ITEMS FOR IMPROVING BOND- SLIP BEHAVIOR BETWEEN CFRP SHEETS / CEMENT BASE BONDING AGENT AND BONDING AGENT / CONCRETE INTERFACE

Abstract

This paper concerned with the replacement of Epoxy with cement base matrixes as bonding agents for CFRP sheets. Many items were investigated to improve the bond strength and decrease slippage in strengthening system. More than 25 plain concrete prisms with low compressive strength (20 N/mm2) were used to act as the original weak concrete members. Two main groups of cement base bonding agents were investigated in this research (Portland cement and Grout matrix’s). Three main items were looked for. Item 1: mixture content; it was represented in (cement content, using silica fumes & using short metallic fibers). Item 2: CFRP sheet modification; represented in either: a) making holes in CFRP sheets -hence the cross section area of the CFRP sheets were kept the same as all other specimens- or b) impregnate the CFRP sheets in latex-base adhesive material just before using). Item 3: the strengthening technique; which was represented by both the bonding agent layer thickness & the Curing pressure; (it is a pressure done with a specific value just after applying the strengthening on the concrete prism along 24 hours). Single shear test (pull off test) was carried out to evaluate each parameter effect and the results showed that the cement-base matrixes were a very good alternative for epoxy as a bonding agent. Applying Curing pressure; almost double the bond strength and prevent the failure from occurrence in the surface interval between bonding agent / concrete interface, using latex and making holes in the CFRP sheet enhance the penetration of the bonding agent within CFRP sheet. Portland cement gives higher results than grout. Using silica fumes and even increasing the cement content; both have a negative effect on bond strength.