Alkali threshold level in concrete to trigger the alkali-silica reaction at simulated road pavement environments with alkali supply

To minimize the potential risk of concrete damage due to alkali-silica reaction (ASR) when using ordinary Portland cement in concrete mixtures, the alkali threshold level must be established for specific aggregate combinations. Since deicing salts used in the winter maintenance of highway structures can serve as an external source of alkalis, their impact on alkali threshold determination should be evaluated. An experimental investigation was conducted on concrete specimens subjected to a 60°C performance test, both with and without an external alkali supply. Concrete mixtures were prepared using Portland cements with alkali contents ranging from 0.45 % to 1.2 % Na₂O_eq. Mineral aggregates consisted of blends of potentially reactive coarse granite and natural siliceous sand, characterized by varying degrees of reactivity. The development of concrete expansion over time and associated changes in its dynamic elastic modulus, as well as the characteristics of ASR products in concrete is reported. The chemical reactivity index was determined based on the concentrations of Si, Ca, and Al in test suspensions containing aggregate, CaO, and NaOH. At simulated pavement environmental conditions variations in temperature and relative humidity in concrete were monitored. The effects of exposure conditions on expansion behavior and the composition of ASR products are discussed. The alkali threshold levels derived for such different exposure conditions are compared and analyzed in relation to the varying potential reactivity of fine aggregates.