Research On Composition Design And Bonding Performance Of Basalt Fiber Ultra High Performance Concrete

Ultra high performance concrete(UHPC)is a durable cement-based composite material with exceptional strength that has promising applications in various engineering fields.To enhance its strength and toughness,steel fiber(SF)is commonly added to traditional UHPC.However,the density of steel fiber is approximately three times greater than that of the concrete matrix,making it susceptible to sinking during the mixing processes.While steel fiber is a viable option for reinforcing UHPC,it can be expensive to use,particularly if the content of SF is excessive.This cost can limit the use of UHPC in engineering applications.However,basalt fiber(BF)is emerging as a promising alternative.BF is an inorganic,environmentally-friendly,high-performance fiber material that boasts excellent mechanical properties,high temperature resistance,and resistance to acid and alkali.Moreover,BF is naturally compatible with concrete and has a positive effect on concrete gain.This paper presents a study on the use of resin twisted basalt fibers as a replacement for steel fibers in ultra high performance concrete(UHPC).The aim of the study is to investigate the effects of various parameters such as fiber parameters,water-to-binder ratio(w/b),binderto-sand ratio,and raw material components on the fluidity,mechanical properties,tensile properties,and bonding properties of UHPC.Additionally,the paper revealed the influence law of pull-out process and pull-out energy.This study aimed to clarify the reinforcing and toughening effect of BF on UHPC.Various techniques such as contact angle,SEM,XRD,and MIP were used to achieve this goal.The main results of this study are as follows:(1)The addition of fiber content in UHPC leads to a gradual decrease in fluidity,while the flexural and compressive strengths show an initial increase followed by a decrease.This is due to the fact that fibers impede the formation and propagation of internal cracks.However,if the fiber content is too high,it can lead to clustering of fibers and an increase in the number of weak interfaces within UHPC,ultimately negatively impacting its strength.In consideration of all variables,it was found that the inclusion of 1%12mm basalt fiber(BF)in a sample resulted in the highest compressive and flexural strength,as well as favorable fluidity.(2)The performance of UHPC is significantly impacted by the w/b.As the w/b ratio increases,the fluidity of the fresh UHPC mix increases while the compressive and flexural strength gradually decreases.However,by optimizing the binder-to-sand ratio,the fluidity of UHPC can be significantly improved.When the amount of cementitious material is too low,the strength of UHPC decreases.Additionally,varying the silica fume content within the range of 12.5%to 20%has a relatively small impact on the strength of UHPC.When the superplasticizer content exceeds 1.5%,the fluidity of UHPC remains relatively constant,but its strength decreases.(3)UHPC can achieved stable tensile properties after 28 days of standard curing,with an optimal fiber content range of 1.0-1.5%.Within this range,UHPC can achieved better first crack load,tensile strength,and peak tensile strain.The development of fiber matrix bond properties follows a similar pattern to that of macroscopic mechanical properties.A higher w/b leads to a lower fiber matrix bond strength.However,the bond properties are hardly affected by silica fume and binder-to-sand ratio.BF exhibits superior bonding with UHPC matrix as compared to SF.This is attributed to their contoured surface morphology which facilitates excellent mechanical anchoring and enhances frictional resistance between fibers and matrix.(4)BF exhibited hydrophilic properties and can formed a strong bond with the matrix.The addition of fibers results in a compact and robust network structure within the matrix,which aids in filling and repairing pores and defects.However,an excessive amount of fibers can lead to an increase in harmful pores in UHPC.The hydration products of UHPC remain largely unchanged with the addition of fibers.These products primarily consist of C-S-H gel,Ca(OH)2,AFt,and unhydrated clinker particles.High fiber content in UHPC results in numerous cracks and pores in the matrix surrounding the fibers.To optimize the formation of internal pores and weaken the growth space of CH crystals,it is recommended to reduce the w/b.Thereby improved the bond properties between the fiber and the matrix.