Patch repairs on reinforced concrete structures – Model investigations on the required size and practical consequences

For various reasons, world-wide numerous concrete structures have to be repaired due to corrosion problems of the steel reinforcement. In some cases, frequent use of road salt in past winters, not foreseen during the planning of older traffic structures, has led to damage; in other cases the causes lay in deficient planning and execution, as for example
• irregular, insufficient concrete cover of the reinforcement;
• unsuitable concrete mixture proportions for outdoor structures;
• insufficient concrete curing, subsequently bad concrete quality in the concrete cover.The model investigations described in this paper relate to construction practice, in which local damages due to reinforcement corrosion, e.g., spalls and cracks, are repaired solely in the area of visible surface damage. When damage is dealt with in this way, the carbonated or chloride contaminated concrete is often not removed completely, to avoid stability problems in the structure. In consequence, even after the repair measure there are areas of the reinforcement where there is no guarantee of sufficient protection against corrosion and a high corrosion risk remains. The reinforcement in the repaired area may even accelerate corrosion in unrepaired areas adjacent to it.