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Blended cements, where Portland cement clinker is partially replaced by supplementary cementitious materials (SCMs), provide the most feasible route for reducing carbon dioxide emissions associated with concrete production. However, lowering the clinker content can lead to an increasing risk of neutralisation of the concrete pore solution and potential reinforcement corrosion due to carbonation. carbonation of concrete with SCMs differs from carbonation of concrete solely based on Portland cement (PC). This is a consequence of the differences in the hydrate phase assemblage and pore solution chemistry, as well as the pore structure and transport properties, when varying the binder composition, age and curing conditions of the concretes. The carbonation mechanism and kinetics also depend on the saturation degree of the concrete and CO2 partial pressure which in turn depends on exposure conditions (e.g. relative humidity, volume, and duration of water in contact with the concrete surface and temperature conditions). This in turn influence the microstructural changes identified upon carbonation. This literature review, prepared by members of RILEM technical committee 281-CCC carbonation of concrete with supplementary cementitious materials, working groups 1 and 2, elucidates the effect of numerous SCM characteristics, exposure environments and curing conditions on the carbonation mechanism, kinetics and structural alterations in cementitious systems containing SCMs.

Development of suitable capsules is essential to achieve self-healing by encapsulation. In the context of self-healing concrete, capsules that can be easily mixed into concrete and release the healing agent when cracking occurs are ideally required. The optimization of these properties would allow for a successful implementation at large scale in practical (concrete) applications. In the present work, the suitability of polymeric cylindrical capsules made of poly(methyl methacrylate) (PMMA) to carry healing agent in self-healing concrete has been evaluated. An innovative method to assess more easily the capsules survival during concrete mixing was developed. This method is based on the evaluation of the setting behavior of concrete containing capsules filled with setting accelerator. Capsules with a wall thickness of 0.7 mm were able to resist the concrete mixing process and to rupture at relatively small crack widths (116 μm) after applying a surface treatment to increase the adhesion between the capsules and the cementitious matrix. Next, the self-healing efficiency of the encapsulation materials (glass or PMMA) was evaluated on real-scale concrete beams. The results showed that cracked concrete beams with mixed-in capsules (glass or PMMA) filled with waterrepellent agent showed higher resistance against chloride ingress compared to plain cracked concrete beams. PMMA capsules showed a lower self-healing efficiency (in relation to chloride ingress) compared to glass due to a less favorable distribution of the capsules in the concrete. However, concrete containing glass capsules is susceptible towards alkali-silica reaction.Although optimization of the PMMA capsules is still necessary to improve their distribution in concrete and achieve higher self-healing efficiency, the obtained results indicate that these capsules could be a promising solution towards self-healing concrete.

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