Study On The Mechanical And Durability Performance Of Recycled Concrete With Modified Rubber Powder And Polypropylene Fibers

With the development of society,the requirements for building and transportation facilities multiply daily.Concrete has become the most widely used construction material.Annual production of building waste from statistics recorded until December 2021 has reached 3500million tons,causing heavy social burden.The replacement of natural aggregates with the recycled can be adopted in urban road constructions,but the recycled concrete is short in strength,ductility and durability.Applying the scrap tires rubber powder to the recycled concrete can enhance the frost resistance and plasticity but decrease the mechanical performance.Modified rubber recycled concrete is prepared by rubber Na OH modification and oxidize urea modification method and investigated the varying laws of mechanical properties and durability.Meanwhile,the addition of polypropylene fibers can make a further improvement in mechanical properties.It is aimed to enhance the mechanical properties and durability with the strength demand satisfied.The research is as follows:（1）Process of scrap tires modification:Immerse the 40 and 60 mesh scrap rubber powder by sodium hydroxide modification method and then soak them in potassium permanganate solution,hydrogen peroxide and urea is adopted for oxidation and modification respectively,and drying is in succession eventually.Remove the stearate on the surface of rubber powder and add hydrophilic groups with strong adhesion to cement.The hydrophilicity test was carried out to compare the surface modification of unmodified rubber,Na OH modified rubber and oxidation-urea modified rubber.The hydrophilic coefficient of rubber modified by oxidation and urea increased from 0.18ηto 0.87η.（2）The modified 40 and 60 mesh rubber powder and the unmodified are applied respectively to the recycled concrete,replaced with 40%coarse aggregates,with 5%,10%,15%equal volume substitution of fine aggregates for tests of slump,compression,bending,split tensile,elastic modulus and freeze-thaw.The slump of rubber modified by oxidation and urea was increased,the recycled concrete with 15%dosage of unmodified 40 mesh rubber powder has 20%degradation in compression strength,40%in bending performance,23.3%in split tensile strength and 34.6%in elastic modulus.After the modification of recycled concrete with 60 mesh rubber powder,the improvement in compression strength is 6.3%maximum,bending performance 4.7%,tensile strength 6.9%,axial compression strength 5.2%,which indicates that the mechanical properties of rubber recycled concrete are improved after modification,and 1.7%decrease in mass loss rate during freeze-thaw cycle tests declares the frost resistance promotion.（3）With the addition of polypropylene fibers in 1kg/m~3 dosage in modified rubber recycled concrete,the slump of rubber modified by oxidation and urea was declined,there follows tests of compression,bending,split tensile,elastic modulus and freeze-thaw.The recycled concrete with5%dosage of modified 60 mesh rubber powder has 3.4%degradation in compression strength,14.3%in bending performance,31%in split tensile strength and 16%in elastic modulus,which indicates that the mechanical properties of rubber recycled concrete are improved by polypropylene fibers.After the application of polypropylene fibers with 15%dosage in 60 mesh rubber recycled concrete,the compression strength after freeze-thaw cycle tests can be improved by 0.4MPa,the mass loss ratio is 0.793%,which declares the frost resistance promotion.This paper investigates the impact of rubber oxidize urea modification method on mechanical characteristics and frost resistance for recycled concrete with rubber and polypropylene fibers,which guides the promotion in road performance and application area of rubber recycled concrete.