Frequently Asked Questions

How is SikaWrap CFRP applied to a concrete beam soffit and what surface preparation is required before application?

SikaWrap CFRP application to a concrete beam soffit involves five sequential steps. Step 1 — Substrate preparation: the beam soffit concrete must be prepared to minimum ICRI CSP 3 to 4 roughness — typically achieved by grit blasting or needle gun preparation to remove all laitance, loose aggregate, paint, and contaminants and expose sound concrete aggregate. Any concrete surface defects (honeycombing, voids, cracks) must be repaired flush with SikaTop 122 Plus or Sikadur 31 CF Normal before the CFRP strengthening. The concrete must be dry (below 4 per cent surface moisture). Step 2 — Primer coat: apply Sikadur 330 Component A+B mixed at the specified ratio by brush or short-pile roller to the prepared beam soffit surface; allow primer to become tacky (approximately 1 to 4 hours at 25 degrees C). Step 3 — CFRP fabric cutting and saturation: cut the SikaWrap Hex 230 C fabric to the required dimensions (length and width per the structural design); mix Sikadur 330 and apply a layer to the prepared surface, then lay the fabric onto the epoxy and apply a further Sikadur 330 coat to fully saturate the fabric — the fibres must be completely wetted out with no dry fibre visible. Step 4 — Application: press the saturated fabric firmly onto the primed beam soffit, working from one end to the other, using a laminating roller to compact the fabric and remove air bubbles. For multiple layers, apply the next layer of fabric while the previous layer is still tacky. Step 5 — Final coat: apply a final Sikadur 330 coat over the last fabric layer to seal and protect the laminate surface.

What is the structural capacity increase achievable with one layer of SikaWrap Hex 230 C on the soffit of a 300 mm x 600 mm RC beam spanning 6 metres?

The structural capacity increase from one layer of SikaWrap Hex 230 C on a beam soffit depends on the existing beam design and steel reinforcement — a structural engineer must perform the specific calculation per ACI 440.2R or IS 15988 (Guidelines for Seismic Evaluation and Strengthening of RC Buildings, which references FRP). An indicative order-of-magnitude estimate for a 300 mm x 600 mm beam spanning 6 metres with 3 x 20 mm diameter tension bars (942 mm2 steel) is: one layer of 300 mm wide SikaWrap Hex 230 C at 0.131 mm per layer over 300 mm width provides a CFRP area of 0.131 x 300 = 39.3 mm2. At the design tensile strength of CFRP (typically taken at 55 to 60 per cent of the fibre tensile strength as design strength per ACI 440.2R, approximately 1800 to 2100 MPa) and the tensile modulus of 230 GPa, the additional moment capacity from one CFRP layer on this beam is typically 15 to 25 per cent increase in flexural moment capacity — a significant improvement for a beam loaded to its limit state. For shear strengthening using SikaWrap in U-wrap or full-wrap configuration, the shear capacity increase per layer is typically 20 to 40 per cent depending on beam geometry and configuration. All CFRP strengthening designs must be carried out by a qualified structural engineer with FRP design experience — Space Arc Engineering can connect you with Sika technical engineers who provide design assistance for SikaWrap strengthening projects in Delhi NCR.

Is SikaWrap CFRP strengthening permanent and can it withstand the harsh Delhi NCR climate of high summer temperatures and monsoon humidity?

SikaWrap CFRP laminates bonded with Sikadur 330 epoxy are designed as permanent structural strengthening elements with a design service life matching the remaining service life of the host structure — typically 25 to 50 years. The durability of the CFRP laminate system under the Delhi NCR climate depends primarily on three factors: epoxy glass transition temperature (Tg), UV and heat resistance, and bond durability. Sikadur 330 has a glass transition temperature of approximately 62 degrees C at full cure — in direct solar radiation on a south-facing concrete face in peak Delhi summer, the surface temperature of an exposed CFRP laminate can reach 60 to 70 degrees C. At or above the Tg, the epoxy begins to soften and the mechanical properties are reduced. For CFRP strengthening in exposed outdoor applications (bridge beam soffits, exposed column wraps, exterior facades), apply a UV-resistant epoxy top coat or Sikagard coating over the cured laminate to reflect solar radiation and keep the surface temperature below the Tg. For internal applications (beam soffits in car parks, structural strengthening inside buildings), the epoxy remains well below Tg and no additional heat protection is required. For long-term durability in the monsoon humidity environment, the bond between the CFRP laminate and properly prepared concrete is not significantly affected by periodic wetting and drying — the Sikadur 330 epoxy is waterproof and non-hydrolytic. The primary long-term durability concern is delamination due to impact damage, poor substrate preparation, or very high sustained moisture at the bond interface (submerged applications) — for submerged or permanently wet structural elements, consult Sika technical regarding appropriate primer and protection specification.