136 / 2022-04-28 22:57:09

Flexural behaviors of LC3-recycled concrete beams with CFRP reinforcement and optimization procedure of hybrid reinforcement

LC3 concrete; recycled concrete; CFRP reinforcement; hybrid reinforcement, optimization

LC³ concrete is a new type of environmentally friendly concrete that uses clinker calcined clay and limestone to partially replace ordinary cement clinker used as supplementary cementitious materials (SCMs). Because its raw material, kaolinite clay, only needs to be calcined to about 700°C-850°C and limestone only needs to be ground into powder, it can significantly reduce energy consumption and CO² emissions compared with conventional silicate cement production. In this paper, the effects of different LC³ substitution rates, different reinforcement forms (steel reinforcement, CFRP reinforcement, and mixed reinforcement), and different reinforcement rates on the cracking moment, damage morphology, flexural ultimate bearing capacity, and deflection crack development of LC³-recycled concrete beams were investigated by conducting flexural performance tests on 10 LC³-recycled concrete beams.



It is shown that the LC³ substitution rate has a limited effect on the cracking moment, damage model, flexural load carrying capacity, and deflection of LC³-recycled concrete beams; the modulus of elasticity of LC³-recycled concrete is small compared with that of ordinary concrete, resulting in large deflection of LC³-recycled concrete beams under the same load; the predicted ultimate flexural capacity of reinforced beams according to ACI318, GB50010 and other codes is different from that of the test. The ultimate flexural bearing capacities predicted according to ACI318, GB10 and other codes are basically consistent with the test.  But the ultimate flexural bearing capacities of CFRP beams are slightly lower than the experimental ultimate flexural bearing capacity. And for the mixed reinforced beams, based on simplified materials’ constitutive models, plane-section assumption, equilibrium of force and moment, the flexural bearing capacity calculation model for different damage cases is derived, which is almost consistent with the test.



From the load displacements curves, it can be observed that CFRP beams generate large displacements before damage due to their lower modulus of elasticity than steel reinforcement. The stiffness of the hybrid reinforced beam is significantly improved by the arrangement of an appropriate amount of steel reinforcement, and consequently the deflection and crack development at the time of damage are reduced, but the addition of too much steel reinforcement may also limit the performance of the CFRP bars. In this paper, based on the above-mentioned flexural load capacity calculation model, the yield curvature (φy）and the curvature at peak load (φu) of the reinforcement are solved and the ductility coefficient μ=φy/φu is calculated, and an optimized design procedure applicable to the hybrid reinforced beam is proposed.