Research On Mechanical Properties And Durability Of Willow Fiber Reinforced Concrete

Plant fiber concrete has been widely used in the building materials industry for its advantages of convenient materials,environmental protection,high toughness and good thermal insulation performance.A novel concrete material is proposed in this study,distinct from traditional concrete,by incorporating willow fibers into the mixture.These fibers are made by peeling,splitting,and trimming willow branches into small pieces and soaking them in a Na OH solution,referred to as"willow fibers"in this thesis.The tensile strength of this material can be increased by approximately 20%without additional costs compared to traditional concrete.Thesis call this new material"willow fiber concrete".Taking into account various orthogonal experimental factors（including willow fiber content,pretreatment methods,and willow fiber length）,thesis investigated the compressive strength,splitting tensile strength,and flexural strength of willow fiber concrete specimens.Additionally,durability tests（including freeze-thaw and sulfate erosion tests）were conducted on the willow fiber concrete.The results of both the strength tests and durability tests indicate that willow fiber concrete outperforms ordinary concrete in terms of strength and durability.To further validate the advantages of willow fiber concrete,numerical models of willow fiber concrete beams and plain concrete beams of identical dimensions were developed,and their ultimate load and mid-span deflection were compared and analyzed.The primary research contents of this thesis include the following:（1）Tesis conducted modification tests on willow fibers in this thesis.Willow fibers underwent cold water soaking,boiling,and Na OH solution soaking treatments,and thesis measured their mass changes before and after treatment.The mass loss rate and water absorption rate of the willow fibers were calculated to determine the most effective treatment method（i.e.,ensuring minimal mass loss rate while maximizing water absorption）.Test results revealed that soaking willow fibers in a 2%Na OH solution for 12 hours ensured minimal mass loss rate and maximized water absorption,achieving the goal of enhancing the compatibility between willow fibers and the concrete matrix.（2）To investigate the optimal mix proportion of willow fiber concrete and achieve its best mechanical performance,this thesis employed orthogonal experimental methods to design three mechanical performance tests for willow fiber concrete.Range analysis and multifactor analysis of variance were utilized to examine the effects of fiber content,fiber treatment method,and fiber length on the compressive strength,splitting tensile strength,and flexural strength of willow fiber concrete specimens.Based on these findings,thesis determined the optimal mix proportion for maximizing the mechanical performance of willow fiber concrete.Test results demonstrated that the fiber treatment method had the most significant impact on the three mechanical strengths of willow fiber concrete specimens;compared to plain concrete,the compressive strength of willow fiber concrete specimens with the optimal mix proportion decreased by 4.03%,while the splitting tensile strength increased by 21.7%and the flexural strength increased by 28.5%.（3）Thesis adopted the rapid freezing method for concrete in this study to perform freeze-thaw cycle tests,using indicators such as mass loss rate,relative dynamic elastic modulus,compressive strength,and splitting tensile strength to examine the damage deterioration patterns of willow fiber concrete specimens under freeze-thaw cycles.Test results indicated that,when compared to plain concrete specimens,willow fiber concrete specimens exhibited a relatively smaller mass loss rate,a higher relative dynamic elastic modulus,and similar decay rates for compressive strength and tensile strength.Willow fiber concrete demonstrated higher tensile strength under identical freeze-thaw conditions.（4）Willow fiber concrete specimens and plain concrete specimens were immersed in a 5%Na₂SO₄solution,and thesis studied the erosion effects of sulfates on both types of concrete at different corrosion stages.Results showed that,in comparison to plain concrete,willow fiber concrete maintained a better appearance,exhibited a larger corrosion resistance coefficient,had a higher relative dynamic elastic modulus,and demonstrated a smaller mass loss rate,thus proving to possess superior sulfate erosion resistance.（5）Utilizing finite element numerical simulation software,numerical simulation studies were conducted for two different working conditions.The splitting tensile strength tests of willow fiber concrete and plain concrete were simulated in working condition 1.The comparison showed that the numerical simulation results were in good agreement with the experimental results,verifying the accuracy of the numerical model employed in this study.The bending tests of willow fiber concrete beams and plain concrete beams with identical cross-sections were simulated in working condition 2,using the numerical model from working condition 1.The results revealed that,compared to plain concrete beams,the ultimate load capacity of willow fiber concrete beams increased by 13.4%,and the mid-span deflection decreased by 6%,further illustrating the superior mechanical performance of willow fiber concrete.