Vt. Ngala et al., DIFFUSION IN CEMENTITIOUS MATERIALS .2. FURTHER INVESTIGATIONS OF CHLORIDE AND OXYGEN-DIFFUSION IN WELL-CURED OPC AND OPC 30-PERCENT-PFA PASTES/, Cement and concrete research, 25(4), 1995, pp. 819-826
Citations number
14
Categorie Soggetti
Construcion & Building Technology","Material Science
Steady-state diffusion of dissolved oxygen and chloride ions in hydrat
ed OPC and OPC/30%PFA pastes, hydrated for 2 weeks at 20 degrees C and
10 weeks at 38 degrees C, was studied at water/binder (w/s) ratios 0.
4, 0.5, 0.6 and 0.7. Total porosity and a simple measure of capillary
porosity, the volume fractions of the water lost in specimens from a s
aturated surface dry condition to a near-constant weight at 90.7% rela
tive humidity, were also determined. The diffusion rate of chloride io
ns diminished markedly, to very low values, as the capillary porosity
approached zero. For a given w/s ratio or capillary porosity the chlor
ide ion diffusion coefficient for OPC/30%PFA pastes was about one orde
r of magnitude smaller than that for OPC pastes. The rate of diffusion
of dissolved oxygen also diminished as the capillary porosity reduced
but it was still significant as the capillary porosity approached zer
o. For a given capillary porosity the oxygen diffusion coefficient for
OPC/30%PFA pastes was about 30% smaller than that for OPC pastes. The
results support the view that chloride ion diffusion in pastes of low
capillary porosity is retarded by the surface charge of the hydrated
cement gel. In contrast, the hydrated cement gel is much more permeabl
e to the similarly-sized, neutral oxygen molecule.