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The overlay tester (OT) is a relatively new testing procedure that characterizes the fatigue cracking resistance of asphalt mixtures by evaluating the number of cycles to failure of a specimen. The uncertainty of the results has been a concern to some transportation agencies. A careful experimental evaluation of the OT test protocol reveals the complex stress and strain distributions that should be understood before improving the test. Thus, a study was conducted using the digital image correlation (DIC) and finite element analysis (FEA) methods to analyze the OT testing process and results. The DIC technology can be used to visualize the loading responses of the asphalt specimen and correlate them with the experimental results. The FEA, in addition to predicting the behavior of the hot mix asphalt (HMA), can be used to validate the DIC. Thus, the use of these two methods leads to a better understanding of the OT procedure.

Intelligent compaction (IC) is an emerging technology for quality management of compacted pavement layers. Data collected by a vibration sensor and translated to a stiffness-based parameter is usually called the IC measurement value (ICMV). The ICMVs are coordinated with the global positioning system (GPS) data to assess the geospatial distribution of compacted layer properties. The IC rollers can be equipped with the original equipment manufacturer (OEM) systems that are provided by the vendors. However, with the recent introduction of the after-market or retrofit IC kits, it is possible to collect IC data with most regular vibratory rollers. Even though the use of the IC retrofit kits has been gaining popularity, its performance during the field operation has not been documented extensively. In this study, two dynamic vibratory rollers equipped with the OEM IC systems were employed along a test section. A retrofit kit was also installed on one of the rollers to collect the IC data during the same field operation simultaneously with the OEM system. The geospatial distribution of the ICMVs between the two types of systems for the most part was comparable. However, the magnitudes of the ICMVs among rollers and IC systems were somewhat different. These differences in the ICMVs were attributed to the differences in the vibration sensors and their installation as well as the data reduction algorithms among different systems. The reliability of the results from the OEM systems and retrofit kits seemed to be dependent on the proper installation of the vibration sensors as well as the accurate calibration of the GPS unit prior to the field data collection. A validation system and a standard protocol are needed to harmonize the performance of the IC rollers.

The overlay tester (OT) is considered by several highway agencies as an index test to evaluate the cracking resistance of asphalt mixtures in the laboratory. The OT simulates the reflective cracking mechanism of the opening and closing of joints and/or cracks. The repeatability of the number of cycles to failure measured with the OT is expressed as a concern in reliably characterizing the potential of hot mix asphalt (HMA) mixes to cracking. The work presented in this paper was performed mainly to analyze the repeatability of the number of OT cycles to failure and the fracture energy (FE) measured with the cyclic and monotonic OT methods. The load-displacement curves from the cyclic and monotonic OT tests were compared to select the promising alternative parameters that could serve as surrogate cracking parameters. The performance of the OT test may improve if alternative parameters, such as the maximum load and fracture energy are used to estimate the cracking resistance of the HMA mixes.

This study presents the evaluation of the compaction process on a lime-stabilized clayey subgrade soil using the intelligent compaction (IC) technology. Two test beds with similar clayey subgrade soil were constructed with and without in-situ lime stabilization. These test beds were evaluated using several in situ nondestructive testing devices and an IC-equipped vibratory roller. The results from the study showed significant spatial variability in the in-situ test results and the roller measurements. In comparison to the untreated subgrade, the lime-stabilized test sections demonstrated a reduction in the variability of the roller measurements. The roller measurements on the stabilized section were influenced by the testing time and the underlying support conditions. The laboratory results and the field measurements using the roller and in-situ devices pointed to the improvement in the soil properties after stabilization. The moduli of the stabilized subgrade soil increased by almost two times. Statistical analyses demonstrated the influence of the underlying support condition, the moisture content and the lift thickness variations on the roller measurements.