Design And Key Performance Of Jointless Link Slab For Bridge Deck Made By Ecological High Ductility Cementitious Composites

To solve the frequent damage problem of expansion joints in the medium and small span bridges,ecological high ductility cementitious composites(Eco-HDCC)can be used to cast the jointless link slab for bridge deck,which replaces the expansion joints.Eco-HDCC with a superior ultimate tensile strain and smaller crack width,has a promising engineering application.Basalt fiber reinforced polymber(BFRP)bar is a kind of reinforcing bar.For the comparison with other kinds of reinforcing bars,the tensile elastic modulus of BFRP bar is much closer to that of Eco-HDCC,and a consistent deformation occurs between BFRP bar and Eco-HDCC,which can improve the bearing capacity of structure.BFRP bar can be set in the bridge deck link slab.In order to obtain the design method of jointless link slab for bridge deck made by EcoHDCC,the properties of Eco-HDCC material,BFRP bar reinforced Eco-HDCC and bridge deck link slab structure are investigated.The main content is shown as follows.(1)For the curing age ranging from 28 d to 90 d,with the increase of curing age,the compressive strength,compressive elastic modulus,peak compressive strain,ultimate tensile strength and tensile elastic modulus of Eco-HDCC show an increasing trend,while the ultimate tensile strain decreases.The reaction degree of fly ash and non-evaporable water content increase as the curing age increases.In the design of structure,the compressive stress-strain relationship curve of Eco-HDCC after curing age of 28 d and the tensile stress-strain relationship curve of Eco-HDCC after curing age of 90 d can be used.(2)For the interactive cycles of freeze-thaw and carbonation ranging from 0 to 15,as the interactive cycles increase,the ultimate tensile strength of Eco-HDCC shows an increasing trend at first,and then the value decreases.The ultimate tensile strain,tensile energy,flexural strength,peak deflection and flexural toughness of Eco-HDCC decrease as the interactive cycle increases.Interactive cycle has little effect on the shear strength and peak shear strain of Eco-HDCC.Besides,for the single carbonation cycle ranging from 0 to 15,with the increase of carbonation cycle,the ultimate tensile strength of Eco-HDCC increases,while the ultimate tensile strain and tensile energy decrease.Compared with the tensile property of Eco-HDCC exposed to curing age of90 d and single carbonation cycles of 15,the decrease degrees of ultimate tensile strength and ultimate tensile strain of Eco-HDCC after interactive cycles of 15 are larger.Consider the safety of structure design,the tensile stress-strain relationship of EcoHDCC after 15 interactive cycles is selected,and the designed ultimate tensile strain is1.00%.(3)The bond behaviors of BFRP bar embedded in Eco-HDCC are examined using beam test and direct pull-out test.For the diameter of BFRP bar ranging from 8mm to16 mm and embedment length ranging from 3D to 10D(D means the diameter),as the diameter or embedment length of BFRP bar increases,the peak pull-out force and peak slip of specimen increase,while the peak bond stress decrease.For the cover thickness of BFRP bar ranging from 15 mm to 45 mm,as the cover thickness increases,the peak pull-out force,peak bond stress and peak slip of specimen increase.In addition,the bond stress-slip relationship model between BFRP bar and Eco-HDCC is advised,and the embedment length of BFRP bar is computed.(4)For the diameter of BFRP bar ranging from 8mm to 14 mm,as the diameter increases,the kinking crack angle of BFRP bar reinforced Eco-HDCC specimen decreases.The first cracking load,peak load,peak CMOD,peak deflection and fracture energy of specimen show an increasing trend as the diameter increases.For the cover thickness of BFRP bar ranging from 8mm to 14 mm,when the cover thickness is larger,specimen has a larger kinking crack angle,while the first cracking load,peak load,peak CMOD,peak deflection and fracture energy of specimen are lower.Based on the fracture property test results,BFRP bar with diameters of 10mm?14mm and cover thickness of 25 mm are advised.(5)When the BFRP bar diameter or cover thickness of BFRP bar reinforced EcoHDCC beam is lower,the maximum crack width of tensile deformation at the lateral surface corresponding to gravity center of BFRP bar can be reduced.Besides,BFRP bar diameter,cover thickness and loading type have little effects on the first cracking load.For the diameter of BFRP bar ranging from 8mm to 16 mm,as the diameter increases,peak load of beam increases,and the peak deflection increases at first,then the value decreases.For the cover thickness of BFRP bar ranging from 25 mm to 35 mm,as the cover thickness increases,both the peak load and peak deflection of beam decrease.Peak load and peak deflection of beam are not affected by loading type.In addition,strain at different section height of beam shows a linear trend.The BFRP bar strain and Eco-HDCC strain at the same section height are coordinated.Morever,the ultimate limit states design method of flexural member is proposed,and the design method is verified by comparing the method with the test results.The maximum crack width calculation equation of beam is also advised.Finally,the flexural design method of bridge deck link slab made by BFRP bar reinforced Eco-HDCC is suggested.(6)Based on the small and medium two-span simply supported beam,the reinforcing ratio of BFRP bar at the driving direction is computed according to the flexural design method of BFRP bar reinforced Eco-HDCC,and eight kinds of reinforcing programs are obtained initially.Besides,the mechanical property of EcoHDCC and BFRP bar in bridge deck link slab under the coupled actions of temperature and load are analyzed by Abaqus finite element software.The maximum stress and strain of Eco-HDCC and BFRP bar are roughly same at the eight kinds of programs,and the maximum values are in the range of materials property.The maximum deflection of bridge deck link slab meets the maximum limit ratio of deflection to span requirement.Finally,based on the various aspects,the BFRP bar diameters at driving direction are suggested as 10 mm,12mm and 14 m,and the transverse BFRP bar diameters recommended as 10 mm.