Impregnation and encapsulation of lightweight aggregates for self-healing concrete

• Sodium silicate solution was impregnated in lightweight aggregates (LWA). • Impregnated LWA were coated then embedded in concrete specimens. • Strength regain was remarkable for specimens with the impregnated LWA. • Capillary water absorption was significantly improved in the specimens with the impregnated LWA. • Sodium silicate produced rich silica C–S–H to heal the concrete cracks. This study investigated a technique of impregnating potential self-healing agents into lightweight aggregates (LWA) and the self-healing performance of concrete mixed with the impregnated LWA. Lightweight aggregates with a diameter range of 4–8 mm were impregnated with a sodium silicate solution as a potential self-healing agent. Concrete specimens containing the impregnated LWA and control specimens were pre-cracked up to 300 μm crack width at 7 days. Flexural strength recovery and reduction in water sorptivity were examined. After 28 days healing in water, the specimens containing the impregnated LWA showed ∼80% recovery of the pre-cracking strength, which accounts more than five times of the control specimens’ recovery. The capillary water absorption was also significantly improved; the specimens healed with the impregnated LWA showed a 50% reduction in the sorptivity index compared with the control cracked specimens and a very similar response to the control uncracked specimens. The contribution of sodium silicate in producing more calcium silicate hydrate gel was confirmed by characterisation the healing products using X-ray diffraction, Fourier transform spectroscopy, and scanning electron microscopy.