About the research
Iowa has adopted 14 ft widened concrete slabs (as opposed to the standard 12 ft concrete slabs) in jointed plain concrete pavement (JPCP) design and construction since the 1990s. The additional 2 ft slab paved beyond the normal traffic path is intended to reduce stresses and deflections at the critical concrete pavement edge location by effectively moving the normal traffic path well away from the edge. However, many widened concrete pavements are now approaching 20 years of service life, and some 14 ft widened concrete pavements are experiencing sudden and significant amounts of longitudinal cracking. To understand the causative factors contributing to longitudinal cracking in widened JPCP and to provide recommendations for preventing its occurrence, field investigations were performed at 12 sites in spring and summer 2017. These sites included widened JPCPs of various ages, shoulder types, mix design aspects, environmental conditions during construction, and traffic levels. The location and extent of existing longitudinal cracking, including transverse cracking, were well documented. The amount and severity of cracks were linked to traffic level and shoulder type. Concrete cores were also examined to better understand how the cracking had developed. It was found that the 14 ft widened slabs with tied PCC shoulders outperformed the others in terms of producing less cracking, even though they had experienced higher levels of truck traffic. Widened slabs with granular shoulders were the worst performers, producing higher cracking compared to others. ISLAB 2005 and EverFE 2.25 finite element analysis (FEA) programs were also utilized to demonstrate through numerical analysis the potential of top-down longitudinal cracking for widened JPCP. Transverse joints and wheel paths were found to be critical locations for longitudinal cracking. Widened slabs with skewed joints were also found to have higher potential for longitudinal cracking. Shoulder design alternatives used in Iowa were compared for their effect on longitudinal cracking when they were used adjacent to widened and regular-sized slabs.