A study of the natural self-healing of mortars using air-flow measurements

The aim of this research is to investigate the natural self-healing of mortars using air-flow measurements through a single crack of controlled geometry. Mortars were made with water-cement (W/C) ratios of 0.35, 0.45 and 0.60. For each type of mortar, three crack categories were created: 50 +/- A 15, 105 +/- A 15 and 220 +/- A 35 mu m. Mortars were cracked at the age of 28 days and 6 months. Cracked mortars were stored in air at 23 A degrees C and 100 % R.H. for up to 5 months to simulate the environmental conditions for open-air above-ground concrete structures. During the first month, the kinetics of self-healing is noticeably faster. The self-healing mechanism mainly involves carbonation and the formation of secondary hydration products in the crack volume. For fine cracks (50 mu m), the self-healing rate is slow (5-10 mu m/month). For larger cracks (> 200 mu m), the self-healing rate is faster (15-30 mu m/month), as there is no space limitation for the formation of self-healing products and also because the effective crack opening remains high enough for the supply of external CO2 and water. For crack openings higher than 300 mu m, the final natural self-healing level is less than 20 % after 5 months. For the mortar tested, age at the time of cracking only plays a minor role on self-healing kinetics.