Steel Reinforcement Exposure Before Concreting

How Long Can Steel Reinforcement Cage Remain in the Open Before Concreting?

With Reference to Indian Standards

1. Objective and Importance

The goal is to prevent excessive corrosion of reinforcement before embedding in concrete. Corroded steel continues to deteriorate post-concreting, causing expansion, cracking, and reduced durability.

📌 IS Reference: IS 456:2000 – Clause 12.2.1: Reinforcement shall be free from loose rust, scale, oil, etc., at the time of placing concrete.

2. Understanding Corrosion Impact

• Powdery corrosion (≤15 µm): Forms a passivating layer after embedding.
• Flaky/pitting corrosion: Unacceptable; indicates deep damage.

3. Factors Affecting Allowable Exposure Time

Factor	Effect
Humidity	Increases corrosion rate
Temperature	Accelerates reactions
Rain Exposure	Causes rapid flaking
Contact with soil	Introduces salts
Cement wash	Reduces corrosion risk

4. Typical Exposure Tolerance

Environment	Max Safe Exposure (Unprotected)
Dry (≤60% RH)	15–30 days
Moderate Humidity	7–15 days
Coastal/Monsoon	< 7 days

📌 No fixed duration in IS 456. Site judgment and corrosion levels determine acceptability (SP 34 also recommends this approach).

5. Storage and Handling Best Practices

1. Stack bars above ground on wooden supports.
2. Cover with waterproof sheeting (tarpaulin or plastic).
3. Keep away from soil and running water.
4. Apply cement wash if exposure exceeds 1 month.

6. Visual and Physical Inspection Before Concreting

• Remove loose flakes, scale, dust, and oil.
• Reject bars with pitting or significant surface degradation.

📌 IS 1786:2008 and SP 34 specify that reinforcement bars must be free of corrosion products that affect bond.

7. Cleaning Techniques

Method	When to Use
Jute cloth rubbing	Light powdery rust
Wire brushing	Minor scaling
Sandblasting	Severe rust (not usually onsite)
Cement wash	Preventive for prolonged storage

8. TMT vs. CTD Bars in Corrosion Resistance

• TMT Bars: Better corrosion resistance due to outer martensitic rim.
• CTD Bars: Susceptible to micro-cracks and faster rusting.

📌 As per IS 1786:2008, TMT bars are recommended in aggressive environments for superior corrosion resistance.

9. Cleaning Criteria Before Concreting

• Acceptable: Uniform rust, no pitting, no loose scale.
• Unacceptable: Pitting, flaky rust, oily or soil-contaminated bars.

📌 IS 456:2000 – Clause 12.2.1: Cleaning of reinforcement must be ensured before concrete placement.

10. Recommendations and Summary

• Use cement wash for exposure > 15 days.
• Cover bars properly during storage.
• Inspect and clean reinforcement before use.

Condition	Max Uncovered Time	Recommended Action
Dry, < 60% RH	15–30 days	Light cleaning
Humid or rainy	< 7 days	Cement wash or reject
Coastal	Prefer no exposure	Cement coat + cover