Peter J. Tumidajski

On the relationship between porosity and electrical resistivity in cementitious systems

Abstract The applicability of porosity-electrical resistivity relationships for hardened cementitious systems is addressed. The following equation ln F = ln μ + m · ln e = ln ( τ 2 δ ) + m · ln e relating the electrical resistivity formation factor (F) to the porosity (e), tortuosity (τ) and constrictivity (δ) was tested for Portland cement pastes hydrated up to 29 years and mortar hydrated for 28 days. Results for the well-hydrated pastes and, to a lesser degree, 28 day hydrated mortars followed the relationship.

Effect of sulfate and carbon dioxide on chloride diffusivity

Abstract The effects of sulfate and CO 2 on chloride penetration fronts and diffusivities were determined at 60 months exposure for ordinary Portland cement concrete and concrete incorporating the partial replacement of the cement with slag. It was found that sulfate and CO 2 decrease the chloride penetration and diffusivity in the ordinary Portland cement concrete whereas the opposite behavior is observed for the slag concrete. However, chloride ingress is always considerably less in the slag concrete.

Electrical conductivity of Portland cement mortars

Abstract Mortars containing volume fractions of aggregate less than 0.35 were prepared at w c = 0.35, 0.40, and 0.45 and hydrated for 1, 14, and 28 days. Mortar electrical conductivities were determined by impedance spectroscopy, and the experimental data were fitted to the polynomial, where, σm is the mortar σ m = A + B V a V m + C V a V m 2 + D V a V m 3 conductivity, Va is the aggregate volume, Vm is the mortar volume, and A, B, C, and D are constants. Mortar electrical conductivity behavior appears to involve a competition between the insulating aggregate which lowers the mortar electrical conductivity and the development of a transition zone between the paste and aggregate which increases the conductivity. Values for the transition zone electrical conductivity were determined.

On the Validity of the Katz-Thompson Equation for Permeabilities in Concrete

Hydraulic permeabilities for concrete and for concrete incorporating slag or fly ash have been determined at w/c = 0.65 and 0.55 at 7, 14, 21, and 28 days. Hydraulic permeabilities were also calculated using the Katz-Thompson equation. In all cases, the calculated hydraulic permeabilities were two orders of magnitude lower than experimentally measured hydraulic permeabilities.

An effective diffusivity for sulfate transport into concrete

The effective non-steady state diffusivity of sulfate ingress from a mixed sulfate-chloride solution into Type 50 cement concrete was determined from concentration profiles at various times up to five years. Furthermore, the influence of CO{sub 2} saturation on the effective diffusivity was determined. The time dependence of the effective non-steady sulfate diffusivities were, log (D{sub eff sul}) = {minus}6.6543--0.7626 log (t) and, log (D{sub eff sul}{sup CO{sub 2}}) = {minus}6.2873--0.8559 log (t) where D{sub eff sul} represents the effective sulfate diffusivity, D{sub eff sul}{sup CO{sub 2}} represents the effective sulfate diffusivity of the solution saturated with respect to CO{sub 2}, and t represents the time (months).

Durability of high performance concrete in magnesium brine

The durability of six concretes exposed to magnesium brine was monitored for 24 months. These concretes incorporated ground granulated blast furnace slag, silica fume, and fly ash. The Youngs moduli, chloride penetrations, and median pore diameters were measured. There was a cyclic nature to these properties due to the complicated interaction of hydration with magnesium, chloride and sulfate attack. Mineral admixtures, in combination with a long initial cure, provided the most durable concrete. Concrete with 65% slag had the best overall durability to the brines tested.

A Boltzmann-Matano analysis of chloride diffusion

The Boltzmann-Matano methodology has been applied to calculate the non-steady state chloride diffusion coefficients for concrete. It was found that the chloride diffusion coefficients depend on time and concentration/depth. The chloride diffusion coefficients were expressed as a linear function of the Boltzmann variable.

A rapid test for sulfate ingress into concrete

A rapid test, based on electrochemical polarization, is described for the ingress of sulfate into concrete. The influence of cement type, water/cement ratio and the presence of supplementary cementitious materials on the initial current delivered and total charge accumulated over six hours was investigated. The results correlate with the sulfate penetration depth determined from two year ponding experiments.

On the relationship between the formation factor and propan-2-ol diffusivity in mortars

For porous rocks saturated with saltwater and with solid phases of high resistivity, early work showed that the ratio of the saltwater saturated rock resistivity to the resistivity of the saltwater was inversely related to the respective diffusivities (or permeabilities). The applicability of resistivity-diffusivity relationships for mortars is addressed. The following equation: F = R(mortar)/R(porewater) = D(porewater)/D(mortar) relating the formation factor (F) to the resistivity (R) and diffusivity (D) was investigated for Portland cement mortars and for mortars incorporating silica fume, fly ash and blast furnace slag.

Application of danckwerts' solution to simultaneous diffusion and chemical reaction in concrete

A methodology is presented for the determination of chloride diffusivities when there is simultaneous chloride diffusion and reaction. The methodology does not expressly incorporate a choloride binding mechanism. The chloride diffusivities are comparable to those calculated with the Langmuir binding isotherm.