Materials for Life (M4L) was a 3 year, EPSRC funded, research project carried out by the Universities of Cardiff, Bath and Cambridge to investigate the development of self-healing cementitious construction materials. This paper describes the UK's first site trial of self-healing concrete, which was the culmination of that project. The trial comprised the in-situ construction of five concrete panels using a range of self-healing technologies within the site compound of the A465 Heads of the Valleys Highway upgrading project. Four self-healing techniques were used both individually and in combination with one another. They were: (i) the use of microcapsules developed by the University of Cambridge, in collaboration with industry, containing mineral healing agents, (ii) bacterial healing using the expertise developed at Bath University, (iii) the use of a shape memory polymer (SMP) based system for crack closure and (iv) the delivery of a mineral healing agent through a vascular flow network. Both of the latter, (iii) and (iv), were the product of research undertaken at Cardiff University. This paper describes the design, construction, testing, and monitoring of these trial panels and presents the primary findings of the exercise. The challenges that had to be overcome to incorporate these self-healing techniques into full-scale structures on a live construction site are highlighted, the impact of the different techniques on the behavior of the panels when subject to loading is presented and the ability of the techniques used to heal the cracks that were generated is discussed.

Self-healing concrete has the potential to optimise traditional design approaches; however, commercial uptake requires the ability to harmonize against standardized frameworks. Within EU SARCOS COST Action, different interlaboratory tests were executed on different self-healing techniques. This paper reports on the evaluation of the effectiveness of proposed experimental methodologies suited for self-healing concrete with expansive mineral additions. Concrete prisms and discs with MgO-based healing agents were produced and precracked. Water absorption and water flow tests were executed over a healing period spanning 6 months to assess the sealing efficiency, and the crack width reduction with time was monitored. High variability was reported for both reference (REF) and healing-addition (ADD) series affecting the reproducibility of cracking. However, within each lab, the crack width creation was repeatable. ADD reported larger crack widths. The latter influenced the observed healing making direct comparisons across labs prone to errors. Water absorption tests highlighted were susceptible to application errors. Concurrently, the potential of water flow tests as a facile method for assessment of healing performance was shown across all labs. Overall, the importance of repeatability and reproducibility of testing methods is highlighted in providing a sound basis for incorporation of self-healing concepts in practical applications.

The success of self-healing cementitious materials relies on their ability to repeatedly heal over the lifetime of the material. Vascular networks have a distinct advantage over other self-healing techniques whereby the healing agent in the network can be routinely replenished. The aim of this study was to develop a multiuse vascular network that can be reused over the lifetime of a structure to enable repeated self-healing events in cementitious materials. The feasibility and self-healing efficacy of novel two-dimensional (2D) vascular networks in concrete beams were tested on laboratory-scale specimens before being trialed in situ on larger, structural-scale elements. The vascular networks were formed via linear interconnecting hollow channels filled with a healing agent that is delivered to zones of damage under an externally supplied pressure. This technique was reproducible at large scale and channels were refilled over a test period of 6 months. Of the two healing agents used in this study, sodium silicate (SS) proved easier to handle and supply into the vascular network, but cyanoacrylate (CA) offered greater strength recovery (up to 90%) in a relatively short time scale. The presence of flow networks in the cover concrete tended to act as a crack initiator and this was particularly evident in the larger-scale specimens. Nevertheless, the potential to enhance and enable multiscale healing in cementitious materials has been demonstrated.