Study On Mechanical Properties Of Kevlar Fiber Reinforced Cementitious Composites

Modern buildings require more and more high performance of civil engineering materials,while traditional cement-based materials have congenital defects such as poor toughness,high brittleness and low tensile strength.Therefore,it is of great significance to improve the flexibility and bending deformation capacity of cement-based materials for the development of modern building structures.Fiber reinforced cement-based composites are one of the main ways to prepare cement-based materials with high strength and toughness.As a new type of fiber reinforced material with high strength,high modulus and high toughness,aramid fiber has been widely used in the field of building structure reinforcement in recent years.However,there are few researches on directly adding aramid fiber into cement matrix to enhance the properties of cement matrix composites.In this paper,Kevlar fiber,one of the most representative Arlene fibers,is selected as the reinforcement material of cement-based composite materials.Kevlar fibers were directly mixed into cement matrix to prepare Kevlar fibers reinforced entitious composites(as Referred to as KFRCC).The aim is to study the effect of Kevlar fiber on mechanical properties of cement matrix composites.Five Kevlar fibers with different lengths of 1mm,3mm,6mm,12 mm and120mm were selected in the experiment.Under different Kevlar fiber lengths,the volume dosage of Kevlar fiber was determined according to the working performance of cement-based composite materials when forming.Five different fiber volume mixing ratios of 1%,2%,4%,6% and 8% were designed to study the influence of Kevlar fiber length and dosage on the flexural,compressive,bending and impact resistance of cement-based composites through KFRCC mortar specimen bending test,thin plate bending test and cake impact test.The test results show that:For the compressive properties of KFRCC,the addition of Kevlar fiber can effectively improve the stress concentration distribution in the matrix of KFRCC mortar specimen,so that the compressive properties of KFRCC mortar specimen have been significantly improved,but with the increasing of the dosage of Kevlar fiber,At each fiber length,the compressive properties of KFRCC mortar specimens begin to weaken after reaching the peak value.When Kevlar fiber length is 1mm,3mm,6mm,12 mm and 120 mm,the flexural performance of KFRCC mortar specimen is optimal when the fiber volume content is 6%,2%,2%,2% and 1%,respectively.Compared with the baseline group,they increased by 56.69%,89.33%,104.72%,118.99% and 320.91%,respectively.When Kevlar fiber length is 1mm,3mm,6mm and 12 mm,the compressive properties of KFRCC mortar specimens are optimal when fiber volume content is 6%,4%,2% and 2%,respectively,and increase by 19.05%,21.20%,20.80% and 18.67%compared with the reference group,respectively.However,the compressive properties of KFRCC mortar with 120 mm Kevlar fiber length were lower than that of the reference group,and the compressive properties of KFRCC mortar with 1% and 2% fiber content were 5.87%and 27.37% lower than that of the reference group,respectively.For THE bending performance of KFRCC,the cracking load of the benchmark without fiber group is the failure load,the initial cracking deflection is the maximum deflection,and the incorporation of Kevlar fiber,KFRCC load and deflection have varying degrees of growth.When Kevlar fiber length is 1mm,3mm,6mm and 12 mm,the ultimate bending strength value and maximum deflection value of KFRCC thin plate get the maximum value when fiber volume dosage is 4%.The maximum values were 5.94Mpa/1.48 mm,6.67Mpa/2.87 mm,6.89Mpa/6.98 mm,9.91Mpa/8.04 mm,respectively.When the Kevlar fiber length is 120 mm,the load-deflection curve of KFRCC thin plate bending presents a "sawtooth" increase phenomenon,and when the fiber volume content is 2%,the maximum bending strength and maximum deflection value are 17.23 mpa /11.48 mm,respectively.Kevlar fiber length is longer,when the thin plate is bent,the overall utilization efficiency of the fiber is higher,the bending toughness of KFRCC is better,120 mm long Kevlar fiber KFRCC bending toughness is significantly better than other fiber length groups,and its toughness enhancement is the most significant in 1%dosage.As for the impact resistance of KFRCC,the basic performance of the benchmark non-fiber round cake specimen under impact test is "bursting immediately",and the failure pattern is roughly "one shape",showing obvious brittle failure,while the failure pattern of Kevlar fiber round cake specimen is mainly "three-pointed star" and "T-shape".In addition,the KFRCC round cake specimens with 12 mm and 120 mm fiber lengths are still connected by fibers after being damaged,and the specimens can still remain as a whole.Kevlar fiber length is certain,the impact performance of KFRCC and Kevlar fiber volume dosage is positively correlated,Kevlar fiber dosage is certain,the impact performance of KFRCC with the growth of the length of the first weakened and then enhanced trend,the inflection point roughly occurs in the fiber length of 6mm,That is,when the fiber length is 1mm,3mm,and 6mm,the impact resistance of KFRCC is negatively correlated with Kevlar fiber length,and when the fiber length is 6mm,12 mm,and 120 mm,the impact resistance of KFRCC is positively correlated with Kevlar fiber length.