Reduction of rammed earth's hygroscopic performance under stabilisation: an experimental investigation

One of the acknowledged qualities of rammed earth (RE) is its moisture buffering capacity. Recently, stabilisation of RE has become a common practice to improve the mechanical resistance but very little is known about the effect that stabilisation has on hygroscopic properties. The present study aims to fill this gap by understanding the role that stabilisation plays in the buffering and sorption capacity of RE. The use of alternative stabilisers such as fly ash and calcium carbide residue and a comparison with traditional unstabilised RE (URE) have also been investigated. Moreover, the effect of weathering, simulated by cyclic wetting-drying, on hygroscopic performance has been analysed. Moisture Buffer Value (MBV) testing, moisture and nitrogen adsorption-desorption isotherms and mercury intrusion porosimetry were performed on stabilised samples to examine microstructural phenomena responsible for behavioural changes. URE was confirmed to be a good-to-excellent passive air conditioner according to the MBV scale but its performance seemed to be highly influenced by the soil particle size distribution and mineralogy. Based on the experimental outcomes of the mixtures investigated, stabilisation had a detrimental effect on the moisture buffer capacity of rammed earth, likely due to the inhibition of the physico-chemical interactivity between moisture and clays. Weathering had a variable effect on the buffering capacity, depending on the availability of unreacted particles in the matrix.