Application Of Recycled Aggregate In Pump Concrete And Pervious Concrete

This article studied the basic characteristics of recycled aggregate.Taking recycled aggregate as raw material,we adopted the method of controlling the state of fresh concrete and prepared pervious concrete and low grade(C20/C25/C30)pump concrete.The influence of various factors on the mechanical properties,permeability and partial durability of recycled aggregate concrete were studied.The better recycled aggregate concrete was obtained.The main results are as follows:(1)Compared with natural aggregate,recycled aggregate had complex composition,low packing density and apparent density,high water absorption,crush index and porosity.In the continuous gradation regenerated aggregate,18.5wt% was regenerated aggregate wrapped in waste mortar,2.5wt% was a brick and tile,0.2wt% was the other component(mainly asphalt and glass),its water absorption rate was 2.1%,porosity was 50%,the density was poor,crushing index was 16%,robustness was 6.2,the strength was low.There were many gaps in the hydration products of waste cement slurry,and the internal structure was loose.(2)The effect of particle size,bone glue ratio and recycled aggregate content on the performance of permeable concrete was studied.The optimum regenerated aggregate particle size was 4.75-9.5mm,and the recycled aggregate content was 10wt%,the best comprehensive performance was obtained.When the design porosity was 20%,the optimum bone-glue ratio was 2.83,the porosity was 21.3%,The Permeability coefficient was 3.37mm/s,and the 28 d compressive strength was 19.2MPa.(3)With the large amount of recycled aggregate,the important order of the factors affecting the 28 d compressive strength of pervious concrete was: water reducing agent content> mineral powder content> recycled aggregate content,and the important order of the factors affecting the porosity was: recycled aggregate content> water reducing agent content> mineral powder content.The optimum mixing ratio was mineral powder 20wt%,water reducing agent 1.4wt% and recycled aggregate 50wt%,7d/28 d compressive strength were 20.7MPa and 21.8MPa respectively,the permeability coefficient and porosity were 2.83mm/s and 21.6% respectively.(4)With the increase of the recycled aggregate content,the compressive strength of each pump concrete showed a tendency to decrease.The compressive strength of C20/C25 recycled aggregate pump concrete was lower than that of natural aggregate pump concrete;when the amount of 25wt%,C30 recycled aggregate pump concrete was slightly higher than that of natural aggregate pump concrete.As the amount of admixture increases,the strength decreased gradually.The best volume of recycled aggregate in pump concrete was 25wt%-50wt%.With the increase of fly ash content,the compressive strength of C30 recycled aggregate concrete was increasing,and the best content of fly ash was 35wt%.(5)By orthogonal test,the important order of the factors affecting the 28 d compressive strength of C25 recycled aggregate pump concrete was: sand ratio> regenerated aggregate content> fly ash content,and the optimum mix ratio was fly ash content 28wt%,sand ratio 46%,recycled aggregate content 100wt%,and 28 d compressive strength to 42.2MPa.the important factors influencing 28 d compressive strength of C30 recycled aggregate pump concrete was: recycled aggregate content> fly ash content> sand rate.The optimum mixture ratio was: fly ash content 40wt%,sand rate 47%,and recycled aggregate content 50wt%,the compressive strength was up to 43.9MPa.(6)Compared with the C30 natural aggregate pump concrete,the increase of the fly ash improved the dry shrinkage resistance of the recycled aggregate pump concrete.When the recycled aggregate was 50wt%,the dry shrinkage resistance was better.With the increase of erosion age,the loss rate of concrete strength increased gradually.When the recycled aggregate was 50wt%,the resistance to sea water erosion is relatively superior.At 6 months,the erosion loss rate of seawater immersion was 0.5%,and that of seawater drying and wetting cycle was 43.8%.Therefore,the recycled aggregate content was not more than 50wt%.