This paper investigated the modification mechanism of the desulfurized rubber asphalt, and compared its performances with those of crumb rubber asphalt. The microstructures of desulfurized rubber asphalt and crumb rubber asphalt were identified by using the scanning electron microscope technology, component analysis and infrared spectrum analysis. Conventional and Strategic Highway Research Program (SHRP) performance tests were conducted to evaluate the performances of desulfurized rubber asphalt and crumb rubber asphalt. Mixture performance tests were also performed to characterize the high temperature rutting resistance, low temperature cracking resistance, moisture stability and fatigue life of the desulfurized rubber asphalt mixture and crumb rubber asphalt mixture. It was found that the modification mechanisms of desulfurized rubber asphalt and crumb rubber asphalt are different. The desulfurized rubber can integrate into the asphalt while the crumb rubber mainly exists incompatibly in asphalt. This difference results in the various performances between the desulfurized rubber asphalt and crumb rubber asphalt. Both crumb rubber and desulfurized rubber can improve the performance of asphalt binder and mixture, but the desulfurized rubber asphalt has much lower viscosity and better storage stability than the crumb rubber asphalt. The preparing temperature of the desulfurized rubber asphalt mixture can be reduced by 10∼20°C compared to the crumb rubber asphalt mixture. Moreover, without the interference of solid rubber particles, the desulfurized rubber asphalt can be used in dense-graded asphalt mixture while crumb rubber asphalt mixture tends to use gap gradation with high asphalt content.

This paper proposes a new modeling method to reconstruct hollow shapes of aggregate particles using the discrete-element method (DEM) to accurately characterize the microstructures of aggregates and efficiently predict the mechanical properties of aggregate skeletons. To provide a basis for virtual aggregate reconstruction, two-dimensional images and key morphological characteristics of different aggregate particles are measured using the Aggregate Imaging Measurement System (AIMS). Three different modeling methods—radius-expansion (RE), interior-filling (IF), and contour-filling (CF)—are applied using Particle Flow Code in Two Dimensions (PFC2D) discrete-element software. Whereas RE and IF are conventional methods, the CF method is newly developed for this study. Both laboratory penetration and DEM-based virtual penetration tests are conducted to determine the microparameters for different aggregates. Further virtual penetration tests are then conducted to predict the inner friction resistance of different aggregate skeletons and to compare the accuracy and efficiency of the respective modeling methods. Based on these macromechanical and micromechanical property analyses, it is demonstrated that the newly developed CF modeling method is much more accurate and efficient than the conventional RE and IF methods, respectively.

Recently, a shape memory polymer-based self-healing syntactic foam was proposed and tested as a sealant for expansion joints. The key for success is to train the foam by using a two-dimensional (2D) stress condition (compression in the horizontal or traffic direction and tension in the vertical direction) at a temperature above the glass transition temperature (Tg). However, for practical applications, programming a full-size slab of sealant with a 2D stress condition and under temperature control is not a trivial task. This study demonstrated that the programming with a one-stage 2D stress condition can be replaced by a sequential two-stage one-dimensional (1D) stress condition. To further simplify the programming process, 1D tension programming was conducted at a temperature above the Tg, followed by 1D compression programming at a temperature below the Tg (cold compression). The test results show that the hybrid programming leads to similar shape memory behavior as long as the prestrain level i...

In order to investigate the contact behaviours of tire-pavement under dry condition, the finite element method was applied to establish the numerical model of the tire Bridgestone 205-55-R16 and textured asphalt pavement model . Based on the contact mechanics for elastic pavement, the contact model of three-dimensional tire-asphalt pavement was established according to Lagrangian algorithm. By considering the influence of pavement texture, the friction subroutine was compiled to calculate the tire-pavement adhesion coefficient. The influence of internal inflation pressure and wheel load on contact characteristics of tire-asphalt pavement were discussed respectively under static load and antilock braking system (ABS) state. The results show that when the slip rate is around 15%, the longitudinal adhesion coefficient of the tire reaches the maximum, which is in accordance with the setting of tire adhesion coefficient in tire science. When the tire is in emergency braking, the tire shoulder position and tread centre area are more susceptible to wear, and the contact pressure in centre area is biggest. Under the same wheel load and internal inflation pressure, the mean contact pressure increases by 8.4% and the contact area reduces by 7.7% when tire is at ABS state compared with the condition of static load.

The particle clustering phenomena in reclaimed asphalt pavement (RAP) particles is one of the most important factors to affect the efficient recycling of asphalt concrete. In this study, the particle composition, clustering degree, crushing properties and clustering stability of RAP were studied by extraction test and cantabro-crushing test. It was found that the particles above 4.75 mm were composed mainly of small particles with a large degree of cluster and poor stability. The coarse particles (>4.75 mm) had a great influence on the variation of 4.75 mm sieve. Quantitative indexes of Percentage Loss rate (PL) and Stability Index (w) were proposed to evaluate the clustering degree and the stability of RAP. It provided a meaningful reference for the comparison of different RAP and the different crushing processes. In addition, the RAP could be divided into three kinds of structures, including weak cluster structure, strong cluster structure and old aggregate. The process of crushing the RAP was divided into three stages, which are weak structure-dominated, strong structure-dominated and the broken old aggregate. The weak structure had the largest degree of cluster and worst stability, resulting in a large variability of RAP, and it should be avoided in the crushing process.

Many rubber friction theories or some method combined theories and field-experiments are employed to evaluate the pavement skid-resistance deterioration due to the evolution of surface textures. However, these methods are difficult to be implemented in the analysis of situations with multi-factor coupling and some extreme conditions. This study developed a framework to evaluate the skid-resistance deterioration of asphalt pavements. In this framework, the portable laser scanning was used to create the digital worn pavement model, and a hydroplaning finite element (FE) model for these digital worn pavements was constructed to evaluate coupling effects of the texture evolution and factors of slip ratio, slip angle, velocity and water film on braking-cornering characteristics of tire. In this study, the deterioration of skid-resistance of five typical asphalt pavements due the surface texture wear was systematically investigated by this framework. Compared with previous works, this study established the rubber friction models for each digital worn pavement considering the energy hysteresis of rubber and the power spectrum density of surface texture. And the rubber friction model was used to define the interaction behaviors between the tire and corresponding wore pavements in the FE hydroplaning model, rather than using an empirical friction model or a fixed friction coefficient.