Resistance of cement composites with an alkali carbonate reaction (ACR) to chloride ions and the freeze-thaw cycles

In moderate and cold climates, concrete infrastructures are often exposed to frost, and various de-icing salts are used to prevent the formation of ice on the surfaces. The presence of chloride ions not only triggers steel corrosion in reinforced concrete, but also interacts with the cement matrix. However, the interactions of chloride ions with the products of some decomposition mechanisms, such as the alkali-carbonate reaction (ACR), are not known. The presence of ACR is often reported for concrete mixtures prepared using crushed dolostone rocks. In this study, the durability of 7 month and about 5 year (accelerated ageing) old samples prepared using dolostone aggregate and ordinary Portland cement or slag (GGBS) cement, with a w/c ratio of 0.45, was systematically tested under exposure to freezing and thawing in a 3 % NaCl salt solution (F-T). Mass loss, length change, dynamic E-Modulus and flexural and compressive strengths were used to evaluate the physical and mechanical changes in the cement composites. XRD, SEM/EDS and thermodynamic modelling were used to identify and confirm new reaction products in the hardened cement paste (HCP). The dolostone aggregate was replaced by crushed limestone aggregate in the reference samples. Results showed highly improved durability of the dolostone and ordinary Portland cement samples, compared to the reference samples. However, the slag cement samples required more than 7 months to develop high durability. Reduction in capillary porosity caused by the formation of secondary calcite and hydrotalcite, and due to accelerated cement hydration, the increased concentration of various ions in the pore water and the physically bound chloride ions in the HCP were detected as the main mechanisms responsible for the increased durability of dolostone samples exposed to F-T. • ACR in concrete made with dolostone aggregate has been progressed. • Samples with ACR were exposed to freeze-thaw and chloride cycles. • The same ageing regimes were used in reference concrete with limestone aggregate. • Mechanical properties, change in mass, length and porosity were measured. • Tests supported by XRD and SEM-EDS showed better resistance of the ACR affected concrete.