Study On The Effect Of Basalt Fiber On The Basic Mechanical Properties Of Recycled Concrete

With the rapid advancement of urbanization in China,large-scale reconstruction and expansion projects have generated a lot of construction waste.Recycled coarse aggregate produced by crushing waste concrete,mixed with cement,water,etc.in a certain proportion is an effective way to recycle construction waste.Due to its own defects,recycled coarse aggregates form more complicated interface weak areas in concrete,which makes the performance of recycled concrete inferior to ordinary concrete.Therefore,in order to effectively improve the utilization of construction waste,the primary task is to reduce the adverse impact of recycled coarse aggregate on the performance of concrete.The performance defects of recycled concrete seriously restrict the popularization and application of recycled concrete.Basalt fiber has a high elastic modulus and a relatively high tensile strength.At the same time,it has good durability in alkaline media such as cement and can maintain a high degree of compatibility.Therefore,adding basalt fiber to recycled concrete to improve its mechanical properties is an ideal solution to promote the use of recycled concrete in actual engineering.In order to quantitatively analyze the crack resistance,reinforcement,and toughening effects of basalt fiber on recycled concrete,this paper analyzes the basic mechanical properties such as the early cracking performance,compressive strength,uniaxial compressive stress-strain relationship,bending toughness and other basic mechanical properties of BFRAC Carrying out research can provide the necessary theoretical basis for popularizing the use of BFRAC.In this paper,the replacement rate of recycled coarse aggregate and the volume of basalt fiber are taken as the main influencing factors to explore its influence on the basic mechanical properties of BFRAC.The main research contents and conclusions of this article are as follows:（1）Early cracking performance of BFRACDesigned a test piece group with a recycled coarse aggregate replacement rate of 50%,basalt fiber content of 0,0.1%,0.2%and 0.3%,and a common concrete sample group with fiber content of 0 A total of five groups of specimens were tested for early cracking resistance by the knife edge restraint induction method.The results show that:with the increase of the basalt fiber content,the initial cracking time of the recycled concrete specimen is greatly delayed,and the time is extended by a maximum of 2.6 times.The maximum crack width and cracking area were reduced by 84.8%and 99%respectively.Basalt fiber can effectively improve the early cracking performance of recycled concrete.（2）Compressive strength of BFRACBy making 12 groups of cubes and prism specimens of basalt volume blends of 0,0.1%,0.2%0.3%,and recycled coarse aggregate replacement rates of 0,50%,and 100%,respectively Research on compressive strength and axial compressive strength.The results show that basalt fiber can increase the compressive strength of the recycled concrete cube and the axial compressive strength,but the increase rate shows a trend of increasing first and then decreasing.When the fiber volume is 0.1%,the strength improvement effect is most obvious.The cubic compressive strength is increased by a maximum of7.9%compared to unreinforced recycled concrete;the axial compressive strength is increased by 6.32%.The higher the replacement rate of recycled coarse aggregate,the greater the ratio of axial compressive strength to cubic compressive strength,and basalt fiber has little effect on the ratio of the two.（3）Uniaxial compression stress-strain relationship of BFRACDesign and load rigid elements to perform uniaxial compression test on 8groups of specimens with basalt volume content of 0,0.1%,0.2%0.3%,and recycled coarse aggregate replacement rates of 0,50%,and 100%respectively,to explore basalt The influence of fiber and recycled coarse aggregate on peak strain,peak stress,residual strength and ultimate strain during compression.Finally,the uniaxial compressive stress-strain curve of basalt fiber recycled concrete is obtained.The test results show that with the increase of the amount of basalt fiber,the peak strain,peak stress,ultimate strain and elastic modulus of the curve are steadily increasing;As the replacement rate of recycled aggregates increases,the peak strain of the curve increases while the ultimate strain,peak stress,and elastic modulus all decrease.Based on the stress-strain curve of basalt fiber recycled concrete under uniaxial compression obtained through experiments,the constitutive equation of basalt fiber recycled concrete under uniaxial compression is obtained through theoretical analysis and formula derivation.（4）Bending toughness of BFRACUse the bending toughness evaluation method stipulated in China’s"Fiber Concrete Application Technical Regulations"JGJT221-2010 for 12 groups with basalt fiber content of 0%,0.1%,0.2%,0.3%and recycled aggregate replacement rate of 50%and 100%The specimen is tested for bending toughness.The results show that the addition of basalt fiber can greatly improve the bending toughness and ductility of recycled concrete.The bending toughness index increases with increasing basalt fiber content.Compared with the recycled concrete group,the flexural toughness index I₅of the basalt fiber concrete with the volume content of 0.2%and 0.3%when the replacement rate of recycled aggregate is 50%is increased by 53.7%and 58.8%,and the flexural toughness index I₁₀is increased by 52.4%And 55%,the load-deflection curve area is increased by 199.7%and 225.7%,respectively,showing good bending toughness and ductility.At the same time,when the basalt fiber content exceeds 0.2%,the increase in the ductility of recycled concrete decreases.The replacement rate of recycled aggregate has little effect on the bending toughness of concrete.