| Diffusion mechanisms of ionic species and their relationship to basic material properties have been investigated in water-saturated, hardened cementitious materials. Granulated blast furnace slag, ultra-fine amorphous silica, fine-grained quartz, and low calcium fly ash have been blended with ordinary portland cement to provide a variety of cementitious matrices. Porosity and pore structure of hardened pastes formulated from the above have been evaluated using mercury intrusion porosimetry. The effective coefficients for Cl('-) and Cs('+) have been measured across water-saturated disks of hardened cement pastes using a new technique.; Water-to-cement or water-to-solid ratios during mixing vary from 0.30 to 0.40, while curing and diffusion were carried out between 27(DEGREES) and 60(DEGREES)C in samples cured up to ages of one year. Non-evaporable water content, bulk density, total porosity have been measured, and limited polished section scanning electron microscopy has also been conducted.; The fractional porosity, (epsilon), and the median or modal pore size, r, have been found to be related to the effective diffusion coefficient, D(,eff), of ions in water-saturated hardened cement pastes. The general relationship is given by D(,th)/D(,eff) = C(,1)(epsilon)('C(,2))r('C(,3)), where D(,th) is the diffusion coefficient of an ion at infinite dilution in water. C(,1), C(,2), and C(,3) are constants. Decreasing the water content during paste mixing results in lower ionic diffusion coefficients and porosities. Hardened cement pastes blended with blast furnace slag and amorphous silica show increased ionic diffusion with increase in curing and diffusion temperature. Fly ash and crystalline silica blending lead to lower effective ionic diffusion coefficients at higher temperatures. Blast furnace slag blends exhibit low Cl('-) and Cs('+) diffusion coefficients. Fly ash and amorphous silica blending result in low Cs('+) diffusion, while crystalline silica blending leads to low ionic diffusion at later ages, compared to the parent hardened paste. Hardened cement pastes behave as electronegative semipermeable membranes, retarding the cation preferentially over the anion. The lower effective diffusion of ions in admixture blended portland cement pastes have important application in corrosion problems and nuclear waste management. |
