Comparison of Protective Properties of Concretes with Low Alkali Cement

Abstract

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.