Leung, Chin K. (2009-05). Non-Linear Drying Diffusion and Viscoelastic Drying Shrinkage Modeling in Hardened Cement Pastes. Master's Thesis. Thesis uri icon

abstract

  • The present research seeks to study the decrease in diffusivity rate as relative humidity (RH) decreases and modeling drying shrinkage of hardened cement paste as a poroviscoelastic respose. Thin cement paste strips of 0.4 and 0.5 w/c at age 3 and 7 days were measured for mass loss and shrinkage at small RH steps in an environmental chamber at constant temperature. Non-linear drying diffusion rate of hardened cement was modeled with the use of Fick's second law of diffusion by assuming linearity of diffusion rate over short drops of ambient relative humidity. Techniques to determine drying isotherms prior to full equilibration of mass loss, as well as converting mass loss into concentration of water vapor were developed. Using the measured water vapor diffusivity, drying shrinkage strain was modeled by the theory of poroviscoelasticity. This approach was validated by determining viscoelastic properties from uniaxial creep tests considering the effect of aging by the solidification theory. A change in drying diffusion rate at different RH was observed in the 0.4 and 0.5 w/c pastes at different ages. Drying diffusion rate decreases as RH drops. This can be attributed to a change in diffusion mechanisms in the porous media at smaller pore radius. Shrinkage modeling with an average diffusion coefficient and with determined viscoelastic parameters from creep tests agreed well compared to the shrinkage data from experiments, indicating that drying shrinkage of cement paste may be considered as a poroviscoelastic reponse.
  • The present research seeks to study the decrease in diffusivity rate as relative
    humidity (RH) decreases and modeling drying shrinkage of hardened cement paste as a
    poroviscoelastic respose. Thin cement paste strips of 0.4 and 0.5 w/c at age 3 and 7 days
    were measured for mass loss and shrinkage at small RH steps in an environmental
    chamber at constant temperature. Non-linear drying diffusion rate of hardened cement
    was modeled with the use of Fick's second law of diffusion by assuming linearity of
    diffusion rate over short drops of ambient relative humidity. Techniques to determine
    drying isotherms prior to full equilibration of mass loss, as well as converting mass loss
    into concentration of water vapor were developed. Using the measured water vapor
    diffusivity, drying shrinkage strain was modeled by the theory of poroviscoelasticity.
    This approach was validated by determining viscoelastic properties from uniaxial creep
    tests considering the effect of aging by the solidification theory.
    A change in drying diffusion rate at different RH was observed in the 0.4 and 0.5
    w/c pastes at different ages. Drying diffusion rate decreases as RH drops. This can be
    attributed to a change in diffusion mechanisms in the porous media at smaller pore radius. Shrinkage modeling with an average diffusion coefficient and with determined
    viscoelastic parameters from creep tests agreed well compared to the shrinkage data
    from experiments, indicating that drying shrinkage of cement paste may be considered as
    a poroviscoelastic reponse.

publication date

  • May 2009