Strengthening of Flexural Member by Using Post-Tensioning CFRP Strip System

Abstract

The objective of this research was to study the flexural behavior of reinforced concrete slab strengthened by using carbon fiber reinforced polymer plate (CFRP). Slab samples consisted of 3 pieces including the control sample which was strengthened by CFRP at the bottom of slab without post-tensioning, while the other two samples were strengthened by posttensioning with CFRP at 20% and 40% of the tensile strength of CFRP. All samples were tested under four-points bending tests. LVDTs were installed at the bottom of slab to measure the deflection, and strain gauges were installed to measure the strain at the surface of concrete and CFRP. Experimental results showed that control sample without post-tensioning exhibited the lowest performance in bending strength. The delamination between CRFRP and concrete surface was occurred, which led to the sudden drop of applied load. However, samples strengthened by post-tensioning CFRP at 20% and 40% of its tensile strength would exhibit the flexural strength at first cracking of concrete with 76% and 104% higher than that of control samples, respectively. Moreover, it was observed from initial jacking force that CFRP plate with 20% and 40% prestressing had the prestress loss at 22 hours of 4.41% and 4.35%, respectively. This result might be from the adjustment of end clamps, the relaxation of epoxy and CFRP plate as well as creep in concrete. Finally, very good agreement was observed from the comparative results between the predictions using mechanical models and the testing results.