Effect of Chloride and Sulphate Environments on the Compressive Strength, Density and Electrical Resistivity of Ultra-High Performance Concrete (UHPC)

Concrete resistance to chloride ion penetration is an important parameter against the corrosion of rebars. The rapid chloride permeability test has already been used to predict UHPC’s resistance at ages up to 28 days under different curing regimes. However, the simple and non-destructive surface electrical resistivity (ER) method, standard specimens, for longer than 28 days and the effects of sulphate and chloride have seldom been considered in UHPC. Here, the ER and compressive strength (CS) tests were performed on 45 UHPC cylindrical specimen with a diameter of 10 cm and a height of 20 cm cured in water,10% magnesium sulphate and 3.5% sodium chloride solutions for 7, 14, 28, 56 and 90 days. The ER, CS and density increase with age. However, concerning the reduction in ER, the chloride environment was more damaging than the sulphate one. In addition, sulphate had a more destructive effect than chloride on the 90-day CS, so that 3.5% sodium chloride and 10% magnesium sulphate solutions resulted in a decrease after 90 days of 8.73% and 25.5% compared to the control sample, respectively. Furthermore, the curing process affected density’s evolution. Chloride ion penetration was negligible in the specimens cured in water and very low in those cured in the sodium chloride and magnesium sulphate solutions. The results were interpreted by XRD, EDS and SEM. A correlation between ER and CS is proposed.