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This paper investigates the mechanisms of corrosion of seven-wire strands and the reasons for failures in detecting corrosion at early stages. As per ASTM G109 and ACI 222 R-01, a 1-year study on chloride-induced corrosion of seven-wire prestressing strands embedded in various concretes was conducted. The type of corrosion current circuits in the prismatic specimens with one top and two bottom strands was investigated. Unlike solid rebars, the concrete resistivity had a limited role on the type of corrosion circuits in strand systems, with a high probability of corrosion occurring between different wires in the top strand itself. This may be due to the flower-like geometry and the complex corrosion mechanisms within the top strand. It is recommended to perform other electrochemical measurements on the top strand – prior to making conclusions. Also, until about 6% corrosion loss is reached, the rust will fill the interstitial space between the seven wires and will not exert expansive stresses on the surrounding concrete. Hence, no staining/cracking will be visible on the concrete surface – a serious structural safety issue – necessitating frequent chloride/corrosion condition assessment of prestressed-concrete structures.

Self-healing technologies provide the long-term resilience of concrete structures by enabling self-diagnose and self-repair of damages (aging cracks, cyclic load damages, and corrosion-induced cracks). However, self-healing technologies require special additives and materials in addition to the ones in conventional concrete. Hence, it is often perceived to have higher environmental impacts, and therefore, it is necessary to understand the same. This study is aimed to analyse the life cycle assessment (LCA) of concrete with microcapsules produced by different techniques to investigate the sustainability of these concretes. Two microcapsule techniques, namely complex coacervation and membrane emulsification, were studied at the laboratory scale and then projected to the industrial scale. The analysis shows that the concrete with microcapsules does not adversely impact the emissions in the production stage if supplementary cementitious materials are used. Further, if the beneficial effects of the self-healing technologies are considered in the use phase, the impacts are much lower. Thus, this assessment gives meaningful insights by identifying major impacts in the production of self-healing technologies and helps to improve their design and application in concrete.

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In Europe, about 55% of concrete bridges are about 50 years old and require non-structural rapid repair strategies to reinstate the aesthetic and durability performances. Existing strategies focus primarily on superficial restoration that continues to demonstrate premature deterioration due to inevitable micro-crack formations that further propagate to macro-cracks leading to the ingress of moisture along with harmful ions. In this study, the benefits of self-healing technology to control moisture ingress at the microscale were investigated. For this, tailored microcapsule with inorganic healing agent, specifically, commercially available water-repellent agent (SIKAGARD 705L) was added to mortar with two types of commonly used binders namely CEMI 52.5N and CEMI 52.5R. The compatibility assessment in terms of capsule integration, fresh and hardened properties was done. The baseline healing efficiency of the mortars without any healing additions was obtained to understand the autogenous healing capacity of the reference mortars. Subsequently, the reference mortar mixes were compared with mixes containing varying fractions of microcapsules (3, 5, and 10%) for autonomous healing efficiency with capillary absorption as the main durability function. The healing efficiency was further investigated for two different crack mouth widths (<250 μm and >350 μm); representative of non-structural residual crack widths. In mortars with microcapsules, a maximum reduction of sorptivity coefficients up to 82% and 78% with CEMI 52.5N and CEMI 52.5R mortars, respectively, for specimens cracked after 7 days of curing was observed. Subsequently, a synergetic effect of autogenous healing action and autonomous water-repellent action for durability recovery was identified and proved useful for repair mortar applications. The healing agent investigated, capsule content, and healing environment considered in the current study lay a foundation for further optimisation to improve the performance and to suit different applications.