Flexural behavior of composite beams after the ultimate limit state externally strengthened with CFRP sheets bonded with high-temperature resistant matrix

In this paper the alkali-activated slag cementitious materials (AASCM) which strength at 600°C is larger than that of AASCM at room temperature, were prepared to paste CFRP sheets to strengthen four simply supported unbonded prestressed composite beams encased circular steel tube truss after ultimate limit state. Test on flexural behavior of these four beams was performed. Moreover, normal section load-bearing capacity of these beams and the curve load-deflection at mid-span were obtained. Experimental results show that it is feasible to strengthen concrete members with CFRP sheets bonded with AASCM. Based on the experimental results and theoretical study, computational method of stiffness is proposed for calculating bending rigidity and normal section load-bearing capacity of concrete simply supported beams strengthened with CFRP sheets bonded with AASCM. Formula of bending rigidity calculation was founded which results are in good agreement with testing data.