The Traffic Speed Deflectometer (TSD) is increasingly utilised as a nondestructive tool for measuring continuous deflections in asphalt pavements. These deflections are calculated from real-time measurements of deformation velocities recorded using the device’s laser vibrometer, combined with the vehicle's travelling speed. However, existing methods for calculating TSD deflections are limited by accuracy and computational efficiency constraints. To address these issues, an improved deflection calculation method was developed. First, finite element (FE) simulations were performed to clarify the deflection slope distribution characteristics of typical flexible and semi-rigid pavements under various conditions. Various fitting curves were then applied to the deflection slope data to identify the most suitable models, and an improved curve area integration method was employed to calculate the corresponding deflection values. Additionally, the impact of different subgrade moduli on the far-end deflection basin of semi-rigid pavements was analyzed, allowing for the determination of the zero-response position of the deflection slope, leding to a proposed correction method for TSD measurements. Finally, the improved deflection calculation method was validated through comparative error analysis with TSD-measured values and FE model results, demonstrating its accuracy and reliability. The findings are expected to support more precise TSD deflection basin determination, improving pavement condition assessment.

Asphalt concrete overlay is typically designed to be thin to minimise maintenance and rehabilitation costs, which makes it challenging to be compacted and may affect its bonding conditions with the existing pavement. The short-term preheating involves swiftly heating the pavement surface before overlay paving commences, aiming to enhance the bonding conditions between the overlay and the existing pavement. Implementing the preheating approach requires a comprehensive understanding of thermal behaviours exhibited by existing pavement under short-term preheating and the factors affecting it. In this research, the feasibility of using electric heating tubes as short-term preheating heat source was analysed, and a finite element (FE) model for analysing the thermal behaviour of asphalt pavements under rapid preheating was developed. The key control parameter between the heat source and the pavement were determined and calibrated by field tests. Further sensitivity analyses of the effects of multiple factors on the thermal response of the pavement during rapid preheating were conducted, and a prediction model of the maximum pavement temperature achievable through preheating was developed. The established prediction model is expected to provide references for implementing short-term preheating in pavement overlay construction.

This research aimed to investigate the attenuation mode of the layer modulus of asphalt pavement in accelerated pavement testing (APT). A full-scale experimental section was constructed and tested using the APT facility. Two non-destructive testing (NDT) methods, named falling weight deflectometer (FWD) technique and portable seismic property analyzer (PSPA) test, were used to obtain the layer moduli of asphalt pavement during the APT test. The variation patterns of layer moduli obtained by FWD and PSPA tests were calculated and compared after the temperature was corrected to 20 ℃. It was found that the variation pattern of surface layer modulus based on field FWD measurements was consistent with the one measured from PSPA tests. That is the modulus of the surface layer increases with the APT load repetitions firstly and then decreases with the rise of the repetitions. The modulus values of the surface layer measured from PSPA tests are obviously larger than those backcalculated based on deflection basins. The ratio of the measured surface layer modulus based on the PSPA test to the backcalculated one based on the FWD test ranges between 2.06 and 2.71. The backcalculated base layer modulus always declines with the increasing loading repetitions. The attenuation patterns of the surface layer modulus and the base layer modulus in the damage stage are described as E_a=421100*N^-0.6119 and E_b=128000*N^-0.1096, respectively.

The asphalt-based pavement performance evaluation includes the derivation of the dynamic moduli and loading frequencies of pavement layers under various traffic- and climatic-induced loading conditions. The traffic-induced strain pulses and loading frequencies of commonly used (semi-rigid, flexible, and steel deck) asphalt pavements were experimentally determined by vehicular loading field tests with embedded strain gauges for different axle loads, motion speeds, and temperatures. It was found that the axle load values had no noticeable effect on the pavement loading frequency, which was mainly controlled by the vehicular motion speed. The transverse frequencies were found to be higher than longitudinal ones, while the distributions of loading frequencies by pavement depth differed for three pavements under study. The frequency values at temperatures over 35 °C exceeded those at lower temperatures, while in the temperature range from 4 to 31 °C, the motion speed vs. loading frequency relations for three pavements were nearly identical. The loading frequency f increased approximately linearly with the motion speed V, according to the unified fitting equation for three types of pavements under study, namely f = 0.127 × V. This unified equation was further proved valid to predict the dynamic modulus properties of field asphalt pavement layers. Moreover, several previous prediction models for loading frequency, including the Brown model, Ullidtz model, MEPDG procedure and Ulloa model, were compared to the results in this study. These previous models were found to overestimate the loading frequencies within the asphalt layer. The prediction errors of the Brown model and the Ullidtz model were pronounced. The loading frequencies calculated by the MEPDG procedure and the Ulloa model need to be modified by dividing 2.8 and 1.7, respectively.

The modulus of asphalt mixture is traditionally measured from the laboratory dynamic modulus test. However, different laboratory test methods often lead to obviously different test results. To evaluate the moduli of asphalt mixtures as constructed in field pavements, this study back-calculated the moduli of the pavement layers, based on measured strain data in Accelerated Pavement Testing (APT). Field tests were conducted to measure strains at different locations of the built pavement section at different temperatures and wheel motion speed. The loading frequencies of the asphalt layer subject to different motion speeds were calculated based on the duration of measured strain pulses. Subsequently, the relationship between the motion speed and the loading frequency was established. An finite element (FE) model of the pavement section was created, which was used to back-calculate the moduli of asphalt pavement layers using the measured strain data. Based on the back-calculation results at different loading conditions, the master curve of the field asphalt layer was determined. This master curve was further used to compare with that obtained from laboratory uniaxial compressive test. The relationship between the field and laboratory moduli was determined to be E_Laboratory= 1.298E_Field.