Thermodynamic and experimental study on chloride binding of limestone containing concrete in sulfate-chloride solution

Concrete's durability where sulfate and chloride ions coexist is a challenging issue. In addition, utilization of limestone powder (LS) in blended cements tended to result in physically and chemi-cally different hydration processes compared with other cements. The present study aims to eval-uate Cl- ingress into concrete samples containing LS in the presence of sulfates in exposure envi-ronment. In this regard, 3 different exposure conditions of 165 g/l NaCl, 27.5 g/l Na2SO4 + 165 g/l NaCl, and 55 g/l Na2SO4 + 165 g/l NaCl solutions have been designated. Compressive strength, capillary water absorption, surface electrical resistivity, and rapid chloride ions migra-tion tests have been carried out and the total and water-soluble Cl- penetration profiles were de-termined. Besides these experimental studies, thermodynamic modelling was conducted to simu-late the phase assemblage of samples before and after exposure to NaCl and Na2SO4 solutions. Ac-cording to the results, using LS in concretes is followed by an increase in permeability and a de-crease in compressive strength, which agree well with the outcomes of thermodynamic model-ling. In the case of single Cl- attack, adding LS results in up to 60.7% and 36.0% increase in ap-parent and non-steady state Cl- diffusion coefficients, respectively. In addition, both thermody-namic modelling and experimental studies show that the presence of sulfate ions decreases the chemical Cl- binding ability of binders, and the Cl- diffusion coefficient of samples exposed to the combined condition increases. However, by increasing the sulfate ions concentration, the Cl- ingress may be retarded.