Evaluation of FWD Load Transfer Efficiency Measurement

Abstract

This report documents an evaluation of load transfer efficiency (LTE) of dowel jointed concrete pavements. Measurement of LTE of transverse joints in concrete pavements is universally conducted using a falling weight deflectometer (FWD) device. LTE is an important parameter affecting pavement performance. Due to the importance of the results for maintenance decisions, the accuracy of the measurement technique is investigated in this report. The availability of instrumented dowel fitted concrete slabs in West Virginia Smart Road (Corridor H, Route 33 as well as Goshen Road, West Virginia) offers a unique opportunity to examine the accuracy of determining the LTE of transverse joints using FWD. For this purpose, FWD tests were conducted on both pavement sites at different times during years 2003, 2004, and 2005. Thirty transverse joints were tested along the slab edges as well as along the wheel-path. Trend analysis was performed to evaluate the effect of design features and site conditions on LTE. Key findings from this study are: (1) LTE was found to be a complex parameter that depends on many factors that include load position, testing time, slab temperature, and load transfer device. (2) Testing time and season were found to have a significant effect on the measured LTE. (3) The slabs fitted with 32 mm (1.25 in.) diameter dowels displayed higher variability of the measured LTE than those fitted with 38 mm (1.5 in.) diameter dowels. (4) Joint opening changes daily and seasonally as the ambient temperature changes. As the amount of joint opening increases due to slab contraction during winter, the measured LTE generally decreases. (5) Poor correlation was found between the deflection-based LTE and the percentage of the load transferred through the load transferring devices mounted across the transverse joint.