Investigation of concrete bond using steel, threaded stainless steel and FRP rebars

Abstract

The problem of steel corrosion in concrete structures subjected to corrosive environments has encouraged the use of alternative materials such as stainless steel and fibre reinforced polymers to be used as reinforcement in concrete. The bond achieved between concrete and reinforcement is very important in order for the two materials to act compositely and provide adequate transfer of forces in a member. The bond behaviour depends on the properties of the reinforcement used and mostly on the surface texture of the reinforcing bar. This dissertation investigates the bond behaviour of 4 different types of reinforcing bars of 10mm diameter embedded in normal strength concrete. The reinforcing bars used in this investigation consisted of ribbed steel, threaded stainless steel and, glass and carbon fibre reinforced polymer bars (GFRP, CFRP). The bars were embedded in concretes of target compressive strengths 20, 30 and 40MPa. A total of 36 cube specimens were cast and the bond strength of each bar was recorded via pull-out test after 28 days. The specimens failed in a pull-out mode because of the diameter of the bars and adequate confinement provided by the surrounding concrete. The investigation resulted in an increase in bond strength as the concrete compressive strength increased. The change in compressive strength of concrete did not affect the bond failure of the bars except those made of GFRP. The investigation concluded that the threaded stainless steel obtained the highest bond strength in all the concrete grades. The GFRP also performed well, obtaining bond values comparable to those obtained by the steel bars.