The Influences On Stress-strain Curves Of Recycled Concrete Enhanced By Recycled Aggregate Cured By CO₂

It's environmental to crush waste concrete as recycled aggregate for cyclic utilization,and it also can solve the lack of natural aggregate.As a product of concrete crushing,the recycled aggregate is born with many defects that caused by mechanical crushing.The old cement mortar covering the recycled aggregate will certainly decrease the performance of the recycled aggregate.In the experiment,we use CO2 curing pressurization method to achieve the performance improving of the recycled aggregate,and this green method can absorb carbon dioxide.When under pressure,the carbon dioxide will reacts with old mortar.The reaction product will fill the pores within the aggregate and improve the interfacial transition zone of mortar and aggregate,with the result that it can enhance the recycled aggregate.The main research content and results are as follows:1.Setting the carbonization period(Oh,6h,12h,24h,48h,72h)of recycled aggregate and the carbon dioxide gas pressure(0.1 MPa,0.4MPa,0.8MPa)in sealed container as variables,we compared the basic properties of carbonized recycled aggregate and uncarbonized recycled aggregate and studied on effects of carbonation on mechanical properties of recycled concrete.Results show that the carbonation of recycled coarse aggregate processing can improve its performance,and the compressive strength,elastic modulus of recycled concrete with carbonized aggregate is higher than the recycled concrete's with uncarbonized aggregate.The optimal way of carbonization of recycled coarse aggregate is keeping the CO2 pressure in the reaction vessel at 0.4MPa,and the recycled coarse aggregate carbonization period is 24 hours.2.Using natural coarse aggregate,carbonized recycled aggregate and uncarbonized recycled aggregate to make 9 sets of concrete prism(including 54 pieces of 100mm× 100mm×300mm prism),and determining the stress-strain curves of concrete under uniaxial compression to study on the effects of the replacement rate and carbonation of recycled coarse aggregates on the constitutive relations of the concrete under uniaxial pressure.The failure mode of concrete shows:Under uniaxial compressive stress,concrete prisms show diagonal shear failure.The angle between principal inclined crack and the load perpendicular of recycled concrete is wider than natural aggregate concrete.However,the age of concrete and the carbonization of recycled coarse aggregates have no obvious influence on the angle.3.Study on the influence of carbonization of recycled coarse aggregate on the recycled concrete stress-strain curves.The contrast between recycled concrete with carbonized aggregate and recycled concrete with uncarbonized aggregate indicate:When recycled coarse aggregates replacement rate is same,the peak stress of recycled concrete with carbonized aggregate is higher,while the peak strain and ultimate strain are smaller,and the slope of upward section of curve is greater.When the recycled coarse aggregates replacement rate is 50%,70%or 100%,the steepness of downward section of curve of recycled concrete with carbonized aggregate is smaller and the ductility is also greater.4.The determination of Poisson's ratio of various concrete indicate that when the ratio of ?/fc is 0.3,the Poisson's ratio of various concrete is about 0.2,and there is no significant difference.5.According to the results,the stress-strain curve of recycled concrete with uncarbonized aggregate,recycled concrete with carbonized aggregate and natural aggregate concrete were fitted by using dimensionless equation,obtaining a suitable mathematical relation.