Current Recommendations to Mitigate Chemical Deicer Distress
Guidance to address conventional physical freeze-thaw deterioration in the presence of deicers, including scaling, is well-documented (Kosmatka and Wilson 2016; ACI 2016). Recommendations include the use of a relatively low w/cm (0.45 or lower), entrainment of an air-void system capable of relieving osmotic and hydraulic stresses generated as ice forms, good finishing practices so that the w/cm and the entrained air-void system is not altered at the surface, and adequate curing to support cement hydration. To avoid physical freeze-thaw damage at joint locations, it is essential that the concrete does not become critically saturated. This occurrence can be minimized through design, construction, and maintenance strategies that (1) reduce the ingress of water-salt solutions into joints, and (2) quickly drain these solutions from the joint. These steps will help avoid critical saturation of the concrete that would lead to freeze-thaw damage in even a few cycles.
Recommendations for addressing chemical deicer distress are still under development, but research has focused on the need to (1) reduce the amount of calcium hydroxide present in the HCP, or (2) decrease the access of salt solution into the concrete. The use of supplementary cementitious materials (SCMs) will reduce the amount of calcium hydroxide in the HCP as well as decrease the permeability of the concrete, thereby reducing salt solution ingress. The ability of SCMs to reduce calcium hydroxide is partially due to dilution, in which the portland cement is replaced by SCMs, and partially by the consumption of calcium hydroxide through the pozzolanic reaction that occurs with certain SCMs (e.g., fly ash, slag cement and silica fume). Reducing calcium hydroxide results directly in a reduction in the formation of calcium oxychloride, as illustrated in figure 8, which also illustrates that cement source/composition influences the amount of calcium oxychloride that forms (Weiss and Farnam 2015).
Another method for reducing salt solution ingress is through some type of barrier. Research has suggested that the application of certain penetrating sealants (i.e., certain silanes, siloxanes, soy methyl ester polystyrene, and others) directly to concrete joints may provide a barrier to the ingress of chemical deicers and offer some level of protection (Sutter et al. 2008; Weiss and Farnam 2015). Laboratory studies and field test site monitoring are underway to determine the efficacy of this strategy.
AASHTO PP-84 (AASHTO 2017) describes a test method based on low-temperature differential scanning calorimeter (LT-DSC) that can be used to evaluate the potential reactivity of HCP and a salt solution by measuring the heat associated with calcium oxychloride formation (Weiss and Farnam 2015; Monical et al. 2016). If proven reliable, this method will provide a method for optimizing the composition of the cementitious materials by minimizing the potential for formation of calcium oxychloride. It will be possible to test specific portland cement and SCM systems, making this a practical screening tool for selecting materials for use under anticipated deicing conditions.
