Effect Of Polypropylene Fiber On Mechanical Properties Of Concrete Under Cyclic Loading

Concrete is the most important and the largest amount of building materials in China’s construction engineering.Due to the inhomogeneity of concrete components and the external static and dynamic loads,there are often micro pores and micro cracks in the concrete,and these damages and cracks do have a substantial impact on the mechanical properties of concrete,thus bringing adverse effects to the project consequence.Therefore,it is necessary to study and analyze these damages.In recent years,more and more attention has been paid to the static and dynamic damage characteristics of concrete,which has become a hot issue.As one of the fiber aggregates of concrete,polypropylene fiber is widely used.Polypropylene fiber can weaken the shrinkage,dry shrinkage and cracks of concrete due to external load,adverse reaction and temperature change by reducing the scale and scale of original cracks of concrete,so as to improve the crack resistance,impermeability,impact resistance and abrasion resistance of concrete,increase the toughness of concrete and prolong the service life of concrete.In addition,the fibers dispersed in the concrete can play the role of anchorage,and can absorb part of the energy to reduce the damage degree when the structure is subjected to external load.In this paper,the uniaxial compressive strength test,cyclic loading and unloading test and dynamic mechanical properties test of plain concrete and polypropylene fiber concrete are carried out respectively,and the influence of polypropylene fiber on the mechanical properties of concrete is analyzed.The results show that the mechanical properties of the two materials are similar but different in uniaxial compression test.Their uniaxial compressive strength and peak strain are similar.However,the failure mode of polypropylene fiber reinforced concrete is different from that of plain concrete.In the cyclic loading and unloading test,the damage increases with the increase of cyclic threshold and axial strain,but the damage degree of polypropylene fiber reinforced concrete is obviously less than that of plain concrete.In the cyclic loading and unloading experiments,the loading and unloading curves of both of them show a trend from dense to sparse.After cyclic loading,the decrease of strength of polypropylene fiber reinforced concrete is less than that of plain concrete,and the increase of peak strain is also less than that of plain concrete.After different degrees of damage,their mechanical properties and damage modes are different.The higher the damage degree of concrete is,the denser and larger the internal cracks are.When the incident energy is the same,the denser the cracks are,the smaller the energy consumption density is,the greater the fragmentation degree is,and the less the mass fraction of the larger fragmentation is.The plain concrete with different strain rates shows strong brittleness after reaching the peak point.The difference is that polypropylene concrete shows a certain ductility after reaching the peak point,which indicates that fiber plays a bridging role here.