Concrete characterization through fracture mechanics and selected pavement applications

The tensile strength used in the design of concrete structures, such as concrete pavement systems, has typically been determined based on small test specimens. It is well known that strength values obtained from different specimens can be largely different. Naturally, one must question the applicability of strength values obtained from these conventional specimens to an actual structure. This deficiency is encompassed within effects of specimen (or structure) size and geometry on the strength. Given that fracture parameters can be used to determine concrete strength, a simplified tension test method, based on the fracture mechanics theory, is developed to determine fracture parameters. Special emphasis is given to concrete pavement systems where tension type tests are particularly important since most distresses in such structures are due to tension-induced cracking. Applications of the method to determine concrete fracture resistance are also discussed as they apply to concrete pavement sawcut depth and timing requirements. In order to investigate crack growth in concrete materials under both monotonic and cyclic loading, a cohesive zone model (CZM) is presented. The often disregarded mixed fracture mode common in most real fracture problems is considered by coupling normal and tangential behavior within the cohesive zone. Based on the CZM, subsurface crack formation and subsequent spalling development in concrete pavements are investigated. Stresses due to temperature and moisture variation are considered when investigating crack formation. Then crack evolution due to load repetitions is studied. A model for spalling development in concrete pavements due to subsurface crack evolution is proposed. Finally, a method that characterizes the mortar-aggregate interfacial resistance to fracturing in concrete is also presented. Weak interfacial debonding has been found to be a primary factor in the formation of subsurface cracks in concrete pavements which cause subsequent spalling.