Effect of ion chelating agent on self-healing performance of Cement-based materials

Ion chelating agent, a novel crystalline additive, is used to improve the self-healing performance of cement-based materials on freeze-thaw damage and surface crack for prolonging service life of the construction. The pore size distribution, internal structure and compressive strength of mortar with ion chelating agent before and after freeze-thaw as well as self-healing were investigated by nuclear magnetic resonance, scanning electron microscope and mechanical property test. The width of surface crack of the mortar during self-healing was measured. The results show that the microstructure and mechanical properties of mortars are improved by ion chelating agent. After 28 days of curing, harmful pores (larger than 0.1 μm) proportion of mortar with 0.5 wt% ion chelating agent of the cement (C2) declines by 42.3%, compressive strength increases by 26.8%, and much needle-like crystals exists in pores comparing with the control mortar (C0). After 100 freeze-thaw cycles, the compressive strength loss, mass loss and harmful pores proportion of C2 reduce by 38.0%, 29.2% and 28.7% relative to C0. After curing in water for 28 days, the compressive strength recovery ratio of C2 is 51.8%, and lots of needle-like crystals are formed in pores and micro-cracks. Energy dispersive spectrometer analysis indicates that the main components of these needle-like crystals are calcium carbonate, CSH and ettringite. Besides, the surface crack of 0.32 mm width for C2 is self-healed and X-ray diffraction analysis shows that the self-healed product in the crack is calcium carbonate.