Table 4.1: Required reliability index bSLS,50 for a life time of 50 years
4.3 Parametric Study
The calculations are based on the models given in 22.214.171.124 and 126.96.36.199. All input values are given as stochastic variables (mean, standard deviation, type of distribution). The output of the program is the reliability index p as a function of the lifetime. In this study the reliability index p is considered for a lifetime of 50 years.
The type of cement has a strong influence on the concrete resistance against carbonation. Concretes with Portland cement are exposed to carbonation they show a decreasing porosity in the carbonation zone resulting in higher resistance against ongoing carbonation. In concretes with blastfurnace cements or with cements with pozzolanic additions (e.g. fly ash), on contrary, the porosity of the concrete increases after carbonation and the carbonation of the concrete sometimes progresses faster (as the diffusion of CO2 takes place through the carbonated zone). The influence of different types of cement is not considered. In the calculations two different concrete mixes (favourable and unfavourable) were studied.
The w/c ratio of the concrete mixes were chosen according to the requirements in prEN 206-1. The cement content was kept constant (320 kg/m3) for all concrete mixes, because there is only a minor influence on the carbonation process. The material resistance was determined under laboratory conditions. The length of the curing period also has a strong influence on carbonation. In the calculations the curing time was assumed to be 2 days for CEM I and 3 days for CEM III/B. The climatic conditions were determined according to statistical data from local weather stations. All calculations were performed for European locations with moderate and hot climate to show the influence of temperature.
In the following, durability design calculations for nominal covers of 30 and 35 mm, for different climates and for different cements (CEM I and for CEM III/B) are performed. In Figure 4.2 the results of the calculations are shown.
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