In this study, the dynamic behavior of asphalt pavement from the Rolling Dynamic Deflectometer (RDD) was investigated. The effect of the loading frequency to the RDD deflections was evaluated by conducting RDD tests on several road sections. Stationary RDD tests were done to measure the forced and free vibration response of the pavement in which steady-state and decaying response signals were observed. It was found that aside from calculating the peak-to-peak deflections from the RDD forced vibration, the pavement’s natural frequency and damping ratio can be determined from the RDD free vibration response. To verify whether the measured natural frequency and damping ratio represent the dynamic response of the pavement system, a frequency sweep response (FSR) test was conducted. First, the repeatability of free vibration testing was studied by evaluating the measured responses at different locations. Then, a steady-state vibration equation was used to predict the response of the pavement system from a sinusoidal loading using the damping ratio and natural frequency measured in the field. The measured deflections from field FSR testing showed a good correlation with the predicted response, suggesting that the measured natural frequency and damping ratio represent the pavement at a unique stiffness parameter, $k$ .

Double bituminous surface treatment (DBST) has been a widely utilized pavement maintenance material due to its capability to restore the surface roughness of existing pavement and provide a layer of protection against weathering, aging, and moisture. However, DBST is highly prone to aggregate loss at an early stage, which is a very common problem experienced by surface treatment. Therefore, to lessen the aggregate loss and prolong the service life of DBST, fiber additive can be incorporated to strengthen the adhesion between the asphalt emulsion and aggregates. This study investigated the performance of glass fiber-reinforced polymer-modified DBST against aggregate loss by conducting laboratory tests using typical DBST as the benchmark of the test results. Four laboratory tests were chosen to represent different loading applications on the surface of the pavement: the bitumen bond strength (BBS) test, the sweep test, the Hamburg wheel-track test (HWT test), and a one-third-scale model mobile load simulator (MMLS3) model. Furthermore, the curing time of the asphalt emulsion was considered in the BBS test and sweep test. Based on all results from the conducted laboratory tests, polymer-modified DBST with glass fiber reinforcement presented an increased resistance to aggregate loss compared with typical DBST. Moreover, it was found that a longer curing time of the asphalt emulsion, whether it was typical or modified, strengthened the surface treatment’s resistance to aggregate loss.

Cambodia’s transportation sector has exhibited tremendous growth in the past decades together with its economic advancement. However, these improvements are only focused on the national and provincial roads, leaving the rural roads underdeveloped. A large percentage of the rural roads in Cambodia are unpaved while those paved roads are in deteriorated condition, making these rural roads prone to structural failure when subjected to heavy truck traffic and massive rainfall. Therefore, an innovative pavement material shall be used in the construction and rehabilitation of Cambodian rural roads. In this study, a composite pavement testbed consisting of a roller compacted cement (RCC) base layer and a modified double bituminous surface treatment (DBST), namely multi-layered bituminous surface treatment (MAST), was constructed in Cambodia and its performance was evaluated. To have a point of comparison, the testbed was divided into three sections with varying combinations of surface and base layer: (1) MAST surface with an RCC base, (2) MAST surface with an aggregate base, and (3) DBST surface with an aggregate base. Initially, a visual inspection was conducted to investigate the surface condition of the testbed. To assess the structural capacity, a light-falling weight deflectometer device was used. Meanwhile, the surface roughness was evaluated through the sand patch test. Lastly, the pass-by test was performed to quantify the noise level of the pavement. Based on the results, the proposed composite pavement performed significantly superior to the typical pavement in Cambodia, which is the third section. In summary, the composite pavement with MAST as the surface layer and RCC as the base layer was observed to be suitable for heavy truck traffic loading and the environmental conditions of Cambodia.

Pavement response depends not only on loading magnitude and pavement material properties but also on the pavement’s dynamic parameters such as inertia, resonance, and damping. In a previous study, it was found that by using rolling dynamic deflectometer (RDD) free vibration testing, the resonant natural frequency and the damping ratio of the pavement could be determined, which is essential in determining the pavement stiffness, $k$ . In this study, a back-calculation approach using RDD-measured deflections considering the natural frequency and loading frequency was proposed. A three-dimensional (3D) finite-element (FE) model was established simulating RDD loading on a three-layered pavement system consisting of asphalt, subbase, and subgrade. Using the FE model, a synthetic database composed of different pavement conditions and deflection responses was developed. The synthetic database was trained to predict natural frequency and deflections using deep-learning neural networks (DLNN). A back-calculation algorithm was then established determining the pavement modulus and thickness using the pavement’s natural frequency, deflection response, and RDD loading frequency. The proposed approach was validated by comparing the RDD and falling-weight deflectometer (FWD) back-calculated modulus using static and dynamic analysis. The RDD back-calculated modulus at 25 Hz was found to have good correlation with the FWD back-calculated modulus with an assumed hitting frequency of 33 Hz. In addition, modulus values of field cored specimens were compared with the RDD back-calculated modulus and were found to have good correlation.

Asphalt pavements in hot and humid regions such as Southeast Asia are highly susceptible to moisture-induced debonding, especially when WMA is produced using marginal aggregates or less favorable gradation conditions. This study develops an anti-stripping-focused polymer-modified WMA system using SBS and a silane-based liquid additive. This study focuses on evaluating the coupled contribution of SBS-related binder cohesion and silane-related interfacial adhesion under poor gradation conditions, and verifies the selected system through binder-level, mixture-level, durability, and cost-efficiency evaluations. SBS contents of 4.0%, 4.5%, and 5.0% by binder mass were combined with silane dosages of 0%, 0.05%, 0.10%, and 0.15%. The mixtures were evaluated using MSCR, Marshall stability and flow, dry and wet ITS, TSR, Hamburg Wheel Tracking, SCB, and Overlay Test. SBS alone increased dry ITS and Marshall stability, but silane-free mixtures still showed low TSR values of 71.7–73.3%. The optimum mixture, S4.5-Si0.10, achieved a dry ITS of 0.94 MPa, wet ITS of 0.80 MPa, TSR of 85.1%, and Marshall stability of 13.8 kN. MSCR results confirmed that SBS reduced accumulated strain at both 0.1 and 3.2 kPa, while silane did not adversely affect binder deformation resistance. In Stage 2, the optimized SBS–silane mixture under poor gradation reduced Hamburg final settlement by 54.7% compared with the poor-gradation control. SCB work of fracture increased from 1.34 J to 5.20 J, and Overlay Test results confirmed improved load retention. The optimized mixture also reduced the annualized cost index by 27.2%. These findings demonstrate that a balanced SBS–silane WMA system can improve debonding resistance and durability under hot and humid pavement conditions.