Experimental investigation on the effect of alkaline environment on the mechanical properties of aggregate rock

Abstract

Aggregate generation from waste rock materials is an effective measure to solve the problem of waste disposal and reduce the high cost of concrete engineering materials. The aim of this study was to explore effects of hydrochemistry on the physical, mechanical, and fatigue properties of aggregate red sandstone and to evaluate the fatigue damage mechanisms. Red sandstone samples were immersed in NaOH solution. The NaOH crystals precipitated to produce hydrophobic white material to fill the internal pores, thus increasing the internal density of red sandstone. The chemical reaction caused reduction in the contents of minerals. The two processes occurred simultaneously and exhibited a competitive relationship. The mass change rate, P-wave velocity, compressive elasticity modulus, and compressive strength of the specimen increased with the increase in NaOH concentration. The tensile strength and Mode I fracture toughness initially increased and then decreased with the increase in NaOH concentration. The sample lost its strength after immersion in 20 mol/L NaOH. Dynamic mechanical analysis showed that the temperature increase led to moisture dissipation below the temperature threshold, which increased the energy storage modulus. The microstructure of red sandstone became loosely arranged under the dissolution effect of NaOH. Needle-like crystals were attached to the surface of sandstone particles, and the surface of particles become rough. The bending fatigue deflection-time curve exhibited a three-stage variation pattern. The fatigue life initially increased and then decreased with increase in NaOH concentration. An inverted S-shaped damage evolution model was developed with the residual deflection as the damage factor associated with the initial damage of chemical immersion, and the model was consistent with the experimental results.