CFRP vs RC Jacketing vs Steel Jacketing: Choosing a Column Strengthening Method

When an assessment shows that columns in an existing building are under-strength, there are three main ways to strengthen them: reinforced concrete (RC) jacketing, steel jacketing, and carbon fibre reinforced polymer (CFRP) wrapping. Each works, but each suits different situations.

RC jacketing

A new layer of reinforced concrete — typically 75–150 mm thick — is cast around the existing column, with new longitudinal bars and ties. The surface of the old column is roughened and dowels are drilled in so the old and new concrete act together.

• Strengths: large increases in axial capacity, stiffness and ductility; uses familiar local materials and skills; generally the most economical per unit of strength gained.
• Limitations: enlarges the column, taking floor space; adds weight; needs formwork and curing time; new bars may need to pass through slabs to provide continuity.
• Best for: severely deficient columns, buildings where significant strength increase is required, and where small increases in column size are acceptable.

Steel jacketing

Steel angles are fixed at the column corners and connected with steel battens or plates, sometimes with grout between steel and concrete. The steel confines the concrete and can share load.

• Strengths: fast installation; minimal increase in size; no long curing period; immediate load sharing when properly detailed.
• Limitations: steel needs corrosion and fire protection; connections to beams and slabs require careful detailing; can be noisy and involve welding in occupied buildings.
• Best for: quick strengthening where space is limited and moderate strength gain is enough.

CFRP wrapping

Sheets of carbon fibre fabric are bonded around the column with epoxy resin. The fibres confine the concrete, increasing its axial strength and — especially — its ductility. Design is commonly carried out following ACI 440.2R guidance.

• Strengths: very light and thin, so column size barely changes; fast to apply; minimal disruption; excellent corrosion resistance; very effective at improving ductility and shear capacity.
• Limitations: higher material cost; confinement benefit is greatest for circular columns and reduced for rectangular ones with sharp corners; needs a sound substrate and careful surface preparation; requires fire protection where fire ratings apply.
• Best for: operating factories where downtime is costly, columns needing ductility and shear improvements, and situations where space is at a premium.

Quick comparison

	RC jacketing	Steel jacketing	CFRP
Axial strength gain	High	Moderate–high	Moderate
Ductility improvement	Good	Good	Excellent
Increase in size	Significant	Small	Negligible
Speed / disruption	Slowest	Fast	Fastest
Material cost	Lowest	Moderate	Highest
Corrosion concern	Low	Needs protection	Very low

It is rarely one method for the whole building

Most real projects combine techniques. Heavily overloaded ground-floor columns might receive RC jackets, while upper-floor columns needing only ductility improvement are wrapped in CFRP. Foundations may also need strengthening if column loads increase.

Workmanship is everything

All three methods depend on surface preparation, correct anchorage and quality control. Bond tests for CFRP, concrete strength tests for jackets and weld inspections for steel should be part of every specification.

Our retrofitting team designs strengthening schemes from the results of a Detailed Engineering Assessment, comparing options on cost, disruption and performance before work begins.