Determination of Effective Depth to Measure Temperature Required for Structural Evaluation of Asphalt Pavements

Abstract

Performance evaluation of asphalt concrete (AC) pavements requires measurement of the temperature at a specified depth. Most of the guidelines recommend a fixed depth from the top of the pavement surface. Researchers have also suggested taking depth as a fraction of the thickness of the AC layer. However, variability in depth value is not considered and correlated with the total thickness of the AC layer. This study aims to arrive at a depth at which the measured temperature will be the best representative temperature of the AC layer. Four instrumented test sections with varying AC layer thickness were constructed and temperature data at different depths were recorded for an entire year. It was observed that the temperature gradient sets in and depends upon the layer thickness, time of the day, and environmental conditions. To negate their effect, an effective depth concept was proposed. Two approaches, based on weighted average temperature and inflection point theory, were used to arrive at the effective depth. The results from both approaches were found to be similar. The effective depth was found fluctuating within the top 20% to 50% of the AC layer, and was influenced by the total thickness of the AC layer. The effective depth converged to a midpoint depth of the AC layer when the pavement temperature exceeded 40°C. The temperature measurement at the effective depth further recommended an optimal time for scheduled maintenance.