Experimental research on mechanical properties of the composite beams strengthened with carbon fiber sheets using alkali-activated slag cementitious materials

At present, organic epoxy adhesives are usually used when strengthening concrete structures with carbon fiber sheets, but the softening points of organic adhesives are too low, most of which lie between 60°C and 80°C. Because temperatures are high in summer, the surface temperatures of concrete bridge structures are often higher than the softening points of organic adhesives in some areas and the concrete structures strengthened with carbon fiber sheets using organic epoxy adhesives are difficult to meet heat resisting requirements. Therefore, the alkali-activated slag cementitious materials (AASCM) with the strength at 600°C no lower than that at the normal atmospheric temperature were selected to paste carbon fiber sheets to strengthen 4 beams over the state of ultimate bearing capacity, and the mechanical properties of these 4 bonded prestressed truss concrete composite beams encased with circular steel tubes were studied by experiments. The test values of the flexural carrying capacity of these beams and the mid-span P-f curves presenting the two-fold line were obtained. On the basis of the test results, the calculation method of the flexural carrying capacity of the mentioned type of stiffened beams was presented in consideration of the influence of loading onto the original beams. The calculation formula of stiffness was set up, which is solved in good agreement with the test results.