Durability of Mechanically Loaded, Freeze Thawed Concrete Determined By Water Absorption

Abstract

The design of concrete bridges is primarily focused on strength characteristics. However, it is often the case that durability characteristics, specifically early deterioration of the bridge deck, requires expensive repairs before the designed service life of the bridge can come to term. Lin et al. (2012) identified the development of microcracks as a possible source of this early deterioration. He proposed that these microcracks propagated due to high local compressive stress induced by overweight trucks. The resulting permeability increase caused by the propagation of these microcracks is not significant enough to cause the kind of early deterioration of bridge deck observed in the field. However, the combined effect of mechanical loading and F/T can cause much more severe microcrack development, and thereby, deterioration of concrete. Currently there are very few efficient ways of measuring the deterioration of concrete bridge decks. Standard tests are available for concrete samples, including ASTM C215 (dynamic modulus), ASTM C1202: Rapid Chloride Ion Penetration (RCIP), and Electrical Surface Resistivity (ESR). Alternatively, water absorption, measured by ASTM C642, can be used to determine the deterioration of concrete. The benefits of using water absorption to measure concrete durability include; relatively quick test periods, and no requirements on sample dimensions; thus, lending itself more to field testing of concrete cores extracted from bridge deck. There is precedence correlating water absorption to the durability of concrete. Lin et al. (2012) observed that water absorption was directly proportional to the amount of charge passed in RCIP tests. There were several concerns with this study, therefore, the claim that water absorption correlated to the durability of concrete required further validation. In this study, mechanically loaded, F/T concrete cylinders were subjected to a variety of tests including; dynamic modulus, water absorption, and ESR. An inversely proportional relationship was found between absorption and ESR with a coefficient of determination (R2) of 63.5%. This strong relationship very clearly provides supporting evidence to help validate the original conclusion proposed by Lin et al. (2012), that water absorption directly relates the durability of concrete.