The Effect Of Recycled Aggregate Treated By Carbon Dioxide On Properties Of Recycled Concrete

Recycled aggregate concrete is formed by certain or all recycled aggregate substitution ratio,the mechanical properties of recycled aggregate concrete are depended on recycled aggregate,compared with natural aggregate,recycled aggregate has higher water absorption,crushed value and has lower apparent density,which casued lower strength and durability for recycled aggregate concrete.Thus,recycled aggregate concrete was restricted in civil engineering.Recycled aggregate was treated by CO₂,its water absorption and crushed value could be decreased,and apparent density could be increased,which are helpful to mechanical properties of recycled aggregate concrete.Thus,CO₂ enhancement method of recycled aggregate has two advantages,on the one hand,the technique can caputure and absorb CO₂ at atmosphere,lowering greenhouse effect;on the other hand,The efficiency of recovery and treatment of recycled aggregate was developed,contributing to resourse recycle.This main contents investigated has two aspects :1.the influence of recycled coarse aggregate treated by CO₂ on compressive strength,drying shrinkage as well as autogenous shringkage of recycled concrete.2.the influence of recycled fine aggregate treated by CO₂ and Pozzolanic slurry on fludity,compressive strength,carbonation depth,chloride penetration resistance as well as Vickers microhardness distribution at new and old ITZs of recycled mortar.The effect of recycled coarse aggregate treated by CO₂ on the recycled aggrate concrete has showed that recycled coarse treated by CO₂ can increase compressive strength 5.2% at 50% replacement ratio and 14.7% at 100% replacement ratio compared with un-treated recycled aggregate concrete.Meanwhile,the drying shrinkage can decrease about 20% and autogenous shrinkage can decrease 37.5% above.After carbonation,attached mortar porosity has decreased which improved compressive strength and shrinkage resistance of recycled aggregate concrete.The effect of recycledfine aggregate treated by CO₂ and pozzolanic slurry on the recycled aggregate mortar has indicated that recycled aggregate treated by carbonation and pozzalanics slurry both could develop mortar properties obviously.The amplitude improved of properties of recycled aggregate mortar from large to small array silica fume slurry treatment,nano-silica slurry treatment,CO₂ treatment and fly ash slurry treatment.At 28 d age,each compressive strength has improved 55.2%,39.4%,24.4%,17.6%.Carbonation depth has decreased 37.2% for silica fume slurry treatment and has decreased 28.7% for CO₂ treatment.Chloride penetration coefficient has decreased 84.1% for silica fume slurry treatment and has decreased 66.8% for CO₂ treatment.Meanwhile,there is a correlation between compressive strength and carbonation depth,chloride penetration coefficient,as well as hardness of ITZs,which indicate that the better ITZs has advantage of compressive strength and penetration resistance.Thus,CO₂ treatment and pozzalanics slurry treatment are two efficient methods to enhance the properties of recycled aggregate and recycled aggregate concrete.