Effect of salts on earthen materials deterioration after humidity cycling

摘要

Salt weathering leads to destruction of many valuable cultural heritage monuments and porous building material. The present study aims at providing more laboratory evidence for evaluating the effects of salt precipitation on the deterioration process.In view of this, the remoulded soil specimens were mixed with three kinds of salts (i.e., NaCl, Na2SO4 and their mixture) with different salt concentrations, and the specimens were kept in environment cabinet for undergoing different wet-dry cycles. After each cycle, the ultrasound velocity measurements were employed to monitor the deterioration process. For the specimens that have suffered three wet-dry cycles, the mechanical properties (i.e. shear strength and compression strength) were determined to evaluate the degree of deterioration. Furthermore, considering the realistic conservation environment of earthen sites, mechanical stability of these specimens against sediment-carrying wind erosion was conducted in a wind tunnel. These experiments results indicate that the overall average velocities of the specimens after the third cycle are significantly lower than those subjected to only one cycle. Ultrasound velocity, mechanical strength and wind erosion rate decrease when salt content increases. However, the internal friction angle increases firstly, and then decreases with the increase in salt content added to the specimens. Na2SO4 contributes most of the surface deterioration, while NaCl plays little role in the deterioration. The damage potential of the salt mixture is less obvious and largely dependent on the crystallisation location.