Self-healing concrete can repair itself by closing micro-cracks and thus protect itself from ingress of deleterious gasses and liquids that can affect its durability. Many self-healing concepts have been developed in the recent years which target on the recovery of water tightness after cracking. Among those systems, the bio-based healing agents have shown promising results regarding the crack sealing performance. This paper studies the crack sealing efficiency of bio-based healing mortar with expanded clay particles. The investigation of sealing performance is conducted through experimental and computational approaches. Image processing and crack permeability test results are compared with results obtained by computer simulations. The study reveals that the experimental approaches might overestimate the crack closure percentage, while the computer simulation mostly underestimates the crack sealing. Finally, recommendations are given to improve the results obtained by both methodologies.

Superabsorbent polymers (SAPs) have potential to be used as healing agent in self-healing concrete due to their property to attract moisture from the environment and their capacity to promote autogenous healing. A possible drawback, however, is their uptake of mixing water during concrete manufacturing, resulting in an increased volume of macro-pores in the hardened concrete. To limit this drawback, newly developed SAPs with a high swelling and pH-sensitiveness were developed and tested within the FP7 project HEALCON. Evaluation of their self-sealing performance occurred through a water permeability test via water flow, a test method also developed within HEALCON. Three different sizes of the newly developed SAP were compared with a commercial SAP. Swelling tests in cement filtrate solution indicated that the commercial and in-house synthesized SAPs performed quite similar, but the difference between the swelling capacity at pH 9 and pH 13 is more pronounced for the self-synthesized SAPs. Moreover, in comparison to the commercial SAPs, less macro-pores are formed in the cement matrix of mixes with self-synthesized SAPs and the effect on the mechanical properties is lower, but not negligible, when using high amounts of SAPs. Although the immediate sealing effect of cracks in mortar was the highest for the commercial SAPs, the in-house made SAPs with a particle size between 400 and 600 μm performed the best with regard to crack closure (mainly CaCO₃ precipitation) and self-sealing efficiency, after exposing the specimens to 28 wet-dry cycles. Some specimens could even withstand a water pressure of 2 bar.

Within the European FP7 project HEALCON, Non-Destructive Testing (NDT) and monitoring techniques are developed and combined to characterize the effects of self-healing mechanisms in small and full-size specimens. In the first stage, healing mechanisms were evaluated at lab-scale. Specimens containing encapsulated polymer precursors were cracked and reloaded after the healing period. During loading, healing and reloading, NDT techniques (acoustic emission analysis, vibration analysis and ultrasonic measurement) were applied to help understanding the cracking behavior, capsule breakage and healing efficiency. Moreover, the effect of the flexibility of the polymeric healing agent on the crack re-opening during reloading was investigated on cracked and healed mortar specimens, using acoustic emission and digital image correlation techniques. The results show the applicability of NDT methods to evaluate the self-healing efficiency for small specimens. Comparing the NDT techniques, some of them (e.g. ultrasound) seem to be good candidates for in situ monitoring of the healing efficiency.

Self-healing concrete has drawn a lot of attention in recent years. There are numerous projects worldwide that work on the development of self-healing agents. Among those, bacteria-based self-healing concrete is a very promising solution to prevent durability problems in concrete that are related with cracking. Bacteria-based self-healing concrete not only provides sealing of open micro-cracks that endanger the structure’s health, but it also has economical and environmental benefits, since it will extend the lifetime of the structure and reduce repair costs. In this study, the bacteria-based self-healing agent consists of alkaliphilic bacterial spores, organic mineral precursor compounds and LightWeight Aggregates (LWA). Although the success of the concept has been proven in previous research, in this study an optimized method for the incorporation of the organic compounds into the LWA has been developed. The method allows more of the organic compounds to be stored into the LWA. This paper focuses on comparing performance on mechanical properties and sealing efficiency of cracks of mortar samples from past and current research. The initial hypothesis of the study was that the lightweight mortar with the higher amount of healing agent will show faster and more efficient crack sealing capacity. The comparison revealed different results than expected. In fact, the sealing efficiency trend proved to be similar for the two studies which was speculated to be due to oxygen limitation rather than healing agent limitation in permanently water submersed specimens.