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In this study, cracking formation and repair due to autonomous healing of concrete beams, tested in two stages of bending (loading-reloading) are reviewed. Encapsulated PU-based healing agent is embedded into concrete beams and is released when crack formation triggers and actuates the chemical repair process. The released agent fills the open crack and seals the fractured area. The potential mechanical recovery of the damage is investigated. Advanced optical and acoustic experimental methods evaluate the mechanical response of the composite material. Acoustic Emission monitors breakage of the capsules embedded into the specimens and locates and quantifies the damage occurred. In parallel, Digital Image Correlation visualizes the controlled crack opening/closure and reopening due to bending. Correlation of the experimental results obtained by both techniques gives a full view of the healing efficiency of the proposed system. Monitoring of potential differentiations at the formation of the fracture process due to capsule breakage phenomena is the main aim of this research. [ABSTRACT FROM AUTHOR]

Acoustic emission (AE) is a monitoring technique that has proven its suitability in and outside of the laboratory in characterizing the structural condition of materials. In composites for construction and repair, several breakthroughs have been recently noted involving mainly fracture mode evaluation based on the AE waveform characteristics. However, the acquired signals, apart from the cracking source strongly depend on the size and shape of the plate specimens. While the effect of wave propagation distance has been studied, the effect of the lateral dimension of the plate has not been given proper attention, being a broken link in translating the results from small coupons to real size plates. This paper examines wave propagation from artificial sources as well as actual AE signals in textile-reinforced cement (TRC) plates indicating the strong differences in the results that are attributed just to the shape and size of the specimens and showing that interpretation toward the actual sources is firmly connected to geometric factors.

Concrete is prone to crack formation in the tensile zone, which is why steel reinforcement is introduced in these zones. However, small cracks could still arise, which give liquids and gasses access to the reinforcement causing it to corrode. Self-healing concrete repairs and seals these small (300 µm) cracks, preventing the development of corrosion. In this study, a vascular system, carrying the healing agent, is developed. It consists of tubes connected to a 3D printed distribution piece. This distribution piece has four outlets that are connected to the tubes and has one inlet, which is accessible from outside. Several materials were considered for the tubes, i.e., polymethylmethacrylate, starch, inorganic phosphate cement and alumina. Three-point-bending and four-point-bending tests proved that self-healing and multiple self-healing is possible with this developed vascular system.

Autonomous crack healing in concrete is obtained when encapsulated healing agent is embedded into the material. Cracking damage in concrete elements ruptures the capsules and activates the healing process by healing agent release. Previously, the strength and stiffness recovery as well as the sealing efficiency after autonomous crack repair was well established. However, the mechanisms that trigger capsule breakage remain unknown. In parallel, the conditions under which the crack interacts with embedded capsules stay black-box. In this research, an experimental approach implementing an advanced optical and acoustic method sets up scopes to monitor and justify the crack formation and capsule breakage of concrete samples tested under three-point bending. Digital Image Correlation was used to visualize the crack opening. The optical information was the basis for an extensive and analytical study of the damage by Acoustic Emission analysis. The influence of embedding capsules on the concrete fracture process, the location of capsule damage, and the differentiation between emissions due to capsule rupture and crack formation are presented in this research. A profound observation of the capsules performance provides a clear view of the healing activation process.