A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering in Structural Engineering, School of Engineering and Technology

Self - healing performance of mortars with different additives was experimentally investigated by using crack width as an indicator of damage degree. The crack was created by splitting method. Crack width measurement was performed through a digital microscope with the computer software. The additives studied were fly ash, expansive additive, silica fume, crystalline admixture and limestone powder. The curing conditions were water submersion, periodic wetting and submersion in lime saturated water. Th e ages of mortars at cracking were 3 and 28 days. The crack width was varied to observe the effect of damage degree on the self - healing. Experimental results indicated that all types of mortars showed their self - healing performance to close the cracks to some extent. It was found that each additive in each mortar has its own preferable condition (curing condition, mortar age at cracking and crack width) to heal the cracks with its best capability. Crystalline admixture with 1%added was the best additive f or self - healing of small cracks in a mortar. Especially when cracked at the age of 3 days with 0 {u2013} 0.1 mm crack width, its self - healing rate was higher than the other types of mortar. Silica fume with 10%added was found to be most effective to heal the cra ck generated at the age of 28 days. It showed the best self - healing performance in both small and large cracks (0 {u2013} 0.3 mm). From investigation of curing condition, the results showed that only mortar with crystalline admixture could do heal completely in wet - dry cycles with the crack width range of 0 {u2013} 0.1 mm. However, it was observed that when subjected to wet - dry cycles self - healing performance of all mortars became worse than those cured in water. It was so concluded that the continuity of water contact of the crack surfaces is essential in the self - healing. Moreover, it was found that the age of specimen at cracking and crack width as damage degree also influenced the self - healing. The younger the mortar, the faster (and more possible) the cracks are co mpletely healed. For damage degree, it was observed that the smaller cracks were healed faster than the larger ones. From FT - IR results, the healing products of all mortars were mainly composed of calcium carbonate. Therefore, precipitation of calcium carb onate was likely to be the main mechanism of self - healing of the cracks in the mortars in this investigation.

Thesis (M.Eng.) - Asian Institute of Technology, 2010