In reinforced concrete, the carbonation of the concrete cover can lead to the loss of passivation of the reinforcing steel. As a consequence, steel corrosion might occur. The current trend to concretes with reduced clinker content, often in combination with pozzolanic substances, increases the risks for damage due to carbonation, as the Portlandite content in the concrete is reduced significantly. This is an important limiting factor for the quantities of calcined clays that can be used in concrete. For this reason, it was investigated whether an increase in the Portlandite buffer could improve the carbonation resistance. The basic suitability of this approach was confirmed. This should make it possible to increase the clinker replacement rate with supplementary cementitious materials. Furthermore, an alternative approach based on a binder with γ-C2S was investigated. This usually inert phase reacts with atmospheric CO2 and moisture, forming additional phases. This effect was found to densify the concrete surface to such an extent, that an extremely high carbonation resistance was achieved. Furthermore, the densification also increases the resistance against chloride ingress. The incorporation of γ-C2S could thus help to achieve a good durability for low carbon concretes.