concrete cover

Figure 4.2: Reliability index versus concrete cover for environmental class XC2 (w/c=0,6,service life 50 years) a) for CEM 142,5 R (curing 2 days) b) for CEM III/B 42,5 NW HS NA (curing 3 days)

It can be seen that the reliability index for the calculated values depends on the concrete cover, the location and the type of cement. Especially in the case of a CEM III/B, the reduction of the concrete cover by 5 mm results in a decrease of the reliability index of almost 50 %. This means a reduction of life time of more than 15 years.

It is interesting to see that the choice of a different type of cement has a bigger influence than the reduction of the concrete cover. However it needs to be taken into account that part of the effect depending by the type of cement can be counteracted by prolonged curing. Environmental class XC3

For environmental class XC3 the same concrete covers are required as for XC2, but the required w/c ratio for class XC2 is higher. It can be seen, that this improvement of the concrete quality (porosity) also has an important effect on the carbonation (compare Figures 4.2 and 4.3).

Apart from this the same trends can be observed. The reduction of the nominal concrete cover from 35 to 30 mm has a big influence on the reliability index, even more pronounced than for concretes with a w/c ratio according to the requirements for XC2.

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