Preparation And Properties Of Steel-UHMWPE Hybrid Fiber Reinforced Ultra High Performance Concrete

Ultra High Molecular Weight Polyethylene Fiber(UHMWPEF)has excellent mechanical properties,High impact resistance,good corrosion resistance,acid and alkali resistance,etc.The hybrid fiber composed of UHMWPE and steel fiber has excellent mechanical properties in cement-based composites.However,due to the defects of UHMWPE fiber,such as smooth surface,no active functional group,and poor adhesion between UHMWPE fiber and concrete matrix,its application is limited.Therefore,it is necessary to modify the surface of UHMWPE fiber.In this paper,the surface of UHMWPE fiber was modified by the method of surface oxidation,and the modified UHMWPE fiber and the fixed volume of steel fiber hybrid fiber were mixed into the cement matrix composite material,and three specimens of different forms of steel-UHMWPE hybrid fiber concrete were prepared after 28 days of standard curing.The static mechanical properties of steel-UHMWPE hybrid fiber concrete were preliminarily analyzed and summarized through the load-deflection and stress-strain curves measured by axial tensile test,axial compression test and four-point bending test.From the macroscopic failure form and microscopic mechanism of steel-UHMWPE hybrid fiber concrete,the influence of UHMWPE fiber on the concrete matrix under macro and microscopic conditions was preliminarily explored,and the similarities and differences of failure forms of concrete under the conditions of different UHMWPE fiber content,different UHMWPE fiber length,and single and mixed mixing of UHMWPE fiber were explored.The influence of UHMWPE fiber on concrete matrix was further analyzed.Specific results are as follows:(1)Surface modification and proportion design of UHMWPE fiberAfter potassium permangate-treated UHMWPE fiber,the surface of the fiber containing oxygen groups(--OH,--C=O and--C--O groups)increased,the melting point and crystallinity increased slightly,and cracks were formed.Due to the etching of potassium permanganate,the molecular chain of the fiber surface degrades,resulting in many cracks.These cracks will affect the adhesion of concrete matrix and provide more favorable conditions for the interaction between fiber and matrix.Using multiple composite material system theory and maximum density theory as guidance,cement as cementing material,quartz sand as aggregate,design steel-UHMWPE hybrid fiber cement matrix composite with water-cement ratio of 0.21.(2)Static mechanical propertiesThe tensile strength of steel-UHMWPE hybrid fiber reinforced concrete is 7.55 MPa,which is110% higher than that of single steel fiber reinforced concrete.The axial tensile strengths of the groups SFM01,SFM02,SFM03,SFM04,and SFM05 with a volume content of 0.1%～0.5%UHMWPE are 6.72 MPa,7.04 MPa,7.36 MPa,7.30 MPa,and 7.55 MPa,respectively,and the difference in the axial strength is the largest.Less than 1MPa,according to the increase of 0.1%of fiber volume content,the increase is 5%,4%,-0.8%,3% respectively.The corresponding axial tensile strengths of steel-UHMWPE hybrid fiber reinforced concrete with UHMWPE fiber lengths of 6mm,12 mm,and 18 mm are 7.48 MPa,7.55 MPa,and 7.39 MPa,respectively.The flexural strength of single-mixed steel fiber reinforced concrete is 15.05 MPa,followed by single-mixed UHMWPE fiber reinforced concrete with a flexural strength of 18.58 MPa,and the highest is steel-UHMWPE hybrid fiber reinforced concrete with a flexural strength of 14.73 MPa.The corresponding flexural strengths of the groups SFM01,SFM02,SFM03,SFM04,and SFM05 with a volume content of 0.1%～0.5% are 24.19 MPa,30.02 MPa,25.34 MPa,26.06 MPa,and 25.34 MPa,respectively.5MPa.The corresponding flexural strengths of steel-UHMWPE hybrid fiber reinforced concrete with UHMWPE fiber lengths of 6 mm,12 mm and 18 mm are28.30 MPa,25.34 MPa and 32.76 MPa,respectively.The compressive strength of the ultra-high performance concrete mixed with steel fiber is77.93 MPa,the compressive strength of the UHMWPE fiber is 88.04 MPa,and the compressive strength of the steel-UHMWPE hybrid fiber reinforced ultra-high performance concrete is106.33 MPa,compared with the single-doped steel.Fiber,the compressive strength of UHMWPE fiber is increased by 36.4%,and the compressive strength of steel fiber is increased by 20.7%compared with that of UHMWPE fiber alone.The compressive strength effect is much better.The corresponding axial compressive strengths of the groups SFM01,SFM02,SFM03,SFM04,and SFM05 with a volume content of UHMWPE of 0.1% to 0.5% are 94.04 MPa,102MPa,105.87 MPa,106.41 MPa,and 106.33 MPa,respectively.When increasing from 0.1% to 0.2%,the compressive strength increased by 8.5%,when the UHMWPE fiber content increased from 0.2%to 0.3%,the compressive strength increased by 3.8%,while the UHMWPE fiber content was0.3%,0.4%,0.5% % compressive strength is almost the same.The corresponding axial compressive strengths of steel-UHMWPE hybrid fiber reinforced ultra-high performance concrete with UHMWPE fiber lengths of 6 mm,12 mm and 18 mm are 100.74 MPa,106.33 MPa and 110.81 MPa,respectively.When the fiber length is 12 mm,the compressive strength is5.5% higher than that when the fiber length is 6mm,and the compressive strength when the fiber length is 18 mm is 4.2% higher than that when the fiber length is 12 mm.(3)Microstructure mechanismAccording to the SEM images of each group,it is observed that when the content of flexible fibers exceeds 0.3%,the fibers in the concrete matrix appear to agglomerate.The interface between the fiber and the concrete matrix is damaged.Pulling failure,when multiple fibers agglomerate,only one or two main fibers of the agglomerated fibers are completely destroyed,and the mechanical properties of the modified UHMWPE fibers cannot be fully exerted,which is in line with the negative fiber hybrid effect.,when the content of a certain fiber is greater than a certain value,the performance growth slows down,which explains the phenomenon that the compressive strength of the concrete matrix does not continuously increase significantly with the increase of the fiber content.When the UHMWPE fiber length is 18 mm,the ability of the fiber to bridge cracks is the strongest,and the flexural and compressive strengths reach the maximum at the three lengths.The length of UHMWPE fiber can affect its pull-out energy when it fails in cement-based composites.It is observed that the critical pull-out length of UHMWPE fibers below 12 mm is usually greater than the actual length,while the critical pull-out length of UHMWPE fibers above 12 mm is smaller than the actual length.,the longer the UHMWPE fiber length,the greater the pull-out failure energy and the better the mechanical properties.