| Cement mortar attached to the surface of recycled aggregate, which weaken the interface between fresh cement mortar and recycled aggregate. There are pores and cracks in interfacial transition zone, resulting poor durability, such as:impermeability, frost resistance, carbonation, resistance to chloride ion resistance. Preliminary tests show that, filling right amount of fly ash into recycled aggregate interface enhanced interface dense and cohesive effect and improved the durability of recycled concrete. As the same amount of fly ash replace cement, the strength index of modified recycled concrete changes. Damage morphology, carrying capacity, hysteretic behavior, ductility and energy dissipation capacity need further study.The tests were carried out for two modified recycled aggregate concrete interior joints with the recycled aggregate replacement ratio of 100% and the same amount of fly ash to replace 15%. Adding fly ash to recycled concrete joint, to investigate seismic performance, such as failure mechanism, hysteretic behavior, stiffness degradation, energy consumption performance and ductile character. Results show that the mechanical and failure process of modified recycled concrete frame joints go through four stages:the initial cracking, the fully cracking, the ultimate and the failure stage. The shear failure happens in the joint core area, which indicates the obvious brittle damage of recycled concrete. The beam longitudinal reinforcement in proper amount can fully yield before shear failure in the joint, whose hysteretic curve is plumper. The reasonable axial pressure changes direction of the principal tensile stress and delay joint launching cracks. The RAC specimens show a fine ductility and energy consumption performance, which can satisfy the requirements of seismic performance and be applied in constructional engineering.Based on the experimental research, considering constitutive relation and CDP model of recycled concrete, simulate specimens ZJ-1 and ZJ-2 by finite element analysis software ABAQUS. Simulated and experimental values of the representative load trends similarly. The constitutive model of recycled concrete has no proven stress-strain relationship, with more brittle than ordinary concrete, leading to the simulation skeleton curve decline gently at the destruction stage. The software can not effectively simulate cracks in specimens, resulting in no slip and pinching phenomenon in hysteresis curve. |
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