Soojun Ha

Effects of Creep and Built-In Curling on Stress Development of Portland Cement Concrete Pavement under Environmental Loadings

An adequate evaluation of stress developments in concrete is essential to ensure well-performing and long-lasting portland cement concrete (PCC) pavement designs and construction. In this study, the effects of creep and built-in curling (BIC) on the stress history of PCC pavements under environmental loadings were investigated primarily through a series of field tests and numerical data interpretations. To identify the stress-dependent strain component within the in situ measured total strain, a nonstress cylinder (NC) was employed in the field tests. The identified stress-dependent strains from the field tests were converted to stresses using a step-by-step numerical method. To investigate the effect of creep on stress developments, stress histories were computed in two different ways—one with elastic analysis and the other with viscoelastic analysis—and then their difference (stress relaxation) over time was evaluated. The finding indicated that creep may be a key element in the evaluation of long-term stresses and, in turn, the design and analysis of PCC pavements. Furthermore, this study examined the impacts of BIC on the residual stresses of PCC pavements. The result showed that BIC may affect the early-age stress development, but it has little influence on the long-term environmental stress state.

Mechanism of Transverse Crack Development in Continuously Reinforced Concrete Pavement at Early Ages

The transverse crack in continuously reinforced concrete pavement (CRCP), more specifically transverse crack spacing and crack widths, has been cited as one of the most important pavement structural responses determining CRCP performance. Efforts have been made to predict crack spacing and crack widths for given environmental conditions and traffic loading, pavement structure, and material properties, with the primary objective of developing rational CRCP designs. However, that most transverse cracks develop at or near transverse steel implies substantial interactions between transverse steel and other factors causing transverse cracks. These interactions have not been fully incorporated in the theoretical models developed so far to predict transverse crack spacing and crack widths in CRCP. This study investigated the interactions between transverse steel and other factors and identified the mechanisms of transverse crack development at or near the transverse steel. Drying shrinkage and temperature drop in concrete cause concrete volume contractions in all directions (not just transverse and longitudinal, but vertical directions as well). Interactions between concrete volume contraction vertically and transverse steel cause larger concrete tensile stresses at or near transverse steel than at other areas and cause a higher probability of transverse cracks near transverse steel. Traditionally, subgrade drag theory has been used in the design of transverse steel even though current practice is to place just enough transverse steel to support longitudinal steel during concrete placement. If transverse cracks have such substantial effects on CRCP performance as currently thought, interactions between transverse steel and other factors should be considered in the design of optimum transverse steel.

Behavior of Tied Multiple-Lane Portland Cement Concrete Pavement: Effects of Environmental Loading and Dowel Bar Use

Tie bars are used at longitudinal construction joints (LCJs) in portland cement concrete (PCC) pavement primarily to keep lanes from separating. As more lanes are tied together because of ever-increasing traffic volume, concerns about the potential for longitudinal cracking have led to the use of dowel bars at LCJs. However, a survey of a number of state highway agencies (SHAs) revealed that few of them have guidelines and design standards for the use of dowel bars at LCJs and that no in-depth studies conducted in this area have been identified. The effects of multiple lane ties and dowel bar placements in PCC pavements are analyzed in this paper to provide basic information on whether dowel bars are really needed, and if they are, where they should be placed and what their advantages and disadvantages are. Field testing verified that the longitudinal cracking potential is greater as slab thickness and lane width increase. The effects of multiple lane ties and dowel bar placements at LCJs are evaluated with numerical analysis. Placing dowel bars in lieu of tie bars reduces the longitudinal cracking potential, and the effectiveness of using dowel bars is enhanced when they are applied to thicker and wider pavements. However, the use of dowel bars could result in increased potential for lane separations.