Experimental Study On The Bond Performance Between Resin Concrete And Glass Fiber-Reinforced Polymer Bar Under Freeze-Thaw Cycle

At present,the traditional reinforced concrete is still the mainstream material in the building structure,but some of its shortcomings limit their use,for the building is often subjected to freeze-thaw cycle and corrosion environment,the use of traditional reinforced concrete materials often can not meet its use requirements.With the continuous improvement of the level of the construction industry,new building materials are also constantly bringing forth the new,GFRP bars and resin concrete are widely used for their excellent mechanical properties and durability.As a new material,whether they can work together as well as the traditional reinforced concrete structure needs further research and exploration.Therefore,based on the original ratio of resin concrete in the research group,the optimal resin content was determined by studying the influence of resin content（8%,10%,12%,14%,16%）on its mechanical properties.On this basis,the mechanical properties were improved by adding fly ash（0%,5%,10%,15%,20%）.SEM was used to analyze the microstructure of fly ash before and after incorporation,and the optimum fly ash content was determined according to the test results.Secondly,the ability of resin concrete to resist freezing-thawing damage was studied by freezing-thawing cycle test.Finally,the effects of freezing-thawing cycles（0,50,150,250）,bond lengths（2.5d,5d,7.5d）and diameters of GFRP bars（8mm,12mm）on the bond properties of GFRP bars and resin concrete were studied by pull-out test.Based on the experimental results and the existing bond slip constitutive model between FRP bars and concrete,the bond slip constitutive model suitable for GFRP bars and resin concrete is established,and the calculation formula of basic anchorage length between GFRP bars and resin concrete is deduced.The conclusions are as follows:（1）With the increase of resin content,the compressive strength,flexural strength and splitting tensile strength of resin concrete increase first and then decrease.When the content of resin is 12%,the compressive strength and splitting tensile strength of resin concrete reach the peak value,and the strength increases 30.99% and 34.11% respectively compared with the content of 8%.The flexural strength reaches the peak when the resin content is 14%,and the strength increases by 11.34% compared with the content of 8%.Considering comprehensively,12% resin content is taken as the latest resin concrete ratio.（2）The strength of resin concrete with fly ash is improved compared with that without fly ash.With the increase of fly ash content,the compressive strength,flexion strength and splitting tensile strength of resin concrete show a trend of rising first and then decreasing.When the fly ash content is 10%,the compressive strength,flexural strength and splitting tensile strength reach the peak value,and the strength increases by 15.59%,11.09% and 10.53% respectively compared with that without fly ash.It is observed by SEM scanning electron microscope that "sea-island" structure is formed in resin concrete after adding fly ash,which makes the inner structure of resin concrete more perfect and its performance improved.Considering comprehensively,10% fly ash content is taken as the ratio of the latest resin concrete.（3）After 250 freezing-thawing cycles,it is found that the freezing-thawing cycle has little damage to the surface and mass loss of resin concrete,which can be ignored basically.The compressive,flexural and splitting tensile strength of resin concrete decreased by 9.77%,11.71%and 28.44%,respectively.It can be seen that the influence of freeze-thaw cycles on the splitting tensile strength of resin concrete is greater than that of compressive strength and flexural strength.After 250 freeze-thaw cycles,only 0.37% of resin concrete was lost.（4）The failure modes of GFRP bars and resin concrete pull-out specimens are mainly pull out failure and splitting failure.All GFRP bars and resin concrete specimens without freezing-thawing cycle are pull out failure,and some of them after freezing-thawing cycle appear splitting failure.The bond slip curve of GFRP bars and resin concrete can be divided into four sections: micro-slip section,slip section,descending section and residual section.The ultimate bond strength between GFRP bars and resin concrete decreases with the increase of the diameter of GFRP bars,bond length and the number of freeze-thaw cycles.（5）The bond slip constitutive model between GFRP bars and resin concrete was established and compared with the experimental curve.The results show that the bond slip curve between GFRP bars and resin concrete is in good agreement with the model curve.The calculation formula of basic anchorage length of GFRP bar and resin concrete is deduced,and the anchorage length calculated under freezing-thawing condition is compared with the anchorage length obtained in this paper.After verification,it is found that the basic anchorage length formula obtained in this paper can also meet the requirements of basic anchorage length under freezing-thawing cycle.