thermal comfort during summer, and the contribution of walls for passively controlling indoor humidity. The results show that hygric properties were only slightly affected by the use of stabilizers, while the thermal conductivity was 33% higher for RE stabilized with lignin, consequently increasing the heating demand at whole-building scale. All RE walls were effective in reducing temperature oscillations in summer. In the particular case of a canicular event, the indoor temperature was reduced by up to 10 degrees compared with the outdoor value. The indoor humidity also benefited from the passive regulation by RE walls, regardless of whether a stablizer was used.

Automated summary

This study evaluated the impact of three biopolymers as stabilizers on the hygrothermal behavior of rammed earth (RE) at material and building scale. The hygrothermal properties of the RE were characterized, including sorption isotherm, water vapor permeability, thermal conductivity, and specific heat capacity. Simulation at whole-building scale was conducted using the hygrothermal data to assess heating demand, thermal comfort, and passive control of indoor humidity. The results showed minimal influence on hygric properties due to stabilizers, but the thermal conductivity of RE stabilized with lignin was 33% higher, resulting in increased heating demand. RE walls effectively reduced temperature oscillations in summer and could lower indoor temperature by up to 10 degrees during hot weather. Indoor humidity also benefitted from the passive regulation of RE walls, regardless of stabilizer use.