Influence Of Quality And Substitution Rate Of Recycled Coarse Aggregate On Mechanical Properties Of Recycled Concrete

In twenty-first Century, China’s urbanization process is accelerating, which results from two aspects, as follows: on one hand, a large quantity of natural resources has been consumed by new buildings; on the other hand, as so many old buildings have been demolished, a trend that the city is being surrounded by the construction waste emerges. Recycled concrete technology is the perfect solution for the problems of the shortage of building materials and environmental pollution caused by construction waste. But because of the poor performance of recycled aggregate, the application of recycled concrete is severely limited. Many researchers have studied the strengthening technology of recycled aggregate, which can be roughly divided into two parts: physical strengthening method and chemical strengthening method. Different preparation techniques and strengthening ways produce different quality of recycled coarse aggregate. Due to replace rate and quality of recycled coarse aggregate have a great effect on performance of recycled concrete, it is necessary to study how the quality, replacement ratio of recycled coarse aggregate, and the amount of cementitious materials affect the performance of recycled concrete.With the support of National Natural Science Foundation of China(51378270, 51208272), we carried out the following research works:1.In accordance with effective strengthening methods of recycled coarse aggregate, we prepared six different qualities of recycled coarse aggregates: the simple crushing recycled coarse aggregate(JP); a particle shaping recycled coarse aggregate(YK); the double particle shaping recycled coarse aggregate(EK); the simple crushing recycled coarse aggregate chemical enhancement(JPH); a particle shaping recycled coarse aggregate chemical enhancement(YKH); the double particle shaping recycled coarse aggregate chemical enhancement(EKH).2.The influences of that replacement ratio and the quality of recycled coarse aggregate, and amount of cementitious materials on the workablity and mechanical performance of recycled concrete were studied, and based on test results, the strength formulas of recycled concrete concrete were established.3.The strength grade of cementitious materials has significant influence on concrete strength on the condition of fixed mix ratio of concrete; hereby, the effects of strength of cementitious materials on the mechanical performance of recycled concrete were studied. We studied the effects of ordinary Portland cement(P.O 52.5,P.O 42.5,P.O 32.5), respectively, compound mixing with fly ash(10%, 20%, 30%, 40%), on the 28 d compressive strength of recycled aggregate concrete.Results show that, the performance of recycled concrete after reinforcement in physics and chemistry has been improved significantly. Taking the addition of cementitious material 400kg/m3 as an example, when the replacement rate is 100%, comparing with ordinary concrete, the water consumption, 28 d compressive strength of the recycled concrete with JP, JPH,YK, YKH, EK, EKH is increased, decreased by 11.1%, 19.7%; 8.6%, 24.5%; 6.6%, 9.8%; 4.6%, 15.6%; 6.1%, 1.4%; 2.5%, 14.4%, respectively.. The mechanical properties of EK recycled concrete after physical enhancement is the best. Even though 28 d compressive strength of EKH recycled concrete is slightly decreased after physical and chemical composite compound reinforcement, its workability is optimal, besides, pore structure and permeability durability have been improved efficiently, so its comprehensive performances are the best.Through experimental analysis, supposed 28d compressive strength of recycled concrete as dependent variable Y, cement/water ratio (C/W) and replacement ratio of recycled aggregate ((?)%) of recycled concrete as independent variables (X1, X2), we can derive 28d compressive strength formulas of recycled concretes with JP, JPH, YK, YKH, EK, EKH as respectively. The factor of intensityformula (?) seen, Regeneration quality of coarse aggregate on mechanical properties of recycled concrete adverse effect size:JPH recycled coarse aggregate >YKH regeneration of coarse aggregate >JP regeneration of coarse aggregate =EKH regeneration of coarse aggregate >YK regeneration of coarse aggregate >EK recycled coarse aggregate.Different grade of cementitious material can produce different effects on the mechanical properties of recycled concrete, as experimental results show that, the ordinary portland cement mixed with fly ash (0%,10%,20%,30%,40%) can be configured with the strength grade between C15～C60 of recycled concrete.