Evaluation of Slab Shape Under Controlled Environmental Conditions

During the curing of Portland cement concrete (PCC) pavements, temperature and moisture gradients in the concrete cause pavement slabs to deform from their initial as-placed shape. Daily and seasonal environmental cycling can then cause the slabs to expand and contract horizontally with changes in average temperature and moisture conditions, and curl and warp vertically as temperature and moisture gradients change through the slab depth. This article reports on a study that evaluated slab shape under controlled environmental conditions. In the study, two 3.66 m (12 ft) wide, by 13.72 m (45 ft) long, by 254 mm (10 in) thick concrete pavements were constructed in the Ohio Accelerated Pavement Loading Facility (APLF). Transverse contraction joints were placed at 4.57 m (15 ft) intervals to create three contiguous 4.57 m (15 ft) long slabs in each pavement. Dowel bars were added to the joints in one pavement, and the other pavement was left undoweled. Results demonstrated large upward vertical deformations along the slab edges early in the curing cycle, and these deformations continued to increase throughout the duration of the tests. The slightly smaller vertical movements observed in the doweled pavement were attributed to the presence of the dowel bars. The authors conclude that by restraining joint movement, dowel bars transferred load to adjacent slabs and reduced slab deformation. They note that forces in the dowel bars were smaller than expected from reports on previous investigations, particularly during the curing process. When modeling PCC pavements, loss of support from the base should be considered as dead and live load stresses are generated in cantilevered slabs.