Quantao Liu

Induction Healing of Porous Asphalt Concrete Beams on an Elastic Foundation

AbstractThe objective of this paper is to evaluate the healing capacity of steel wool–reinforced porous asphalt concrete. The healing is initiated with induction heating. Bending fracture tests on an elastic foundation are used to prove the healing mechanism. Porous asphalt concrete beams on an elastic foundation were fractured at 5°C; subsequently, they were heated with induction energy, and finally fractured again. The recovered fracture resistance of the beams was used as a healing indicator. Totally fractured porous asphalt beams can regain 78.8% of their bending resistance (strength) when induction heating is applied. It was also found that the optimal heating temperature is 85°C for porous asphalt beams to obtain the highest strength recovery. Reheating of the fractured beams does not decrease the recovery of the flexural resistance, which means that the heating can be repeated when cracks return. On the basis of these findings, it is expected that the healing potential of porous asphalt concrete an...

Healing of Porous Asphalt Concrete via Induction Heating

ABSTRACT The lifetime of porous asphalt pavement is only about 11 years. In this research, a porous asphalt concrete with long lifetime, based on a healing mechanism triggered by means of induction heating, is explained. Conductive fillers (steel fibers and steel wool) are added to porous asphalt concrete to enhance its electrical conductivity and induction heating is used to increase the temperature locally, just enough to increase the healing rate of asphalt concrete to heal the micro-cracks and to repair the bond between aggregates and binder. The main purposes of this research are to examine the electrical conductivity, particle loss resistance and induction heating speed of electrically conductive porous asphalt concrete and prove that damage in the material can be healed via induction heating. It is found that long fibers with small diameter are better than short fibers with bigger diameter to make porous asphalt concrete electrically conductive, induction heatable and have high particle loss resistance as well. Finally, it is also proved that damage in porous asphalt concrete can be healed via induction heating.

Optimization of Steel Fiber Used for Induction Heating in Porous Asphalt Concrete

An electrically conductive porous asphalt concrete used for induction heating and subsequently healing of cracks is prepared by adding conductive materials (steel fibers and steel wool) in this research. In this paper, the optimization of steel fiber used for induction heating is reported based on the electrical resistivity, induction heating speed and particle loss resistance of porous asphalt concrete. It is found that porous asphalt concrete containing steel fiber with smaller diameter or longer steel fiber is more electrically conductive and induction heatable than that containing the same content of steel fiber with bigger diameter or short steel fiber. It is also found that steel wool type 00 with length of 9.5 mm is more effective than short steel fiber type 1 and steel wool type 000 to improve the particle resistance of porous asphalt concrete. Finally, 8% (by volume of bitumen) of steel wool type 00 is considered as the best option used for induction heating in porous asphalt concrete.

Induction Healing of Porous Asphalt

Research on the induction healing of porous asphalt is summarized. Steel wool is added to porous asphalt concrete to make it electrically conductive and suitable for induction heating. When microcracks occur in the material, an induction generator is used to heat the material to close the cracks by the high-temperature self-healing of bitumen. The electrical resistance and induction heating speed of porous asphalt concrete reinforced with steel wool are examined. Porous asphalt concrete containing steel wool is found to be electrically conductive and can be heated with induction energy. The mechanical properties of this porous asphalt are also studied. Steel wool can reinforce porous asphalt concrete by increasing its strength, particle loss (raveling) resistance, and fatigue resistance. Furthermore, the induction healing effect of this porous asphalt concrete reinforced with steel wool is evaluated. It is proved that the fatigue life of induction-healing porous asphalt can be extended significantly by the application of induction heating. It is also found that the optimal heating temperature for the best healing effect is 85°C. These findings indicate that the self-healing potential of porous asphalt concrete and the durability of porous asphalt pavement are improved by induction heating. Finally, a test section was paved on the Dutch A58 motorway with a porous asphalt layer containing steel wool. Because asphalt concrete exhibits better self-healing at higher temperatures, the future for the application of induction-healing porous asphalt concrete appears to be promising.

Study of Antiultraviolet Asphalt Modifiers and Their Antiageing Effects

Ultraviolet (UV) radiation causes serious ageing problems on pavement surface. In recent years, different UV blocking materials have been used as modifiers to prevent asphalt ageing during the service life of the pavement. In this study, three different materials have been used as modifiers in base asphalt to test their UV blocking effects: layered double hydroxides (LDHs), organomontmorillonite (OMMT), and carbon black (CB). UV ageing was applied to simulate the ageing process and softening point, penetration, ductility, DSR (Dynamic Shear Rheometer) test, and Fourier Transform Infrared Spectroscopy (FTIR) test were conducted to evaluate the anti-UV ageing effects of the three UV blocking modifiers. Physical property tests show that base asphalt was influenced more seriously by UV radiation compared to the modified asphalt. DSR test results indicate that the complex modulus of asphalt before UV ageing is increased because of modifiers, while the complex modulus of base asphalt after UV ageing is higher than that of the modified asphalt, which shows that the UV blocking modifiers promote the antiageing effects of asphalt. FTIR test reveals that the increment of carbonyl groups and sulfoxide groups of modified asphalt is less than that in base asphalt. Tests indicate the best UV blocking effect results for samples with LDHs and the worst UV blocking effect results for samples with CB.

Predicting the performance of the induction healing porous asphalt test section

The induction healing concept of porous asphalt was developed at Delft University of Technology and was proven very successful in the laboratory. A porous asphalt test section with this self healing concept was also paved on Dutch highway A58. This special porous asphalt contained 4% steel wool (by volume of bitumen). A number of cores were drilled from this test section to predict its performance. Beams were also prepared with the same materials as used in the test section. Experiments were done on these specimens to study the mechanical, heating and healing properties. It is found in Cantabro test that the particle loss resistance of porous asphalt concrete is improved by addition of steel wool. The improvement in particle loss resistance will delay ravelling on the pavement. It is also proven that the cores containing steel wool can be heated quickly with induction energy. Finally, it is found that the fatigue life of the beamsis extended greatly by applying induction heating during the rest period. The damage (cracking) in the porous asphalt beams ishealed by induction healing. Based on these findings, it is concluded that the life time of the test section will be extended by the reinforcement of steel wool and induction heating.

Preparation and Thermal Properties of Molecular-Bridged Expanded Graphite/Polyethylene Glycol Composite Phase Change Materials for Building Energy Conservation

Using phase change materials (PCMs) in building envelopes became a reliable method to improve indoor comfort and reduce buildings’ energy consumption. This research developed molecular-bridged expanded graphite (EG)/polyethylene glycol (PEG) composite PCMs (m-EPs) to conserve energy in buildings. The m-EPs were prepared through a vacuum absorption technique, and a titanate coupling agent was used to build a molecular bridge between EG and PEG. SEM, mercury intrusion porosimetry (MIP), the leakage test, microcalorimetry, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FT-IR) were conducted to characterize the morphology, pore structure, absorbability, and modifying effects of the m-EPs. The phase change temperature, latent heat, thermal stability, and thermal conductivity of the m-EPs were determined by a differential scanning calorimeter (DSC), TGA, and a thermal constants analyzer. Results showed that the maximum mass ratio of PEG to EG without leakage was 1:7, and a stable connection was established in the m-EPs after modification. Compared with the unmodified EPs, the supercooling degree of the m-EPs reduced by about 3 °C, but the latent heats and initial decomposition temperatures increased by approximately 10% and 20 °C, respectively, which indicated an improvement in the thermal energy storage efficiency. The thermal conductivities of the m-EPs were 10 times higher than those of the pristine PEGs, which ensured a rapid responding to building temperature fluctuations.

Microfluidic Synthesis of Ca-Alginate Microcapsules for Self-Healing of Bituminous Binder

This work aims to develop an original alginate micro-emulsion combining with droplets microfluidic method to produce multinuclear Ca-alginate microcapsules containing rejuvenator for the self-healing of bituminous binder. The sizes of the Ca-alginate microcapsules could be easily controlled by tuning flow rates of the continuous and dispersed phases. The addition of a surfactant Tween80 not only improved the stability of the emulsion, but it also effectively reduced the size of the microcapsules. Size predictive mathematical model of the microcapsules was proposed through the analysis of fluid force. Optical microscope and remote Fourier infrared test confirmed the multinuclear structure of Ca-alginate microcapsules. Thermogravimetric analysis showed that the microcapsules coated with nearly 40% rejuvenator and they remained intact during the preparation of bitumen specimen at 135 °C. Micro self-healing process of bituminous binder with multinuclear Ca-alginate microcapsules containing rejuvenator was monitored and showed enhanced self-healing performance. Tensile stress-recovery test revealed that the recovery rate increased by 32.08% (in the case of 5% microcapsules), which meant that the Ca-alginate microcapsules containing rejuvenator could effectively enhance the self-healing property of bituminous binder.

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.

Thermally Activated Healing of Fatigue Damage in Asphalt Binders

Asphalt binder is a self-healing material and it has a potential to heal faster with increased temperatures. This paper investigates the thermally activated healing of fatigue damage in three asphalt binders, trying to answer the question: At what temperatures do asphalt binders heal? After fatiguing the sample, a heating treatment was applied and the sample was fatigued for the second time. The recovered fatigue life and the recovered accumulated dissipated energy are used to quantify the thermally activated healing rates of asphalt binders. It is found that these two healing indexes coincide well with each other in different healing conditions. Base asphalt binders can heal the fatigue damage completely after heating for 20 min at the softening-point temperatures. Styrene–butadiene–styrene (SBS)-modified asphalt binder can achieve full healing at a temperature 20°C below its softening point, where the elastic recovery of the SBS chain segment may play an important role in healing. It is also found that healing of fatigue damage in asphalt binder is highly strain dependent: the healing ratio is higher at high strain amplitude. It proved that thermally activated healing can be repeated when damage returns in asphalt binder. It is concluded that thermally activated healing of fatigue damage is definitely useful to increase the fatigue life of asphalt binders and different asphalt binders should be heated to certain temperatures related to their specific softening points.