ABSTRACT Integrated surface protection systems made of thermal-sprayed zinc coating and a sealing coating are being used to protect the reinforcement from corroding in chloride contaminated concrete. In this connection, the thermal-sprayed zinc coating should provide cathodic protection until the structure is mostly dried out even through the sealing coating. To detect the drying-out non destructive methods are required, which enable to measure the humidity profiles of the concrete. An easy and cost effective solution for that is the use of Multiring-electrodes. Resistance measurements between adjacent metal rings with defined distance and known location in the concrete cover enable a monitoring of moisture distribution inside the concrete, which is well known to be the main parameter for corrosion assessment. Beside the moisture content, the resistance is influenced by th¥ concrete composition, the salt content, and the temperature. Based on measurements on concrete specimens of different compositions the influence of various parameters are shown, and by using of correlation functions the moisture distribution could be determined.
INTRODUCTION During the last years numerous and sometimes very severe failures occurred at chloride contaminated reinforced concrete structures which required expensive rehabilitation measures. Especially traffic surfaces exposed to de-icing salts in the winter. months or structures near the sea coast or in aggressive soils are affected. In parking garages and at bridges the damage is particularly severe. This is due to the fact that large amounts of chlorides can penetrate into horizontal areas and reach the reinforcement level within a few years resulting in high corrosion rates. First consequences of corrosion are cracks and spalled areas. For traffic structures over the years this could lead to a non-tolerable reduction of the load-bearing capacity.
For the rehabilitation of such concrete areas with considerable chloride contents even in higher depths different strategies can be used:
Conventional techniques like
. removing of chloride contaminated concrete cover,
. shot blasting of the reinforcement with
subsequent coating and
. application of a new concrete cover
as well as cathodic protection systems with impressed current are relatively expensive. Another possibility for moderate aggressiveness of the chlorides is the drying out process of the infected concrete!. For practical applications this technique is usually not used as it is not known how long it takes for sufficient drying out of the concrete.
In order to reduce the costs new rehabilitation techniques should be developed. Within the scope of a research project a new system was tested which combines the principle of drying out with a temporary cathodic corrosion protection for the transitional period until a sufficient decrease of the electrolytic resistance of the concrete is achieved and thus the corrosion risk after rehabilitation is eliminated. The temporary cathodic protection consists of a thermally sprayed zinc layer on the concrete surface, and for the drying out process a commercial and approved surface protection system (SPS)2 is used which is suitable for the loads occurring in parking decks.
The experiences with sprayed zinc layers on concrete surfaces have shown that the service life of such zinc layers for cathodic corrosion protection purposes are limited. Under normal conditions it varies between 5 and 10 years, sometimes even longer. This period corresponds roughly to the necessary time for sufficient drying out of the concrete in order to eliminate corrosion risks of the reinforcement. Therefore, the positive proper