Chloride Penetration Resistance of Mortar and Concrete
Chloride-induced corrosion of reinforcements has a significant impact on the durability of marine structures. In the past, damages to such structures have shown that chloride penetration resistance cannot be reliably ensured even if structures comply with DIN 1045, which is why supplementary regulations on the composition of concretes exist for waterways constructions, in addition to the option of directly testing chloride penetration resistance.
The exposure to chloride of marine structures is especially high in the tidal, splash and spray zones (exposure class XS3). Structural elements such as jetties, wharves and wall parts above higher low water are typically exposed, as are the bearing piles of such structures. Examinations of existing structures have shown that for typical concrete coverings of 4 to 5 cm, the chloride contents in reinforcements start to become critical when an age of around 40 to 50 years is reached. This is also the age when first obvious damages due to chloride-induced corrosion typically occur (picture 1). However, hydraulic structures are designed for a planned service life of 80 to 100 years.
This is why the BAW's Supplementary Technical Contract Conditions applicable to new hydraulic structures (ZTV-W LB 215) and to the repair of existing hydraulic structures (ZTV-W LB 219) stipulate that - in the case of exposure classes XD3 and XS3 - concretes according to DIN 1045 and sprayed concretes according to DIN 18551 may only be used for new structures and repair work if cements containing granulated slag (share of granulated slag = 21 wt.%) or fly ash (minimum fly ash content of 50 kg/m3) were used in their production. In addition, the concrete covering must be thicker than specified by DIN 1045 (cmin= 50 mm).
In addition to the descriptive requirements, a new method is available for evaluating the chloride penetration resistance of concrete and, in particular, of repair materials (mortar and air-blown mortar/sprayed concretes), the composition of which is often not known. The test method can be used to determine a material-specific chloride migration coefficient; a more detailed description is available in the BAW Code of Practice "Chloride Penetration Resistance" (picture 2). The Code of Practice defines limits for the migration coefficients found in concretes, sprayed concretes or repair mortar. As an aid for the planner, It also includes an assessment diagram for estimating the service life as part of a durability assessment (picture 3).