Experimental Research On Mechanical Properties Of Polymer Recycled Aggregate Concrete Based On Meso-level

The shortcomings of recycled aggregate concrete,such as low compressive strength,low modulus of elasticity,low shear strength and poor durability,have caused its limited application in practical engineering.Recycled aggregate concrete is a mixed material,and its mechanical properties mainly depend on the properties of the recycled aggregate itself and the interface properties between the recycled aggregate and cement mortar.In this paper,tests were conducted to research the way of property enhancement of recycled aggregates,and on the basis of the best enhancing method,further analysis was given to the interface bonding performance between recycled aggregates and cement mortar.Combined with a micro-performance test,the research also shows the microscopic appearance of the surface of the recycled aggregate in the polymer recycled aggregate concrete,as well as the interface between the recycled aggregate and cement mortar.And the research also analyzes the mechanism of the coarse aggregate in the modified recycled aggregates concrete and the interface between the recycled coarse aggregate and cement mortar.Detailed research are as follows:First of all,in order to enhance the various properties of recycled aggregates,the mechanical stirring method,nanometer silica slurry and styrene/acrylic polymer latex(hereinafter referred to as polymer)soaking method were used to process the recycled coarse aggregates with diameter between 4.75mm～19.5mm,and to reflect the enhancement effect of the properties of the recycled coarse aggregate by measuring the five indicators of water absorption,crushing value,apparent density,bulk density and void ratio.The test results show that the crushed value,water absorption rate and bulk density of the recycled coarse aggregate soaked in styrene/acrylic polymer latex were reduced by 32.7%,16.9% and 7.1% respectively,and the apparent density and void ratio were increased by 2.9% and 2.6% respectively.It shows that the polymer has a significant effect on enhancing the properties of recycled coarse aggregate.Secondly,in order to analyze the interface bonding performance between the polymer-modified recycled coarse aggregate and cement mortar,specimens concerning interface bonding tensile and interface bonding shear strength before and after the modification were designed,and three factors were considered : the strength of cement mortar,the polymer and the surface roughness of the recycled aggregate.Through the mechanical properties test,the bonding properties of the interfacebetween the polymer-modified recycled aggregate and the cement mortar were analyzed.The test results show that the polymer can significantly enhance the interface tensile and shear resistance between the recycled coarse aggregate and the cement mortar;the interface bond tensile and shear properties increase with the strength of the cement mortar;With the increase of the surface roughness of the recycled aggregate,the interface bonding tensile properties are significantly enhanced,and the shear strength is slightly enhanced;the interface shear strength increases with the increase of normal stress.Finally,three polymer-modified recycled aggregate concretes with different strength grades were designed,and the effects of polymers on the compressive strength and splitting tensile strength of recycled aggregate concrete were analyzed based on macroscopic mechanical performance tests.Combined with the micro-performance test,the micro-performance of the surface of the recycled aggregate in polymer-modified aggregate concrete and the interface between the recycled aggregate and the cement mortar was analyzed,and the mechanism of the effect of modified aggregate and its interface on the macro-performance of the concrete was further explained.