Drying/Hydration in Cement Pastes During Curing.
Drying/Hydration in Cement Pastes During Curing.
(3583 K)
Bentz, D. P.; Hansen, K. K.; Madsen, H. D.; Vallee, F.;
Griesel, E. J.
Materials and Structures, Vol. 34, No. 243, 557-565,
November 2001.
Keywords:
cements; drying; hydration; curing; microstructures;
simulation; x ray absorption
Abstract:
As concrete cures in the field, there is a constant
competition for the mixing water between evaporation and
hydration processes. Understanding the mechanisms of
water movement in the drying/hydrating cement paste is
critical for designing curing systems and specialized
rendering materials, as well as for selecting repair
materials and methodologies. In this work, X-ray
absorption measurements indicate that fresh cement paste
dries uniformly thoughout its thickness, as opposed to
exhibiting the sharp drying front observed for most
porous materials. Furthermore, in layered composite
cement paste specimens, water always flows from the
coarser-pore layer to the finer one, both when coarser
pores are produced by using an increased water-to-cement
ratio (w/c) and when they are present due to using a
cement with a coarser particle size distribution at a
constant w/c. Conversely, no clear differential water
movement is observed between layers of cement paste and
mortar of the same nominal w/c. Based on the results of
these experiments, drying has been introduced into the
NIST CEMHYD3D cement hydration and microstructure
development model, by emptying the largest water-filled
pores present at any depth in the model specimen at a
user-specified (drying) rate. With this addition, the
CEMHYD3D model produces results in good agreement with
experimental observations of both the drying profiles
and the hydration kinetics of thin cement paste
specimens.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899