Volume 38, Issue 1 (January 2010)
Effects of Base Support and Load Transfer Efficiency (LTE) on Portland Concrete Pavement Performance
This paper presents the results of seven field investigations (US59, IH20, SH342, US75, US90, MLK Blvd., and US96) to identify the underlying causes of settling and irregular cracking in Portland cement concrete (PCC) pavement. Settling and cracking are not intended, and they are detrimental to the long-term performance of PCC pavement. The falling weight deflectometer and dynamic cone penetrometer were utilized to characterize the load transfer efficiency (LTE) and base support conditions. It was found that when there is adequate base support (e.g., a modulus>345 MPa), the irregular cracks remain tight even after decades of truck trafficking, as evident in the IH20 and MLK projects. Irregular cracks on these projects were caused by late or too-shallow saw cutting. In areas that had 50 % lower base moduli, the cracks typically grew to about 57 mm. The subsidence and settling on US59 and US75 were observed in the areas with LTE in the range of 40 %. Tie bars were found to be ruptured in those areas. When LTE exceeds 80 %, the tie bar was intact and no settling was observed. The maximum deflections were approximately eight to ten times higher in the area with settling than the area without settling. It is because the low load transfer efficacy would lead to higher deflection under truck trafficking. The high deflection would initiate pumping and then settling. Despite severe spalling observed before the overlay on US96, the stone-mastic asphalt overlay is now 5 years old, and no visible cracks can be observed. This is because of the high LTE (exceeding 85 %) and sufficient base support (modulus exceeding 1378 MPa). The results from the seven projects investigated indicate that base support and LTE play a critical role in concrete pavement performance. To minimize the cracking and settling, it is preferable to have a base modulus and LTE exceeding 345 MPa and 80 %, respectively.