The bonding condition between pavement layers plays an important role in the performance of pavement structures. In this paper, a three dimensional finite-element (3D-FE) program was used for modeling the mechanistic responses (stresses and strains) in the asphalt concrete (AC) layers by simulating two layer interfacial bonding conditions, namely fully bonded and debonded (i.e., the layer separated but still considering friction). The 3D-FE modeling incorporated actual measured vertical tire-pavement contact pressure (TPCP) and assumed horizontal TPCP, including investigating the effects of vehicle acceleration and deceleration. The results of these computational modeling are presented in this paper and indicated that the layer interfacial bonding condition has a significant effect on some pavement mechanistic responses such as the tensile, compressive, and shear stresses/strains in AC pavement structures. In general, layer interface debonding (or separation) was analytically found to indirectly exacerbat...

Conductive asphalt concrete with high thermal conductivity has been proposed to improve the solar energy collection and snow melting efficiencies of asphalt solar collector (ASC). This paper aims to provide some insight into choosing the basic materials for preparation of conductive asphalt concrete, as well as determining the evolution of thermal characteristics affected by environmental factors. The thermal properties of conductive asphalt concrete were studied by the Thermal Constants Analyzer. Experimental results showed that aggregate and conductive filler have a significant effect on the thermal properties of asphalt concrete, while the effect of asphalt binder was not evident due to its low proportion. Utilization of mineral aggregate and conductive filler with higher thermal conductivity is an efficient method to prepare conductive asphalt concrete. Moreover, change in thermal properties of asphalt concrete under different temperature and moisture conditions should be taken into account to determine the actual thermal properties of asphalt concrete. There was no noticeable difference in thermal properties of asphalt concrete before and after aging. Furthermore, freezing–thawing cycles strongly affect the thermal properties of conductive asphalt concrete, due to volume expansion and bonding degradation.

In this study, the aged asphalt binder and mixture were laboratory prepared through short-term ageing testing and long-term ageing testing. Firstly, the effect of rejuvenator on physical properties of aged asphalt binders was investigated. In addition, a series of laboratory tests were performed to evaluate the influence of ageing and rejuvenator content on the mechanical properties, durability and dynamic characteristics of asphalt mixtures. Physical test results of asphalt binder testified that rejuvenator used can efficiently recover the aged asphalt binder. However, the effect of ageing and rejuvenator content exhibits different trends depending on the physical property tests conducted. Moreover, artificially aged asphalt mixture with rejuvenator has better ability to resist moisture damage and ravelling. In addition, the ITSR value is more suitable to evaluate the moisture susceptibility for asphalt recycling. Although rejuvenator improves the thermal cracking resistance and fatigue property of aged asphalt mixture, rejuvenated mixture shows greater modulus and inferior ability to resist reflective cracking than the unaged mixture. Moreover, rejuvenated mixture shows less dependence on frequency at high temperature regions and stronger dependence at low temperature regions compared to unaged and long-term aged mixtures.

Microbial induced carbonate precipitation (MICP) provides an alternative method to stabilize the soil. To further improve the reinforcement effect, this study aims to propose a strategy by incorporating the mixing MICP method with pretreatment procedure. A series of laboratory tests were performed to investigate the preparation parameters (including the moisture content and dry density of the soil, the concentration of urea and CaCl₂ in cementation solution), the engineering properties, the CaCO₃ distribution as well as the mineralogical and micro structural characteristics of pretreatment-mixing MICP reinforced soil (PMMRS). Based on the orthogonal experiment results, the optimum preparation parameters for PMMRS were determined. The UCS of PMMRS was more strongly dependent on the moisture content and concentration of CaCl₂ than the concentration ratio of CaCl₂ to urea. Moreover, it was testified that incorporation of pretreatment procedure improved the stabilization effect of traditional mixing MICP method on the clayed sand (CLS). The UCS of PMMRS specimen was increased by 198% and 78% for the pure CLS and the simple mixing MICP reinforced soil, respectively. Furthermore, the CaCO₃ products generated consisted of the aragonite, calcite and vaterite, which distributed unevenly inside the specimen no matter the lateral or vertical direction. The reason for the uneven distribution might be that oxygen content varied with the regions in different directions, and hence affected the mineralization reaction. In addition, the mineralization reaction would affect the pore structure of the soil, which was highly related to the stabilization effect of MICP reinforced soil.

In any given asphalt concrete (AC) pavement structure, the permanent deformation (PD) in each AC layer has an influence and contributes differently to the total pavement rutting. The degree of influence will generally vary as a function of the AC modulus and layer thickness. Presently, most of the AC material/layer PD characterisation and analyses are based on laboratory and/or field testing in combination with stress-strain modelling under assumed circular and uniformly distributed wheel loading. In this paper, a three-dimensional finite element program, ANSYS, incorporating measured vertical tyre–pavement contact pressure (TPCP) was utilised for computing the PD of each AC layer with different variables such as the AC layer modulus, AC layer thickness, TPCP levels, vertical wheel loads, and tyre inflation pressure. A strain energy concept was also proposed for evaluating the PD rate and contribution of each AC layer. The corresponding results indicated the following: (1) the PD contribution of each AC layer varies as a function of the AC modulus as theoretically expected; (2) the intermediate AC layer significantly contributes to lateral deformation; however, both the intermediate and top AC layers significantly contribute to vertical PD; (3) the AC layer thickness and the magnitude of the lateral TPCP hardly influence the PD of the intermediate AC layer; (4) the PD influence of small light trucks can be quite substantial depending on the loading conditions and cannot be neglected in the analysis of this nature; (5) the distribution of the TPCP has a very significant influence on the PD of the top AC layer and is more pronounced as the TPCP gets more non-uniformly distributed.