Experimental investigation of the bond strength between GFRP and steel bars and soil-cement

Steel rebars have been used in soil-cement mixtures to increase their flexural capacity in shoring projects. However, the interaction of the reinforcing rebars and soil-cement and their bond strength has been rarely considered. A practical formula for predicting the rebar-soil-cement bond strength considering the strength characteristics of both has not been developed. The current study performed 60 pullout tests of rebars embedded in soil-cement and analyzed the pullout mechanisms as well as the effective parameters on the pullout force. The test parameters were rebar type, size and embedded length. Smooth, ribbed steel and GFRP rebars in diameters of 8 and 12 mm were tested. A pullout frame was added to a universal testing machine and the load-displacement behavior of the rebars and induced cracking were analyzed. The results showed that the prevailing failure mechanism during pullout of the rebars from the soil-cement was slippage and not cone/splitting failure. During slippage, some the soil-cement adhered to the rebar between its ribs because of the low compressive strength of the soil-cement. With a 50 % increase in rebar diameter, the bond strength decreased about 18 % and 30 % for the ribbed and GFRP rebars, respectively. This indicates the importance of the rebar diameter on the bond strength. The steel rebars exhibited greater bond strength with soil-cement in comparison with the GFRP rebars. A new equation has been proposed to calculate the reinforcement-soil-cement bond strength by applying a reduction factor to the ACI equation.