EVALUATION OF BONDING BETWEEN ULTRA-THIN PORTLAND CEMENT CONCRETE AND ASPHALTIC CONCRETE

Ultra-thin whitetopping (UTW) has evolved as a viable rehabilitation technique for deteriorated asphalt cement concrete (ACC) pavements. Numerous UTW projects have enabled researchers to identify key elements responsible for the successful performance of UTW. They include foundation support, interface bonding condition, portland cement concrete (PCC) thickness, fiber reinforcement usage, and joint spacing. Interface bonding condition is the most important of these elements because it enables the pavement to act as a composite structure; thus, reducing interface stresses and allowing an ultra-thin PCC overlay to perform adequately. The impact of external variables on the elements and the interaction between elements in UTW performance has not been thoroughly investigated. The objective of HR-559 by the Iowa DOT and ISU/CCE was to investigate the interface bonding condition between an ultra-thin PCC overlay and an ACC base over time, considering ACC surface preparation, PCC thickness, fiber reinforcement usage, and joint spacing variables. The goal of identifying potential debonding between the layers of pavement was researched in laboratory testing using instrumented flexural test beams and mechanical loading machines. In full scale field-testing, interface strains at the PCC/ACC interface were measured four times each year and the falling weight deflectometer deflection responses were measured at some 35 locations annually along a 7.2 mile Iowa Department of Transportation UTW project HR-559. This paper reflects on the results of the field deflection testing portion of that work.