Experimental study on mechanical properties of sprayed ECC under quasi-static and cyclic loading

The tunnel lining will be subjected to the cyclic action of high ground stress during service. However, there is a lack of research on the damage evolution mechanism of sprayed engineered cementitious composites (ECC) under cyclic loading. Herein, we studied the strain rate effect and fatigue damage evolution mechanism of sprayed ECC by conducting compression and bending tests at different quasi-static strain rates and high-stress cyclic loading-unloading compression and bending tests. The results show that with the increase of strain rate, the compressive peak stress and bending strength of sprayed ECC show an upward trend, as well as the increase of the change rate. At 8.3 x 10-3 s-1, the compressive SGF is 1.52, with an energy storage limit density of 0.501MJ/m3. At 2.1 x 10-2 s- 1, the bending SGF is 1.52, with a peak fracture energy of 49.29 J. In addition, under the compression test, the tensile shear failure of specimens develops from finer double shear planes to coarser multiple shear planes. Under the bending test, the position of the main crack of specimen is gradually transferred from the mid-span to both sides. Under high stress cycle test, the input energy and dissipation energy of the two tests have the similar trend, showing "U" type. The variation of elastic energy and dissipation energy conversion rate exhibits a "U" type with different directions. At the last loading, the dissipation energy conversion rate of compression test is 46.8%, while that of bending test is 70.4%. The damage variable of specimen increases significantly with the increase of the number of cycles, accompanied by an increase in the degree of breakage. In addition, the damage variables based on deformation characteristics are higher than those based on energy characteristics.