Durability of Binary Concrete Mixtures Cured Below Freezing Using Non-Chloride Accelerators

Abstract: Cold weather presents significant complications to concrete construction due to slowed strength development and the potential for early age frost damage. Typical protection measures, such as heated enclosures, slow the pace of construction and increase the cost and emissions associated with winter operations. Off-the-shelf non-chloride accelerators (NCA) – dosed in quantities tailored to the specifics of a concrete placement – can be used in lieu of traditional protection measures, providing significant time, energy, and cost savings. This approach, now known as ARCTEC (Additive Regulated Concrete for Thermally Extreme Conditions), has been developed and refined over several decades of research at the USACE ERDC (Engineer Research and Development Center) CRREL (Cold Regions Research and Engineering Laboratory).
Until recently, CRREL research into the use of accelerators for cold weather protection focused on concrete mixtures containing 100% portland cement to maximize the heat produced during hydration. However, most modern mixture designs contain supplementary cementitious material (SCM) as a percent replacement of portland cement to improve long term durability. This study evaluated durability and mechanical properties of concrete mixtures containing slag or fly ash in combination with significant quantities of NCA. Mixtures containing different amounts and types of NCA were evaluated up to 90 days of age. Mixtures contained either 15% class F fly ash, 30% grade 120 ground-granulated blast furnace slag (GGBFS), or 100% type II portland cement. A set of binary mixtures without NCAs were cured at room temperature to act as controls. A known effect of NCAs is a reduction in surface resistivity measurements due to an increase in the conductivity of the pore solution. The study was designed to isolate this effect to quantify the impact of SCMs on resistivity.
Results of this study indicate that SCMs enhance the durability properties of concrete mixtures cured at subfreezing temperatures with quantities of NCA within manufacturer recommended maximums. Mixtures containing 30% GGBFS and NCA, when cured below freezing, matched the 90-day resistivity of their room-temperature counterpart. Strength testing, which occurred in parallel with the durability evaluation, indicated no loss in mechanical performance for mixtures cured below freezing. Additionally, results of the study indicate that GGBFS may enhance the acceleration caused by NCAs. Overall, the results of this study demonstrate the viability of SCM’s for durability enhancement in combination with the ARCTEC approach to cold weather construction.