Effectiveness of strengthening pre-loaded RC beams with CFRP strips in conventional and accelerated strengthening procedures

Abstract

This paper analyses the results obtained from the testing of reinforced concrete beams additionally strengthened with composite materials pressed into the concrete cover using the near-surface-mounted reinforcement (NSMR) method. The testing program comprised two series of beams with cross-sectional dimensions of 0.12 x 0.30 x 3.30 m. The series differed in the amount of longitudinal steel reinforcement, 0.51% and 1.00%. Three beams were cast in each series. One beam was assigned as the control beam, while two other beams were strengthened with carbon fibre strips. A two-component thixotropic epoxy resin was used as a bonding agent. One of the two beams was cured for 7 days (to the product information document). The bonding process in the other beam was accelerated to last 1.5 hours by heating the strip up to 70°C. As the strengthening of "new" elements is not an accepted practice in engineering, the beams were pre-loaded. The load was maintained during the strengthening procedure and curing period (for 7 days and 1.5 hours) and then the beams were monotonically loaded to failure. The comparison of load capacity results for the CFRP strengthened and control beams revealed the effectiveness of the strengthening method. The paper also presents the strengthening technique in the NSMR application with the prototype heating device.