Definition
Unbonded repair is a repair system where the new repair material is not intended to rely on direct adhesion to the existing concrete substrate for structural performance, allowing it to function independently.
Explanation
This approach is used where substrate movement, severe contamination, differential behaviour, or design requirements make bonded repair unsuitable. Instead of relying on surface adhesion, the repair may be supported by mechanical fixing, reinforcement anchorage, formwork systems, or separate structural support.
Examples include some overlay systems, jacketing works, encasement repairs, and independent waterproofing systems where the new element must tolerate movement or environmental exposure without debonding from the original concrete.
Although surface preparation is still important, the design focus shifts from bond strength to stability, load transfer, and movement accommodation. This can be particularly useful in heavily deteriorated structures where reliable substrate bonding cannot be achieved.
Why It Matters
Unbonded repair provides a practical solution where bonded systems would be unreliable or short-lived. Correct specification helps avoid recurring failures and ensures the repair performs effectively under real site conditions.