Experimental study of strain-temperature behavior of earthen materials under freezing-thawing cycles

Earthen constructions can experience severe damage under coupled action of moistening and freezing-thawing (F-T). This paper proposes an experimental study on the F-T behavior of earthen samples at different liquid saturation degrees (SL0). Normal moisture conditions during winter were investigated using two values of relative humidity (RH): RH = 75% and RH = 95% which led to saturation levels lower than 35% for the tested earth. Pathological conditions of earthen walls were studied with samples at high liquid saturation (SL0 = 75%, SL0 = 85% and SL0 = 95%). Axial strain and temperature of samples were measured during 12 F-T cycles conducted between +10 ∘C and − 20 ∘C. An experimental device was designed to maintain axial stress of 0 or 100 kPa on samples during the freezing-thawing test to reproduce loading conditions at the top and the basement of an earthen wall. The measurement of strains and temperature shows that earthen samples did not exhibit any freezing-thawing effect under the investigated normal moisture conditions. The results indicated that F-T deformations depend mainly on the initial liquid saturation. A microstructural approach can identify necessary moisture conditions for freezing-thawing in porous materials. Shrinkage during freezing and expansion during thawing were observed in the range of saturation investigated in this study. This mechanism was attributed to the drying shrinkage of clay particles due to the cryo-suction process during ice formation. The axial loading significantly increased residual strains developed at the first F-T cycles. Two creep tests at +20 ∘C and − 20 ∘C concluded that axial loading and freezing-thawing induced a combined effect on deformations in unsaturated earthen materials.