Guidelines for Corrosion Prevention, Monitoring and Remedial Measures for Concrete Bridge Structures
2008 Edition

IRC SP 80 recommends various protective coatings for reinforcing steel and prestressing elements. For rebars, hot-dip galvanizing with zinc coatings of at least 915 gm/m² (125 microns) in aggressive environments and 610 gm/m² (85 microns) in normal conditions is advised, ensuring ductility and corrosion resistance while avoiding chloride-contaminated areas. Fusion Bonded Epoxy Coatings (FBEC) with thickness between 0.1 to 0.3 mm provide high corrosion protection and maintain bond strength above 80% of uncoated bars but require careful handling. Cement polymer composite coatings involve two-layer applications compatible with alkaline concrete, offering corrosion resistance through electron neutralization. Other specialized coatings like epoxy-phenolic and polyurethane are used based on case-specific requirements with manufacturer guarantees. For prestressing steel, anti-corrosion treatments for anchorage, complete grouting with zero-bleed cement grout, temporary protection via phosphate/lubricants and vapor phase inhibitors in ducts, and permanent protections such as controlled shot peening and HDPE or polypropylene sheathing are specified to preserve durability.

Moisture control as per IRC SP 80 involves a combination of design, detailing, material selection, and construction practices aimed at minimizing water ingress. Key measures include limiting crack widths by regulating reinforcement spacing (max 200 mm) and bar sizes, reducing expansion joints by favoring continuous decks and integral structures, and applying waterproof membranes beneath deck wearing surfaces. Concrete must be dense with a low water-cement ratio (maximum 0.40 for PSC/HPC), incorporating mineral admixtures such as fly ash and silica fume to reduce permeability. Proper curing for at least 14 days is essential to enhance impermeability. Use of clean water with controlled chlorides and sulphates, quality aggregates, coated or galvanized reinforcements, and HDPE corrugated ducts for prestressing tendons further aids in moisture resistance.

IRC SP 80 specifies several quality control tests to ensure the performance of epoxy and metallic coatings. Metallic (hot-dip galvanized) coatings undergo hammer and knife adhesion tests, thickness measurement, Preece copper deposition test, hydrogen evolution evaluation, and stripping tests as per relevant IS standards. Epoxy-based coatings require manufacturer certification per ASTM A-882-M-91, bond strength tests, and tensile strength assessments following IS:14653. Fusion Bonded Epoxy Coatings (FBEC) are tested for chemical resistance (no blistering or softening), resistance to applied voltage (no failure under 2V in saline solution), adhesion (no cracks or disbonding after bending), abrasion resistance (weight loss ≤ 100 mg per 1000 cycles), impact resistance (no bond loss after repeated impacts), hardness (Knoop hardness ≥16), thickness uniformity, and continuity with limited holidays. These tests ensure durability and adherence to performance criteria.

Electrochemical methods in IRC SP 80 utilize the electrochemical nature of steel corrosion for monitoring. Potential mapping or open circuit potential (OCP) measurement uses a standard reference electrode placed on the concrete surface to record corrosion potentials of embedded steel, classifying corrosion risk levels based on voltage readings (e.g., potentials below -350 mV vs Cu-CuSO4 indicate high corrosion probability). Resistivity mapping employs a four-probe Wenner array to measure concrete electrical resistivity, where lower resistivity values correspond to higher corrosion risk due to increased moisture and ionic content. Combining these methods enables accurate, non-destructive identification and assessment of corrosion-prone areas, facilitating targeted maintenance.

To prevent corrosion, IRC SP 80 referring to IRC:21-2000 recommends minimum clear covers for reinforcement as 40 mm for moderate exposure, 50 mm for severe exposure, and 75 mm for zones subjected to alternate wetting and drying. For prestressing steel, a minimum clear cover of 75 mm from the sheath's outer surface is specified, with cable spacing not less than 50 mm or equal to the duct diameter, whichever is greater. Grouping of cables is discouraged; if unavoidable, vertical grouping up to two cables is permitted. Reinforcement bars should have a maximum spacing of 200 mm to control crack widths within 0.2 mm (severe) or 0.3 mm (moderate) limits. Additional measures include using dense concrete with a low water-cement ratio, incorporating mineral admixtures to reduce permeability, ensuring adequate curing (minimum 14 days), and employing coated or galvanized reinforcement for enhanced corrosion resistance.