The objective of this study is to identify probable processes responsible for premature deterioration of the concrete pavement of selected major state highways in Iowa and, if possible, to determine the major causes of the premature deterioration of concrete pavements.
Our project consists of three major tasks outlined in a research plan which has been developed in collaboration with the Iowa DOT. The first task consisted of field inspections of deteriorated concrete and collection of as much information as available on the pavement projects such as the concrete mix designs and constituent materials, the mixing, consolidation and curing of concretes, test records, and inspection reports. Specimens of both deteriorated and un-distressed pavements, constructed from the same concretes, have been collected.
In the second task, the concrete specimens were subjected to petrographic examination using visible light microscopy and scanning electron microscopy coupled with image analysis, and X-ray powder diffraction analysis. The intent of these investigations was to identify the major degradation process(es) causing premature deterioration of the pavement and if more than one major process was identified, assess their relative contributions.
Task three involved the attempt to identify the causes of deterioration by application of microstructure simulation, hydration simulation, and micro-mechanical models developed at NIST. Through a combination of backscattered electron and X-ray imaging, the microstructure of the distressed concretes was established. Segmenting images into constituent phases and "healing" the cracks via image processing provides a starting microstructure for operation of the models. Modeling of deterioration processes involves selected expansion of phases in accordance with proposed deterioration mechanisms. Analysis of the stress fields after a series of expansion cycles formed a basis for predicting the crack patterns associated with the different modes of deterioration. Comparison of the predicted stress fields and resulting crack patterns provided additional information regarding the potential mode(s) of deterioration.