Damage constitutive model of stirrup-confined recycled aggregate concrete after freezing and thawing cycles

Abstract

The inferior quality of recycled coarse aggregates (RA) relative to natural coarse aggregates (NA) is usually considered as unfavorable for the freeze-thaw durability of concrete. In order to study the uniaxial compressive behavior and stress-strain relationship of stirrup-confined recycled aggregate concrete (RAC) after exposure to freeze-thaw cycles (FTCs), 48 short columns incorporating different levels of RA (γ% ;i.e., 0, 30%, 70% and 100%) were fabricated and subjected to different numbers of FTCs (N; i.e., 0, 100, 150 and 200), finally these specimens were submitted to uniaxial compression tests. The effect of RA substition and FTCs on the main mechanical parameters, such as compressive strength, peak strain and ductility coefficient were discussed. A uniaxial compression damage constitutive model based on the strain equivalence hypothesis and modified Loland damage theory was established, and the evolution rule of damage variables were also studied. It was shown that the concrete with RA exhibited good freezing resistance, but the peak strain of RAC was generally larger than that of NAC, and the ductility coefficient of RAC was less than that of NAC. Compared with the experimental data, the proposed damage constitutive model was shown to be applicable to confined RAC after different numbers of FTCs. For specimens with different levels of RA, the evolution law of damage variable as increasing of strain were similar. The growth rate of freezing-thawing damage variable increased as the increment of N when the RA replacement was less than 30%, but decreased when the RA replacement reached to 70% and 100%.