Concrete deteriorates. All of it. Always. The only variables are how fast and from what cause. The question that reaches us regularly from contractors, project managers, building owners is: what do I do about it? The answer starts with understanding what kind of deterioration you’re dealing with.
Understanding Concrete Deterioration: It’s Not All the Same
Carbonation: COâ‚‚ reacts with calcium hydroxide in the concrete, reducing pH. When pH drops below ~9, the passive oxide layer protecting steel reinforcement breaks down and corrosion begins. A phenolphthalein indicator test on a freshly broken surface reveals the carbonation depth.
Chloride-induced corrosion: In coastal environments, chloride ions penetrate concrete and trigger steel corrosion directly. More aggressive and localised than carbonation-induced corrosion.
Alkali-Silica Reaction (ASR): Reaction between alkali in cement and reactive silica in aggregate, producing a gel that absorbs water and expands, causing map cracking.
Mechanical damage: Impact, abrasion, overloading, settlement. Structural issue first, repair second.
When to Patch
Patching is appropriate when deterioration is localised (less than 30–40% of surface area), the underlying concrete is sound beyond the patch zone, and structural integrity is not compromised.
Correct patch repair sequence: Break out to minimum 25mm depth. Remove all delaminated concrete. Clean and treat reinforcement wire brush to bright metal, apply corrosion-inhibiting primer (Fosroc Nitoprime Zincrich, Sika MonoTop 910S). Apply bonding bridge. Apply polymer-modified repair mortar in layers. Cure properly minimum 7 days wet curing.
Products: Fosroc Renderoc range, Sika MonoTop repair mortars, MC-Bauchemie Nafufill range, Buildmart BS Smartbond 100 System
When to Rehabilitate
Rehabilitation is required when deterioration is widespread (more than 30% of surface area) or a protective coating is needed to arrest ongoing deterioration. Options include protective anti-carbonation coatings, penetrating silane/siloxane treatments, bonded overlays of 20–50mm polymer-modified mortar, or sprayed concrete (shotcrete) for large-area rehabilitation.
When to Replace
Replacement is indicated when structural capacity is genuinely compromised, the deterioration mechanism cannot be arrested cost-effectively, or repair cost exceeds 50–70% of replacement cost. This decision requires a structural engineer, not a repair products distributor.
The Reinforcement Corrosion Problem
By the time you see spalling, the corrosion process has been underway for years. The visible damage is the late-stage symptom, not the beginning. Breaking out only the spalled zone and patching over corroded rebar that is still actively corroding will result in failure within 3–5 years.
Full repair sequence: Break out to fully expose corroded rebar. Wire brush to near-bright metal. Apply corrosion-inhibiting primer to rebar and cut faces. Apply bonding bridge. Apply repair mortar in layers. Apply protective coating if environment warrants.
For technical guidance on concrete repair, chat with Divya on WhatsApp or visit store.technotrade.in
