Degradation of rammed earth under soluble salts attack and drying-wetting cycles: The case of Fujian Tulou, China

Rammed earth is a common construction material for thousand years throughout the history of human civilization. The strength degradation of rammed earth under salts attack and drying-wetting cycles needs to be assessed. In this study, chemical analyses were conducted on rammed earth materials sampled at different wall heights from a demolished Fujian Tulou for the measurements of salinity. The degree of salinity was found to increase from the top to the bottom of the wall. To better understand the salt effect, sodium chloride (NaCl), sodium sulfate (Na2SO4), and calcium chloride (CaCl2) were mixed in various contents with desalinated soils to produce remoulded specimens for strength tests. The unconfined compressive strength (q(u)) and the cohesion (c) were reduced with the increase of the salinity degree. The influence of single salt attack was not apparent on the variation of q(u) or friction angle phi, but it was significant on the cohesion variation. The soil attacked by Na2SO4: CaCl2 = 1:1 mixed salt had the lowest q(u) and phi values. The Ca(2+ )cations from CaCl2 salt reacted with the SO42 anions from Na2SO4 to form crystals with increasing volume, leading to strength deterioration in rammed earth materials.