Concrete fracture toughness increase by embedding self-healing capsules using an integrated experimental approach

An alternative solution to repair cracks in concrete has been recently established, namely autonomous healing by embedding repair agent into concrete during casting. The agent is included into small-size capsules that break as cracks form. As the agent is released into the crack void, it solidifies fast permitting crack sealing and mechanical restoration. Most of literature studies focus on the healing system design and the repair efficiency assessment. However, limited knowledge exists on the effect of the macro-capsules themselves on concrete mechanical behaviour. This is a crucial subject as the healing mechanism should not compromise the material mechanical properties. The paper investigates the effect of capsules on damage resistance by considering fracture constitutive models. Fracture toughness of samples with capsules increases up to 35% compared to the reference. Acoustic emission is applied to assess the capsules effect on fracture processes. Events localization indicates fracture process zone expansion by 40%. It is proven that the capsules beneficially contribute as local reinforcement perturbating the crack path and forming multiple microcracks (additionally verified by Digital Image Correlation). In summary, an integrated experimental protocol is developed to highlight the concrete toughness enhancement by adding capsules.