Self-healing behavior of strain-hardening cementitious composites with MgO-type expansive agent after drop weight impact loading

Abstract

Strain-hardening cementitious composites (SHCC) are usually subjected to a variety of dynamic loads during service period. The self-healing behavior of SHCC after damage of static loading have already been studied in detail, however, the corresponding investigation regarding the influence of dynamic loading is limited. In this paper, drop weight impact tests were used to introduce cracks into SHCC samples incorporated with MgO-type expansive agent (MEA), followed by different exposure conditions, including water, seawater, saturated Ca(OH)2 solution and 3 % NaCl solution. The self-healing effect of SHCC was evaluated by crack width, capillary water absorption and the recovery of impact resistance. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and thermogravimetric analysis (TGA) were performed to distinguish reaction products of self-healing, revealing the self-healing mechanisms. The results show that cracks with small size of SHCC incorporated with MEA can be closed under these four exposure conditions, and the crack widths <10 μm and 60 μm are completely closed after 7 days and 60 days, respectively. The normalized water absorption also shows cracked SHCC after healing in seawater have a better self-healing compared to the other three conditions, and the impact resistance of the specimens with age of 7 d after 120 d of healing in seawater is improved by 20.1 %. In addition, the microscopic analysis of SEM, XRD and TGA shows that the main reaction products of self-healing in seawater and 3 % NaCl solution are portlandite, calcite and brucite.