Abstract
The possible beneficial impact of self-healing on chloride transport through cracks has been assessed for two bacteria-based self-healing mortar mixtures in comparison with Ordinary Portland cement mortar. Intact self-healing specimens featured lower chloride transport coefficients thanks to a denser microstructure and to the formation of a layer of calcium carbonate on their surface. However, self-healing of cracks of cracked mortar specimens did not significantly reduce chloride penetration during 28 days of chloride exposure compared to cracked and non-healed specimens. On the other hand, this study demonstrated that self-healing of 150–200 µm wide cracks reduced chloride ingress during shorter term (14 days) chloride exposure in comparison to cracked but non-healed specimens. The results of this study suggest that self-healing of cracks through calcium carbonate formation results in water blockage (sealing) of cracks but that the limited amount of limestone formed creates an imperfect barrier against diffusion of chloride ions through the apparent porous limestone. The short-term positive effect of self-healing with respect to reduced chloride ingress could be beneficial in applications where chloride exposure is limited or non-permanent such as concrete structures irregularly exposed to deicing salts or located in the splash zone in marine environments.
Highlights
The durability of concrete is a major issue for both industry and academia worldwide
- The chloride penetration resistance of intact speci mens derived from self-healing mixtures was higher than of those derived from Portland cement based mixture
Self-healing was more limited and mainly present at certain locations only, leaving the crack depth largely un-healed. - The possible beneficial influence of self-healing on chloride pene tration of cracked specimens could not be observed in specimens subjected to the Rapid Chloride Migration (RCM) test. - Cracked and self-healed specimens subjected to the free chloride diffusion test showed a positive effect on resistance towards chloride penetration
Summary
The durability of concrete is a major issue for both industry and academia worldwide. By healing a crack completely it is expected that less or no harmful agents from the outside environment (i.e. CO2 and chlorides) can penetrate the material resulting in an increase of service life of the concrete structure This assumption is confirmed by many studies that investigated the effectiveness of autogenous healing of micro-cracks in reducing the chloride penetration of concrete as a function of many inter-related parameters [4,10,11,12,13,14]. Yoon and Schlangen [12] observed that complete self-healing of 25 μm wide cracks blocked chlorides ingress and, restored the chloride penetration resistance to that of un-cracked specimens They reported that micro-cracks with a width equal or lower than 40 μm did not significantly influence the chloride penetration properties of cracked concrete. It was reported that crack widths smaller than 135 μm only show marginal effects on the effective diffusion coefficient of mortar specimens, while crack widths larger than 135 μm can seriously reduce the service life of concrete structures through acceleration of initiation of steel bar corrosion
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