Experimental Study Of Old And New Concrete Interface Mechanism Of Paste

The issue of bond between new and old concrete exists widely in the work of repair andstrengthening engineering of new or existing concrete structure. With the application of newmaterial and new technique to the practice of structure repair by enlarging section method, thetechnique of embedded steel bar in the interface of new and old concrete is used more andmore popularly. In particular,in the reconstruction or reinforcement of unsafe old bridge,technique of embedded steel bar is applied widely in order to make new and old concretewhole and bear the load together perfectly. However, research either domestic or overseasabout bond property, force transfer mechanism and bond collapse mechanism of the interfacewith embedded steel bars is reported lightly. When the embedded depth of the bar is small forthe limit of the original structure dimension, the study about the computation of the bondshear stress and the shear design value is particularly seldom performed.Firstly,consdering different influence factors,the full-range shear experiment of12groupswith36Z-shape specimens is executed. The bond shear capacity of interface is studied aswell as the degree of influence such as interface roughness, agent, strength of new and oldconcrete, the depth of embedded bar.Secondly, Five Zone-Three Layer bond model of new and old concrete is proposed basedon the interface shear test, which could apply to analysis of bond mechanism either withembedded bar or without.Thirdly, the interface ultimate shear capacity of new and old concrete is studied based onthe model test results and the interface failure mechanism research result. The practicalformula of interface shear strength is proposed with the roughness between1.8mm and3.0mm, which is consistent with model test results.Fourthly, for the strengthening structural member by enlarging section method, theinterface shear design value under the external load is studied according to the limit state-method.