Research On The Effect Of Reinforced Recycled Aggregate On The Performance Of Steam-cured Concrete

The recycling of construction waste has become an important measure for resource sustainability,economic sustainability and low-carbon environmental protection.Waste concrete accounts for the largest proportion in the demolition of construction waste,but its application range is limited by the high water absorption,high crushing value and low density of recycled aggregate after crushing.Therefore,in this paper,the recycled aggregate was treated by carbonization,dopamine hydrochloride solution and C-S-H crystal nucleus suspension to enhance the mechanical properties and durability of recycled concrete.(1)The recycled fine aggregate was carbonized by atmospheric pressure carbonization,pressure carbonization,carbonated water carbonization and continuous carbon dioxide liquid-solid carbonization.The water absorption,crushing value and apparent density of recycled aggregate before carbonization treatment are 8.29%,25.5%and2420kg/m~3respectively.After carbonization,the water absorption and crushing value of recycled aggregate decreased,and the apparent density increased slightly.Among them,the recycled aggregate carbonized with carbonated water for 48 hours has the following characteristics:the lowest water absorption(7.11%),the lowest crushing value(23.5%),and the highest apparent density(2610kg/m~3).The mortar made from recycled aggregate carbonized with carbonated water for 48 hours has the highest compressive strength,which is increased by 54%.(2)Due to the difference of carbonization conditions and carbonization time between atmospheric pressure carbonization and pressure carbonization,the initial moisture content of aggregate is different.The initial moisture content of recycled coarse aggregate is 20%when carbonized at atmospheric pressure for 3 and 7 days.When the pressure carbonization time is 1 hour,the initial moisture content of recycled coarse aggregate is 20%.When the pressure carbonization time is 2 days,the initial moisture content of recycled coarse aggregate is 40%.(3)Intermittent carbon dioxide liquid-solid carbonization consumes the same amount of carbon dioxide as continuous carbon dioxide liquid-solid carbonization when treating the recycled coarse aggregate.The water absorption of recycled aggregate treated by intermittent carbon dioxide liquid-solid carbonization decreased by 19.2%,and the crushing value decreased by 18.3%.The water absorption of recycled aggregate treated by continuous carbon dioxide liquid-solid carbonization decreased by 8.2%,and the crushing value decreased by 5.3%.(4)The recycled coarse aggregate was treated by atmospheric pressure carbonization,pressure carbonization,intermittent carbon dioxide liquid-solid carbonization and continuous carbon dioxide liquid-solid carbonization.Pressure carbonization treatment has the best effect on improving the compressive strength of recycled concrete,which is increased by 22.1%.Intermittent carbon dioxide liquid-solid carbonization treatment has the second effect on improving the compressive strength of recycled concrete,which is increased by 19.3%.(5)The treatment of recycled aggregate with C-S-H crystal nucleus suspension can effectively improve the compressive strength and durability of recycled concrete.With the concentration of C-S-H crystal nucleus suspension of recycled aggregate from 1%to 20%,the compressive strength of recycled concrete first increases and then decreases.When the concentration of C-S-H crystal nucleus suspension is7%,the compressive strength of recycled concrete reaches the maximum value.On the 28th day,the compressive strength of recycled concrete increased by 12.8%,the chloride ion permeability coefficient decreased by 42.5%,and the carbonation depth decreased by 43.2%.Because the nucleation particles on the surface of recycled aggregate provide nucleation sites for the interface between recycled aggregate and new slurry,promote cement hydration.And the particle size of nucleation particles is small,which can fill the pores in the new interface transition zone(ITZ)and make the matrix structure denser.(6)The recycled aggregate was soaked in dopamine hydrochloride solution with the concentration of 1g/L for 12 hours,18 hours and 24hours respectively.After soaking,the dopamine coating was formed on the surface of the recycled aggregate.The compressive strength of recycled concrete made from recycled aggregate soaked for 18 hours was significantly improved.According to the microstructure analysis,the performance of recycled concrete was improved.Because the dopamine hydrochloride on the surface of aggregate promoted the formation of AFt and CH,filled the pores between recycled aggregate and slurry,reduced the porosity of ITZ and forms a denser ITZ.