Influence Of Steel-polyethylene Hybrid Fiber On Mechanical Properties Of Ultra High Performance Concrete Containing Coarse Aggregate

Coarse aggregate-containing ultra-high performance concrete(UHPC-CA)is a new type of cement-based material.Concrete is low.At present,there are not many engineering applications of ultra-high performance concrete containing coarse aggregate at home and abroad.In order to speed up its popularization and application,this paper mixed steel fiber(Steel fiber,SF fiber for short)and polymer into the ultrahigh performance concrete containing coarse aggregate.Polyethylene fiber(PE fiber for short),studied the influence of steel fiber and polyethylene fiber with different volume dosages on the flow properties and mechanical properties of ultra-high performance concrete,and preliminarily determined the optimal dosage of fiber.The experiment(SEM electron microscope scanning test)analyzes the influence mechanism of the fiber.The main research results are as follows:(1)The fluidity of UHPC-CA decreases with the gradual increase of polyethylene fiber content.When the volume content of polyethylene fiber is 0.9% of the maximum content,the slump of UHPC-CA is less than 100mm;steel fiber It has little effect on the fluidity of UHPC-CA.When the content of steel fiber is 1.5%,the slump expansion of UHPC-CA is less than 500 mm,so the content of steel fiber is in the range of 0.5%-1.0%,and the content of polyethylene fiber is 0.5%-1.0%.The dosage range is 0.3%-0.6%,and the optimal volume dosage of steel fiber and polyethylene fiber is 1.0% and0.6%,respectively.(2)The compressive strength of UHPC-CA increases significantly with the increase of the volume content of steel fibers.When the volume content of steel fiber is 1% and the volume content of polyethylene fiber is 0.3%,the cubic compressive strength and axial compressive strength are increased by 41.2% and 52.7%,respectively,and it shows a positive hybrid effect.Therefore,according to the analysis of compressive strength and mixing effect,it is suggested that the optimal blending fiber ratio is: the volume content of steel fiber is 1%,and the volume content of polyethylene fiber is 0.3%.(3)The flexural strength of UHPC-CA was greatly affected by the single doping of steel fiber or polyethylene fiber.When the content of steel fiber was 1% and that of polyethylene fiber was 0.6%,the flexural strength was increased by 77.5%.Therefore,according to the analysis of flexural strength and mixing effect,it is suggested that the optimal blending fiber ratio is: the volume content of steel fiber is 1%,and the volume content of polyethylene fiber is 0.6%.(4)With the addition of steel fiber and polyethylene fiber,the splitting tensile strength of UHPC-CA is improved.When the volume content of steel fiber is 1% and the volume content of polyethylene fiber is 0.3%,the splitting tensile strength is increased by 105%,and it shows a positive hybrid effect.Therefore,according to the splitting tensile strength and hybrid effect analysis,the recommended optimal blending fiber ratio is: steel fiber content volume ratio of 1%,polyethylene fiber content volume ratio of 0.3%.(5)The effect of hybrid fibers on the hydration products and microstructure of UHPC-CA was studied by scanning electron microscopy experiments on UHPC-CA,and the bonding degree between steel fibers,polyethylene fibers and mortar was observed.The results show that the interface transition area between steel fiber and mortar is filled with C-S-H gel,which greatly improves the compactness of concrete;there are many holes near polyethylene fiber,and there is a large shadow area in the interface transition area between steel fiber and mortar,and excessive polyethylene Fibers weaken the internal structure of concrete.