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The fracture toughness (KIC) of Mode I cracked sandstone exposed to sodium sulfate was investigated in this study. The uniaxial behavior of sandstone specimens soaked in different sodium sulfate solutions was determined for different strain rates. The results revealed that the strain rate has a significant and positive influence on the deformation and strength characteristics of sandstone. Compression strength gradually increased with strain rate at an increased slope, but peak strain decreased gradually with an increase in strain rate. The physical–mechanical characteristics and brittleness of sandstone gradually declined with increasing immersion time under sodium sulfate attack, but its plasticity increased significantly. There were holes and pitting corrosions in specimen surfaces exposed to sodium sulfate attack, and the edges and corners were somewhat weakened. Chemical damage variables were proposed to analyze the damage degree of sandstone, based on the change in porosity. Based on the testing results, regression analysis was conducted to determine the relations between ion concentrations (Ca2+ and Mg2+) in corresponding sodium sulfate solutions and for corresponding degrees of damage, and indirectly realize correlations between physical–mechanical characteristics, damage degree, and ion concentration. [ABSTRACT FROM AUTHOR]

With the actual environments of the joint rock in the bank slope of the Three Gorge Reservoir region (in China) as the background and considering the research concept that the effect of sodium sulfates and the dry–wet (D–W) cycle on rocks as interactive and inseparable, a test plan for D–W cycles was designed to study the D–W cycle damage of the mechanical characteristics and their correlations with the strength properties of sandstone with a Mode-I crack exposed to a sodium sulfate attack. Based on the crack's propagation radius and a damage variable reflecting a change in porosity, the degree of D–W cycle mechanical degradation was quantitatively analyzed. The mechanical characteristic of sandstone exhibited obvious damage under sodium sulfate attack and D–W cycles, among which the degree of D–W cycle degradation of the KIC was the greatest, whereas the internal friction angle was relatively the lowest. Meanwhile, apparent consistency was observed between the KIC and compression, and between the KIC and tensile strength of specimen exposed to the sodium sulfates attack under D–W cycles. Moreover, an evident corresponding relationship existed among the deterioration damage of the mechanical properties, corresponding ion concentrations dissolved in sodium sulfate solution, and deterioration degree of the physical characteristics of sandstone. Meanwhile, the correlation relationships among physical and mechanical properties, D–W cycle damage degree, and ion concentration were obtained. [ABSTRACT FROM AUTHOR]

Cracks will be introduced into mortar specimens and embedded copper sheets to simulate fractured concrete according to the designed 20 mm crack lengths and angles. By taking into consideration the actual environment of a hydro-fluctuation belt for a typical bank slope in the Three Gorges Reservoir Region of the Yangtze River, China, a dry–wet cycle testing program will be designed to study the mechanical properties of the fracture mortar specimens immersed in different sulfate solutions. The failure characteristics and modes of the fracture mortar specimens will be measured and analyzed. The tests results show that the strength initially decreased and then increased with an increasing crack angle from 0° to 90°, and this was the smallest for the specimens with a 45° angle. Deterioration occurred in the specimens subjected to dry–wet cycles in different sulfate solutions. The damage extent is expressed as the change in elasticity. A formula for damage evolution of the fracture specimens will be proposed and the relationship between the deformation properties and damage properties of the specimens will be developed for the combined action of dry–wet cycles and sulfate attack. Based on the proposed damage model, the damage evolution equation and elastic damage constitutive model will be derived under the combined action of dry–wet cycles and sulfate attack, and this damage constitutive relation could be used to the study damage evolution for the fracture mortar specimens under the combined effects of dry–wet cycles and sulfate attack. [ABSTRACT FROM AUTHOR]