Influence of Calcium Nitrate and Sodium Hydroxide on Carbonation Induced Steel Corrosion in Concrete

Recent developments in concrete technology, together with sustainability concerns and requirements related to digital concrete fabrication technologies, lead to increased usage of chemical admixtures in order to achieve the needed concrete performance. However, the consequences that these compounds may have for the long-term durability are unknown, particularly concerning steel reinforcement corrosion. Here, we study the effect of NaOH and Ca(NO3)2 as common examples of a hydration activator and accelerator, respectively. It is found that both admixtures considerably increase the steel corrosion rate in carbonated concrete (by up to a factor of 20). Corrosion tests in mortar as well as in aqueous solutions, together with porosity measurements of the mortars, provided evidence that the impact of the admixtures can be mainly found in modifying the electrochemistry, that is, by introducing an additional reduction reaction or by a catalyzing effect. An estimation revealed that at usual dosages, these adverse effects will prevail for a substantial portion of the design service life of a structure, as these species will not be consumed during decades.