H Nuclear Magnetic Resonance Characterization of Portland Cement: Molecular Diffusion of Water Studied by Spin Relaxation and Relaxation Time-Weighted Imaging.
H Nuclear Magnetic Resonance Characterization of
Portland Cement: Molecular Diffusion of Water Studied
by Spin Relaxation and Relaxation Time-Weighted Imaging.
Wang, P. S.; Ferguson, M. M.; Eng, G.; Bentz, D. P.;
Ferraris, C. F.; Clifton, J. R.
Journal of Material Science, Vol. 33, 3065-3071, 1998.
portland cement; molecular diffusion; water; nuclear
Water molecular dynamics in a hardened Portland cement
were characterized by proton Fourier transform nuclear
magnetic resonance (NMR) at 400MHz. Three different
types of water molecule (physically bound, chemically
bound and porous trapped) were observed. When the
hardened cement sample, was heated at 105 deg C, the
physically bound water diffused out of the sample as a
function of the heating time while the chemically bound
water remained in a stable form. A trace amount of the
porously trapped water was also detected to remain in
the cavities of the hardened cement even after heating
for up to 20 h at this temperature. The loss of the
physically bound water proved to be a
diffusion-controlled process as evidenced from the NMR
data and from a gravimetric technique. A Pake doublet
was observed in the NMR spectra. This is a result of the
oscillation of the water molecules with hindered
molecular motions due to their entrapment in the cement
pores. Soaking the dried samples in water resulted in
the diffusion of water back into the hardened cement as
physically bound water. Nuclear spin-spin relaxation
time, T2-weighted imaging showed that the distribution
of the physically bound water inside the cylindrical
sample formed a doughnut shape after overnight soaking.
The residual air in the cement pores may have slowed
down the diffusion rate of the water molecules back into
the dried cement.