Healing Temperature Research Articles

Nanoimprinting of Crosslinked Polyurethane / Polycaprolactone Blends: Scratch Recovery of Surface Topographies.

Scratch recovery of micro-nano-patterned polymer surfaces extends the service life of products that require tunable surface properties and contributes to more sustainable development. Scratch recovery has been widely studied in bulk and 4D-printed polymers via intrinsic self-healing mechanisms. Existing studies on self-healing of micro/nano-scale polymeric surfaces are limited to the recovery of controlled tensile or compressive strain. Scratch recovery requires material transport to close the gap created by a scratch. Here, for the first time, scratch recovery of thermally nanoimprinted polymer surfaces in a heterogeneous polymer is reported. A blend of Polyurethane (TPU) and poly(caprolactone) (PCL) with selectively crosslinked TPU imparts shape-memory properties, and the uncrosslinked PCL retains chain mobility for molecular diffusion during scratch recovery. Scratch recovery of nanoimprinted micro-pillars has been achieved spontaneously and completely by heat and without any pressure input. The healing temperature is determined to be the melting point of PCL at 60°C. Rapid recovery is also achieved at 60 s with complete closure of scratch width of 5µm and topography recovery of the nanoimprinted micro-pillars.

Finite element analysis of crack propagation, crack-gap-filling, and recovery behavior of mechanical properties in oxidation-induced self-healing ceramics

The oxidation-induced self-healing of cracks is an attractive function for the application of ceramics in high-temperature structural components requiring high reliability. To further optimize materials or components for practical applications, the development of numerical simulation techniques is of importance. In this study, we examined crack growth, crack-gap-filling by oxide, and re-cracking behaviors in chevron-notched specimens under various load and temperature conditions by adopting a finite element analysis (FEA) approach incorporating a damage-healing constitutive model based on fracture mechanics and oxidation kinetics. Furthermore, by implementing the mechanical properties and oxidation kinetic parameters of reported self-healing ceramics composites into the FEA, we examined the effects of the composition and composite structure on the cracking and healing behaviors. Crack-gap-filling simulations suggested that the damage variables gradually decreased from the crack tip, and the minimum healing time was determined by the time required for the complete filling of the element at the crack mouth with the largest crack opening width. Furthermore, the recovery of the stiffness and strength could be successfully reproduced after complete healing with a reasonable healing temperature and time. The proposed FEA approach could also contribute to estimating the minimum healing time required at various temperatures to heal a given damage for various composites.

Multiscale study on fatigue healing performance and molecular healing behavior of self-healing SBS modified bitumen

Self-healing polymer modified bitumen based on dynamic chemical bonds is a potential approach to improve the durability of bitumen pavement and save fossil energy. Herein, a novel self-healing SBS modified bitumen on the basis of dynamic disulfide bonds and hydrogen bonds was prepared. Firstly, an aliphatic disulfide (A-ALD) with disulfide bonds and hydrogen bonds was synthesized. Then A-ALD/SBS modified bitumen (A-ALD/SMB) was prepared by blending A-ALD and SBS modified bitumen. The chemical structure and microstructure of A-ALD/SMB were evaluated. In addition, the self-healing performance of A-ALD/SMB at the macroscopic scale and the self-healing behavior at the molecular scale were investigated by a combination of fatigue healing test and molecular dynamics (MD) simulation. The chemical structure analysis showed the formation of disulfide bonds and hydrogen bonds in A-ALD, and A-ALD was successfully attached to the CC bonds in SBS. Fluorescent images revealed that a better network structure appeared in A-ALD/SMB and formed a two-phase continuous morphology. The optimal dosage of A-ALD in SBS modified bitumen was 0.6 %. The fatigue healing test results indicated that A-ALD markedly enhanced the self-healing ability of SBS modified bitumen, and prolonging resting time and raising healing temperature can increase the self-healing performance of A-ALD/SMB. When the damage degree, healing temperature, and resting time were 30 %, 30 °C, and 60 min, respectively, the healing rate of A-ALD/SMB was 98.5 %, which was 30.2 % higher than SMB. The MD simulation results showed that the A-ALD enhanced the molecular diffusion capacity of SBS modified bitumen, and crack healing time of A-ALD/SMB was earlier than that of SMB under the same conditions. When the healing temperature was 40 °C, the time for the A-ALD/SMB and SMB molecular chain segments to start contacting and healing was 27 ps and 49 ps, respectively, which was improved by 44.9 % for A-ALD/SMB compared to SMB. Furthermore, the self-healing behavior of A-ALD/SMB at the molecular scale was consistent with the self-healing performance at the macroscopic scale under different healing temperatures and damage degrees. This study provided a theoretical basis for exploring the self-healing mechanism of SBS modified bitumen.

Method for evaluating healing state of self-healing ceramics using acoustic emission

Previous studies have evaluated the volume expansion rate of oxidation products and healing temperature and time. However, the bonding strength between the product and the matrix is yet to be appropriately evaluated. To develop a self-healing agent selection method for ceramics, this study proposed a method for examining the healing state and fracture behavior of self-healing ceramics through acoustic emissions (AE) generated during three-point bending tests. This study fabricated completely and incompletely healed SiC30 vol%/Al2O3 composite specimens by adjusting the healing time, and the crack length was assessed employing linear fracture mechanics, and effect of healing state on cumulative AE energy and AE frequency. The crack lengths were compared with those of the kinetic model of crack healing. The crack lengths of the 5-h healed specimens were estimated by linear fracture mechanics to be 12.5 μm for incomplete and 10.4 μm for complete healing, while that estimated by the kinetic model were 13.5 μm, indicating the usefulness of the kinetic model in the initial stages of crack healing. Furthermore, while the AE frequency at the initial stage of fracture was dominated by peaks below 100 kHz in damaged or incompletely healed specimen, there was a relatively high frequency peak of over 200 kHz in smooth and completely healed specimen, The average cumulative AE energies of smooth, damaged, 5 h-healed (incompletely), 5 h-healed (completely), and 24 h-healed specimens were 395, 0.89, 26.8, 189, and 318 V・μs, respectively. Thus, the AE energy that accumulated until rupture tended to increase as healing progressed, these findings suggest that the AE method can be used to determine healing conditions. These results will help establish a method for selecting self-healing agents according to the environment in which they are used.

Study on the Factors Affecting the Self-Healing Performance of Graphene-Modified Asphalt Based on Molecular Dynamics Simulation.

To comprehensively understand the impact of various environmental factors on the self-healing process of graphene-modified asphalt, this study employs molecular dynamics simulation methods to investigate the effects of aging degree (unaged, short-term aged, long-term aged), asphalt type (base asphalt, graphene-modified asphalt), healing temperature (20 °C, 25 °C, 30 °C), and damage degree (5 Å, 10 Å, 15 Å) on the self-healing performance of asphalt. The validity of the established asphalt molecular models was verified based on four physical quantities: density, radial distribution function analysis, glass transition temperature, and cohesive energy density. The simulated healing time for the asphalt crack model was set to 200 ps. The following conclusions were drawn based on the changes in density, mean square displacement, and diffusion coefficient during the simulated healing process under different influencing factors: Dehydrogenation and oxidation of asphalt molecules during the aging process hinder molecular migration within the asphalt crack model, resulting in poorer self-healing performance. As the service life increases, the decline in the healing performance of graphene-modified asphalt is slower than that of base asphalt, indicating that graphene-modified asphalt has stronger anti-aging properties. When the vacuum layer in the asphalt crack model is small, the changes in the diffusion coefficient are less pronounced. As the crack width increases, the influence of various factors on the diffusion coefficient of the asphalt crack model becomes more significant. When the crack width is large, the self-healing effect of asphalt is more dependent on these influencing factors. Damage degree and oxidative aging have a more significant impact on the healing ability of graphene-modified asphalt than healing temperature.

The Production of Porous Asphalt Mixtures with Damping Noise Reduction and Self-Healing Properties through the Addition of Rubber Granules and Steel Wool Fibers.

Conventional asphalt roads are noisy. Currently, there are two main types of mainstream noise-reducing pavements: pore acoustic absorption and damping noise reduction. However, a single noise reduction method has limited noise reduction capability, and porous noise-reducing pavements have a shorter service life. Therefore, this paper aimed to improve the noise-damping performance of porous asphalt mixture by adding rubber granules and extending its service life using electromagnetic induction heating self-healing technology. Porosity and permeability coefficient test, Cantabro test, immersion Marshall stability test, freeze-thaw splitting test, a low-temperature three-point bending experiment, and Hamburg wheel-tracking test were conducted to investigate the pavement performance and water permeability coefficients of the mixtures. A tire drop test and the standing-wave tube method were conducted to explore their noise reduction performance. Induction heating installation was carried out to study the heating rate and healing performance. The results indicated that the road performance of the porous asphalt mixture tends to reduce with an increasing dosage of rubber granules. The road performance is not up to the required standard when the dosage of rubber granules reaches 3%. The mixture's performance of damping and noise tends to increase with the increase of rubber granule dosage. Asphalt mixtures with different rubber granule dosages have different noise absorption properties, and the mixture with 2% rubber granules has the best overall performance (a vibration attenuation coefficient of 7.752 and an average absorption factor of 0.457). The optimum healing temperature of the porous asphalt mixture containing rubber granules and steel wool fibers is 120 °C and the healing rate is 74.8% at a 2% rubber granule dosage. This paper provides valuable insights for improving the noise reduction performance and service life of porous asphalt pavements while meeting road performance standards.

Study on self-healing performance of microcracks in SBS/waste rubber powder composite-modified asphalt based on molecular dynamics simulation

The internal microcracks in asphalt materials can heal spontaneously under suitable conditions, and understanding the characteristics of the self-healing behavior of asphalt materials is crucial for evaluating the fatigue life of asphalt pavements. In this paper, a molecular model of modified asphalt microcracks was created by introducing modifier molecules into the virgin asphalt model, and the self-healing process of the asphalt microcrack model under different healing conditions was investigated, which revealed the effects of modifier materials and healing temperatures on the healing performance of asphalt. The results show that the effect of healing temperature on asphalt healing performance is more significant than the modifier material, the relative concentration of molecules at the microcrack healing and the healing temperature is positively correlated; asphalt material healing free volume fraction with the increase in healing temperature gradually increases, the incorporation of modifiers can reduce the free volume fraction growth caused by high-temperature healing, improve the healing stability of modified asphalt. The asphalt ductility specimen crack healing test shows that when the healing temperature exceeds 45 ℃, there is a decreased increase in self-healing rate; taking into account the high-temperature healing is easy to make the asphalt material produce permanent deformation, this paper determines the optimal healing temperature in the vicinity of 48 ℃. The research results have certain reference and application values for asphalt pavement damage repair.

Dynamic constitutive model of Fe–Cr–Ni stainless steel based on isothermal true stress-strain curves

Austenitic Fe–Cr–Ni stainless steel is widely used in aviation, chemistry, energy, due to its excellent properties of high-temperature performance. In this study, the splitting Hopkinson pressure bar with high-temperature system was employed to evaluate the dynamic mechanical properties of Fe–Cr–Ni stainless steel. The true stress-strain curves were obtained under varying conditions, including variable strains, strain rates and temperatures. The true stress increases and levels off as the true strain increases, while increases as the strain rate increases, but decreases sharply as the deformation temperature rises. The deformation temperature is consist of healing temperature and adiabatic temperature. The adiabatic temperature rise related to the specific heat capacity was calculated. The actual deformation temperatures were calculated under different strains by combining the true stress-strain curves. The true stress-strain curve under variable temperature was corrected to the stress-strain curve under isothermal state by using the thermal softening rate, which decoupled the strain and temperature. The Power-Law and Johnson-Cook constitutive models were fitted based on the real stress-strain isothermal curve. The fitting accuracy of Power-Law model was 1.61% for different strain rates at room temperature in average, 3.51% for fixed strain rate at different temperatures. While the fitting accuracy of Johnson-Cook model was 2.94% for different strain rates at room temperature in average, 6.18% for fixed strain rate at different temperatures.

Use of Figueiredo’s technique for treating extensive infected skin lesions – a case report

Demonstrate that a low-complexity surgical technique can effectively solve problems of extensive skin lesions in cities where microsurgical techniques are not available. We present a 59-year-old male patient with diabetes mellitus and an extensive and infected lesion in his right ankle region, suggestive of a diabetic foot. Urgent surgical treatment was performed with debridement of the devitalized tissues, drainage of a large amount of purulent secretion, and exhaustive washing with 0.9% saline solution. After a new debridement, abundant washing with 0.9% saline solution and coverage of the extensive bloody area with a polypropylene prosthesis were performed. He remained under outpatient follow-up, and subsequently, twice, new cleanings were performed, and a small diameter mesh was applied due to the good evolution of healing. A good range of motion was maintained in the right ankle and foot, with the medial wound completely healed, leaving only a small area of the lateral wound to complete the healing process. Figueiredo’s technique, described in 2017 for fingertip lesions, uses a flexible thermoplastic polymer, which can be obtained from a small portion of silicone from a saline bag, to form a semi-occlusive dressing that allows the drainage of secretions and provides a favorable environment and temperature for healing. The exact limits of this technique are not yet well established, but the practice has shown excellent results in larger lesions. Figueiredo’s technique is a simple, low-cost, and effective option for treating extensive infected skin lesions. Level of Evidence IV; Therapeutic studies; Case Report.

Effect of aging level on the healing properties of an induction-heated ultra-thin wearing course and its mechanism

Electromagnetic induction heating can accelerate crack self-healing in asphalt concrete and extend its service life. In the maintenance project of existing pavements, induction heating and ultra-thin wearing course can be combined by paving functional induction heating wearing course. However, the ultra-thin wearing course is directly affected by the environment and loading, and undergoes aging in the service process. Thermo-oxidative aging is an irreversible and important mechanism that seriously affect the rheological and healing properties of asphalt. Therefore, the purpose of this work is to examine the impact of thermo-oxidative aging on the induction heating-healing of an ultra-thin wearing course mixture. Firstly, the AC-5 induction heated ultra-thin wearing course (IHUC) containing 1 % steel wool fiber by aggregate mass was prepared. Subsequently, the IHUC was aged to six different levels. Then, the induction heating and healing properties of the aged IHUC were evaluated. Simultaneously, the aged asphalt binder was extracted and its rheological characteristics and chemical alterations were studied. The outcomes showed that the heating rate of IHUC decreased, but the temperature gradient effect reduced at higher aging level. The optimal healing temperature of IHUC shifted to a higher temperature region and the healing rate decreased. Both heating cycles and thermo-oxidative aging reduce healing effectiveness, but the impact of heating cycles is less compared to aging. Rheology and chemical structure test results of extracted asphalt binder showed that the transformation of the molecular structure caused the fluidity and self-healing properties of asphalt were decreased. This ultimately decreased the healing rate of IHUC.

Self-healing analysis of steel slag asphalt mixture under microwave heating through laboratory fatigue-healing test and microscopic characterization method

Steel slag is an eco-friendly low-carbon building material that has been widely used for pavement construction in recent years. In this study, the steel slag aggregate (SSA) is used to replace a part of the basalt aggregate in the porous asphalt mixture to improve its microwave absorption ability. Microwave heating promotes the self-healing capability of steel-slag asphalt mixture. We designed and conducted 16 groups of fatigue-healing tests based on an orthogonal experimental design to analyze the influence of various factors, including the degree of damage, healing temperature, and rest time, on the self-healing ability of the steel slag asphalt mixture. The ratio of the number of cyclic loads after healing (N1) to the number of cyclic loads before healing (N0) is defined as the healing index. The results of the range analysis demonstrate that the healing temperature presents the greatest impact on the healing rate of fatigue damage, followed by the degree of fatigue damage; the rest time has the least impact. The fatigue damage healing rate gradually decreases with the increase in the degree of damage. It first increases and then decreases with the increase in the healing temperature. It increases with the rest time. The optimal healing state of the steel slag porous asphalt mixture involves heating to 80℃ with 60 % degree of damage followed by resting for 8 hours. CT scanning technology is used to observe the crack distribution before and after healing. The CT images and a 3D reconstruction of the asphalt mixture demonstrate that obvious healing of cracks can be observed after microwave heating, and microwave heating does not significantly affect the porosity of the asphalt mixture. The nano-indentation indicates that the Young’s modulus and hardness of the asphalt mortar in the cracking area increased by 16.8 % and 22 %, respectively, after healing due to microwave heating, which can be attributed to the ageing of the asphalt.

Research on Fatigue Self-healing of Asphalts Modified by Thermoplastic Polyurethane (TPU) with Different Soft Segments

Research on asphalt fatigue and self-healing performance can more accurately model the damage and self-healing evolution principles in practical applications. In order to analyze the rationality of evaluation indexes based on rheology to evaluate the self-healing properties of TPU modified asphalt, a dynamic shear rheometer (DSR) was used in this study to perform time, temperature, and frequency sweep tests of TPU modified asphalt for analyzing the fatigue self-healing properties of TPU modified asphalt over a broader range of temperatures and loading frequencies. This method can improve the accuracy of the fatigue failure determination criteria of TPU modified asphalt and clarify the material performance parameters of TPU asphalt modifiers. The results showed that the increase in hard segment content (Ch) and isocyanate radical index (r) can effectively alleviate the decrease in shear deformation resistance of modified asphalt caused by the increase in N (load repetition). Nf50 (the number of loads when the normalized modulus drops to 0.5) is more suitable to evaluate the fatigue life of TPU modified asphalt compared with Np20 (the number of loads when the DER-N curve is offset by 20% deviation from the linear undamaged line) and N2 (the number of load times corresponding to the intersection point of the tangent line of the DER–N fitted curve and the undamaged line). The degree of self-healing will also increase with the increase in Ch and r. Besides, the higher the healing temperature and the healing time, the longer the fatigue life. The effects of the self-healing evaluation index (HI) on the self-healing index of TPU modified asphalt were as follows: healing temperature > healing time > soft segment >Ch >r > degree of damage > degree of aging > degree of self-healing.

Experimental investigation on the self-healing properties of ester-exchanged vitrimeric CFRP laminate with microchannels

Epoxy vitrimer theoretically achieves an unlimited healing cycle drawing support from dynamic molecular chains. The healing conditions required for microvascular systems are variable and flexible. Current research has often focused on a single healing system, further exploration is needed for a dual healing system that combines the advantages of both. In this study, the effects of curing agent and catalyst content on the performances of vitrimer, as well as the healing parameters on the healing efficiency were studied. And then the vitrimeric CFRP (vCFRP) laminates with microchannels were prepared, and the three-point bending tests were implemented to characterize the healing efficiency of CFRP with a single and dual healing system. The results indicated that the cured vitrimer exhibited the best comprehensive performance when the molar ratio of reactants was 1:1:0.07. The healing temperature had the greatest impact on the healing efficiency of vitrimer, followed by the catalyst content and the healing pressure. The two healing systems could improve the mechanical properties of laminates, especially the healing efficiency of CFRP with dual healing system reached 134.5 %. The healing agent in the microchannels could heal micro-damage, and the healability of the vitrimer could still be utilized after the healing agent was exhausted.

Road Performance and Self-Healing Property of Bituminous Mixture Containing Urea-Formaldehyde Microcapsules.

Urea-formaldehyde (UF) is a common shell material for self-healing microcapsules; however, the influence of urea-formaldehyde microcapsules (UFMs) on the road performance of bituminous mixtures and the sensitivity of their healing abilities remains unclear. In this paper, UFMs were prepared via in situ polymerization (ISP), followed by an investigation into the road performance of UFM self-healing bituminous mixtures through various tests, including wheel tracking, immersed Marshall, freeze-thaw splitting, low-temperature bending, and three-point bending fatigue tests. Subsequently, the impact of the damage degree, healing duration, and temperature on the self-healing property was discussed. The results indicated that incorporating 3 wt% UFMs into bitumen significantly improved the high-temperature stability and fatigue resistance of the bituminous mixture; for example, its dynamic stability and fatigue life could be increased by about 16.5% and 10%, respectively. However, it diminished the thermal crack resistance, as evidenced by decreases in bending tensile strength and strain by 3.7% and 10.1%, respectively. And it did not markedly improve the moisture susceptibility. Additionally, the maximum improvement observed in the healing rate was about 9%. Furthermore, the healing duration and temperature positively influenced the bituminous mixture's self-healing, whereas the degree of damage exerted a negative impact, with a relatively significant effect.

The crack-healing performance of asphalt mixture based on acoustic emission system

The self-healing properties of asphalt pavements reduce the need for frequent maintenance and repair of cracks and promote road sustainability. In this study, multiple healing tests were conducted under different healing conditions using the semicircular bending "crack-heal-crack" test. The beneficial effects of the healing temperatures and times were determined. However, below 60 °C, the healing index of asphalt mixture does not exceed 0.4. The peak healing indices of the 70# asphalt mixture in the fourth healing stage were 86% of the initial healing index. This correspond to the SBS# asphalt mixture parameters of 88%. Using the acoustic emission system, changes in the ring count and energy of the specimens before and after the healing were compared. The healing index of the cumulative ring count proposed in this study sufficiently correlates with that of the peak load. According to the three-dimensional time-difference positioning method, at the initial loading stage of the prehealing specimen, cracks first appeared at the top of the specimen in contact with the load, then concentrated near the prefabricated incision at the bottom, and finally expanded upward. When the specimen was loaded once again after healing, cracks mainly developed from the bottom upward.

Investigation of Self-Healing Performance of Asphalt Mastic-From the Perspective of Secondary Aging.

Reclaimed asphalt pavement (RAP) has been widely utilized because it is an environmentally friendly and economical material. The performance of recycled asphalt mixtures will deteriorate gradually with the secondary aging process of asphalt, including the self-healing property. To further understand the self-healing characteristics of asphalt after secondary aging, taking 70# petroleum asphalt, SBS-modified asphalt, and extracted old asphalt mastics as objects, the fatigue self-healing test and fracture self-healing test were conducted to simulate the intermediate-and low-temperature healing behaviors of different asphalt mastics. The impact of healing time, healing temperature, and aging degree of mastics on the healing performance was systematically investigated. The results show that the original unaged asphalt mastics present excellent fatigue healing properties with an index of 0.796 and 0.888 for 70# petroleum and SBS-modified asphalt mastics, respectively. The secondary aging process causes significant impact on the healing properties, leading to a great drop in the corresponding index, which decreased to 47.5% and 72.5% of that of the unaged ones. The fracture healing ability of all mastics was much inferior to the fatigue healing. After secondary aging, the fracture healing index values of 70# petroleum asphalt, SBS-modified asphalt, and extracted old asphalt mastics were all as low as around 0.3, indicating similar performance can be found in the secondary aged SBS-modified asphalt mastics and 70# asphalt mastics. Overall, after secondary aging, the fatigue damage of SBS-modified asphalt mastics can be cured effectively by self-healing, but the fatigue and fracture self-healing properties of 70# asphalt mastics are difficult to recover. These results could provide an innovative view to understand the fatigue and fracture healing characteristics of recycled asphalt pavement after secondary aging.

Study on induction healing properties of OGFC asphalt mixture with high elasticity and high viscosity modifier

Induction healing is a promising preventive maintenance method of asphalt pavement, but the healing properties of Open-Graded Friction Course (OGFC) asphalt mixture with high elasticity and high viscosity modifier (HEV) were not clear. OGFC asphalt mixture used for induction heating was prepared by adding steel wool fibers and HEV. The effects of HEV and steel wool on the properties of OGFC mixture were studied. The particle loss resistance, water stability, porosity, induction heating and self-healing properties of OGFC-13 asphalt mixture with different steel wool contents were measured. The results showed that HEV slightly improved the properties of resistance to particle loss, fracture strength and water stability of OGFC-13 asphalt mixture, had little effect on the induction heating rate and porosity, but reduced the healing rate by 10%. The addition of steel wool to OGFC-13 can enhance the particle loss resistance, heating rate and healing effect, and the optimal dosage is 8% of the volume fraction of bituminous binder. The healing rate rose steadily as the heating temperature increased. At the optimal healing temperature of 110 ℃, healing depth ratios of the mixtures without and with HEV were 56.3% and 43%, respectively, and the fracture energy healing rates were 72.4% and 63.1%, both at a high healing level. The incorporation of steel fibers and HEV reduced the porosity and water permeability of OGFC very slightly, and the porosity and water permeability of OGFC did not change significantly after induction heating. It is concluded that induction heating has a potential to heal the cracks within OGFC mixture with HEV to prevent surface raveling which is the primary damage of OGFC.

Evaluation of the microcapsules on the rheological and self-healing performance of asphalt

The objective of this study was to prepare microcapsules and investigate their impact on the self-healing properties of asphalt. Microcapsules with various core–shell ratios were prepared by enveloping soybean oil with Melamine-Urea-Formaldehyde (MUF) resin through an in-situ polymerization method. The laser particle size analyzer, thermogravimetric analyzer, and scanning electron microscope were utilized to character the microcapsules and determined the optimal core–shell ratio. The rheological and self-healing performance of the microcapsule-modified asphalt were examined through frequency sweep, multi stress creep and recovery (MSCR), and Fatigue-Healing-Fatigue (F-H-F) tests conducted using a dynamic shear rheometer (DSR). The results indicate that microcapsules with various core–shell ratios exhibit uniform particle distribution and excellent thermal stability. Specifically, microcapsules with a core–shell ratio of 1:2 display a smooth appearance. The incorporation of microcapsules into asphalt impedes the flow of asphalt molecules and increases the initial flow temperature. When the microcapsules rupture, the released soybean oil modifies the rheological behavior of the asphalt, leading to a decrease in stress sensitivity and rutting resistance. Simultaneously, the remaining MUF resin imparts additional elastic recovery properties to the asphalt. The self-healing performance of microcapsule-modified asphalt was significantly enhanced, with a notable improvement observed as the microcapsule dosage increased. Moreover, elevating the healing temperature and extending the healing time were found to be effective strategies for enhancing the self-healing properties of microcapsule-modified asphalt. When the healing temperature matches the initial flow temperature, the healing index HI of 5% microcapsules modified asphalt approached nearly 100% within 5 min of healing time.

Film formation kinetics of polystyrene latex‐based nanocomposites with a broad particle size distribution

AbstractThe present study article aims to clarify the effect of colloidal polystyrene (PS) latexes with a broad particle size distribution on film formation kinetics of multi‐walled carbon nanotube (MWCNT)‐added polymer nanocomposites by considering theoretical film formation models. Experimentally, light transmitted from nanocomposite films, each having different weight fractions of MWCNT, was recorded at different annealing temperatures via UV–Visible spectrophotometry. Optical data set was then theoretically elaborated by taking into account void closure and Prager‐Tirrell models. Activation energies of viscous flow (ΔH) and backbone motion for reptating PS chains (ΔEB), minimum film formation (T0) and healing (Th) temperatures were then computed from optical data. Experimental results revealed that ΔH required for void closure phenomenon remained unaffected by both nanofiller and size distribution of latexes. On the other hand, it was found that ΔEB for backbone motion promoted upon the addition of nano‐fillers into latex particles. Our experimental findings suggested that film formation from MWCNT‐added latex films with a broad particle size distribution mainly originates from void closure mechanism since ΔH for viscous flow suppresses ΔEB acquired for backbone motion of repeating PS chains to a great extent.Highlights A broad size distribution effect of PS on film formation was investigated. Voids closure and Prager‐Tirrell models were applied to spectroscopic data. Activation energy of viscous flow is unaffected by size distribution of PS. Latex film formation with varying size distribution stems from void closure.

Research on Fatigue-Healing Performance of Asphalt Mixture Based on the Semicircular Bending Test.

In order to study the self-healing performance of macroscopic fractures of asphalt mixtures, semicircular bending (SCB) tests were used to test 90# base asphalt mixtures, SBS (Styrene-Butadiene-Styrene) modified asphalt mixtures, and SBS + CR (Chloroprene Rubber) composite modified asphalt mixtures. The F-H-F (the asphalt mixture specimen was fatigued for a certain number of times, then healed under certain conditions, and then fatigued until destroyed) test was carried out, and the fatigue life recovery rate of the fatigue test before and after healing was defined as the healing index (HI). The gray correlation analysis method was used to judge the influence degree of influencing factors on fatigue-healing according to the correlation index. The results show the type of asphalt has the most significant influence on the healing ability of the asphalt mixture. In the case of complete healing, the fatigue-healing performance of the SBS + CR composite modified asphalt mixture was the best, followed by the SBS-modified asphalt mixture, and 90# base asphalt. When the healing temperature is close to the softening point of asphalt, the healing performance of 90# base asphalt is better when the healing temperature is low. When the healing time is longer, the healing performance is better, and there is an optimal healing time. The healing index decreased with the increase in the degree of damage. When the degree of damage is too large, the asphalt mixture will be difficult to heal.