Frequently Asked Questions

What is the complete repair sequence for using MC-RocTec 222 to repair delaminated and spalled concrete at the soffit (underside) of a reinforced concrete bridge beam, including reinforcement treatment?

Delaminated and spalled concrete at the soffit of reinforced concrete bridge beams is one of the most critical and common structural defects in Indian infrastructure, caused by chloride-induced corrosion of the steel reinforcement in the concrete cover zone. The repair sequence for MC-RocTec 222 involves multiple stages addressing the root cause (corrosion) as well as the symptom (spalled concrete). Stage 1 — Condition assessment. Before commencing any repair, conduct a full condition survey of the beam soffit using a hammer-and-tap survey to identify all hollow-sounding (delaminated) areas even where spalling has not yet occurred. Mark all delaminated areas with chalk. Use a phenolphthalein indicator test to map the carbonation depth (carbonation reduces the pH of the concrete, depassivating the steel reinforcement and accelerating corrosion). Use a concrete cover meter (Profometer) to identify the reinforcement layout and cover depth in the repair area. Stage 2 — Break out to sound concrete. Using chipping hammers or grinders, break out all delaminated, hollow-sounding, and carbonated concrete to beyond the carbonation front and to a minimum of 25 mm behind the reinforcement bars. The break-out must expose sound, hard concrete with aggregate particles visible at the prepared face. The perimeter of the repair area must be saw-cut to a minimum 10 mm deep vertical edge — never feather the repair edge — to prevent adhesion failure at the repair perimeter. Stage 3 — Steel reinforcement treatment. Grit blast the exposed corroded reinforcement bars to Sa 2.5 standard (near-white metal surface) to remove all loose corrosion products. Measure the remaining bar diameter — if cross-sectional loss exceeds 20 percent, the structural engineer must assess the need for additional bars to be installed. Apply one coat of MC-Bauchemie MC-Cor, a corrosion inhibitor and bonding primer (zinc-rich epoxy or cementitious corrosion inhibitor) to the clean steel reinforcement bars by brush, allowing to dry before mortar application. Stage 4 — Substrate preparation and bonding slurry. Pre-wet the concrete substrate with clean water to saturated surface dry (SSD) condition. Apply MC-Bauchemie Nafucryl or MC-Dur 1225 bonding slurry (cement plus polymer bonding agent) by stiff brush to the prepared concrete substrate and the surrounding concrete surface, working the slurry into all prepared pores. Apply the MC-RocTec 222 repair mortar while the bonding slurry is still tacky. Stage 5 — Mix and apply MC-RocTec 222. Add the powder to the specified quantity of clean water (approximately 4 to 4.5 litres per 25 kg bag — check current TDS) and mix with a paddle mixer for 3 to 5 minutes to a smooth, lump-free consistency. For overhead soffit application, use the repair mortar at a stiff consistency (reduce water slightly from the standard dose to minimize sag). Apply MC-RocTec 222 in layers up to 25 mm per application for overhead work (thicker layers sag before setting). Allow each layer to reach initial set (firm, approximately 2 to 4 hours) before applying the next layer. Stage 6 — Finishing and curing. Finish the repair face flush with the surrounding concrete surface using a steel or plastic float. Apply a curing compound (MC-Bauchemie curing membrane or wet hessian) immediately after finishing and maintain for a minimum of 7 days. Stage 7 — Protective coating. After the repair mortar has cured for 7 days, apply a compatible protective surface coating (carbonation barrier coating such as MC-Bauchemie MC-Color or equivalent anti-carbonation elastomeric coating) over the entire beam soffit including the repaired areas and the surrounding parent concrete, to prevent future carbonation and chloride ingress and extend the service life of the repaired structure.