The combined pressure-decay technique with rheometry is developed to measure the diffusivity of carbon dioxide (CO 2 ) in bitumen at temperatures of 30, 50, and 70 °C and pressures of 2 and 4 MPa. Mixing due to shear imposed by a rheometer allows rapid direct measurement of the equilibrium pressure in CO 2 −bitumen systems accurately. The comparison of the measured equilibrium pressures with the values obtained from the data regression demonstrates significant discrepancies, which can lead to a great deviation in the diffusivity, up to 5-fold different than the true values. The measured values for the diffusivity of CO 2 into the bitumen increase with temperature, following the Arrhenius equation. By changing the temperature from 30 °C to 70 °C, the diffusivity increases by 88% at 2 MPa and 54% at 4 MPa. The diffusivity also increases with the pressure, suggesting the ease of diffusion at the presence of the CO 2 molecules in the liquid phase. The effect of pressure is more dominant at lower temperatures while the diffusivity increase is 53% at 30 °C, compared to 25% at 70 °C. Furthermore, the findings demonstrate that the CO 2 −bitumen system does not follow any constant pattern in the diffusivity−viscosity− temperature relationships, which is due to the ongoing phase change at the studied temperature range.
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