This paper studies the potential of using expanded clay lightweight aggregate impregnated with sodium monofluorophosphate (Na2FPO3) solution which is eventually encapsulated by a cement paste layer to produce a self-healing system in blast furnace slag cement mortars. It was found that the technique significantly improved the quality of the interfacial transition zone in mortars subjected to carbonation shrinkage. Consequently the frost salt scaling durability of blast furnace slag mortars was evidently promoted. The findings from ESEM and EDS studies showed that the healing mechanism would be due to the combination of treatment by Na2FPO3 solution and calcium hydroxide supplied from the cement paste coating layer.