| Engineered Cementitious Composites(ECC)is a new type of fiber reinforced cement matrix composites,which is systematically designed based on the basic principles of fracture mechanics and micromechanics and can be used in the field of Civil Engineering.The ECC can show obvious characteristics of tensile strain-hardening properties and multi-cracks when bearing the tensile load.In order to make sure that the ECC can bring into play its superior performance better in the application of engineering,it is necessary to own reliable bonding and anchoring bahaviours between the ECC and steel rebars.Therefore,it is particularly important to carry out relevant studies on the bond behaviours between the ECC and steel rebars.Nowadays most of the existing studies on the bond behaviours between the ECC and steel rebars focus on the single-fiber reinforced cement matrix composites,but the fact is that when adding two different fibers into the ECC,for the matrix properties there will be a great improve at different levels.Therefore,in this paper,high performance steel-polyethylene hybrid fiber reinforced and high ductility cement matrix composites(HECC)was made by steel fiber and polyethylene(PE)fiber.By sloting the steel rebars and pasting the strain gauge,the bond and anchorage behaviour of HECC with steel rebars was systematically studied by the pull-out test.The main work and research results in this paper are as follows:(1)Considering four factors:fiber type,matrix strength,steel rebars’ diameter and load condition,a total of twenty groups of sixty specimens were designed and fabricated,then the bond-slip relation curves under monotonic load and the bond-slip hysteretic relation curves under cyclic load and the skeleton curve were obtained.The study results show that the bond-slip curve under monotonic load can be divided into four stages:micro-slip stage,descent stage and residual stage.The bond-slip hysteretic curve under cyclic load can be divided into six stages:micro-slip stage,slip and initial crack development stage,multi-cracks steady stage,descent stage,cracks’ reclosure stage and friction stage,and then the failure mechanism of each stage was revealed.(2)Compared with normal concrete,PE fiber and steel fiber specimens,the ultimate bond stress of HECC under monotonic load is increased respectively by27.83%,24.09% and 37.83%.The ultimate bond stress of HECC under cyclic load is also greatly increased.The number of cracks on the surface of specimens decreases greatly and the specimens remains intact.The hysteretic loops of HECC are plump and the pinching phenomenon is weaken,HECC owns excellent energy dissipation performance.The increase of matrix strength is beneficial to restrain the crack development and improve the bond behaviours to a certain extent.When the diameter of steel rebars incresases from 20 mm to 25 mm,32mm and 36 mm,the ultimate bond stress under monotonic and cyclic load has a downward trend.Compared with the monotonic load condition,cyclic load weakens the ultimate bond stress of HECC to a certain degree.(3)Based on the characteristics of the bond-slip curve between HECC and steel rebars,the existing bond-slip constitutive model is modified.And also based on the distribution law of the bond stress along the bond length,the position function of the bond stress was fitted.Finally,combined with the modified average bond stress-slip constitutive relation and position function,a more refined bond-slip constitutive model considering the effect of anchorage position was proposed. |
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