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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.

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.

To investigate the effects of different wavelength ranges of UV lights on chemical compositions and macro-properties of asphalt, three UV lights were used to conduct the aging test of asphalt for 1–288 h. The elemental analysis and Fourier transform infrared spectroscopy (FTIR) were performed to analyze the chemical changes of asphalt, the surface micro-topographies of asphalt before and after UV aging were studied by atomic force microscopy (AFM). In addition, the physical performance, viscosity and rheological performance of asphalt was studied with softening point test and dynamic shear rheometer (DSR), respectively. The chemical compositions and structures analyses show that the oxidation mechanism exists during the UV aging of asphalt binder. The numbers of bee-like structures in AFM height figures decrease obviously after UV aging, meanwhile the sizes of which increase. The relationships of RCC, RCS and SPI values with UV expose time follow a power function model in the first 24 h, while follows a liner model after 24 h. UV lights with different wavelength ranges have significantly different effects on the chemical compositions and macro-properties of asphalt. The UV 350–370 nm has the most obvious aging effect on asphalt binder, second is the UV 340–380 nm, the UV 200–400 nm has the lightest aging effect.

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.

It is consensual that the self-healing property of asphalt concrete can repair the damage inside it during high temperature and rest period. In order to not affect the traffic, the rest period of asphalt pavement is very short and uncontrollable; so, it is necessary to obtain enough high temperature in a limited time to achieve higher healing efficiency of asphalt concrete. The purpose of this paper is to study the induction heating efficiency and healing behaviors of asphalt concretes doped with different conductive additives. Steel fiber, steel grit, and steel slag were added to asphalt mixtures as conductive additives to prepare induction healing asphalt concretes. The steel grit and steel slag were added to replace the aggregates of corresponding particle size by equal volume to ensure the consistency of asphalt concrete volume, which can avoid degrading the performance of asphalt concrete due to the change of porosity. The induction heating efficiency and healing rate of asphalt concrete were quantified by infrared camera and three-point bending-healing experiment, respectively. The results showed that the thermal properties of asphalt concrete changed with the addition of different conductive additives. The asphalt concrete with steel fiber had the best induction heating property. While steel slag had extremely weak induction heating speed, the better thermal insulation property of the asphalt concrete with steel slag resulted in a higher induction healing rate. It was suggested to add steel slag to induction healing asphalt concrete to improve the healing rate.

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.

Self-healing of cracks in cementitious materials using healing agents encapsulated in microcapsules is an intelligent and effective method. In this study, microcapsules were prepared by the melt–dispersion–condensation method using microcrystalline wax as the shell and E-51 epoxy resin as the healing agent. The effects of preparation process parameters and microcrystalline wax/E-51 epoxy resin weight ratio on the core content, particle size distribution, thermal properties, morphology, and chemical composition of microcapsules were investigated. The results indicated that the optimal parameters of the microcapsule were microcrystalline wax/E-51 epoxy resin weight ratio of 1:1.2, stirring speed of 900 rpm, and preparation temperature of 105 °C. The effects of microcapsules on pore size distribution, pore structure, mechanical properties, permeability, and ultrasonic amplitude of mortar were determined, and the self-healing ability of mortar with different contents of microcapsules was evaluated. The optimal content of microcapsules in mortars was 4% of the cement weight, and the surface cracks of mortar containing microcapsules with an initial width of 0.28 mm were self-healed within three days, indicating that microcapsules have excellent self-healing ability for cementitious materials.

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.

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.

In this paper, the snow and ice melting properties of self-healing asphalt mixtures with induction heating and microwave heating were investigated. The self-healing performance of the mixtures during ice melting process was measured with cyclic three-point bending test as well. The results indicated that the snow and ice melting performance of self-healing asphalt mixtures with appropriate heating techniques was remarkable. The average melting velocity of ice melting was improved from less than 1 g/min (previous researches) to more than 10 g/min, while the average snow melting velocity of steel fiber modified asphalt mixture and steel slag asphalt mixture with microwave heating could reach 53.9 g/min and 48.5 g/min respectively. The water from melted ice/snow played a major role in the melting process of snow with microwave heating. However, the moisture from melted ice/snow on the surfaces of crack prevented the thermal healing of asphalt mixtures. It is recommended that another heating process after the melting process should be applied to promote the healing of cracks as well as to prevent the melted snow and ice water on the pavement from freezing.

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.

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.

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 idea of prolonging the service life of asphalt mixture by improving the self-healing ability of asphalt has received extensive attention in recent years. In view of this, this work synthesized three kinds of encapsulating rejuvenator fibers to improve self-healing properties of asphalt mixtures. A series of characterizations were performed to study the morphology, chemical structure and thermal stability of the three kinds of fibers. Subsequently, the road performance of asphalt mixture containing the fiber were investigated, which included high and low temperature, water sensitivity and fatigue performances. Finally, the self-healing performance of asphalt mixture containing the fiber was investigated by 3PB test. The results revealed that the three kinds of encapsulating rejuvenator fibers were successfully synthesized. The fibers had excellent thermal stability, which met temperature requirements in the mixing and compaction process of asphalt mixtures. Road performance of asphalt mixture containing the fiber met the requirements. Self-healing ability of asphalt mixture containing the fiber was improved. Synergistic action of temperature and rejuvenator could further significantly improve the self-healing ability of the asphalt mixture.

Induction heating is a valuable technology to repair asphalt concrete damage inside. However, in the process of induction heating, induced particles will release a large amount of heat to act on asphalt binder in a short time. The purpose of this paper was to study the effect of induction heating on asphalt binder aging in steel fibers modified asphalt concrete. The experiments were divided into two parts: induction heating of Dramix steel fibers coated with asphalt binder (DA) and steel wool fibers modified asphalt concrete. After induction heating, the asphalt binders in the samples were extracted for testing aging indices with Fourier Transform Infrared (FTIR), Dynamic Shear Rheometer (DSR), and Four-Components Analysis (FCA) tests. The aging of asphalt binder was analyzed identifying the change of chemical structure, the diversification of rheological properties, and the difference of component. The experiments showed that the binder inside asphalt concrete began aging during induction heating due to thermal oxygen reaction and volatilization of light components. However, there was no peak value of the carbonyl index after induction heating of ten cycles, and the carbonyl index of DA was equivalent to that of binder in asphalt concrete after three induction heating cycles, which indicated the relatively closed environment inside asphalt concrete can inhibit the occurrence of the aging reaction.

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.

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.

A comparative study was conducted to determine the effects of graphene and carbon nanotubes on the thermo-mechanical properties of asphalt binder using molecular simulations and experiments. Micro-morphology of graphene and carbon nanotubes was measured by scanning electron microscopy. Thermal stability and glass transition temperature were investigated by differential scanning calorimeter. Simulation results indicated that the Tg had slightly changed for graphene-modified asphalt (GMA) and carbon nanotubes-modified asphalt (CNsMA) and that the thermal expansion coefficients and thermal conductivity increased along with the adding amount of graphene or carbon nanotubes. The Tg calculated by density–temperature method was closer than the experimental Tg and the Tg decreased in the order of CNsMA, GMA and asphalt. Young’s modulus of asphalt, GMA and CNsMA were 9.2658, 25.7563 and 17.8249 GPa at 298 K, respectively, which indicated that thermo-mechanical properties of asphalt showed considerable impr...

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.

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.

In this paper, the flow behaviors of asphalt binders were investigated through DSR viscosity-frequency sweep test to find out their potential optimal self-healing temperatures and the real self-healing ratios of the binders at different temperatures were measured through fatigue-healing-fatigue test to confirm the optimal self-healing temperatures. The healing time of asphalt binders needed for full healing was studied as well. It is found that both fresh and aged Pen bitumen binders show near-Newtonian fluid state at their softening point temperatures, at which asphalt binders showed optimal self-healing properties to heal fatigue damage. It is also found that ageing of the binder increases its optimal self-healing temperature. It means that the optimal temperatures of asphalt binders are associated to the bitumen type and ageing. Finally, the Wool and O’s Connor model can be used to determine the healing time needed by asphalt binder to achieve full healing, where the accumulated dissipated energy recovery is recommend as a suitable healing index.

Calcium alginate capsules can gradually release the healing agent inside without rupture under cyclic traffic loading and are a promising self-healing technology for asphalt pavement. However, they have a low strength and tend to release the healing agent too fast. To enhance the strength of calcium alginate capsules and prevent them from releasing healing agent prematurely, calcium alginate-attapulgite composite capsules were synthesized with different synthesis parameters and their physical properties, morphological characteristics, release and healing behaviors were studied respectively. It was found that the incorporation of attapulgite improved the strength of calcium alginate capsules and could prevent the capsules from leaking healing agent during the drying process. The incorporation of attapulgite also slowed down the healing agent (sunflower oil) release speed of the calcium alginate capsules. Calcium alginate-attapulgite composite capsules can release 55.2% of the oil inside after 4 years of service within a medium traffic grade pavement, providing asphalt mixture with the ability to release the oil gradually to suit the cracking process of asphalt pavement. The released oil from the calcium alginate-attapulgite composite capsules improved the self-healing property of asphalt mixture and the capsules maintained their original spherical shape after releasing most of the oil inside.

Ion chelator can chelate calcium ions and migrate in cement-based materials to promote self-healing of cracks. This paper investigated the migration and self-healing abilities of ion chelator in cement-based materials by a novel method. In this method, control mortar without ion chelator and self-healing mortar with ion chelator are poured into the same mold, cracks at different locations of the two kinds of mortars are prefabricated, and the migration of ion chelator from self-healing mortar to the control mortar is assessed by observing the self-healing process of crack in control mortar. Meanwhile, the microstructure and chemical component of self-healing product in cracks at different locations of the control mortar was characterized through scanning electron microscope (SEM) and X-ray diffraction (XRD). The results show that the self-healing ability of control mortar is closely related to the migration distance of ion chelator. When the migration distance of the ion chelator was 2 cm, the crack with a width of 0.37 mm can be sealed after curing for 7 d. When the migration distance of the ion chelator was 5 cm, the crack with a width of 0.26 mm can also be repaired after curing for 7 d. Through SEM observation and XRD analysis, it can be found that the ion chelator promotes the formation of a large number of calcite crystals for sealing the cracks in the control mortar. However, the calcite crystals at the crack will become loose with the increase of the migration distance of the ion chelator.

Ion chelator is a kind of crystalline additive which can accelerate the precipitation of calcium carbonate in cracks of cement-based materials. In this paper, the influences of ion chelator and CO2-rich environment on self-healing capabilities of cement mortar were investigated. The mortars with or without ion chelator were subjected to two gas environments (air and CO2-rich) and three exposure conditions (no water, water contact and water immersion), respectively. The self-healing rate of cracks, water permeability and water absorption of the healed mortars, and microstructure of self-healing product were used to assess the self-healing capability of mortars. The results indicated that the self-healing ability of the mortars cured in CO2-rich environment is stronger than that of the mortars cured in air environment. The excellent self-healing ability of the mortars with ion chelator needs to be stimulated by water contact or water immersion. The relative permeability coefficient and water absorption coefficient of mortar with ion chelator in the CO2-rich environment under water contact or water immersion conditions were significantly reduced. In addition, the bottom surface crack of mortar has better self-healing ability than the top surface crack of mortar. The bottom surface crack up to 0.46 mm can be healed after curing for 28 d when the mortars with ion chelator were cured in the CO2-rich environment under water immersion condition. Scanning electron microscopy showed that the particle sizes of self-healing products (CaCO3) in bottom surface crack were larger than that in top surface crack.

Self-healing capability of the asphalt mixtures containing encapsulated healing agent can be affected by different water components as results of their exposure to aggressive environmental conditions such as the acid rain or saline-alkali solutions in coastal areas. In view of this, this paper aims to study the effect of harmful water environments on the self-healing capability of asphalt mixtures containing a kind of novel composite fibers. The Ca-alginate/SiO2 composite fibers encapsulating healing agent was synthesized by using a microfluidic device. Several tests were conducted to characterize the micromorphology, thermal stability and mechanical properties of the fibers. Effectiveness of the composite fibers in asphalt was observed by fluorescence microscopy. Additionally, three-point bending test was performed to measure the effects of different water environments (including acid, alkali and salt-water solutions) on the self-healing properties of asphalt mixtures with, and without fibers. Furthermore, the mechanism of the effect of different water environments on the self-healing performance of the asphalt mixture was studied by Fourier-transform infrared spectroscopy (FT-IR) and scanning electron microscope (SEM) analysis. Main results showed that the composite fiber encapsulated 61.9 wt% of healing agent, and the fibers could meet the temperature and mechanical requirements during the manufacturing process of asphalt mixture. The composite fiber worked and enhanced self-healing capability of asphalt. Harmful water environments did not weaken the effect of the composite fiber. Compared with the drying condition, the self-healing property of asphalt mixtures containing the composite fibers was further improved after being immersed in alkali and salt-water environment. The results indicated that the sodium ions in the alkaline solution and the salt solution could undergo a de-crosslinking chemical reaction with calcium alginate in the fiber wall, as a result of which more healing agent leaked out to soften and rejuvenate asphalt. In short, the composite fibers encapsulating healing agent worked, and these were successfully applicable into asphalt mixture under different water environments.

Asphalt pavement will be damaged under the action of asphalt aging and moisture damage. Water solution erosion degree is closely related to the aging of asphalt and degradation of the adhesive strength between asphalt and aggregate. In view of this, this paper investigated the effect of water solution erosion on rheological, cohesion and adhesion properties of virgin and aged asphalt. The experiment was performed by immersing asphalt into five different water solutions (includes distilled water, acid solution, alkali solution, sodium chloride solution and sodium sulfate solution) for different time, which was considered to be fully reflect the real service condition within an asphalt pavement in different areas. The rheological properties were evaluated by dynamic shear rheometer (DSR), the cohesion and adhesion properties based on the surface free energy test were got by sessile drop method. Meanwhile, the relationships between asphalt rheological, cohesion and adhesion properties with aqueous solute and water solution erosion time were studied. The effects of water solution erosion on virgin asphalt and its PAV aged asphalt were compared. It was observed that water solution erosion resulted in the increased of asphalt elastic component and stiffness, decreased of asphalt fatigue life and the cohesive force and adhesion to aggregates. This trend was reduced to some extent with the presence of acid, alkali, and salt solutes. Under the action of water solution erosion, PAV aged asphalt showed a worse resistance to water solution erosion. And unlike heat-aging and ultraviolet-aging, the development trends of rheological, cohesion and adhesion properties of asphalt were more complex and variable with the change of asphalt surface component.

The ambient temperatures have significant effect on self-healing capabilities of concretes with microcapsules. Self-healing capabilities of mortars with different shell composition (paraffin, paraffin/PE wax and nano-SiO2/paraffin/PE wax) microcapsules containing toluene-di-isocyanate under the temperature of 10 °C, 30 °C, 50 °C and 60 °C were investigated in this paper. The compressive strength, chloride diffusion coefficient and pore size distribution of mortars containing microcapsules before and after self-healing were characterized by mechanical property test, rapid chloride migration test and nuclear magnetic resonance, respectively. The crack healing ratio of mortars during self-healing period were measured. The self-healing capabilities of mortars containing different microcapsules raised with the increase from 10 °C to 50 °C. Nevertheless, when the temperature reached 60 °C, the self-healing capability of the mortar containing paraffin microcapsules (AM1) decreased obviously, while the self-healing capabilities of the mortars containing paraffin/PE wax microcapsules (AM2) and nano-SiO2/paraffin/PE wax microcapsules (AM3) were almost unchanged. The self-healing capability of AM3 was superior to that of AM1 and AM2 at the same temperature. The compressive strength recovery rate, chloride diffusion coefficient recovery rate and harmful pores ratios of AM3 after pre-damaged at 50 °C for 7 d self-healing were 94.1%, 81.2% and 47.3%, respectively. When the ambient temperature reached 50 °C, the surface cracks of the mortar with three kinds of microcapsules could be completely self-healed in 5 h. However, when the temperature raised to 60 °C, the healing ratio of the crack in AM1 with a width of 0.4–0.5 mm decreased to 49.52% after 6 h self-healing. Meanwhile, the surface cracks of AM3 could be completely self-healed less than 3 h.

Ion chelator is a novel crystalline admixture used for improving self-healing capability of cementitious materials. Studies quantifying this self-healing behavior are limited to fresh-water making it unclear under seawater containing magnesium, sulfate and chloride ions. Therefore, the purpose of this paper is to investigate the effects of ion chelator on pore structure, mechanical property and self-healing capability of seawater exposed mortar. The pore size distribution was evaluated by nuclear magnetic resonance (NMR). The self-healing ability was quantified by compressive strength recovery and visible crack closure test, while the composition of crack healing products was analyzed by X-ray diffraction (XRD). The results indicated that ion chelator improves pore structure and compressive strength of mortar under seawater immersion. After 90 days seawater immersion, the proportion of harmful holes (>0.1 μm) in mortar with ion chelator (MCA) was 30.3%, which is lower than in control mortar (CM). The compressive strength of MCA under seawater for 90 days was 34.4 MPa, while that of CM was 27.4 MPa. The ion chelator enhanced the self-healing capability of pre-damaged mortar remarkably. After 28 days seawater immersion, compressive strength recovery rate of MCA under fresh-water and seawater was 94% and 80%, respectively. And the maximum crack width completely healed in MCA under seawater is up to 350 μm, while around 240 μm in MCA under fresh-water. XRD analysis revealed that the crack-healing products in MCA under seawater immersion were magnesium hydroxide and calcium carbonate.

The objective of this paper was to study the effect of hydrodynamic impact on durability and healing performance of inductive asphalt concrete (IAC) through moisture induced sensitivity test (MIST). AC-13 inductive asphalt concrete containing steel fiber was designed and Marshall specimens were prepared to suffer MIST in orthogonal condition. After MIST, cutting was performed to observe the corrosion of steel fibers inside while semi-circular bending (SCB) test was conducted to evaluate the mechanical properties. Then fracture-healing procedure was carried out to investigate the strength recovery ratios of the specimens before and after MIST. Meanwhile, the crack healing ratio and change of air voids inside asphalt concrete were observed by computed tomography (CT) scan test. The results showed that there was no corrosion of steel fibers inside samples after short term simulation in the laboratory. The tensile strength and fracture energy decreased after MIST. The changing trends of strength recovery ratio and fracture energy recovery ratio were consistent with that of tensile strength. CT-scan indicated that the healing ratio of crack was up to 92.3%. The initial air void content of asphalt concrete was 4.7%, 5.7% after adding steel fibers, and 4.87% after induction heating. However, the air void changed from 5.7% to 6.8% after MIST. Orthogonal test factor analysis showed that temperature was the most significant factor affecting the durability of asphalt concrete during MIST.

Ion chelator is a novel crystalline admixture which can promote the self-healing of cracks in cement-based materials. In this paper, the self-healing capability of the surface and internal cracks of mortars with ion chelator of different age were investigated by the change of crack width, water permeability, recovery of compressive strength and X-ray computer tomography test. The results indicated that the surface crack up to 0.4 mm on the mortars with 0.5 wt% ion chelator pre-cracked at different age can be repaired after standard curing for 30 d. According to the water permeability test, the mortars with ion chelator pre-cracked at 3 d and 28 d have excellent self-healing ability for internal cracks, and the relative permeability coefficient of the mortars with 0.5 wt% ion chelator decreases most significantly. The compressive strength recovery test of mortars shows that ion chelator can promote the self-healing of internal cracks within the mortars. After curing for 56 d, the compressive strength recovery ratio of the mortars with 0.5 wt% ion chelator pre-loaded at 28 d reached 99.5%. And the X-ray computer tomography displayed that the self-healing process of cracks in mortars was from outside to inside.

This paper investigates the heating characteristics and induced healing efficiencies of asphalt mixture containing steel fiber under induction heating and microwave heating. The heating characteristics of an asphalt mixture with different heating methods were studied with an infrared camera. The healing performance of the asphalt mixture specimens in different healing conditions were investigated by observing the crack closure and testing the fracture resistance recovery after healing. The results showed that the heating speed at the surface of asphalt mixture with induction heating was much higher than that with microwave machine heating, under a similar output power and the same method of radiation. While the temperature distribution within the asphalt mixture under induction heating was quite uneven, microwave heating resulted in a more uniform temperature distribution. The effective heating depth of microwave heating is much higher than that of induction heating. Gradient healing occurred within the sample heated with induction healing, while a uniform healing effect can be achieved with microwave heating.

The aging effect of ultraviolet (UV) radiation on bitumen has gained increasing attention from researchers, resulting in the emergence of a new method to simulate the UV aging that occurs during the service life of bitumen. However, the UV aging degree is closely related to bitumen thickness and the effect of UV radiation on aging depth is not clear. The relationship between ultraviolet (UV) radiation and bitumen UV aging depth was investigated in this paper. Three groups of samples were UV aged using different aging procedures to investigate the bitumen aging mechanism of UV radiation. The results from the first group showed that UV aging depth increased along with aging time. After aging for five hours, the complex modulus of the second and third layers increased. The second group’s results indicated that the aging effect of ozone was small and that the increase in aging depth was uncorrelated with ozone. The results from the third group showed that the transmittance of bitumen increased after UV aging and that the real reason why aging depth increased was permeation.

Diatomite is an inorganic natural resource in large reserve. This study consists of two phases to evaluate the effects of diatomite on asphalt mixtures. In the first phase, we characterized the diatomite in terms of mineralogical properties, chemical compositions, particle size distribution, mesoporous distribution, morphology, and IR spectra. In the second phase, road performances, referring to the permanent deformation, crack, fatigue, and moisture resistance, of asphalt mixtures with diatomite were investigated. The characterization of diatomite exhibits that it is a porous material with high SiO2 content and large specific surface area. It contributes to asphalt absorption and therefore leads to bonding enhancement between asphalt and aggregate. However, physical absorption instead of chemical reaction occurs according to the results of FTIR. The resistance of asphalt mixtures with diatomite to permanent deformation and moisture are superior to those of the control mixtures. But, the addition of diatomite does not help to improve the crack and fatigue resistance of asphalt mixture.

Layered Double Hydroxides (LDHs) are a family of intercalated functional materials with a layered structure and regarded as an effective modifier to improve the UV ageing resistance of bitumen. However, the preparation of LDHs modified bitumen is very complicated and time-consuming. Based on the theory of Stokes’ law and the equation of the terminal velocity, pre-dispersion and microwave heating were proposed in this research to promote the dispersion of LDHs powder in bitumen matrix. LDHs modified pre-dispersed bitumen (LDHs-PDB) particles were first prepared and then were dispersed in bitumen matrix with the assistance of microwave heating. The cosolvent was optimized and the dispersion of LDHs in the modified bitumen was characterized by the laser particle size analyzer. It is found that the utilization of pre-dispersion alone could slightly improve the dispersion of LDHs in bitumen. The combination of pre-dispersion and microwave heating significantly improved the dispersion of LDHs in bitumen matrix. Although the distribution is still not uniform, it is believed that a reasonable design of the size distribution of LDHs-PDB particles may result in a uniform vertical distribution of particles in bitumen matrix.

Layered double hydroxides (LDHs) modified asphalt is a typical solid-liquid mixture that is concentrated suspensions of solid particles in solutions. The influence of dodecyl benzenesulfonic acid (DBSA) and polyvinyl alcohol (PVA) on the rheological properties and solubility of LDHs modified asphalt (LMA) were investigated by dynamic shear rheometer, molecular dynamic simulations and optical microscopy. Research results indicated that the addition of DBSA or PVA to LDHs modified asphalt resulted in enhancement of the cracking resistance, stress relaxation and creep behavior at lower temperature. The solubility parameters of surface active agent and LMA showed that PVA and DBSA can contribute to the solution of LDHs in asphalt. The effect of PVA was better than DBSA. The morphology of LMA implied that the distribution of LDHs was uniform when 0.5wt-% DBSA or PVA were added and increasing DBSA contents under certain levels increased the uniformity of LDHs..

The comprehensive properties of SBS-modified asphalt mixtures containing layer double hydroxides, including high-temperature stability, water sensitivity, fatigue resistance and low-temperature anti-cracking properties, were studied in this research. It is found that layer double hydroxides–SBS asphalt mixtures show higher retained Marshall stability, freeze-thaw-splitting strength ratio and dynamic stability both before and after ultraviolet aging. It means that the addition of layer double hydroxides to SBS-modified asphalt mixture increases its water damage resistance and rutting resistance. Layer double hydroxides–SBS asphalt mixtures show higher flexural strength and strain than SBS-modified asphalt mixture after ultraviolet aging. It means that the addition of layer double hydroxides improves the long-term low-temperature property of SBS-modified asphalt mixture. The fatigue life of ultraviolet-aged SBS-modified asphalt mixture is also slightly improved by addition of layer double hydroxides...