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Experimental studies have been undertaken to understand the link between hydric state and mechanical behaviour of rammed earth. Prismatic rammed earth sample of 15 cm × 15 cm × 45 cm, structured as a wall element with several layers, were subjected to one dimensional drying in laboratory. The kinetic of drying was monitored by continuous weighing the sample and humidity measurement at a regular interval. Suction was then used to represent the hydric state. Simultaneously, unconfined compressive strength was performed after 0, 2, 3, 4, 6, 8 and 19 weeks of drying. Digital image correlation was used to determine the stiffness of samples. Results show an increase up to 60% of the maximum in compressive strength in the first 3 weeks of drying which is correlated with a sharp decrease in water content in the sample. The suction was correlated with the evolution of mechanical performances of the samples during the drying. [ABSTRACT FROM AUTHOR]

• Extended hygrothermal characterization of unstabilized rammed earth. • Low influence of density and grain size distribution on sorption isotherm. • High influence of density on thermal conductivity and vapor resistance factor. • Same linear dependency of thermal conductivity on moisture content for different soil compositions. • Vapor transfer resistance factor for a large span of relative humidity. Although hygrothermal properties of rammed earth represent great potential for improving thermal comfort during hot summers, still little knowledge is available about this topic. The literature lacks complete sets of hygrothermal characteristics of rammed earth, although they are fundamental for heat and moisture transfer modeling necessary to predict earthen building performances. The present work reports the results of a large collaboration between four academic laboratories in order to obtain an extended hygrothermal characterization of rammed earth, focusing on the material used in a modern construction in Lyon, France. The aim of the article is to provide for the same kind of soil an extend characterization on a large span of relative humidity to provide complete set of material properties for heat and moisture transfer simulation. The hygrothermal measurements cover adsorption and desorption isotherm, intermediate isotherm loop, specific heat capacity, dry thermal conductivity, moisture-dependent thermal conductivity and water vapor resistance factor for a large span of relative humidity. In addition, the capillary rise test was performed to estimate the liquid transport coefficient for suction and redistribution. The results show that variations in the density of the samples have a low impact on sorption isotherm, while they have a non-negligible impact on thermal conductivity and water vapor permeability. Surprisingly, variations in the grain size distribution do not produce a significant modification in the sorption isotherm, while hysteresis slightly reduces when bigger grains are added to the soil composition. Approximation of empirical model coefficients for the determination of moisture-dependent thermal conductivity is proposed for rammed earth materials. [ABSTRACT FROM AUTHOR]