Basis of Selection of Concrete Repair Method
In repair process we take some action to correct/replace damaged, deteriorated or faulty components, materials or any elements of concrete structure. In our previous post we have discussed about symptom and causes of concrete deterioration; only after determining actual cause/causes of deterioration, a repair method is selected. The considerations that are taken into account are:
a. Modification or adjustments required to prevent cause of deterioration; when possible. The adjustments are as follows:
• Modification of pattern of water drainage
• Correcting differential subsidence of building foundation
• Eliminating origin of cavitation that may produce deterioration.
• Eliminating exposure of member to deleterious chemicals
• Providing provisions to accommodated differential movement.
b. Constraints encountered in repair work, as discussed in previous post, are accessibility, expected design life, weather, making operation of facilities during repair work and also limitations provided by owner. In concrete construction and repair work weather plays important role in scheduling operation sequence and also methods; extreme cold and extreme hot condition provides severe problems to behave coherent of existing concrete and repaired portion of concrete.
c. In item (a) we have discussed about some modifications; in many case we can’t avail such adjustment like continuous exposure of deteriorated concrete and repaired concrete to deicing agents. We know deicing agents contain chlorides salts which are very injurious to concrete. This exposure may have other deleterious chemicals too. As these causes cannot be removed, we can define these inherent problems of repaired elements.
d. Often environmental issues are part of government law or imposed by owner. The constraints in selecting repair/rehabilitation methods of concrete is considered sometimes important or minimal; this include
• Vapors from certain application of coating, sealers and membranes
• Particles from demolition of concrete containing silica aggregate
• Noise
• Other hazardous waste
e. Methods should be based on expected life of concrete member or structure. The merits and demerits of providing temporary or permanent repair should be considered carefully.
f. Structural safety is important issue during repair work and also completion of repair. The special considerations should include
• Negative moment section in beams/slabs
• Cantilever member
• Connections/joints details
• Spandrel beams(precast)
• Columns
Where concrete removed or cutting of reinforcing bars alter capacity (shear/bending/compressive or tensile) of member, proper supports, strengthening or shoring should be considered in propose method.
g. Availability of materials and technical feasibility of methods or material often define repair method. In some cases, repair materials may not have sufficient technical data as literature provided by manufacturer may not be based on representative tests considering in application, method and environmental condition.
h. Contractor’s capability to handle and execute specialized method and materials.
i. Consideration of combination of methods & materials to achieve most economical repair procedure.