Minimizing joint opening is crucial to ensure adequate load transfer across the
joints in ultra-thin whitetopping (UTW) pavement. Several UTW parking lot projects completed at the University of Illinois indicated that the initial joint cracks occurred at every 5 to 8 joints
(for 4 by 4 ft panels). The result of this large crack spacing was wider openings at these initial crack locations and reduced load transfer. The primary objective of this theoretical thermal stress calculation for UTW was to determine if the initial crack spacing at early ages (e.g., 24 hours)
can be approximately predicted for UTW sections, and if it is possible to promote additional cracks to propagate at early ages. The two types of thermal stresses considered are axial thermal stress due to uniform temperature change in the slab and curling stress due to temperature differential
through the slab thickness. Temperature profile data and laboratory elastic and fracture parameters are presented for several concrete mixtures at early ages. The analytical model coupled with the measured data revealed that 4 by 4 ft UTW panels will not crack at every saw-cut joint for the concrete mixtures and climatic conditions evaluated. Larger joint spacing, such as 6 by 6 ft, is sufficient but still may not propagate cracks at every joint. Initiating more joint cracks at early ages can be attained by higher stresses in the concrete layer (e.g., more slab restraint or
longer slab sizes), lower material fracture properties, or a deeper notch depth.Illinois Center for Transportation; the Illinois Department of Transportation, Division of Highways; and the U.S. Department of Transportation, Federal Highway Administration.published or submitted for publicationis peer reviewe
