--- title: "Preventive measures against corrosion" subject: "Concrete Technology and Masonry Structure" chapter: 6 key: "semester_5/concrete_technology_and_masonry_structure:corrosion-preventive-measures" source: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/corrosion-preventive-measures site: BCT Engineering --- # Preventive measures against corrosion Concrete Technology and Masonry Structure · Chapter 6: Concrete durability - Asked in: 2082 Baisakh, 2 marks; 2066 Chaitra (old course), 3 marks; 2066 Bhadra (old course), 3 marks (asked 3 times) - Video: [Corrosion in Reinforced Concrete: Causes, Effects, Prevention | RCC Durability Explained](https://www.youtube.com/watch?v=ITxS6YMVtCw) — Real civil - Answer checked by Claude Sonnet 5.5 on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/corrosion-preventive-measures - Whole chapter: https://www.bctengineer.com/md/semester_5/concrete_technology_and_masonry_structure/chapter-6 ## Question Write preventive measures against corrosion of steel reinforcement in concrete (how can reinforcement be protected from rusting on an RCC structure?). ## Short answer Prevent corrosion by using dense, impermeable concrete with low water-cement ratio (max 0.40–0.55), adequate cement and curing. Provide sufficient cover (20–75 mm by exposure), limit chlorides, use blended cements, and apply protective coatings or cathodic protection. ## Answer **Preventive measures against corrosion of reinforcement** 1. **Dense, impermeable concrete:** low w/c (max 0.40 to 0.55 by exposure), enough cement (min 300 to 360 kg/m$^3$), good grading, full compaction and curing (IS 456, Table 5, Cl. 8). 2. **Adequate cover:** nominal cover for RCC members of 20 mm (mild), 30 mm (moderate), 45 mm (severe), 50 mm (very severe) and 75 mm (extreme exposure), using cover blocks (IS 456, Table 16 and Cl. 26.4). 3. **Limit chlorides and sulphates** in aggregate, water and admixtures (IS 456 Table 7; no sea water for RCC); avoid calcium chloride. 4. **Cement type:** use PPC, slag or sulphate-resisting cement in aggressive areas, with fly ash or silica fume to reduce permeability. 5. **Crack control:** limit crack width to 0.3 mm (IS 456, Cl. 35.3.2) by detailing and joints. 6. **Protected steel:** epoxy-coated or galvanised bars, stainless steel, or corrosion-resistant (CRS / Fe 500D) TMT bars. 7. **Corrosion inhibitors** (calcium nitrite) in the concrete mix. 8. **Surface protection:** waterproof coating, sealers or cladding, and proper drainage with no ponding; a damp-proof course. 9. **Cathodic protection** (sacrificial anode or impressed current) for existing structures, and timely repair of cracks. 10. Regular inspection and maintenance. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which concrete mix choice helps most to prevent corrosion? A. High w/c for easy placing B. Minimum cement with no curing C. Low w/c with enough cement, good grading, full compaction and curing D. Sea water mixing for strength Answer: C. Dense, impermeable concrete slows ingress of CO2, chlorides and oxygen. (Key point: Dense concrete) 2. What is the role of adequate cover and cover blocks? A. Cover is only needed for appearance B. Cover keeps aggressive agents away from the bar for longer, so nominal cover rises from 20 mm (mild) to 45 mm (severe) and 75 mm (extreme) C. Cover should be reduced in severe exposure D. Cover blocks increase the w/c ratio Answer: B. More cover delays carbonation and chlorides reaching the steel. (Key point: Adequate cover) 3. Which is a correct protective measure for the steel itself? A. Epoxy-coated or galvanised bars, stainless steel, CRS bars, or corrosion inhibitors such as calcium nitrite B. Plain mild steel without any coating C. Adding calcium chloride D. Using more water in the mix Answer: A. Coated or resistant bars and inhibitors keep the steel passive or resist attack. (Key point: Protected steel and inhibitors) 4. What is used for existing structures and what crack width limit applies? A. Waterproofing only; crack width up to 3 mm is fine B. Cathodic protection (sacrificial anode or impressed current); crack width limited to 0.3 mm C. Cathodic protection is only for new bars; limit 1 mm D. No protection is possible Answer: B. Cathodic protection stops anodic dissolution; cracks give easy access so are limited and repaired. 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