▽ +06.00Strengthening
Strengthening concrete structures
Strengthening columns, beams and slabs with concrete jacketing, carbon fibre, bonded plates and injection — executed to the approved structural design and the manufacturer’s data.
When?
When does a structure need strengthening?
Strengthening raises — or restores — the load capacity of a structural element; repair rebuilds a damaged section and protects it. A building may need both.
- A change of use or new loads: an extra floor or heavy equipment.
- Design or construction shortfalls: lower concrete strength or missing reinforcement.
- Deterioration: corroded reinforcement and loss of section.
- New openings in slabs, or load-bearing walls removed.
- Newer code requirements.
Methods
Four ways to strengthen
Concrete jacketing
The column or beam is enlarged with new reinforcement and concrete or high-performance grout around it, with dowels fixed in epoxy into the existing element and a bonding agent between old and new.
When it fits: A large capacity increase, where a bigger section is acceptable.
Carbon fibre (FRP)
Carbon-fibre sheets or laminates bonded with epoxy to a prepared surface: full wraps on columns for confinement, U-wraps on beams for shear, and laminates on the tension face for bending.
When it fits: Added capacity with almost no change in section or weight, and relatively quick installation.
Steel plate bonding
Steel plates bonded with structural epoxy adhesive and anchored to beams and slabs, then protected against corrosion.
When it fits: More bending or shear capacity, where exposed steel is acceptable.
Epoxy injection
Dormant structural cracks are injected with epoxy to restore the element’s continuity — often before the other methods.
When it fits: Dormant cracks whose cause is known, with the engineer’s approval.
Crack injection
| Method | Typical use | Section change | Notes |
|---|---|---|---|
| Concrete jacketing | Columns, beams and footings | Increases | Needs formwork and curing time |
| Carbon fibre | Column confinement, beam shear and bending, slabs | Almost none | Careful surface preparation; UV and fire protection where required |
| Steel plates | Beam and slab bending and shear | Slight | Anchors and corrosion protection |
| Epoxy injection | Cracked elements | None | Restores continuity; adds no capacity beyond the original |
Execution
From assessment to the as-built record
Assessment and tests
A visual survey and damage mapping, with the tests the engineer sets: cores, rebound hammer, cover and rebar scanning, carbonation depth.
Design and approval
The strengthening design by the responsible structural engineer, then approval of the method statement and materials.
Temporary support
Propping and load relief before work, where the design requires it.
Surface preparation and repair
Weak concrete removed, steel treated and the section rebuilt, then the surface prepared for what will be bonded or cast.
Concrete repair & protectionInstallation
To the design and the system manufacturer’s data: materials, sequence, application and curing conditions.
Checks and records
Pull-off adhesion tests (ASTM D4541) and tap tests for voids on bonded systems, samples of the new concrete, then the final protection and the as-built record.
Questions
Questions clients ask
When is carbon fibre used instead of concrete jacketing?
When capacity must rise without enlarging the section or adding weight, or where casting new concrete is impractical; the structural engineer decides from the required load and the element’s condition.
Can a column damaged by rebar corrosion be strengthened?
Yes, once it is repaired first: damaged concrete is removed, the steel cleaned and treated or supplemented, the section rebuilt, then strengthened to the design.
Does strengthening need a structural design?
Always. The structural engineer sets the method, materials and details — for FRP systems with references such as ACI 440.2R — and we execute to the approved design and the manufacturer’s data.
Can a floor be added to an existing building?
Only after a structural assessment confirms the columns and foundations can carry it, or defines their strengthening, and after the required permits.
How is carbon-fibre strengthening protected?
With a top coat against UV and abrasion, and fire protection where the design calls for it, because the adhesive is sensitive to high temperatures.
Does strengthening require vacating the building?
Not always. It depends on the elements, the loads and the temporary support, and is set in the work plan with the engineer and the owner.
Next step
An element that needs strengthening?
Send the assessment report or structural design and photos of the elements for a detailed execution offer, or ask for a site inspection.