Search

Micro-cracks are generated inside asphalt materials as a result of the action of external environmental factors, such are aging, extreme temperature and moisture. Asphalt binder is a self-healing material with the ability of automatically repair its damage during rest periods. However, this autonomous process in the damaged asphalts is limited and inefficient at low temperatures. In this sense, several studies for synthesizing encapsulated rejuvenators have been developed in recent years to improve the self-healing capability of bituminous materials and thereby to extend their service life. This paper presents the synthesis of two different Ca-alginate polymeric fibers encapsulating rejuvenator by microfluidic device: i) hollow Ca-alginate polymeric fibers encapsulating rejuvenator jets, and ii) compartmented Ca-alginate polymeric fibers encapsulating rejuvenator droplets. The synthesis mechanism of the fibers was analyzed by hydromechanics, and the effect of different structures on the properties of polymeric fibers was investigated. Also, the improved self-healing properties of asphalt bitumen containing the fibers were studied. Scanning electronic microscopy (SEM), polarizing microscopy (PM), Fourier transform infrared spectroscopy (FT-IR), and thermogravimetric analysis (TGA) were used to evaluate the fiber synthesis process. The self-healing capability of bitumen with fibers was monitored from a micro-perspective by fluorescence microscopy (FM). It was found that the improved asphalt self-healing process using polymeric fibers containing rejuvenator can be explained in several physical-chemical stages. Tensile stress-recovery tests and modified ductility tests were conducted and demonstrated that the addition of polymeric fibers can enhance the asphalt self-healing property at low temperatures. However, it was proved that the hollow Ca-alginate polymeric fibers play a more significant role in improving the bitumen self-healing ability than compartmented Ca-alginate polymeric fibers due to the higher content of encapsulated rejuvenator inside them.

To investigate the aging degradations of dominant wavelength of UV radiation on asphalt binder, five narrow-band UV radiations with different dominant wavelengths, namely 300, 320, 340, 360 and 380 nm, were used to age asphalt. After the UV aging, the aging degradations of the UV radiations on the chemical compositions, physical properties, rheological properties and complex viscosities of asphalt binder were tested by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), physical property test, and dynamic shear rheometer (DSR) respectively. The results show that all UV radiations, with the dominant wavelengths from 300 nm to 380 nm, can cause the aging degradations on the neat asphalt, UV aging can change the chemical compositions of asphalt, as well as the macro-performance of asphalt, such as physical and rheological performance. While, the molecules of asphalt have different susceptibilities to different wavelengths of UV radiations, different dominant wavelengths of UV radiations have different aging degradations on asphalt, it is not that a UV radiation with shorter wavelength (higher photon energy) definitely produces more serious aging effect on asphalt. Making into comparison, under the same aging condition, the asphalt binder aged by the UV – 360 has the highest aging degree, followed with the asphalt binders aged by UV – 340, UV – 320, UV – 300 and UV – 380, respectively.

Previous studies showed that Mg-Al layered double hydroxides (Mg-Al LDHs) had well anti-ultraviolet (anti-UV) aging properties when used in the asphalt materials, but it cannot contribute to improve the self-healing properties to repair cracks caused by UV aging under the microwave radiation. Fe3O4 has well microwave absorption and based on the layered structure and large surface area of Mg-Al LDHs, the primary objective of this work was to synthesize Fe3O4-decorated Mg-Al layered double hydroxides magnetic nanosheets, to envisage that the added bitumen modifier has both enhanced anti-UV aging properties and microwave absorption properties. Three modifiers were obtained by the adhesion of Fe3O4 magnetic particles on the surface of Mg-Al LDHs nanosheets, and named as L1F1 (the mass ratio of LDHs: Fe3O4 = 1:1), L2F1 (the mass ratio of LDHs: Fe3O4 = 2:1) and L1F2 (the mass ratio of LDHs: Fe3O4 = 1:2). Morphology, phase composition, chemical structure, anti-UV aging properties, static magnetic properties and microwave absorption properties of them were detected by different analytical methods. Results demonstrate that all magnetic nanosheets present the ferromagnetic behavior, L2F1 shows the lowest MS value among three types of magnetic nanosheets, and the value increases from 28.67 emu·g−1 to 56.78 emu·g−1 with augmented Fe3O4-LDHs ratio. Additions of Fe3O4 significantly enhance the anti-UV aging properties and microwave absorption properties of Mg-Al LDHs. The maximum RL value of L1F2 is recorded as more than two times of that of LDHs, and L1F2 shows the best anti-UV aging properties and microwave absorption properties among all magnetic nanosheets.

In this research, Ca-alginate capsules containing sunflower oil with different water/oil (W/O) ratios were synthesized and their physical properties, morphological characteristics, thermodynamic performance, oil content and survivability after mixing and compaction were studied to select the most suitable capsule for asphalt mixture. Finally, the capsules with a W/O ratio of 10:1 were incorporated into asphalt mixtures to investigate their oil release characteristics under fatigue loading and the effect of the multi-cavity Ca-alginate capsules on the self-healing properties of asphalt mixtures through three-point bending test. It was found that 2.5 wt% sodium alginate solution can well encapsulate sunflower oil and exchange with Ca2+ to form multi-cavity capsules. The sizes of the multi-cavity capsules increase with the decrease of W/O ratio. The compressive strength, thermal stability and survivability of the capsules after the mixing and compaction of asphalt mixture decrease with the decrease of W/O ratio. It is believed that the capsules fabricated with a W/O ratio of 10:1 are most suitable for asphalt mixture. The capsules can release the sunflower oil into asphalt mixtures under fatigue loading and the oil release ratio increases with the increase of the cycles of fatigue loading, leading to a significant healing of asphalt mixture. Asphalt mixture containing multi-cavity capsules can reach up to 180% recovery of the fracture energy under fatigue loading, which means that the oil released from the capsules can soften and rejuvenate asphalt mixture.

More than ten kilometers of test road with the layered double hydroxides (LDHs) modified asphalt binder was constructed to field evaluate the LDHs effect on the aging resistance of asphalt concrete, after four years of road service, asphalt concrete specimens were collected from the compared road (without LDHs), test road (with LDHs) and tunnel (without LDHs), respectively. Then, 1.5 cm surface mixture of every specimen was cut into three layers to reclaim the asphalt binders, labeled as layer 1, layer 2 and layer 3 from surface to interior. The chemical structures and oxygen contents of reclaimed asphalt binders were investigated by the Fourier infrared spectrometer (FTIR) and elemental analyzer, respectively. Meanwhile, the dynamic shear rheometer (DSR) was conducted to study the rheological performance such as complex modulus, phase angle and viscosity of reclaimed asphalt binders. In addition, the three points bending test was conducted by universal testing machine (UTM) at the temperature of −10 °C, the parameters of bending strength (RB), bending strain (eB) and bending modulus (SB) were used to evaluate the low temperature crack resistance of asphalt concrete from all these three sections respectively. The results show that, with the increase of pavement depth, the aging degree of asphalt concrete tends to decrease; the aging depth of asphalt pavement in field is within 1.0 cm. LDHs can not only decrease the aging rate of the surface asphalt concrete, but also decrease the rate of the aging diffuses into the inner of asphalt pavement, the chemical structures and technical performance of LDHs modified asphalt binders are closer to the initial status of which. The values of RB and SB of asphalt concretes from both test road and tunnel are lower than that of asphalt concretes from compared road, meanwhile, the values of eB of asphalt concretes from test road and tunnel are higher. The low temperature crack resistances of asphalt concretes of tunnel and test road are much better than that of compared road. Hence, LDHs can significantly improve the aging resistance of asphalt concrete in field.

Microcapsules with toluene-di-isocyanate (TDI) as core and paraffin as shell for self-healing of concrete were prepared using melt condensation method, and the effects of preparation temperature, agitation rate and paraffin/TDI mass ratio on core fraction of microcapsules were studied. The size distribution and morphology of microcapsules were characterized by laser particle size analyzer and scanning electron microscopy (SEM). Components of the microcapsules were analyzed by Fourier transform infrared spectrometer (FTIR). Finally, the effect of microcapsules on self-healing ability of mortars was evaluated, which indicated that preparation temperature, agitation rate and paraffin/TDI mass ratio had significant effect on core fraction of microcapsules. The optimum microcapsules could be prepared with a paraffin/TDI mass ratio 1:2 and an agitation rate 600 rpm at 75 °C. The core fraction of microcapsules prepared with optimum parameters was 66.5%, and the particle size was between 30 and 300 µm, mainly concentrated on 90 μm. SEM showed that the microcapsules were regular spheres and the shell thickness was about 1/10 of the diameter. FTIR confirmed that the TDI was successfully encapsulated in the paraffin shell. Compared with the control mortar, compressive strength of the mortar with 3% microcapsules (by mass of cement) increased by 28.2%. The reserved ratio of compressive strength was 77.2% under 60% fc0 pre-load after 48 h self-healing. The cracks with a width of less 0.4 mm on the mortar were rapidly self-healed by the microcapsules in 6 h.

Traditional asphalt mixtures can't absorb microwave energy efficiently, which limits the development of microwave heating technology in the field of road maintenance. Based on the microwave heating characteristics of basalt aggregates, the overall microwave self-healing rate of the asphalt mixture can be enhanced. The basalt was tested by XRF, XPS, XRD and electromagnetic parameters to reveal its microwave heating mechanism. Through the heating rate test, SCB test and fatigue test of asphalt mixture, its heating characteristics, flexural strength, fatigue resistance and self-healing performance were studied. The results showed that the excellent wave-absorbing properties of basalt are highly correlated with the elements of Si, Fe and Al. Its TanδM was slightly larger than TanδE, which indicated that basalt can absorb microwave energy through dielectric loss and magnetic loss. The aggregate type and particle size both affected the microwave heating rate of the aggregates. After microwave heating, the flexural strength and fatigue resistance of asphalt mixture with basalt and limestone aggregates can recover at least 65% and 23% respectively.

Conventional asphalt mixture has poor microwave absorbing performance and microwave heating efficiency. Based on the characteristics of dielectric loss of scrap tire pyrolysis carbon black (PCB), it is proposed to improve the microwave absorbing performance and self-healing rate of bitumen. The phase composition and electromagnetic parameters of PCB were tested to reveal its microwave heating mechanism. The preparation parameters, heating characteristics and self-healing properties of PCB modified bitumen were studied through the dispersion uniformity test, microwave heating test and SCB test. The main phases of PCB are microwave absorbing carbon and silicon, indicating that PCB is a good electric loss microwave absorbing material. 40 min is the recommended mixing time of 15% PCB modified bitumen. PCB's dosage, microwave frequency and microwave heating time have significant effects on the microwave heating characteristics of PCB modified bitumen. PCB can improve high-temperature stability, thermal conductance, heat storage capacity and self-healing rate of bitumen.

Calcium alginate capsule encapsulating rejuvenators are a new approach to enhance the self-healing property of asphalt, but the release and self-healing properties of calcium alginate capsu...

Due to the effects of traffic loading and environmental parameters, micro cracks would generate and develop in asphalt pavements during its service life. Encapsulations containing liquid rejuvenator for improving the self-healing ability of bitumen has a bright prospect. To avoid the rupture of encapsulations during the mixing, paving and compaction of asphalt mixture, the wall of which must be excellent in thermal stability and mechanical properties. In this research, a novel compartmented Ca-alginate/silica self-healing fiber encapsulating rejuvenator was synthesized by microfluidic method. Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) confirm that the compartmented Ca-alginate/SiO2 self-healing fibers are successfully synthesized, nano silica composites are incorporated into the “egg-box” structure of Ca-alginate by physical adsorption and intermolecular interaction. The optimum content of SiO2 can be determined by the morphology analysis. Thermogravimetric analysis and long-term thermal stability test show that the addition of SiO2 can significantly improve the thermal stability of compartmented Ca-alginate self-healing fibers. In addition, the compartmented Ca-alginate/SiO2 fiber has no leakage in bituminous binder under the temperature of 180 °C for 1 h. Nanoindentation test indicates that the addition of nano SiO2 can increase the stiffness and rigidity of Ca-alginate wall and decreases the deformation. Three-point bending experiment shows that the fibers can survive in the process of mixing and compaction of asphalt mixture. Meanwhile, the fibers enhance the self-healing property of asphalt mixture.

To improve the compatibility of layered double hydroxides (LDHs) with asphalt binders, the sodium stearate was used to organically modify the LDHs (SS-LDHs). In order to investigate the improvement effects of LDHs and SS-LDHs on the aging resistance of asphalt mixtures in laboratory and field, two kinds of aging simulating tests were conducted in laboratory and a test road was paved with LDHs and SS-LDHs modified asphalt mixtures, respectively. The chemical structure and viscosity of asphalt binders reclaimed from asphalt mixtures were tested by Fourier transform infrared spectroscopy and Brookfield viscometer respectively to investigate the LDHs and SS-LDHs effects on the anti aging properties of asphalt mixtures. Finally, the semi-circular bending test was conducted by universal testing machine to test the blending strength and fatigue life of asphalt mixture before and after aging. The results show that, at the same aging condition, the carbonyl index and viscosity aging index of reclaimed asphalt binders with LDHs or SS-LDHs are lower than that of reclaimed asphalt binders without LDHs and SS-LDHs, while the styrene-butadienestyrene index is higher, the increment of semi-circle flexural strength and the reduction of fatigue life is less than that of asphalt mixtures without LDHs and SS-LDHs, which indicates that LDHs and SS-LDHs can improve the anti thermo-oxidative aging and anti UV aging performance of the asphalt mixture. In comparison, the improvement effect of SS-LDHs on the anti aging performance of asphalt mixture is much better than that of LDHs.

In this paper, the flow behaviors and self-healing properties of two asphalt binders with different ageing degrees were investigated. Fourier transform infrared spectroscopy (FTIR) test was first used to characterize the ageing degrees of the binders. Then, frequency sweep test was conducted to calculate the flow behavior indices of asphalt binders with different ageing degrees to determine their self-healing threshold temperatures and fatigue life recovery test was performed to investigate their real self-healing rates. The capillary flow test was finally carried out to simulate the flow ability of asphalt binders with different ageing degrees within cracks in asphalt. It was found in FTIR that the carbonyl index increased with the ageing degree of the binders and tended to level off once the binders approached their ageing limits. With the deepening of ageing, the self-healing threshold temperature and the flow activation energy of asphalt binders increased and their healing performance was getting worse. Once the asphalt binders were aged to a certain extent, no self-healing threshold temperature can be found and the fatigue-healing rate was very low. A strong correlation between self-healing threshold temperature, flow activation energy and self-healing ratio can be found.

Layered double hydroxide (LDH) could improve the aging resistance of an asphalt binder. However, the previous work all arbitrarily selected only one dosage of LDH such as 3% or 5%, which could not be enough to know the effect of LDH and its dosage on the pavement performance and aging resistance of an asphalt binder accurately, it is important to investigate the LDH effect on the properties of asphalt from more widely ranges of dosages. Meanwhile, the LDH and asphalt binder interaction is still unclear. In this paper, six dosages (from 2% to 7%) of Mg-Al-CO32−-LDH were conducted to modify the styrene-butadienestyrene modified asphalt (SBS MA). The Fourier transform infrared spectroscopy (FTIR) and X ray diffraction (XRD) results indicate that there is no chemical reaction between LDH and SBS MA, the blending of LDH and SBS MA is a physical way. The rheological properties of SBS MA are studied by both dynamic shear rheometer (DSR) and bending beams rheometer (BBR), the results show that LDH can improve the high temperature performance of SBS MA, and does not significantly weaken other properties of SBS MA by controlling LDH dosage to be lower than 4%. The FTIR, complex modulus and VAI results show that LDH can significantly improve both the thermal oxide aging and UV aging resistances of SBS MA. LDH dosage of 4% is suggested to be the optimal dosage after considering the effect of LDH on the aging resistance and pavement performance of asphalt binder.

The layered double hydroxides (LDHs) has been widely used as the anti-aging modifier to improve the anti aging performance of an asphalt binder, but for the different chemical and physical properties of LDHs with asphalt binder, the compatibility of them is not very well, therefore the best modification effect can not be obtained. The sodium stearate was designated to organically modify the LDHs to enhance its improvement effect on the anti aging performance of asphalt binder. The modern test instruments such as Fourier transform infrared spectroscopy, X-ray diffractometer, scanning electron microscopy, ultraviolet visible spectrophotometer were used to investigate the sodium stearate effect on the characteristics of LDHs. In addition, the LDHs modified styrene–butadienestyrene modified asphalt (LDHs/SBS MA) and sodium stearate organically modified LDHs (SS-LDHs) modified styrene–butadienestyrene modified asphalt (SS-LDHs/SBS MA) were prepared by the melt blending method, the thin film oven test and UV aging test were conducted to simulate the short term thermo-oxidative aging and UV aging of asphalt binder respectively. Finally, the chemical structure, viscosity, and complex modulus of LDHs/SBS MA and SS-LDHs/SBS MA before and after aging were tested respectively. The results show that the sodium stearate can improve the compatibility of LDHs with styrene–butadienestyrene modified asphalt binder (SBS MA). Both LDHs and SS-LDHs can improve the anti thermo-oxidative aging and anti UV aging performance of SBS MA. Notably, the improvement effect of SS-LDHs on the anti aging performance of SBS MA is much better than that of LDHs.

Phase change materials (PCMs) have been widely applied as heat storage and thermal regulation units in many areas. However, the utilization of PCMs in asphalt pavements for thermal regulation is still limited because of the low thermal conductivity and melted phase leakage of the common used solid-liquid PCMs. The aim of this paper was to prepare a shape-stabilized expanded graphite (EG)/polyethylene glycol (PEG) composite phase change material (EG/PEG) with high thermal conductivity, and to verify its feasibility of regulating temperatures of asphalt binder. EG and PEG were selected as supporting material and working substance respectively. The EG/PEG composites and their modified asphalt binders were fabricated respectively by vacuum adsorption and physical blending process. X-ray diffraction (XRD) and differential scanning calorimeter (DSC) analyses indicated that the crystallization ability and phase change behavior of PEG was hindered by the increase of EG in the composites. The nitrogen adsorption analyses revealed that the EG matrix had an adsorptive limitation to PEG. The aforementioned results indicated that the maximum mass ratio of EG and PEG in the composites without any leakage during the melting period was 1:7. This conclusion was also proved by scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) spectrum. The thermogravimetric analyses (TGA) verified the viability of EG/PEG composites during the hot mixing process of asphalt mixture. The thermal analysis experiments indicated that the thermal conductivity and compatible stability of asphalt binder were improved by adding EG/PEG composites, and the thermal regulation effects of EG/PEG composites on the asphalt binder was verified by a thermocouples proved.

Concrete buildings used in severe cold regions are susceptible to freeze-thaw damage, resulting in internal cracking and surface spalling of concrete. Microcapsules can self-repair concrete cracks and improve the durability of concrete. This paper focuses on the effects of toluene-di-isocyanate (TDI) microcapsules on the frost resistance and self-repairing capability of concrete under freeze-thaw cycles. The mass and mechanical properties of concrete were measured before and after freeze-thaw cycles. The pore size distribution and microstructure of the concrete were characterized using nuclear magnetic resonance and scanning electron microscopy (SEM). The mechanical properties and permeability of freeze-thaw damaged concrete were assessed by compressive strength tests and rapid chloride migration (RCM) tests after self-repairing. The frost resistance and self-repairing capability of concrete containing microcapsules were also evaluated by ultrasonic test. The results showed that the concrete containing nano-SiO 2 /paraffin/PE wax encapsulated TDI microcapsules (CON3) had better frost resistance and self-repairing capability than the concrete containing other microcapsules. After 100 freeze-thaw cycles, the mass loss rate and compressive strength loss rate of CON3 were only 1.63% and 13.6%, respectively. After 7 d of self-repairing, SEM images showed that repairing products with network structure appeared in the pores of CON3, which improved the microstructure of concrete. The harmful pores proportion, compressive strength recovery rate, chloride diffusion coefficient recovery rate, maximum amplitude and dominant frequency maximum amplitude of CON3 were 47.8%, 96.9%, 84.6%, 77.99 mV and 8.37 mV, respectively.

The responsive calcium alginate/nano-Fe3O4(CA@Fe3O4) capsules can actively release the inner rejuvenator via the stimulation of microwave, thus being a prospective preventive maintenance method for effectively enhancing the self-healing level of asphalt concrete. In view of this, this paper investigated the self-healing property of asphalt mixture containing CA@Fe3O4 composite capsules under the action of microwave. The CA@Fe3O4 capsules encapsulating asphalt rejuvenator were fabricated based on reaction principle of ion exchange. Several tests were conducted to characterize the morphological structure, thermal stability, mechanical resistance and relative healing agent content of the capsules. Meanwhile, the spatial distribution and rejuvenator release from the capsules in asphalt mixtures after mixing and compaction process were also explored. Besides, the surface temperature distribution and self-healing capacity of asphalt concrete beams without and with capsules were investigated after microwave action. Meanwhile, the rejuvenator release ratios of capsules within mixture beams were also quantificationally analyzed. The experimental results indicated that the CA@2%Fe3O4 capsules showed multi-cavity structure with healing agent stored inside. Meanwhile, the mechanical resistance and thermal stability of the capsules all were up to the manufacturing requirements of asphalt mixtures in laboratory. The asphalt mixtures with CA@2%Fe3O4 capsules showed superior healing level under the action of microwave due to the combined effect of thermal induction and rejuvenator healing. In short, the CA@2%Fe3O4 capsules can obviously enhance the self-healing capacity of asphalt mixture compared with normal CA capsules.

Many researchers have conducted the Thin Film Oven Test (TFOT) before ultraviolet (UV) ageing to simulate the thermal-oxidation ageing process of bitumen, but the effect of TFOT procedure on UV ageing is still unknown. In this research, three ageing procedures were used to investigate the influence of TFOT procedure on UV ageing. Test results indicated that TFOT has a severer effect than UV radiation when bitumen thickness is 3 mm and bitumen thickness has a great influence on the ageing degree. Results of different ageing procedures shows that performing TFOT firstly is more appropriate for experimental analysis in UV ageing method.

Self-healing microcapsules show great potential in extending the service life of concrete, but it is a challenge to achieve the smart release of the healing agent from the microcapsules. In this research, Novel Microcapsules Raptured by Microwave (NMRM) with unique core–shell structure for self-healing concrete were successfully produced. The core content was calculated and the surface morphology and size distribution of NMRM were explored by Scanning Electron Microscope (SEM) and Dynamic Light Scattering (DLS). The temperature variations of specimens were monitored by a thermal infrared imager. Furthermore, the effects of NMRM dosage on the fundamental performance of concrete was investigated and self-healing behavior of the mortar and concrete were evaluated. As a result, rapture of microcapsules with 5% graphite can be quickly triggered under the microwave irradiation. The 60% fc0 pre-damaged concrete with 5% NMRM possessed 92.6% of CSRR. The purpose of this investigation is to provide a new trigger for microcapsule rupture on the specific location with cracks at the right time for self-healing concrete.

Sulfate attack causes internal cracking of concrete and affects the durability of concrete structures. The durability of concrete under sulfate attack is crucial to structural safety and serviceability. Microcapsules can self-heal microcracks in concrete and improve its durability. Microcapsules with isophorone diisocyanate (IPDI) as the healing agent and paraffin wax, polyethylene wax, and nano silica as shells were prepared to improve the sulfate resistance and self-healing properties of concrete. The mass loss, mechanical properties, impermeability, and pore size distribution of the concrete after sulfate dry-wet cycles were determined. Ultrasonic testing was used to evaluate concrete sulfate resistance and self-healing properties, as a prominent nondestructive testing technique. The results showed that the addition of microcapsules significantly improved the sulfate resistance and self-healing properties. Concrete containing nano silica/paraffin wax/polyethylene wax encapsulated IPDI microcapsules exhibited good sulfate resistance and self-healing properties. Scanning electron microscopy revealed that concrete containing microcapsules exposed to sulfate attack produced healing products with a mesh-like structure in the pores after a 14-d self-healing. These healing products can improve microstructure and self-healing properties.

Calcium alginate capsules encapsulating rejuvenator are a promising self-healing technology for asphalt pavement, but the high cost and low preparation efficiency of the capsules cannot meet the requirements of application. This research proposed an efficient method for preparing low-cost calcium alginate capsules using industrial calcium sodium and self-developed reaction kettle. To enhance the strength and assure the survival of the capsules in asphalt mixture, attapulgite was incorporated in different proportions to form composite shell capsules, and their microstructure, thermal stability, mechanical strength, and release behavior of the rejuvenator were investigated. It was found that the composite shell capsules prepared with 2.0 wt% industrial sodium alginate solution and industrial sodium alginate to attapulgite ratio 1:1 had clear multi-cavity structure, high thermal stability, and sufficient mechanical strength for their use in asphalt mixture. The multi-cavity composite shell capsules within asphalt mixture can gradually release the rejuvenator inside in wheel tracking test. The test result showed that the capsules can release 82.67% of the rejuvenator and significantly soften the binder when they suffered 115,200 cycles of compression loading (equivalent to 7 years traffic loading on capsules within a medium traffic grade pavement), indicating that the rapid prepared composite capsules can release rejuvenator to soften asphalt binder and enhance the crack-healing property of asphalt pavement during the service life.

Steel slag is the desirable substitution of natural aggregate in asphalt mixture. Nevertheless, the high-water absorption and heavy metal ions pollution are the primary problems of recycling steel slag. This study involved silicone resin to process the steel slag for preventing it from water and improving heavy metal ions leaching problems. The sealing effect of silicon resin on steel slag was also verified by the micro measurement. The results show that the leaching concentrations of all heavy metal ions were generally reduced after treatment of silicone resin. The solid silicone resin formed the airtight membranous on the steel slag surface and effectively improved the heavy metal ions leaching problems. The boundary of elements distribution between steel slag and silicone resin area are obvious, which indicates that the silicone resin effectively and completely seals the steel slag surface. The water absorption rates, adhesion and microstructure of steel slag were also improved by silicone resin. The organic asphalt and silicone exhibit superior adhesion due to the rule of the likes dissolve each other, and it isolates steel slag from water, and reduces the stripping risk of asphalt binder.

The three stage rutting behavior of several asphalt mixtures was investigated. Confinement, moisture, stress and temperature significantly affected rutting. Absence of a physically induced confinement stress by the metallic sides the wheel tracking testing mold had the highest influence on rutting, followed by temperature, moisture and lastly stress. A higher primary rutting rate indicated a lower flow number (F N ) and a faster failure rate. A linear model could relate the transition point between the primary stage and the mixtures’ flow numbers. It was independent of the testing conditions, methods and types of mixtures. A new three stage model was proposed and could simulate the rutting development of mixtures better than the Francken model. The F N of mixtures under different conditions of testing could also be related to parameter ‘c’ of the new model using a similar power law equation. The primary rutting rate, the primary transition point and parameter ‘c’ of the new model could be used in mixture characterization.

In this paper, two different designs of self-healing asphalt mixtures were promoted, the asphalt mixtures were healed through heating fibers or aggregate respectively. Induction heating and microwave heating were applied respectively to provide healing atmospheres. The thermal conductivity and temperature raising tests were conducted to measure the heating performance of those two self-healing asphalt mixtures. Infrared images were used to demonstrate the temperature field of asphalt specimens during heating. Cyclic fracture-healing test with three-point bending method was recorded to investigate the healing performance of the designed asphalt mixtures. It is concluded that asphalt mixtures containing steel fibers or steel slags could be healed with appropriate heating methods. It is also indicated that the healing performance of samples with microwave heating was a little better than the healing performance of steel fiber modified asphalt mixture with induction heating. The steel slag asphalt mixture showed a better performance of healing with the microwave as the temperature distribution was more uniform. Furthermore, the locally overheating and temperature uneven distribution remained to be big problems in the self-healing performance of asphalt mixtures in practical application.

The paper offers an investigation for the viability of basic oxygen furnace slag sludge in asphalt mixture. The sludge has adequate clearance and relatively high Ridgen void. Its zinc element and toxic leachate content meet the requirements for Class III underground water in China. Therefore the BOF sludge is applicable to the filler requirements. Its alkalinity, vesicular texture, and large surface area nature all give contributions to the improvement of road performance for asphalt mixtures. Indirect tensile strength test and three points bending test respectively demonstrate that the BOF sludge added asphalt mixtures show acceptable and better moisture and low temperature crack resistance over the mixtures with limestone powder.

In this paper, the induction healing behaviors of both warm mix asphalt and hot mix asphalt were investigated and compared through damage-healing-damage test. The steel fibers used for making asphalt mixture conductive were first optimized according to the thermal conductivity and induction heating speed of the mixture. Then, the gradient induction heating characteristics, cracking and fatigue resistance, and self-healing ratios of both warm mix asphalt and hot mix asphalt were studied. It is found that warm mix asphalt and hot mix asphalt have similar induction heating speed. The Aspha-Min based warm mix asphalt shows slightly higher fatigue resistance but slightly lower self-healing ratios than hot mix asphalt mixture. Both warm and hot mix asphalt mixtures have very high fatigue life ratios with induction heating, which means that induction heating can improve the durability of WMA. The optimal induction heating temperature of warm mix asphalt is slight lower than that of hot mix asphalt due to the remaining active ingredient, which also deceases the healing ratio slightly. It is also found that the healing ratios of both warm and hot mix asphalt mixtures are highly strain-dependent and the mixtures obtained best healing behaviors at medium microstrain amplitudes.

This paper re-evaluates the effect of sunflower oil capsules on the mechanical and self-healing properties of dense-graded asphalt mixtures. Different percentages of capsules (0.50 wt%, 0.75 wt% and 1.00 wt%) were mixed into dense asphalt. The influence of capsules on the properties of asphalt such as density, indirect tensile strength, particle loss, fatigue life, and self-healing, has been investigated. The distribution and integrity of the capsules has been also evaluated by means of CT Scans. It has been proven that capsules can survive the mixing and compaction process of asphalt mixture, do not decrease its mechanical properties and they rupture and release the oil under a high compression loading. Higher capsule content in the mixture resulted in higher oil release ratios. Furthermore, the oil released from the capsules significantly increased the self-healing capability of mixtures. Results from previous research were validated, where it had been found that 0.5% of capsules is the optimal content to obtain good mechanical performance, without affecting the rheological properties of dense-graded asphalt mixtures.

The ultraviolet (UV) aging of asphalt is one of the main factors to reduce the service span of asphalt pavement. However, the increasing behavior of aging depth of asphalt is still not clear. The research work on the aging behaviors of asphalt is good for understanding the aging mechanism of asphalt, and developing anti-aging technologies for asphalt pavement. In this research, three UV lights with different intensities were generated to age the asphalt binder. After the aging, the asphalt was stripped layer by layer with the dissolution stripping method. The rheological properties and chemical structure of asphalt from different depths were tested with Fourier transform infrared spectrometer (FTIR) and dynamic shear rheometer (DSR) respectively. The results show that under a same condition, the aging effect of UV light with higher intensity on asphalt is more significant than that with lower intensity. The UV aging of asphalt is a process of gradual development, which starts from the surface of asphalt and gradually develops to the deeper part of asphalt. Therefore, with time going, the aging depth of asphalt will increase gradually, and a gradient aging degree also exists in asphalt from different depths. Moreover, even at a same depth, the aging status of asphalt is also different if aged by UV lights with different intensities. The growth behavior of aging depth of asphalt can be divided into two stages, which can be characterized by a two-stage model. During 0–24 h, it accords with the power model; after 24 h, it accords with a linear model.

Calcium alginate capsules can release internal rejuvenator under cyclic loading to repair cracks and rejuvenate aged asphalt, thus being a promising preventive maintenance technology for asphalt pavement. However, this cyclic loading induced oil release pattern is passive and cannot ensure timely release of rejuvenator from the capsules at due time. In view of this, this paper prepared a kind of novel calcium alginate capsules that could release internal healing agent rapidly under microwave excitation. Calcium alginate/nano-Fe3O4 composite capsules were synthesized by sharp hole coagulation bath method. The morphology, mechanical strength, thermal stability and rejuvenator content of the capsules were characterized by a series of tests. Meanwhile, the surface temperature distribution and oil release ratio of the capsules under microwave irradiation were quantitatively analyzed. The results showed that the calcium alginate/nano-Fe3O4 composite capsules had obvious multi-chambers structure with rejuvenator encapsulated inside. The mechanical strength and thermal stability of the capsules meet the requirements of mixing and compaction of asphalt mixtures. Most importantly, the capsules could release internal rejuvenator under short time irradiation of low-frequency microwave. In short, the introduction of nano-Fe3O4 provided calcium alginate capsules an effective oil release capacity under microwave irradiation, which is expected to improve the self-healing ability of asphalt pavement containing capsules actively.

The unreinforced concrete pavement with electric heating pipes (UCP-EHP) has been widely used to melt the snow and ice on the pavement because the melting process is easy to conduct and control. However, the stress damage caused by the internal elevated-temperature is totally different from other situations, and its cumulative effects would cause severe structural failures to the unreinforced concrete pavement. To reduce stress damage, this paper investigates the above-mentioned damage characteristics under different pavement structures and working conditions through numerical simulations and develops the cumulative stress damage model to predict the residual life of the UCP-EHP. Firstly, the numerical model of the UCP-EHP was established to investigate the stress damage caused by internal thermal stress, and then it was verified by the validation experiments. Secondly, to reduce the stress damage, the stress damage characteristics were investigated under different pavement structures and working conditions through numerical modeling. Afterward, the optimum pavement structure with minimum stress damage was recommended based on the above analysis. Finally, the cumulative stress damage prediction model was derived, and the corresponding residual life of the UCP-EHP is predicted. Based on the prediction model, the residual life ratio of the UCP-EHP can be calculated when the number of cyclic heating is within 100. The conclusions of this paper can enrich the structural design of the UCP-EHP in terms of stress damage analysis.

Internal microcracks that occur in cement-based materials during the service process could be self-repaired using microcapsules. However, the chemical activity of the repairing agent is affected by the external environment. In this paper, the self-repairing ability of mortar containing paraffin/toluene-di-isocyanate (TDI) microcapsules was studied under different external environment (humidity and temperature). The pore size distribution, mechanical properties, impermeability and surface crack width of the control mortar (CM) and mortar containing microcapsules (MM) were measured and compared. The reaction kinetics of TDI during the self-repairing process of MM was investigated using pseudo-first-order and pseudo-second-order kinetics models. The self-repairing ability of MM was enhanced when increasing RH (relative humidity) from 50% to 95% at 20 ℃. When MM was kept under 60%fc0 pre-load and allowed 7 d for self-repairing at a relative humidity of 95%, the proportion of harmful pores, compressive strength reserved ratio and chloride diffusion coefficient recovery ratio were 28.1%, 80.9% and 68.1%, respectively, and cracks with an initial width of 0.4–0.5 mm self-repaired within 6 h. With the increasing of temperatures, the self-repairing ability increased at first but then declined. When the temperature was 50 ℃ at 50% RH, the proportion of harmful pores, compressive strength reserved ratio and chloride diffusion coefficient recovery ratio of MM under 60%fc0 pre-load for 7 d of self-repairing were 25.8%, 83.5% and 72.1%, respectively, and cracks with an initial width of 0.4–0.5 mm self-repaired within 5 h. Under different external environment and pre-loads, the curing reaction of TDI during the self-repairing process of MM was a pseudo-second-order kinetics model, which indicated that the humidity and temperature had a significant impact on the self-repairing ability of the mortar.

As one of the major distresses of asphalt pavement, the moisture damage usually results in a very serious loss of strength and structural deformation. This paper aimed to study the healing properties of asphalt concrete suffered moisture damage. Both microwave heating and induction heating were applied in this research to activate healing. A series of experiments including freeze-thaw splitting test, Marshall Immersion test and three-point bending test were conducted to evaluate the healing performance of asphalt concrete. It was found that the heating speed of asphalt mixtures was enhanced at the presence of water. The results also indicated that both microwave heating and induction heating could only partially heal the loss of strength of asphalt mixtures suffered moisture damage due to structural deformation of the samples, which could not be healed with heating technics. The presence of moisture significantly decreased the healing rate of asphalt mixtures induced by induction heating or microwave heating. It was believed that the moisture on crack surfaces could prevent the thermal healing of cracks. It is recommended that the asphalt mixtures be healed in dry condition rather than at the presence of water.

In this paper, a surface modification method was proposed to introduce strong polarity groups to rubber surface to generate a strong chemical bond between the rubber and the cement matrix. Rubber was first oxidized with KMnO 4 solution and then sulphonated with NaHSO 3 solution. The Fourier transform-infrared (FT-IR) spectra and contact angle measurement showed that the oxidation and sulphonation process introduced a large number of hydrophilic hydroxyl and sulfonate to crumb rubber and decreased the contact angle between rubber surface and water, thus greatly improved the interfacial bonding strength between crumb rubber and cement paste. After the rubber surface modification, the adhesion strength of the rubber and cement paste was increased by 41.1%. It was also found in the mechanical tests that the rubber surface modification was quite useful to enhance the compressive strength and impact strength of rubber-cement concrete. The compressive strength of the concrete with 4% modified rubber powder was 48.7% higher than that with ordinary rubber powder. Based on the results, it is concluded that the surface modification of crumb rubber with KMnO 4 and NaHSO 3 solutions is an effective method to improve the mechanical properties of rubber-cement concrete.