混杂钢纤维UHPC拉伸韧性及其评价方法OA北大核心CSTPCD

To investigate the strengthening and toughening effects of hybrid steel fibers on the tensile properties of ultra-high performance concrete(UHPC),eight groups of UHPC dog-bone tensile specimens were designed and manufactured considering the type,volume content and hybrid mode of steel fibers.The tensile damage process,stress-strain curves,tensile characteristic parameters and fracture energy of hybrid steel fiber reinforced UHPC were analyzed by uniaxial tensile tests.Additionally,a quantitative method for determining the initial tensile cracking point of UHPC was proposed based on an analysis of its tensile properties,and optimized indicators for evaluating the tensile toughness of UHPC were further established.The results indicate that hybrid steel fiber reinforced UHPC exhibits the tensile failure modes of multi-crack developing and oblique fracture,and its tensile stress-strain curves display clear strain hardening characteristics.A hybrid of short-straight and hooked-end steel fibers can significantly enhance the tensile stress level and strain-hardening characteristics of UHPC,whereas the interaction of long-straight and hooked-end steel fibers reduces the tensile properties.The highest level of tensile toughness in UHPC is achieved when a blend of 1.0％ hooked-end and 1.0％ short-straight steel fibers is used.This is due to the remarkable pre-peak toughening effect of the hooked-end steel fiber,resulting in excellent pre-peak toughness,which is 18.89％-32.56％ higher than that of UHPC with 2.0％ short-straight steel fiber.Long-straight steel fibers provide a stable and better toughening effect during the entire deformation stage of UHPC.Increasing the content of long-straight fibers can improve the tensile toughness of UHPC by approximately 30％.However,the blending of hooked-end fibers weakens the toughening effect of long-straight fibers due to fiber agglomeration and matrix damage,reducing the tensile toughness of UHPC by more than 10％.Finally,a classification scheme of UHPC tensile properties is proposed considering the fiber toughening and toughness level according to the existing standards and the evaluation results of the UHPC tensile toughness.