Study On Preparation Of Recycled Concrete From Recycled Aggregate And Its Performance

In this paper, recycled aggregate was prepared through crushing and rod milling, using waste concrete from a research institute in Nanning as starting material. The recycled aggregates were sized into coarse aggregate and fine aggregate with grain size in5mm-20mm,0.16-5mm respectively. The aggregates had a various of properties, such as good stability, good gradation, high mechanical strength, low porosity and low density with amount of mortar in the surfuce.In the same landslide requirement, recycled concretes with W/B=0.55and0.35ratio were prepared. The recycled coarse and fine aggregate double mixing concretes with substituent ratio of0%,30%,50%,70%and100%, respectively, was used to analysis the proportion impacts on apparent density of fresh concrete and compressive strength of hardened concrete. In addition, Single-doped recycled fine aggregate with substituent ration of0%,30%,50%,70%, respectively, was used as replacement of natural fine aggregate to prepared concrete. And their compressive strength, anti-chloride ion ability, and porosity were investigated. At the same time, the relationship of the property of recycled concrete with the doped amount of recycled fine aggregate was analyzed. Orthogonality experiment (L934) was applied to study the effect factors on the strength and anti-chloride ion ability of recycled concrete, including W/B, fly ash, the replacement of recycled coarse and fine aggregate. In addition, mercury compressive strength test was applied to analysis the micro pore structure of recycled concrete in28d age.The results showed that, in the two different W/B ratio condition, the apparent density of double mixing fine and coarse recycled concrete was decreased with the increase of the substituent ratio of recycled aggregate. The recycled concrete made from double mixing of recycled fine and coarse aggregate, had higher strength than normal concrete. And the strength increased with the increase of the substituent ratio. Only with0.35W/B ratio, compressive strength of concrete at90d with100%recycled fine and coarse aggregate substituent decreased.To The single-doped fine aggregate recycled concrete, in two different W/B ratio condition, This concrete had slightly increased strength of7d and90d, the highest up to116.2%of control concrete. However the28d strength was slightly decreased.Electric flux experiment demonstrated that,0.35W/B ratio, recycled fine aggregate with substituent ration of30%/7d、28d、90d electric flu decline.0.55W/B ratio,The concrete withfine aggregate have little variation,with the substituent increase, the electric flux recycle concrete was a slightly increase.Micro pore structure study illustrated that, the main factor that affected the strength and anti-chloride ion penetration ability of recycled concrete was the ratio of good pores (d≤100nm) to bad pores(d>100nm).The porosity of the concrete with fine aggregate has shownnegative correlation between28d age’s compressive strength. The correlation coefficient is up to0.976. Total pressure mercury into the volume has shown positive correlation between electric flux. The correlation coefficient is up to0.989.Orthogonality experiment proved that, the contribution of different factors to the7d,28d and90d’s strength, and electric flux and28d’s porosity and good pores affect were in the following order:the ratio of water to concrete> fly ash replacement>recycled fine aggregate replacement>recycled coarse aggregate replacement, the ratio of water to concrete>fly ash replacement>recycled coarse aggregate replacement>recycled fine aggregate replacement, respectively. An optimized combination method was made for different ages. Fly ash could significantly improve the28d age’s pore size distribution of recycled concrete.