Study On Properties Of UHPC Materials And Mechanical Properties After Freeze-thaw Cycles

Ordinary concrete is mainly composed of water,cement,sand,stone and other materials,with low bearing capacity and high porosity.When ordinary concrete is used in ocean engineering,ordinary concrete is vulnerable to seawater erosion and freeze-thaw damage,resulting in short service life of buildings in ocean engineering.Ultra-High Performance Concrete(UHPC)has excellent mechanical properties and durability.The application of UHPC in marine engineering is bound to be the general trend.In this paper,materials such as PⅡ52.5 cement,silica fume,secondary fly ash,S95 mineral powder,steel fiber,water,quartz sand,sea sand,machine-made sand,and polycarboxylate superplasticizer are used to configure ultra-high performance concrete.Slurry flow properties,UHPC compressive and flexural strengths,UHPC axial tensile stress-strain curves and durability.The main research contents and basic research results are as follows:The effects of water-binder ratio,silica fume content,fly ash content,mineral powder content,and water-reducing agent content on the fluidity of UHPC cement paste were studied through experiments;The effects of dosage,mineral powder dosage,fly ash dosage,steel fiber dosage and different types of sand on the mechanical properties(compressive strength,flexural strength)of UHPC;in addition,the UHPC axis with different steel fiber dosage was studied Tensile stress-strain curve.The research results show that the water-binder ratio,fly ash,mineral powder,and water-reducing agent are all beneficial to the rheological properties of UHPC,and the water-reducing agent has the most significant effect.The improvement of the fluidity of UHPC pulp is the most obvious.The steel fiber has the largest improvement in the compressive strength and flexural strength of UHPC.When the volume fraction of steel fiber reaches 2%,the compressive strength of UHPC exceeds 190 MPa.The impermeability test,electric flux test and rapid freeze-thaw test were carried out on UHPC.The test results show that:UHPC has excellent impermeability performance,and the water seepage height of UHPC is basically below 11 mm.The amount,mixing sand,and mixing water all have a certain influence on the impermeability of UHPC;UHPC has excellent resistance to chloride ion corrosion,and the maximum electric flux value of UHPC is only 586.22 C,which belongs to the category of extremely low.among which,the water-binder ratio of UHPC,the mixing sand,and the mixing water all have varying degrees of influence on the resistance to chloride ion erosion of UHPC;after 500 freeze-thaw cycles of fresh water and seawater,the mass loss rate of UHPC The maximum is less than 1%,and the relative dynamic elastic modulus is basically maintained at more than 90%.After 500 freeze-thaw cycles,the flexural strength and compressive strength of UHPC begin to lose.Compared with freshwater freeze-thaw cycles,seawater freeze-thaw cycles.The relative dynamic elastic modulus and strength of UHPC under cyclic action decreased more greatly.