Large-scale laboratory trials of smart aggregates for self-healing in concrete under different curing regimes

Abstract

To develop concrete with self-healing properties, a promising approach, through the incorporation of smart aggregates within the concrete mix, was tested in large-scale laboratory trials. In this work, lightweight aggregates impregnated with sodium silicate and sodium nitrate, as potential self-healing agents, and encapsulated in polyvinyl alcohol coating were prepared and deployed as 30% replacement of the coarse aggregates by volume in 150 mm × 200 mm × 1000 mm beams. The beams were then cured in three different environments: outdoor exposure, distilled water and seawater. To evaluate the self-healing efficiency, multiple cracks, 100–700 μm in width, were created using four-point bending tests and confirmed through microscopy observations and ultrasonic wave measurements. The concrete beams containing the developed smart aggregates showed a considerable regain of stiffness and flexural strength after healing compared to the control specimens under all three curing conditions. The measured reduction in water ingress of the healed sections demonstrated significant recovery of water tightness (50% more) compared to the control specimens. The contribution of the sodium silicate and sodium nitrate cargo released from the aggregates to the proliferation of the healing products was evident but needs further investigations on the size effect to realise the full potential of the healing mechanism.