SORPTIVITY-BASED SERVICE LIFE PREDICTIONS FOR CONCRETE PAVEMENTS

SORPTIVITY-BASED SERVICE LIFE PREDICTIONS FOR CONCRETE PAVEMENTSDale P. Bentz, Mark A. Ehlen, Chiara F. Ferraris, and Edward J. GarbocziNational Institute of Standards and Technology100 Bureau Drive Stop 8621Gaithersburg, MD 20899-8621 USAABSTRACTThe degradation of concrete pavements is often controlled by the transport of a deleteriousspecies (chloride or sulfate ions, or water in the case of freeze/thaw) into the concrete. With thisin mind, a three-year research project, funded by the Federal Highway Administration, hasculminated in the development of sorptivity-based service life models for concrete pavementsand bridge decks. To develop a service life model, one needs to identify and model thesuspected degradation mechanism, develop laboratory tests to evaluate the critical materialproperties, and adequately characterize the exposure environment. For this project, degradationmechanisms for sulfate attack (ettringite-induced expansion) and freeze/thaw degradation(critical saturation of the air void system) have been postulated. To evaluate sorptivity, alaboratory-based testing protocol for conditioning and assessing the sorption properties of fieldconcrete cores has been developed and submitted to ASTM committee C09 for standardization.To characterize the exposure environment, a one-dimensional finite difference computer modelwhich utilizes typical meteorological year weather data supplied by the National RenewableEnergy Laboratory has been developed to predict the concrete pavement surface temperature andtime-of-wetness history for a wide variety of geographical locations throughout the UnitedStates. Finally, these methods and computational tools have been integrated into a computersoftware package, CONCLIFE, which provides sorptivity-based service life predictions.NOMENCLATUREt = time (s)A = surface area (m