Shaopeng Wu

Laboratory Study on Ultraviolet Radiation Aging of Bitumen

The effects of ultraviolet (UV) radiation on degradation of bitumen have received much attention from both academic and industrial points of view. However, quantitative evaluations of bitumen photo-oxidation in pavements have apparently not been determined. In this study, the effects of photo-oxidation of bitumen were investigated by exposing pressed thin films of bitumen. The data for thermal aging only were compared with corresponding data for photo-oxidation from exposure to UV radiation. The levels of aging were evaluated by following increases in the carbonyl functional group, and increases in viscosity. The results indicated that both thermal and UV aging occurred during exposure in the UV radiation oven test for thin bitumen films of both unmodified and SBS-modified bitumen. UV aging had a significant effect on bitumen properties, particularly when the bitumen film thickness was less than 150 μm. Results also showed that the level of UV irradiation intensity had a significant influence on the level of photo-oxidation of the bitumen.

Investigating the Self Healing Capability of Bituminous Binders

ABSTRACT In the Netherlands, the loss of stone at the surface of porous asphalt wearing courses (ravelling) results in a limited service life. Ravelling is caused by repeated traffic fatigue loadings and climatic influences. Bituminous materials exhibit a healing capability which is helpful to extend the service life. However, aging is expected to limit this positive effect. Therefore, upgrading the self-healing capability of the bitumen in time is of major importance. Inspired from mimicking nature, several chemical treatments can be used to improve the self healing capability of asphalt mixtures when the binder starts to harden due to aging, or when micro cracks have initiated. Possibilities of self-healing improvement are discussed in this paper. Preliminary results of measurements of the self healing capability of bituminous binders are also presented.

Effect of aging on the morphology of bitumen by atomic force microscopy.

Effect of aging on the morphology of bitumen was investigated. Two bitumens were aged according to the thin film oven test (TFOT), pressure aging vessel (PAV) test and ultraviolet (UV) radiation, respectively. The morphology of the binders before and after aging was characterized by atomic force microscopy. The physical properties and chemical compositions of the binders were also measured. The results showed that aging affected the bitumen morphology significantly. Aging increased the overall surface stiffness of the bitumen and made the bitumen surface more solid‐like. The extent of these changes was dependent on aging conditions. TFOT decreased the contrast between the dispersed domains and the matrix, which contributed to the single‐phase trend of the binders. The effect of PAV aging on morphology of the binders was dependent on the base bitumen. In one case, it further accelerated the single‐phase trend of bitumen in comparison with that after TFOT. In the other case, it caused the phase separation of bitumen. In both cases, PAV aging increased the surface roughness of the binders obviously. As a result of UV aging, the contrast between the matrix phase and dispersed phase was increased due to the difference in sensitivity to UV radiation of the bitumen molecules, which caused or further promoted the phase separation in the binders. Regardless of the aging procedure carried out, a strong correlation was observed between the changes in morphology and physical properties as well as chemical compositions of the binders before and after aging.

Numerical simulation on the thermal response of heat-conducting asphalt pavements

Using asphalt pavements as a solar collector is a subject of current interest all over the world because the sun provides a cheap and abundant source of clean and renewable energy, which can be captured by black asphalt pavements. A heat-conducting device is designed to absorb energy from the sun. In order to validate what parameters are critical in the asphalt collector, a finite element model is developed to predict the thermal response of the heat-conducting device compared to the conventional asphalt mixture. Some factors that may affect the asphalt pavement collector are considered, including the coefficient of heat conductivity of the asphalt pavement, the distance between pipes with the medium, water, and the pipes diameter. Ultimately, the finite element model can provide pavement engineers with an efficient computational tool that can be a guide to the conductive asphalt solar collectors experiment in the laboratory.

Characterization of Organic Surfactant on Montmorillonite Nanoclay to Be Used in Bitumen

In the past decades, montmorillonite nanoclay has been used successfully to strongly improve properties of polymers. Similar improvements to nanoclay modified bitumen were expected, so the montmorillonite nanoclay was adopted to modify bitumen. To understand the interaction with bitumen, it was of fundamental importance to know the composition of organic surfactant on montmorillonite nanoclay. Two organically modified montmorillonite (OMMT) nanoclays available in the market were studied to characterize the composition of the surfactant through X-ray photoelectron spectrometry and simultaneous differential scanning calorimetry and thermogravimetric (DSC-TG) analysis. From the measurements it could be concluded that there was a difference between the surfactants. One surfactant was composed of two states of nitrogen: quaternary ammonium and probably amine or nitrile. The other surfactant only contained quaternary ammonium. In general, C—C bonds could be detected very well for the two surfactants and there were no other functional groups, such as carboxylic, hydroxyl, ketone, etc. However, it was unclear if the surfactants had C=C bonds. DSC-TG analysis indicated that the two OMMTs showed very different thermal behavior, but at temperatures below 200°C no problems were expected.

Piezoresistivity of Graphite Modified Asphalt-Based Composites

Asphalt and its composites are electrical insulating materia ls, whose resitivity ranges from 10~10 . The conductive performance of the asphalt-based composite can be mark dly improved with the addition of conductive materials such as graphite. The electrically modified asphalt composites exhibit self-sensing ability to strain, defects , and temperature. Conductive asphalt-based composite would have a profound effect on pavement deicing, dam age testing, highway traffic monitoring and so on. Materials such as Koch AH-70, basalt aggregate, limestone powder and graphite particles were used to prepare a conductive aspha lt-based composite in this study. Special attention was placed to its conductive behavior and piezor esistivity. The results show that when the graphite content in asphalt-based composite increases to a critical content, the resistivity declines rapidly. Beyond the critical content, the r ate of resistivity varying with the graphite content becomes smooth. Temperature has a remarkable eff ect on the electrical conduction of the asphalt-based composites. There is a turning point of resisti vity with the increase of temperature. Dynamic and static compressive loadings also affec t the resistance obviously. The reasons may involve the proximity effect, microcracks and the sta ggered arrangements of conductive pass-ways.

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).

Influence of demolition waste used as recycled aggregate on performance of asphalt mixture

The influence of demolition waste (DW) on the performance of asphalt mixture was investigated in this paper. DW was processed into recycled aggregate of different sizes which can be divided into recycled coarse aggregate (RCA, particle size of>4.75 mm) and recycled fine aggregate (RFA, particle size of≤4.75 mm). Three types of AC-25 asphalt mixture were prepared: RCA asphalt mixture prepared with RCA and limestone fine aggregate; RFA asphalt mixture prepared with RFA and limestone coarse aggregate; and the ordinary asphalt mixture prepared with natural limestone coarse and fine aggregate. A series of laboratory tests on recycled aggregate and asphalt mixture were carried out, including scanning electron microscopy test, immersion Marshall test, freeze–thaw split test, bending test at low temperature and rutting test at high temperature. Results showed that RCA asphalt mixture has higher optimal asphalt content and greater rutting resistance than the other two types. The cracking resistance of RCA asphalt mixture at low temperature is better than that of RFA asphalt mixture; while the water damage resistance of RFA asphalt mixture is better than that of RCA asphalt mixture. However, all these performances can meet the requirements of Chinas technical specifications. It can be seen that DW can be used in preparing asphalt mixture with satisfactory performance, especially for application in hot and dry environments. RCA asphalt mixture has lower temperature sensitivity while RFA asphalt mixture has lower water sensitivity.

Analysis of Characteristics of Electrically Conductive Asphalt Concrete Prepared by Multiplex Conductive Materials

The main objective of this paper is to analyze the characteristics of electrically conductive asphalt concrete (ECAC) by adding multiplex electrically conductive materials. First, it is proved that all the mechanical properties of ECAC meet the design requisition in this study. The effects of filler type, filler content, and mixed fillers on the resistivity of asphalt concrete were then systematically investigated. Experimental results showed that the combination function of mixed fillers has appreciable advantages over single powder in electrical conductivity. Both laboratory and field tests were conducted to prove that the ECAC provides an efficient method for snow melting through direct current. In addition, an infrared imaging technology was used to assess the temperature field distribution. Furthermore, the effects of temperature, voltage, and temperature circulation on the resistance of ECAC were explained by the break and rebuild of conductive pathways. Finally, X-ray computed tomography provides insight into the mechanisms of conductivity enhancement for mixed fillers. It is shown that the conductive chain formed in ECAC largely depends on the conductive filler’s distribution in asphalt mortar.

On Cold Materials of Pavement and High-Temperature Performance of Asphalt Concrete

With global climate becoming warmer more and more attention is being paid to cold materials. Lower surface temperature contributes to decrease the temperature of the ambient air as heat convection intensity from a cooler surface is lower. Such temperature reductions can have significant impacts on cooling energy consumption in urban areas, a fact of particular importance in hot climate cities. The black surface of asphalt pavement absorbs more heat from the sun, and higher temperature of pavement surface contributes to increase the effect of the urban heat island, but affects the performance and life span of a pavement. Asphalt pavements form an integral part of any transportation system and are typically engineered to last 15 years or more, but many have been failing early due to potholes, cracks, raveling and other problems. Cool pavement are mainly aimed to decrease the effect of asphalt pavement on the urban heat island, but the influence of cold materials on the high-temperature performance of asphalt concrete pavement is paid little attention relatively. In this paper, it’s discussed that the effect of asphalt-pavement high temperature and its improving measures. And the mechanism of cool pavements is introduced, and possible technologies applied to asphalt pavements are reviewed. The idea of asphalt concrete pavement with automatic temperature-control is put forward.