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.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2009-05-441 |
| Date | 2009 May 1900 |
| Creators | Leung, Chin K. |
| Contributors | Grasley, Zachary |
| Source Sets | Texas A and M University |
| Language | English |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | application/pdf |
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