Study On Road Performance Of Cement Concrete Used As Recycled Aggregate For Waste Concrete

Our country's level of recycled concrete recycling technology is developing slowly.To closely follow the national blueprint for the “Thirteenth Five-Year Plan”,research on the recycling of used cement concrete is imminent.The compressive strength of concrete is not only affected by the strength of the cement stone,but also depends on the support function of the large particle size aggregate inside the concrete,and the influence of the binding force between the aggregate material and the cement stone,and the above substitution method avoids affecting more than 10 mm.The skeletal support of the natural aggregates,at the same time,the higher surface roughness of the reclaimed aggregates increases the interfitting forces between the aggregates and the aggregates and the cement stones,and increases the bond strength between the aggregates and the cement pastes.It can increase the compressive strength of recycled concrete.In this paper,the coarse aggregate particle size range is set to 5~20mm to prepare cement concrete,coagulate the waste cement.The soil is crushed into coarse aggregates with a particle size of 5 to 10 mm.Recycled coarse aggregates with a particle size of 5 to 10 mm are used instead of equal-sized natural aggregates,with regeneration sets of 0%,40%,70%,and 100%,respectively.Material replacement rate,preparation of recycled concrete with strength class C30.Based on the experiment,the following research results were obtained:First,the recycled concrete specimen obtained by replacing the natural aggregates of equal particle size with 5 to 10 mm of recycled coarse aggregate was used.The parallel test data showed that when the replacement ratio of recycled coarse aggregate was 40%,the average compressive strength of the specimen for 28 days was 48.60 Mpa,which is 9.8% higher than the ordinary coagulation compressive strength value of 44.27 Mpa.The average splitting tensile strength of the specimen for 28 days is 3.69 MPa,which is 9% higher than the ordinary concrete splitting tensile strength value of 3.33 MPa.The mean flexural strength at 28 days was 6.1 MPa,which was 1.5% higher than the normal coagulation bending strength of 6.01 MPa.The main reason is: In this paper,the recycled aggregate in recycled concrete is only 40% of the 5~10mm natural aggregate replaced.In this alternative mode,this part of 5~10mm recycled aggregate is more like a natural aggregate that does not affect 10 mm or more.And the remaining 60% of the 5~10mm natural aggregates in the concrete in the anti-pressure,tensile,anti-folding and other effects of the admixture,this part of the 5 ~ 10 mm of recycled aggregate not only play a certain role in the interior of the eaves,but also Because of its higher surface roughness,the friction and fitting forces between the aggregates and aggregates in the raft and between the aggregate and the cement are increased,and the bond strength between the aggregate and the cement is improved.At the same time,in view of the special nature of the recycled aggregate production process,the used concrete needs to be broken several times to produce recycled aggregates.The selected coarse aggregate of the smallest particle size of the coarse aggregate is used in this paper.In the reclaimed coarse aggregate,the cement mortar still remaining on the surface of the aggregate is not low in the bond strength with the aggregate.The adhesion between the residual cement stone adhering to the surface of the reclaimed aggregate and the new cement mortar is stronger than that of the aggregate and the cement mortar,thereby improving the mechanical properties of the regenerated concrete such as compressive strength,tensile strength,and bending resistance.Second,the physical and mechanical properties of recycled coarse aggregates were experimentally studied.Tests have shown that although the indexes such as water absorption,crushing value,and needle-shaped content of reclaimed aggregates can meet the specification requirements,there is still a significant gap compared with natural aggregates.During the production process of recycled aggregates,it was discovered that large volumes of flake-shaped waste concrete blocks can be preliminarily removed,and the needle-shaped content of recycled aggregates can be reduced.After tests,large volumes of flake-shaped waste concrete blocks are broken to obtain recycled aggregates with a large number of needles.Flaky particles account for 50% of the total mass of recycled aggregate produced.Therefore,the content of needle-shaped particles of 5~10mm recycled aggregates prepared after removing large-scale flake-shaped waste concrete is only 6.5%,which is lower than that of 10.3% of reclaimed aggregates before cutting,which is a reduction of 36%.Third,the test tested the working performance of recycled aggregate concrete.Tests have shown that the working performance of recycled coarse aggregate concrete is slightly worse than that of ordinary concrete.Among them,in addition to similar cohesive properties,the slump,sand content,and water retention properties of recycled aggregate concrete mortar are higher than those of ordinary concrete mortar.difference.In addition,fly ash has a significant effect on improving the working performance of recycled concrete.At the same time,the timing of adding additional water to the reclaimed aggregate has a significant effect on the workability of the recycled concrete mortar.After tests and tests,the use of additional water pretreatment of reclaimed aggregates can effectively improve the mixability of recycled concrete.Fourth,the durability test of reclaimed aggregate concrete shows that the reclaimed aggregate concrete specimens obtained by replacing the natural aggregates with equal diameters with 5–10 mm recycled coarse aggregates are subjected to impact tests,abrasion tests,and impermeability tests.There are the following results.The impact test shows that the impact energy of the specimen is 705.7 Nm which is 14.5% higher than that of the ordinary concrete,which is 616.3Nm,and is less affected by the replacement rate of the recycled aggregate.The wear test shows that the wear resistance of reclaimed aggregate concrete is similar to that of ordinary concrete,and is similarly affected by the replacement rate of recycled aggregate.The impermeability test shows that the composite impervious grade of recycled aggregate concrete specimens with different substitution rates is S10,which is one grade worse than the ordinary concrete impermeability grade S11,and decreases with the increase of the aggregate substitution rate,but when the recycled aggregate When the substitution rate is 40%,impermeability grade S12 of recycled aggregate concrete is one grade higher than that of ordinary concrete.Fifth,based on factors such as high water absorption,high porosity,and high relative surface roughness of reclaimed aggregates,it is recommended that recycled aggregate be used with fly ash because of the great incorporation of fly ash.To compensate for the defects of recycled aggregates,for example,fly ash has a more pronounced effect on the performance of recycled aggregate concrete than ordinary concrete.In addition,although the incorporation of fly ash reduces the early mechanical properties of recycled aggregate concrete,it has little effect on the later mechanical strength.Fly ash also has a significant effect on improving the durability of recycled concrete.The incorporation of fly ash improves the wear resistance and impermeability of the specimen.Comprehensive fly ash improves the comprehensive performance of recycled concrete in terms of work performance,mechanical properties,and durability performance more than ordinary concrete.It is recommended to use fly ash in combination with recycled aggregate.