Study On Bond-slip Behavior Between Retrofitted Layer With High Strength Steel Wire And Polymer Mortar And RC Structures

In recent years,with the transition of Chinese construction industry,it change from the first stage with massive new buildings to the second stage with repair and renovation builidings.Consider this situation,it is critical to choose a better reinforcement for repair,reinforcing or renovation the existing reinforced concrete structure.High strength steel wire and Polymer modified mortar(Polymer mortar for short in the following paper)reinforcement technology has the advantages of making full use of all the high-strength steel wire's excellent characteristics;meanwhile,it can be in coordination with the features of the polymer mortar,which are high dense,fire resistance,high temperature resistance,no pollution,good compatibility,coordination and mutual penetration with concrete.And then this reinforced techinique has gradually brought about widely attention all over the world.The quality of the bonding surface between the reinforcing layer and the concrete is very important to the improvement of the whole structure performance in this reinforcement technique.Occlusal interface between steel wire and polymer mortar,bonding interface between polymer mortar layer and the concrete are two essential interfaces in the reinforcement layer,the study on the slip properties of the interfaces has important practical value on the reinforcing performance analysis and engineering application.In this paper,three tests aiming at the bond behavior of the reinforced layer were studied.The main research contents and results are as follows:1.27 pull-out specimens were tested to research the bond properties between steel wire and polymer mortar;and the effect of embedded length,the diameter of high strength steel wire,polymer mortar compressive strength,and loading speed on bond behavior were investigated.The results showed that:(1)Due to the low strength of the polymer mortar,all failure patters were steel wires pulled out,while there was not obvious damage on the mortar block.The bonding properties of high strength steel wire and polymer mortar was good,and the interface had constant bond strength when there was obvious slip.(2)The bond strength of the interface mainly depended on the mortar strength,while the effect of embedded length and diameter on the bond strength was relatively small.High loading velocity also had positive effect on the strength increasing,while the bearing duration decreasing rapidly,which is detrimental to structural safety.(3)The phase of the bond slip can be divided into three stages: slip period,descending period and attenuation period.2.Based on the double shear tests of 33 test specimens,in this paper,by the method of discussing the influence parameters of shear strength,the bond performance between polymer mortar layer and original concrete were analyzed.The conclusions are:(1)The shear strength is mainly determined by the strength of mortar,the higher the mortar strength is,the greater the shear strength.The high loading rate had a significant effect on the shear strength increasing.(2)When the bond area approached to 150mm×100mm,variation of bond area no longer had effect on the bond shear strength.In the actual reinforcement design,the bond area is always wide enough,and the effect of the change of bond area on the shear strength can be neglected.(3)Because the shear strength of the binding interface is sensitive to variable loading rate,so under dynamic load,the amplified effect of the high loading rate on the internal force should be considered.3.Shear tests of 30 specimens with polymer mortar thin layers were carried out,considering the parameters such as bond area,the thickness of polymer mortar,mortar strength and whether the interface is chiseled or not.Based on the tests,the failure patterns,load-slip curves and strain distribution rules were analyzed.The results showed that:(1)Thin polymer mortar layers most appearred to be fell off entirely,different degree of transverse cracks can be seen on some components;and a few amount of specimens occurred local damage on the side of loading end.The phase of the load-slip curve can be summarized into 3 stages: slip adjustment period,slip period and damage period.(2)The increase of bond area and the thickness of polymer mortar,the improvement of mortar strength was all beneficial to the growth of the interfacial shear failure load.The improvement of mortar strength was the most favorable to enhance the interfacial failure load.(3)The mortar strain increased with the growth of lateral force,when the force approached to the limit range of binding interface capacity,the speed of mortar strain increasing on the loading end slowed down and reached to short-term moderate growth platform.Meanwhile,the mortar strain on the free end rose rapidly,and the specimen failed until the maximum strain.After that all the strain decreased rapidly.(4)The maximum and distribution of the mortar strain were obviously affected by the bond area,the thickness of polymer mortar,the mortar strength and whether the interface is chiseled or not.When the bond area was 350mm×300mm,the maximum strain on the mortar was the biggest,which means that the polymer mortar assumed more shear load by material deformation,and this was beneficial to the safety of the interface.When the thickness of the mortar layer was larger,the strain tended to be evenly distributed.Choosing high strength mortar could show positive effect on the maximum strain decreasing and uniform strain distribution.After the interface was chiseled,the maximum strain was relatively large.