This paper focuses on the effect of the electric field on the thermodynamic model of ion flows in the concrete pore solution. The equation for ion migrations was derived from the mass balance in the multi-component system and material constants. Then, using only one component -chloride ion, a reliable diffusion coefficient was determined from the formulated converse task of the migration equation. Taking into account experimentally obtained distribution of chloride concentrations under the electric field, the diffusion coefficient was determined. The distribution of the chloride concentrations was calculated on the basis of that coefficient. And then, it was compared with the measurement results for concentrations of chlorides penetrating into concrete via diffusion. The lowest mean square error between the experimental and calculated distributions of mass densities indicated the reliable value of the chloride diffusion coefficient.

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This research paper is the result of observations made during tests according to various standards carried out on behalf of industry. The article presents diffusion coefficient values calculated according to the thermodynamic migration model for twenty different concrete mixes and some selected mixes of the codified approaches known as ASTM 1202, NT BUILD 443, NT BUILD 492, ASTM 1556. The method used here, according to the thermodynamic model of migration, allows determination of the value of the diffusion coefficient after short studies of the migration of chloride ions into concrete and was described in earlier works by one of the authors. Unfortunately, when using standard methods, the values of diffusion coefficients differ significantly from each other. In each concrete, diffusion tests were carried out in the conditions of long-term natural diffusion to verify the values determined by standard methods and according to the thermodynamic model of migration. The analysis conducted for this research paper reveals that the chloride permeability test method according to the standard ASTM C1202-97 has an almost 2.8-fold greater dispersion of the obtained results compared to the thermodynamic model of migration. It was observed that the standard NT BUILD 492 has a 3.8-fold dispersion of results compared to the method with the thermodynamic model of migration. The most time-consuming method is the standard method NT BUILD 443. The largest 3.5-fold dispersion of values concerning the reference value are observed in that method. Moreover, a method based on a thermodynamic migration model seems to be the best option of all analyzed methods. It is a quite quick, but laborious, method that should be tested for a larger number of concrete mixes. A great advantage of this method is that it is promising for a wide range of concrete mixtures, both plain concrete and concrete with various additives and admixtures, as well as high-performance concrete.

This paper presents a simple comparative method for evaluating the impact of concrete design on the effectiveness of repair with the electrochemical chloride extraction (ECE) process of reinforced concrete structures. This comparison covered two concretes with different types of used cement. Penetration of chloride ions to induce corrosion processes was accelerated with the electric field. However, the corrosion process itself occurred naturally. When the corrosion process was found to pose a risk to the reinforcement, the profile of chloride ion concentration was determined at the depth of concrete cover. Corrosion current intensity during migration and extraction processes of chloride ions was measured with the LPR method. Then, this serious condition for the structure was repaired with electrochemical chloride extraction. Rates of chloride extraction were determined from the derived concentration profiles. It should be noted that the critical concentration Ccrit = 0.4% at the rebar surface was reached after 21 days of the migration process. Moreover, after the same time of extraction, the concentration was reduced by 95% at the rebar surface, which could suggest that extraction rate was slower than chloride ion migration to concrete within the electric field. Using the migration coefficient for predicting the extraction time, as well as ignoring the variability of the extraction coefficient and the initial concentration over time, may result in too short or unnecessarily long extraction times.

Diffusion process determines the rate of chloride ions penetration in concrete and therefore diffusion coefficient values play a major role in the evaluation of protective properties in concrete with reference to reinforcement. This paper describes tests on protective properties of concrete cover made of ordinary concrete and different types of low alkali cement. The tests on four types of concrete mix which differed in a type of used cement was performed. The following types of cement were applied: in concrete C1 - cement CEM I 42.5 R characterised by high heat of hydration, rapid increase in strength and high early strength. In concrete C2 – cement CEM III/A 32.5 N-LH/HSR/NA characterised by high resistance to chemical aggression. In concrete C3 – cement CEM I 42.5 N/SR3/NA with high chemical resistance, particularly to sulphate corrosion, low content of Na2O alkali, tricalcium aluminate C3A and aluminium oxide Al2O3. In concrete C4 – cement CEM IV/B (V) 32.5 R – LH/NA characterised by a stable increase in strength, increased strength during longer stages of concrete curing. Protective properties of concrete cover for reinforcing steel were specified by determining values of chloride diffusion coefficients describing flow rate of chloride ions in wet concrete. Chloride diffusion coefficients were determined on the basis of the thermodynamic model of chloride flow in the electric field. Migration tests in the electric field were used to determine diffusion coefficients. Then, distribution of chloride concentrations in diffusion tests with the forecast distribution of chloride concentrations, taking into account the obtained values of chloride concentrations was compared. Consequently, reliable values of diffusion coefficients were determined. Also the forecast durability of concrete structure made of tested types of concrete was specified.