Research On The Effects Of Polyethylene Fiber On The Properties Of Ultra High Performance Concrete

Ultra High Performance Concrete is a kind of cement-based composite material,which has excellent durability and ultra high strength.UHPC is widely used in theengineerings all over the world.In order to enhance the tensile and compressivestrength and resilience, Polyethylene fibers are added in the body of UHPC. Based onthe theory of fiber reinforced and toughened, the study shows the influence ofdifferent contents and aspect ratios of PE fibers on the liquidity, mechanical propertiesof UHPC.By the curve of bending tensile load-deflection and axial tensile stress-strain,the best dosage and aspect ratio of PE fibers are initially identified and the effect ofPE fibers on the UHPC is studied. Achieved the following results:(1)Because PE fibers increase the friction of fresh paste,the liquidity of UHPCsignificantly reduces when the content of PE fibers increases. In the case of samecontent of fibers, the length of PE fibers has little effect on the liquidity of UHPC. Byoptimizing the water-cement and powder-sand ratio and partially replacing quartzpowder with ultra-active slag, the liquidity of UHPC can be improved.(2)The study analyses the different lengths and different volume fraction of PEfibers on the flexural strength of UHPC.With the content of PE fibers increasing, theflexural strength dramatically enhanced.The effect of fiber length on the flexuralstrength of UHPC is not obvious.The lowest volume fraction of PE fibers is1%whileless than it, the enhancement is not evident.(3)By the compressive strength testing, the influence of different lengths anddifferent volume fractions of PE fibers on the compressive strength of UHPC isresearched. The results show that the compressive strength is increased in somedegree.With the content of PE fibers increasing,the mobility of the UHPC isdecreasing and the weak interfaces are growing in number,So the increasing ofcompressive strength can not be continued.The effect of fiber length on thecompressive strength of UHPC is not obvious.(4)Ultra-active slag,cement and curing system have some influence in theproperties of UHPC. After replacing ultra-active slag with part of quartz powder,theflow performance of UHPC have a certain degree of increase while the mechanicalproperties decrease. At90℃hot water curing condition, the longer curing time, thehigher compressive and flexural strength while the rate of increase gradually slowes down.CoMPared with ordinary Portland cement, in the same situation of other factors,there is a significant increase in the flexural and compressive strength when usingsulphate resistant cement.(5)According to the flexural tensile test and the load-deflection curve, PE fiberscan improve the flexural tensile toughness of UHPC.Multiple crackings and hardeningdisplacement occur during the test. With the fiber contents increasing, thetoughness,flexural tensile strength and peak deflection is getting better. The toughnessindex of all stages are increasing.(6)According to the axial tensile test and stress-strain curves, PE fibers canimprove the axia tensile force and toughness of UHPC.With the fiber contentsincreasing, the toughness,axia tensile strength and peak strain is getting better.