Abraham Bae

Observed evidence of subgrade moisture influence on pavement longitudinal profile

The relationship between subgrade moisture parameters and pavement profile was explored for 34 asphalt pavements of the seasonal monitoring program (SMP) in the long-term pavement performance (LTPP...

Bond Characteristics at the Interface between HMA Surface and RCC Base

PURPOSES : A composite pavement utilizes both an asphalt surface and a concrete base. Typically, a concrete base layer provides structural capacity, while an asphalt surface layer provides smoothness and riding quality. This pavement type can be used in conjunction with rollercompacted concrete (RCC) pavement as a base layer due to its fast construction, economic efficiency, and structural performance. However, the service life and functionality of composite pavement may be reduced due to interfacial bond failure. Therefore, adequate interfacial bonding between the asphalt surface and the concrete base is essential to achieving monolithic behavior. The purpose of this study is to investigate the bond characteristics at the interface between asphalt (HMA; hot-mixed asphalt) and the RCC base. METHODS : This study was performed to determine the optimal type and application rate of tack coat material for RCC-base composite pavement. In addition, the core size effect, temperature condition, and bonding failure shape were analyzed to investigate the bonding characteristics at the interface between the RCC base and HMA surface. To evaluate the bond strength, a pull-off test was performed using different diameters of specimens such as 50 mm and 100 mm. Tack coat materials such as RSC-4 and BD-Coat were applied in amounts of 0.3, 0.5, 0.7, 0.9, and 1.1l/m to determine the optimal application rate. In order to evaluate the bond strength characteristics with temperature changes, a pull-off test was carried out at -15, 0, 20, and 40 °C. In addition, the bond failure shapes were analyzed using an image analysis program after the pull-off tests were completed. RESULTS : The test results indicated that the optimal application rate of RSC-4 and BD-Coat were 0.8l/m, 0.9 l/m, respectively. The core size effect was determined to be negligible because the bond strengths were similar in specimens with diameters of 50 mm and 100 mm. The bond strengths of RSC-4 and BD-Coat were found to decrease significantly when the temperature increased. As a result of the bonding failure shape in low-temperature conditions such as -15, 0, and 20 °C, it was found that most of the debonding occurred at the interface between the tack coat and RCC surface. On the other hand, the interface between the HMA and tack coat was weaker than that between the tack coat and RCC at a high temperature of 40 °C. CONCLUSIONS : This study suggested an optimal application rate of tack coat materials to apply to RCC-base composite pavement. The bond strengths at high temperatures were significantly lower than the required bond (tensile) strength of 0.4 MPa. It was known that the temperature was a critical factor affecting the bond strength at the interface of the RCC-base composite pavement.

Evaluation of Various Test Devices for the Measurements of Aggregates and Asphalt Mixtures’ Specific Gravity

Current test procedures for determining the density properties of aggregate and hot mix asphalt mixtures (HMA) are time consuming and subjective. The density can have significant impact on the performance of asphalt pavements. Three devices (SSDetect, CoreLok, and CoreDry) which can significantly reduce testing time were independently evaluated. Three experiments were performed to evaluate these devices. In the first experiment, specific gravity and absorption of two aggregate types (coarse sand and number 11 limestone) were conducted. The second experiment evaluated the HMA mixture bulk specific gravity (Gmb) of two mixture types (open graded friction coarse and dense graded). The last experiment examined the HMA Gmb of roadway cores. It is noted that the results from these test devices were compared to their counterpart conventional ones. Ten laboratories in Louisiana participated in this experimental program. In general, the SSDetect single operator and multilaboratories precision of both aggregate specific gravity measurements were better than that determined from American Association of State Highway Transportation Officials (AASHTO) T84. Furthermore, the results from the SSDetect device did meet the AASHTO precision criterion. Also, HMA Gmb precision values for the CoreLok were similar to that of AASHTO T166 for both mixtures. HMA Gmb values computed from results of the CoreDry device were similar to the ones determined from conventional method for the roadway cores.