Optimisation of concrete compositions based on their serviceability limit state: A step towards a further reduction of CO₂ emissions of concrete production

The service life of reinforced concrete structures is usually specified to a minimum of 50 years. One requirement for ensuring the service life is a sufficient durability of the concrete. To ensure this durability, the codes DIN 1045 and EN 206-1 contain descriptive requirements for minimum concrete cover, maximum water-cement ratio, minimum cement content and the constituents. These requirements are based on practical experiences. Complex exposures or special boundary conditions can only be considered vaguely when using these rules.

A more precise prediction of the service life can be performed with the probabilistic models published in the “fib Model Code Service Life Design” (fib-Bulletin 34). Usable probabilistic models exist for the depassivation of the reinforcement steel caused by carbonation or chloride ingress. These models provide an opportunity to describe the influences of the concrete composition on the depassivation of the reinforcement more detailed which can be used for an optimisation afterwards. This optimisation with reference to the serviceability limit state in combination with experimental investigations can be used to close gaps in knowledge referring to the use of cements with several main constituents for which only little practical experiences exist. By doing this, boundary conditions can be drafted to reach a further reduction of the clinker/cement factor and therefore to reduce the CO₂ emissions of the production process of concrete.

The target of this research project is to develop a comprehensive database regarding the material parameters carbonation and chloride resistance for different cement types and concrete compositions. The investigations focus on concrete compositions that contain cements with low clinker/cement factors. Based on the experimental results, service life calculations for typical reinforced concrete constructions with boundary conditions representing the German climate are carried out.

The findings of the investigations shall help to better describe the carbonation and chloride resistance of concrete compositions with new clinker efficient cements. The results therefore form a basis for a safe application of these cements and the associated reduction of CO₂ emissions of the concrete production.