Quantifying the freeze-thaw performance of air-entrained concrete using the time to reach critical saturation modelling approach

Abstract

Many State Highway Agencies have been working to develop performance-based specifications for concrete pavements and concrete bridge decks in freeze-thaw environments. A time to reach critical saturation (TTRCS) model has been proposed to estimate the freeze-thaw performance of concrete. This study evaluates the TTRCS model for thirty different concrete mixtures with varying w/c, air volumes, and quality of air void (size and spacing). Simple quality control test procedures are used to determine the input parameters for the TTRCS model. The estimated time to reach critical saturation is compared with the measured durability factor using ASTM C 666–15. Results indicate that 86% of the mixtures with air volume above 4.5% and a Sequential Air Method (SAM) Number below 0.30 have a normalized time to reach critical saturation of greater than 20, and a durability factor that is greater than 75%. The mixtures with a high range water reducer require a higher volume fraction of entrained air to satisfy the recommended limit for the durability factor. This appears to be due to an interaction between the high range water reducer and air entraining admixture which results in greater air void spacing (i.e., larger air voids). However, the addition of high range water reducer was also found to increase the time to reach critical saturation in the mixtures with a low w/c due to a refined pore structure with a reduction in the connectivity of the matrix pores. Reducing the w/c improves the freeze-thaw performance due to a reduction in the pore volume, connectivity, and absorption rate of the concrete. A relationship is developed to estimate the time to reach critical saturation based on SAM Number and apparent formation factor. In addition, a relationship is proposed to estimate the critical degree of saturation based on air void content and quality.