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Figure 4.4 - Reliability index versus concrete cover for environmental class XC4(w/c=0,50) a) for CEM 142,5 R b) for CEM III/B 42,5 NW HS NA

4.3.3 Chloride penetration

Chlorides are transported in the concrete by the pore water. Processes of diffusion and conveyance by water transport take place which lead to a certain chloride content in the concrete. The time before attainment of a critical chloride content depends mainly on the porosity of the concrete, which may be influenced for example by the w/c ratio and the type of cement. In general, the use of Portland cements leads to a higher permeability of the concrete for chlorides than the use of blastfurnace cements or cements with fly ash.

In this study only environmental class XS3 with nominal concrete covers of 50 and 55 mm was studied. The w/c ratio of the corresponding concrete mix was determined according to EN 206-1 (w/c = 0,45) and the cement content was 320 kg/m3. The climatic conditions (relative humidity and temperature) were determined according to statistical data of local weather stations and the calculations were performed for two European locations close to the sea in moderate and hot climate.

The calculations were performed with two different types of cement [1]: the results for a CEM I with fly ash are shown in Figure 4.4. Alternatively the calculation was performed with CEM I without fly ash [1]. The reliability index for a lifetime of 50 years was below 0, that means that corrosion probability is higher than 50%. Examples have shown that the use of Portland cements in tidal environments (e.g. harbours) has already led to deterioration (cracking) as a result of chloride induced corrosion after 10 years.

The calculation with Portland cement plus fly ash has shown similar trends as in the case of carbonation. Figure 4.5 shows that hot climates result in faster chloride ingress than moderate climates. It can also be seen, that the proposed reliability index is not reached for environmental class XS4.

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