Experimental investigation on the micro damage evolution of chemical corroded limestone subjected to cyclic loads

Micro damage evolution in chemical corroded limestone samples subjected to cyclic loads is investigated using Nuclear Magnetic Resonance (NMR) system. Based on the experimental data of Magnetic Resonance Imaging (MRI), T2 values and porosity, the micro damage evolution process is visualized and analyzed. It is found that the porosity and micro cracking of the corroded limestone samples increase with the cyclic loading, and the micro damage evolution process consists of three distinct stages: micro crack emergence stage, micro damage development stage and damage development accelerated stage. Chemical erosion is found to have a significant influence on the propagation of micro cracks and accelerate the damage development of the limestone samples under cyclic loading. With the same number of load cycles, the chemical corroded samples always have lower peak strength than that of the water softened samples. Before the inflection point in the micro damage-loading cycles curve, the main damage is caused by new micro cracks increase inside the limestone; while after this point, the new micro crack emergence is being restrained, and the existed micro cracks connect into rupture bands. A damage model is finally proposed to quantify the damage evolution of the chemical corroded rocks subjected to cyclic loads.