Experimental Study On Bond Behavior Between Alkali Activated Steel Slag-blast Furnace Slag Concrete And Steel Bars

With the acceleration of industrialized and urbanized level,the production speed of bulk solid waste is also rising by years.The stacking of steel slag and construction waste occupies a large number of land resources,resulting in serious ecological and environmental problems such as soil,water and air pollution.The concrete prepared by steel slag as cementitious material has excellent mechanical properties and durability,but the low activity and stability limit the large-scale application of steel slag.Recycled aggregate is one of the most effective ways of resource’ use of construction waste currently.However,due to the initial and secondary damage of recycled aggregate,its strength is low,and the surface layer is often accompanied by mortar,which leads to the weak interfacial transition zone of concrete and hinders the improvement of its resource utilization.Effective methods are adopted to solve the problems of preparing cementitious materials by steel slag and the defects of recycled aggregate.Using the two to prepare concrete can greatly improve the utilization efficiency of solid waste resources,curb environmental degradation and promote green and sustainable development.In recent years,a large number of researchers have found that steel slag can effectively solve the stability problem after sufficient physical grinding,and the use of alkaline activator can accelerate the hydration process of steel slag in water.Adding slag powder can produce synergistic effect with steel slag to promote the joint hydration of the two.At the same time,the application of steel slag in recycled concrete can improve the interface performance between aggregate and slurry in recycled concrete,and then increase the strength of concrete.Therefore,alkali activated steel slag-blast furnace slag concrete(AASBC)has a good application prospect.In this paper,the mechanical properties of 23 groups of specimens were tested,and the bond behavior between alkali activated steel slag-blast furnace slag natural aggregate concrete(AASB-NAC),alkali activated steel slag-blast furnace slag recycled aggregate concrete(AASB-RAC)and steel bars separately were studied.The failure mode and bond-slip curve of the specimens were theoretical and finite element analysis.The main conclusions are as follows:(1)Taking the substitution ratio of steel slag powder(r1),the substitution ratio of blast furnace slag powder(r2)and the substitution ratio of recycled aggregate(r3)as variables,the cube compressive strength(fcu),splitting tensile strength(fts),axial compressive strength(fc)and elastic modulus(Ec)of 23 groups of specimens were tested.With the increase of r1,fcu、fts、fc and Ec first increased and then decreased;with the increase of r2,mechanical properties showed a significant upward trend;recycled coarse aggregate has a negative effect on the mechanical properties of concrete,and the relationship between fts、fc、Ec and fcu was analyzed through the experimental data to establish the theoretical formula.(2)The bond behavior test of 16 groups of AASB-NAC-steel bar central pull-out specimens was carried out.The design variables included r1,r2,the diameter of rebar(d)and the bond length(la).The Experimental phenomena and data were analyzed.r1=10%、r2=30～40%can be used as reference substitution rates.With the increase of d,τu decreased linearly;τu was linearly related to la/d,and the relationship formula was fitted.(3)Taking r1,r2,r3,d and la as variables,19 groups of AASB-RAC-steel bar central pull-out specimens were tested to explore the influence of different variables on the bond behavior which is similar to AASB-NAC-steel bar specimens.The best substitution ratio of steel slag powder is 10%;the increase of r2 is obviously beneficial to the growth of bond behavior;with the increase of r3,τu and bond stiffness gradually decreased,while τu/fcu increased;with the increase of d and la,τu increased first and then decreased.(4)The classical bond-slip constitutive models and the prediction formulas of peak bond strength and peak slip at home were summarized.After comparison,the classical model with high fitting degree with the experimental value was selected as the prototype.Considering the five influencing factors mentioned above,calculation formulas of peak bond strength and peak slip suitable for bond-slip between AASB-NAC,AASB-RAC and steel bars were proposed respectively.The error between calculated value and test value is very small.(5)Based on ABAQUS software,the interaction between concrete and steel bars is realized by creating a nonlinear spring element.The bond-slip constitutive model proposed above is applied to finite element analysis to simulate and analyze the bond behavior of 33 AASBC-steel bars central pull-out specimens.Comparing the simulated data with the experimental data,the results show that the fitting is reliable,and the average relative error of τuis only about 3%.