Abstract
Abstract Enhanced damage due to the alkali–silica reaction (ASR) in concrete exposed to deicing salt (NaCl) is usually attributed to binding of chloride ions in the hydration products of cement. To balance charge, OH− ions are released into the concrete pore solution which increases alkalinity. However, during NaCl ingress a decrease in the OH− concentration of the concrete pore solution due to potassium leaching would reduce SiO2 solubility and therefore ASR damage. The present work combines expansion measurements with pore solution analysis by ICP-OES and XRD measurements on concretes and hydrated cement pastes. Solubility equilibria calculations were performed with the hydrogeochemical simulation program PHREEQC. The investigations show that the OH− concentration of the pore solution is mainly lowered by potassium leaching during NaCl ingress. The OH− concentration also decreases owing to the formation of Friedel’s salt from ettringite which is associated with the release of sulphate. Although the OH− concentration with NaCl is lower, ASR damage is intensified and the silicon concentration in the pore solution is higher. Higher silicon solubility is explained by the higher total alkali concentration which increases surface silicate solubility, the formation of an aqueous complex NaHSiO 3 0 and a higher ionic strength. These effects promote the sensitivity of silicate minerals to ASR, the formation of alkali silica gel and finally ASR damage.
Highlights
In recent years, cracks were often observed in German motorway pavement and other concrete structures exposed to deicing salt [1]
Since the change in mass of the concretes produced by the uptake of storage solution is similar, it may be assumed that the ingress of NaCl is similar. These results indicate that the alkali content of the cement is no longer decisive for damaging alkali–silica reaction (ASR) in concrete exposed to external alkalis, i.e. low alkali cements in concrete exposed to deicing salt do not always prevent ASR damage as observed by other authors [23, 24]
Up to now the question whether damaging ASR in concrete is promoted by penetrating NaCl and which mechanisms can occur has not been adequately resolved
Summary
Cracks were often observed in German motorway pavement and other concrete structures exposed to deicing salt [1]. The enhancement of ASR damage in concrete structures and pavement exposed to deicing salt has been observed in many other countries and has been the subject of numerous laboratory and field investigations [3,4,5,6,7,8,9,10,11]. To investigate the effect of alkali ingress on concrete expansion, Chatterji et al [4] measured the expansion of mortar prisms (4 9 4 9 16 cm3) made with highly reactive sand during storage at 50 °C in 3 mol/L NaOH or in NaCl solutions with different concentrations (3, 2, 1 and 0.5 mol/L). After about 9 weeks, the expansion of the specimens in the NaCl solutions was considerably higher. With increasing NaCl concentration (from 0.5 to 2 mol/L), the expansion began earlier and the final expansion after 56 weeks was higher
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