Yue Xiao

UV and Thermal Aging of Pure Bitumen-comparison Between Laboratory Simulation and Natural Exposure Aging

ABSTRACT In this paper, several indoor laboratory aging tests and the Natural Exposure Aging (NEA) test were employed as the aging regimes of pure bitumen. The properties of various aged bitumen specimens were investigated by Dynamic Shear Rheometer (DSR) and Fourier Transform Infrared Spectra (FTIR). By this means the differences between the laboratory and natural exposure aging was analysed. Experimental results showed that both thermal and ultraviolet (UV) radiation aging happened during UV radiation oven test and the later was much more prominent on the influence of bitumens properties, in particular, when the binder films was smaller than 100 μm. In a wide range of frequency, complex modulus and phase angle obtained from DSR tests revealed that UV radiation oven test showed a better corresponding relationship with NEA when compared to Pressure Aging Vessel (PAV).

Conductive asphalt concrete: A review on structure design, performance, and practical applications

Conductive asphalt concrete can be used to help pavement snow melting/deicing by an asphalt pavement electrical heater. It is an emerging technology to ensure safety driving during winter time. Based on the Joule heating law, an electric current passing through the conductive asphalt concrete (a conductor) could generate enough heat to prevent snow accumulation and icing on the asphalt pavement surface. This article provides a review on the material design, construction technique, performance evaluation, and engineering applications of conductive asphalt concrete. The literature shows that the conductivity and mechanical properties of conductive asphalt concrete are strongly dependent on the material compositions and mixing programs. Meanwhile, the mechanism of conductivity improvement is identified according to the characteristics of conductive additives. In addition, the effects of service conditions on the resistivity are evaluated. Asphalt pavement electrical heater technique shows some appreciable advantages in environment protection and traffic safety aspects, although it has few applications in the highway industry. It therefore recommends that further investigations on asphalt pavement electrical heater are indispensable and should focus on some covered issues besides the existing research, such as proper material selection, resistivity stability, desirable high operational efficiency, and suitable construction technique.

Fatigue Properties of Layered Double Hydroxides Modified Asphalt and Its Mixture

This study investigated the influence of layered double hydroxides (LDHs) on the fatigue properties of asphalt mixture. In this paper, different aging levels (thin film oven test (TFOT) and ultraviolet radiation aging (UV aging for short)) of bitumen modified with various mass ratios of the LDHs were investigated. The TFOT and UV aging process were used to simulate short-term field thermal-oxidative aging and long-term field light UV aging of bitumen, respectively. The influences of LDHs on the fatigue properties of LDHs were evaluated by dynamic shear rheometer (DSR) and indirect tensile fatigue test. Results indicated that the introduction of LDHs could change the fatigue properties of bitumen under a stress control mode. The mixture with modified bitumen showed better fatigue resistance than the mixture with base bitumen. The results illustrated that the LDHs would be alternative modifiers used in the bitumen to improve the lifetime of asphalt pavements.

Evaluation of Fine Aggregate Morphology by Image Method and Its Effect on Skid-Resistance of Micro-Surfacing

Micro-surfacing is a widely used pavement preventive maintenance technology used all over the world, due to its advantages of fast construction, low maintenance cost, good waterproofness, and skid-resistance performance. This study evaluated the fine aggregate morphology and surface texture of micro-surfacing by AIMS (aggregate image measurement system), and explored the effect of aggregate morphology on skid-resistance of single-grade micro-surfacing. Sand patch test and British pendulum test were also used to detect skid-resistance for comparison with the image-based method. Wet abrasion test was used to measure skid-resistance durability for feasibility verification of single-grade micro-surfacing. The results show that the effect of Form2D on the skid-resistance of micro-surfacing is much stronger than that of angularity. Combining the feasibility analysis of durability and skid-resistance, 1.18–2.36 grade micro-surfacing meets the requirements of durability and skid-resistance at the same time. This study also determined that, compared with British pendulum test, the texture result obtained by sand patch test fits better with results of image method.

The Rejuvenating Effect in Hot Asphalt Recycling by Mortar Transfer Ratio and Image Analysis

Using a rejuvenator to improve the performance of asphalt pavement is an effective and economic way of hot asphalt recycling. This research analyzes the rejuvenating effect on aged asphalt by means of a Mortar Transfer Ratio (MTR) test, which concerns the ratio of asphalt mortar that moves from recycled aggregates (RAP aggregates) to fresh added aggregates when aged asphalt is treated with a regenerating agent and comes into contact with fresh aggregates. The proposed MTR test analyzes the regeneration in terms of the softening degree on aged asphalt when the rejuvenator is applied. The covered area ratio is studied with an image analyzing tool to understand the possibility of mortar transferring from RAP aggregates to fresh aggregates. Additionally, a micro-crack closure test is conducted and observed through a microscope. The repairing ability and diffusion characteristics of micro-cracks can therefore be analyzed. The test results demonstrate that the proposed mortar transfer ratio is a feasible way to evaluate rejuvenator diffusion during hot recycling. The mortar transfer ratio and uncovered area ratio on fresh aggregates are compatible, and can be used to quantify the contribution of the rejuvenator. Within a certain temperature range, the diffusing effect of the rejuvenator is better when the diffusing temperature is higher. The diffusion time of the rejuvenator is optimum when diffusion occurs for 4–8 h. When the rejuvenator is properly applied, the rough and cracking surface can be repaired, resulting in better covered aggregates. The micro-closure analysis visually indicates that rejuvenators can be used to repair the RAP aggregates during hot recycling.

Characteristics of Ceramic Fiber Modified Asphalt Mortar

Ceramic fiber, with a major composition of Al2O3 and SiO2, has advantages of stability at relatively high temperature, big specific surface area and resistance to external mechanical vibration. It has the potential contribution of improving the rutting resistance and temperature sensitivity of modified asphalt binder by proper modification design. In this research, ceramic fiber was introduced into both pen 60/80 and pen 80/100 asphalt binder by different weight ratios. An asphalt penetration test, softening point test, ductility test and dynamic viscoelastic behavior were conducted to characterize and predict the ceramic fiber modified asphalt mortar (CFAM). Research results indicated that the ceramic fiber has a great effect on reinforcement of asphalt, which makes the asphalt stiffer so that the asphalt can only undertake less strain under the same stress. The heat insulation effect of the ceramic fiber will improve the temperature stability. Complex modulus and phase angle results indicate that the ceramic fiber can significantly enhance the high temperature resistance of soft binder.

Initial Self-Healing Temperatures of Asphalt Mastics Based on Flow Behavior Index

Increasing temperature is a simple and convenient method to accelerate the self-healing process of bitumen. However, bitumen may not achieve the healing capability at lower temperature, and may be aged if temperature is too high. In addition, the bitumen is mixed with mineral filler and formed as asphalt mastic in asphalt concrete, so it is more accurate to study the initial self-healing from the perspective of asphalt mastic. The primary purpose of this research was to examine the initial self-healing temperature of asphalt mastic, which was determined by the flow behavior index obtained from the flow characteristics. Firstly, the texture and geometry characteristics of two fillers were analyzed, and then the initial self-healing temperature of nine types of asphalt mastic, pure bitumen (PB) and styrene-butadiene-styrene (SBS) modified bitumen were determined by the flow behavior index. Results demonstrate that the average standard deviation of gray-scale texture value of limestone filler (LF) is 21.24% lower than that of steel slag filler (SSF), showing that the steel slag filler has a better particle distribution and geometry characteristics. Also the initial self-healing temperatures of asphalt mastics with 0.2, 0.4 and 0.6 LF-PB volume ratio are 46.5 °C, 47.2 °C and 49.4 °C, which are 1.4 °C, 0.8 °C and 0.4 °C higher than that of asphalt mastics with SSF-PB, but not suitable for the evaluation of asphalt mastic contained SBS modified bitumen because of unique structure and performance of SBS.

Low temperature properties of UV aged asphalts containing layered double hydroxides modifier

Background In recent years, ultraviolet (UV) ageing of asphalt has attracted worldwide attention from researchers in the asphalt field. The UV radiation can result in the ageing of asphalt and thus influence its performance. So far, a variety of UV blocking materials have been investigated. Aim In this paper, layered double hydroxides (LDHs) were introduced as the UV blocking materials into three different asphalts (S70, S90 and SBS modified asphalt). Methods The low temperature properties, such as equivalent breaking point (EBP) and fatigue factor were tested and applied to estimate the UV blocking effects of LDHs on asphalts. Results The experimental results demonstrated that LDHs could effectively reduce the ageing index of S70 and S90, and lower the degradation rate of SBS modifier.

Self-Healing Property of Ultra-Thin Wearing Courses by Induction Heating

Ultra-thin wearing course (UTWC) has been developed in pavement preventive maintenance for many years. However, how to prolong the service life of UTWC still requires further research. This study introduced AC-5 and SMA-5 asphalt mixtures, which can be induction heated. Steel fiber and steel slag were used in the mixtures as additives. Marshall Stability and induction heating property of mixtures were characterized. In addition, self-healing property of UTWC materials had been emphatically conducted. Adding steel fiber in mixtures led to higher Marshall Stability and lower flow value, while steel slag generally showed a negative effect. Induction heating property showed a positive relationship with the additives. Induction heating time was positively correlated to the healing ratio of the mixtures. Induction heating on the mixtures could recover the strength of mixtures to a certain degree. Mixtures with more steel fiber showed a higher healing ratio. Basalt-steel slag based mixtures showed better healing ratios than the basalt based mixtures. The healing ratios of mixtures illustrated a decreasing tendency as the healing cycle increased.

Residual Fatigue Properties of Asphalt Pavement after Long-Term Field Service

Asphalt pavement is widely used for expressways due to its advantages of flexibility, low cost, and easy maintenance. However, pavement failures, including cracking, raveling, and potholes, will appear after long-term service. This research evaluated the residual fatigue properties of asphalt pavement after long-term field service. Fatigue behavior of specimens with different pavement failure types, traffic load, service time, and layers were collected and characterized. Results indicate that after long-term field service, surface layer has a longer fatigue life under small stress levels, but shorter fatigue life under large stress levels. Longer service time results in greater sensitivity to loading stress, while heavier traffic results in shorter fatigue life. Surface and underneath layers present very close fatigue trend lines in some areas, indicating that the fatigue behavior of asphalt mixture in surface and underneath layers are aged to the same extent after eight to ten years of field service.