Environmental Cracking Research Articles

A Study on the Propagation of Chloride-Induced Stress Corrosion Cracking for Austenitic Stainless Steel at Corrosion Environment

Austenitic stainless steels have been widely used in the petrochemical industry, nuclear power plants and the ship industry due to their high toughness and corrosion resistance. However, these materials are susceptible to environmentally-assisted degradation, such as chloride-induced stress corrosion cracking (CISCC). In this respect, this study investigated CISCC crack propagation rate for austenitic stainless steels, such as type 304L and type 316L, in the corrosion environment. Considering the environment of the spent nuclear fuel canister used in the dry storage system, the test chamber is always maintained at 3.5% NaCl and related humidity (RH) 95% at 60℃. For initiation of CISCC, a test procedure, which has nine pre-cracking procedures for a CT specimen, is suggested. In a test procedure, crack transitioning, which induces the environmental corrosion crack, is observed after mechanical precracking. To determine the CISCC crack length corresponding to each test step, the direct current potential drop (DCPD) method is measured in real-time. In addition, the CISCC crack observed after final fracture is measured using optical microscopy in order to improve the accuracy of the measured crack length. In the test results, CISCC crack resistance of type 316L is better than that of type 304L. Finally, the test results show that the CISCC crack propagation rate is 2.784E-11 m/s for type 304L and is 9.93E-11 m/s for type 316L.

Numerical prediction for life of damaged concrete under the action of fatigue loads

High-speed railways have become a critical component of modern transportation, and ensuring the stability and durability of high-speed railway concrete under environmental and train fatigue loads is essential for ensuring project safety. This paper employs a numerical simulation method to predict the performance and lifespan of high-speed railroad concrete under fatigue loading with environmental damage. The study analyzes the effects of stress level (0.5–0.8), stress ratio (0.1–0.9), and load frequency (5 Hz–40 Hz) on the fatigue performance and lifespan of railway concrete during bending fatigue loading. A four-point bending numerical model of concrete is developed in this paper, which considers elastic modulus decay and surface cracking, in order to quantify the degradation of concrete properties in response to environmental and load-induced cracks. The numerical model is well-validated with experimental results, and the study establishes a correlation between concrete degradation and environmental and load-induced cracks, as well as the fatigue resistance of high-speed railroad concrete. The bending fatigue frequency of concrete should not exceed 25 Hz at high stress levels of 0.7. This study also shows that environment-induced initial damage will greatly reduce the fatigue resistance of concrete, and fatigue life degradation and elastic modulus decay have a nearly linear relationship. This research provides a crucial foundation for the fatigue design of concrete materials for high-speed railroads.

Event identification in acoustic emission from wire breaks in pre-stressing/post-tensioning cables

Steel tendons commonly used in pre-stressed/post-tensioned concrete structural systems can lose cross-section due to corrosion, eventually leading to acoustic emission (AE) events when the stress exceeds the breaking strength of the wires that make up the tendons. Reliable differentiation of wire break AE events from traffic or grout crack events is critical for monitoring large structures, even where the distance between sensors may produce highly attenuated signals. In this paper, the Fuzzy c-means clustering algorithm was employed to differentiate AEs released from breaking wires of steel tendons from a database of 13464 AEs, including wire breaks, environmental and grout crack AEs. Wire breaks and grout crack AEs were collected from axial loading tests of grouted tendons in which the load increased until a wire broke. Environmental acoustic signals were collected from a bridge. Then all the collected AEs were gathered in a database and post-processed to simulate attenuation of up to 20 m from source to sensor. To optimize the speed and reliability of the Fuzzy c-means clustering algorithm, a non-dominated sorting genetic algorithm-II (NSGA-II) was used to find the minimum number of acoustic features needed. The NSGA-II algorithm started with 201 possible acoustic features and found 12 combinations of features that resulted in more than 80% wire break detection accuracy. In contrast, less than 3% of grout cracks and 0% of environmental signals were detected as wire breaks. The proposed method is suitable for deployment in a large sensor network and has sufficiently low-computational requirements for at-the-sensor processing, eliminating the need to send high-frequency sampled data outside the sensor node.

Environmental fatigue crack growth of PV glass/EVA laminates in the melting range

AbstractThe delamination of encapsulants in photovoltaic (PV) modules is a common issue that leads to power loss due to optical losses. Encapsulant debonding is usually examined under monotonic loading conditions subsequent to environmental exposure such as damp heat. Service‐relevant, superimposed environmental‐mechanical fatigue loads are not considered adequately. Hence, the environmental fatigue delamination resistance of thermally toughened double glass laminates with an ethylene vinyl acetate copolymer (EVA) adhesive layer was investigated in this study. Focus was given to the melting range of EVA, in which the non‐crosslinked crystalline phase fraction is already in the partly molten state. Double cantilever beam specimens were tested on an electrodynamic test machine at temperatures of 60, 70, 80, and 90°C and relative humidity (rh) levels of 2%, 30%, 50%, and 80%. The fractured surfaces were characterized by digital microscopy, Fourier transform infrared spectroscopy (FTIR), X‐ray photoelectron spectroscopy (XPS), and differential scanning calorimetry (DSC). The cyclic fatigue tests revealed a decay in delamination resistance at elevated temperature and humidity levels. At 70°C, the delamination resistance was low, regardless of the relative humidity. Most of the laminates failed by debonding. XPS analysis showed a reduction of the C=O and C–O content, along with an increase in Si–O content with increasing relative humidity. For laminates tested at 60 and 70°C, an EVA recrystallization peak was observed in DSC experiments. This peak was shifted to significantly higher temperatures at 80% rh. XPS and DSC indicated local hydrolysis within the porous fracture process zone ahead of the crack tip. Consequently, acetic acid formation led to a decrease in delamination resistance, resulting in lower fatigue threshold values. The investigations confirmed the significant impact of environmental conditions on the fatigue delamination resistance within glass/encapsulant laminates. Notably, acetic acid formation and a significant reduction in delamination properties were observed after around 100 h of environmental fatigue exposure.

Influences of processing conditions on gradient structures in injection‐molded polyethylene caps and their property correlations

AbstractIn this study, the influences of processing conditions, that is, injection speed and holding pressure, on the gradient crystal structural formation in the injection‐molded cap specimens were investigated. Skin‐, shear‐ and core‐layers across the specimen thickness were investigated in detail by using small‐angle x‐ray scattering, wide‐angle x‐ray diffraction, and atomic force microscopy techniques. The results showed that high holding pressure caused high density and large weight of the cap specimens. This strongly contributed to high displacement resistant on applied pressure (doming resistant), while the lamellar thickness (Lc) of the skin layer also played a role. On the contrary, low holding pressure promoted the formation of the random‐oriented lamellae in the core layer, which contributed to high environmental cracking resistance (ESCR). Moreover, the lower injection speed caused the thicker Lc of the skin layer, and this improved the ESCR of the specimen. The results allowed us to propose its failure mechanism.

Cross-sectional microstructural analysis to evaluate the crack growth pattern of weathered marine plastics

Fragmentation of degraded plastics and release of smaller secondary microplastics is usually attributed to the growth of environmental stress cracks. Analysis of crack patterns derived from chemical degradation can be useful not only for assessing the cause of plastic fracture and evaluating the useful lifetime of a product, but it can also potentially provide valuable information on the generation of microplastics. However, the literature with respect to microplastics generation is generally limited to surface observations of polypropylene and polyethylene. Here, we used ion-beam milling to prepare cross-sections of fragments of 15 plastic products made from five commodity plastics (polypropylene, polyethylene, polystyrene, polyvinyl chloride, and polyethylene terephthalate) that were collected at two beaches in Japan, and then we examined the microstructures of those cross-sections by means of scanning electron microscopy and energy dispersive X-ray spectroscopy. Crack growth in the depth direction was examined to provide insights into microplastic generation behavior. In all of the polypropylene samples, and some of the low-density polyethylene and polystyrene samples, cracks with a depth exceeding 100 μm from the sample surface were observed. Considering that crack growth causes fracture of degraded plastic and microplastic release, these observations suggest the release of sharp-edged microplastics from the crack fracture surface. In contrast, in the high-density polyethylene and polyvinyl chloride samples, crack growth was limited to within 20 μm of the sample surface, suggesting the release of irregularly shaped microplastics and additive particles. The present results suggest that the degradation behavior of plastic products in the depth direction is dependent on the type of plastic.

Nanomaterials based self-healing concrete

Concrete after water is the second most-consumed material on this earth. Concrete consists of cement, sand, aggregate and water. It is cheaper, can resist high compressive stress and moulded in a variety of shapes. In general cement materials, in aggressive environments, have very low resistance and durability and service life deteriorate. Due to aggressive environment expansion and cracking of concrete may be enhanced. As a result, microcracks are generated, which shortens the life of buildings. Now, a new concrete known as self-healing concrete, is coming up, which contains fibres or capsules, containing some adhesive liquids. When cracks occur, the fibres or capsules break and the liquid present, heal the crack. During the last years researches have been done on the use of nanomaterials (NMs) in enhancing the healing capability of concretes. Due to advances in the field of nanoscience, self-healing materials have taken new shape. Number of NMs such as nano-silica (n-SiO2), carbon nano-tubes (CNTs), nano-clays, nano calcium carbonate (n-CaCO3), and many other nano-sized materials are being used as healing agents in concretes. However, only a limited studies on the use of NMs in enhancing the self-healing properties of concretes have been made. So, the mechanism of action of NMs as self- healing agent is not been fully understood. This article summarises the latest contributions in the area of NMs based self-healing concrete with mechanistic point of view.

Experimental evaluation of the effect of recycled cross-linked polyethylene on the performance of grouted macadam mixtures

ABSTRACT Grouted Macadam (GM) mixtures – recognized as semi-flexible pavement (SFP) materials – offer strong stability in high temperatures, good durability and high load-bearing capacity. However, these materials are prone to environmental and traffic-induced cracking. Cross-linked polyethylene (XLPE), a common high-voltage cable insulation, faces disposal challenges due to limited recycling technology, often leading to burning or burial of these waste materials. In this study, to enhance GM mixture crack resistance and mitigate the environmental impact of XLPE waste accumulation, XLPE material was used in GM mixtures in two methods. In the first group, 15%, 30%, and 45% of 4.75 to 9.5 mm natural aggregates were replaced in volume, with XLPE pseudo-aggregates of the same size. In the second group, XLPE pseudo-fibers (1.9–2.2 cm in length, 1.5 mm thickness) were incorporated as additives in 0.5, 0.7, and 1 volume percentages. The results of mechanical tests on treated GM mixtures showed that adding recycled XLPE improved durability, with a 24.5% and 29.9% enhancement in samples with the most pseudo-aggregates and pseudo-fibers contents. The fracture strain tolerance (FST) index in low-temperature bending tests also increased by 53.8% and 108.9% in mixtures containing XLPE, highlighting its potential to enhance GM mixture performance in various service conditions.

Conversion of model C6–C9 alkanes and straight-run gasoline over Pt(0.1%)-Fe(5%)/Al2O3 catalysts promoted with various additives

Growing demand for hydrogen promotes the research devoted to the development of new catalysts for hydrocarbons processing in absence of H2 or at its low concentration. In the present work, it was shown that during the conversion of straight-run gasoline on a zeolite-containing polyfunctional catalyst in a hydrogen-free environment cracking, dehydrogenation, isomerization and alkylation take place due to the redistribution of H2 between initial and formed products directly on the catalyst surface. Fine particles (≤50 Å) localize in zeolite cavities and pores of aluminum oxide, while larger ones are on their outer surface.

Modular Paradigm for Composites: Modeling Hydrothermal Degradation of Glass Fibers

Fiber-reinforced composite materials are often used in structural applications in humid, marine, and offshore environments. Superior mechanical properties are compromised by environmental ageing and hydrolytic degradation. Glass fibers are the most broadly used type of fiber reinforcement to date. However, they are also most severely affected by environmental degradation. The glass fiber degradation rates depend on: (1) glass formulation; (2) environmental factors: pH, T, stress; (3) sizing; (4) matrix polymer; (5) fiber orientation and composite layup. In this short review (communication), seven modules within the Modular Paradigm are reviewed and systematized. These modeling tools, encompassing both trivial and advanced formulas, enable the prediction of the environmental ageing of glass fibers, including the kinetics of mass loss, fiber radius reduction, environmental crack growth and loss of strength. The modeling toolbox is of use for both industry and academia, and the Modular Paradigm could become a valuable tool for such scenarios as lifetime prediction and the accelerated testing of fiber-reinforced composite materials.

Effect of stress ratios on corrosion fatigue life of high‐strength steel wires

AbstractIn order to discuss the influence of the stress ratio on the corrosion fatigue life of high‐strength steel wires, a theoretical and experimental investigation was conducted on corroded steel wires at three different stress ratios (R = 0.1, 0.3, and 0.5) under axial tensile fatigue loading. Different S‐N curves of corroded steel wires were regressed from test data. The stress method based on eight mean stress correction models, the strain energy method, and the facture mechanics method considering environmental corrosion and crack closure were proposed to estimate the fatigue life. Preliminary results show that corrosion can reduce the ultimate strength, the yield strength, and the fatigue life. There is a negative correlation between corrosion fatigue life and stress ratio. When R > 0, fatigue life predicted results by using the Morrow and Marin models in the stress method are more efficient and accurate than other models. Likewise, the Zheng model in the fracture mechanics method is in better agreement with test results. The error and scatter of the strain energy method are relatively large. Therefore, the Morrow, Marin, and Zheng models are more suitable to predict the corrosion fatigue life of high‐strength steel wires under different stress ratios.

P137 DEGRADATION RESISTANCE OF PVDF MESH IN VIVO IN COMPARISON TO PP MESH

Abstract Aim To researched the degradation resistance of PVDF mesh by comparing its morphological and chemical condition with PP mesh. Material and Methods PVDF and PP meshes analysed in this study were received from a previous animal experiment. To expose the surface of explanted meshes, a tissue removing method with protease was used and the result of this cleaning process was tested by X-ray Photoelectron Spectroscopy (XPS). The morphological condition of the mesh surface was compared using Scanning Electron Microscopy (SEM) and the chemical condition concerning degradation was analysed through Fourier Transform Infrared Spectroscopy (FTIR). The surface condition of PVDF mesh after 3-, 6-, 12- and 24-month implantation was illustrated and compared with two types of PP meshes. Results XPS revealed an absence of nitrogen, confirming the successful removal of tissue residues using protease. SEM results presented no notable morphological surface change of the PVDF mesh and progressive surface cracking processes over time of both types of PP meshes. FTIR spectra of the implanted PVDF meshes had no considerable difference from the spectrum of the pristine mesh, while FTIR spectra of both types of PP meshes had extra chemical functional groups increasing with implantation time, indicating progressive degradation. Conclusions PVDF mesh does not show signs of degradation up to 24 months after implantation while PP meshes progressively degrade with increasing time under the same conditions, which appears as worsening Environmental Stress Cracks. This study highlights the morphological and chemical stability of the PVDF mesh and demonstrates that the PVDF mesh is more resistant to degradation in comparison to the PP meshes.

Review of Residual Stress Impingement Methods to Mitigate Environmental Fracture Susceptibility

Environmental cracking- and fatigue-related failures threaten all major industries and, to combat such degradation, numerous residual stress impingement (RSI) methods have been developed with varying levels of efficacy and ease of use. Some of the most commonly used RSI methods, such as shot peening, laser shock peening, and low plasticity burnishing, as well as new methods, such as ultrasonic nanocrystal surface modification, are reviewed in the context of corrosion, corrosion fatigue, and environmental cracking mitigation. The successes and limitations of these treatments are discussed, with a focus on their efficacy against these three damage modes based on the available literature. Case studies are reviewed that demonstrate how these treatments have been adopted and advanced by industry, and application-specific research efforts are explored with a focus on future opportunities. Research is identified that illustrates how the utility of these surface treatments may vary between alloy systems, and where the benefits must be weighed against the risks to a component’s service performance.

Recession of BN coatings in SiC/SiC composites through reaction with water vapor

AbstractThe mechanical response of ceramic matrix composites depends critically on the slip along the matrix–fiber interface, which is usually achieved with thin coatings on the fibers. Environmental attack of such coatings (enabled by ingress of reactants through matrix cracks) often leads to significant degradation, through the removal of the coating via volatilization and oxidation of exposed SiC surfaces. The extent of the volatilization region extending from the matrix crack plane (i.e., recession length) is strongly coupled to the formation of oxide, which ultimately fills open gaps and arrests further reactions. This paper presents models to quantify these effects over a broad range of environmental conditions, coating thickness, and matrix crack opening. Analytical solutions are presented for the time to close recession gaps via oxidation, and the associated terminal recession lengths obtained near free surfaces. A broad parameter study illustrates that recession behaviors are controlled by a competition between volatilization and oxidation rates. As such, the extent of recession is highly sensitive to water vapor and temperature, providing an explanation for disparate observations of recession under seemingly similar conditions. The extent of recession in the interior of composites is also illustrated, using a straightforward reaction‐transport model. Recession lengths decay rapidly away from the free surface, with the extent of recession penetration scaling with maximum recession at the free surface.

Influence of shrinkage cracks on the mechanical properties of bolted-type glulam joint with slotted-in steel plate: Experimental study

Environmental shrinkage cracks are obviously observed in bolted-type glulam joints due to the material mechanical-physical properties and high moisture transport rate. The objective of ongoing research mainly presents an experimental study on the mechanical properties of bolted-type glulam joints with cracks. To shorten the test time and control the crack pattern, the outer moisture-induced shrinkage cracks are replaced by preset cracks. Thus, thirteen glulam joints with different preset cracks are designed and tested. The parameters are three locations (i.e., along the top bolts, neutral axis, and bottom bolts), two lengths (i.e., 140 mm, and 330 mm), three depths (i.e., 30 mm, 60 mm, and 118 mm), and two kinds of layouts (i.e., cracks on the same side and different sides). In the experiments, the loading process and failure modes of the joints were observed, the load-displacement relationships were analyzed and the residual bearing capacity of the joints was recorded. The joint exposed to the controlled climate change test showed that longitudinal cracks were easily observed along with the bolts in multiple steel-to-wood joints and four reasons were presented for this phenomenon. Furthermore, significant reduction values were observed due to cracks for joints in terms of their initial stiffness k, peak load Pmax, and displacementΔmax up to 79.3%, 75.39%, and 95.1%, respectively. Additionally, reduction coefficients were proposed for the calculation of residual bearing capacity. The calculation results showed good consistency with the experimental tests.

Use of geosynthetics to mitigate problems associated with expansive clay subgrades

Geosynthetics have recently been used for base course stabilization of roadways subjected to environmental loads associated with the presence of expansive clay subgrades. Repeated cycles of wet and dry seasons have often led to significant, non-uniform moisture changes within clay subgrades, resulting in differential settlements between the roadway edges and its centerline and, ultimately, in environmental longitudinal cracks. This paper quantifies the field performance of different sites in order to assess the effectiveness of using geosynthetics to stabilize the base course of roadways constructed on expansive clay subgrades. This includes evaluation of five full-scale field projects that had been subjected to actual traffic and environmental loads. The long-term performance of geosynthetic-stabilized and control sections was evaluated by quantifying the development and extent of longitudinal cracks and the degradation of the base course stiffness. Collectively, the performance evaluation of the multiple geosynthetic-stabilized and control sections in the five case studies demonstrates that geosynthetics can effectively mitigate roadway problems associated with expansive clay subgrades. In addition, field performance data also indicates that unconfined stiffness and tensile strength may not be sufficient for proper geosynthetic selection, pointing to the need for selecting them using properties that also quantify the soil-geosynthetic interaction.

Sustainable Transfer of Tomato Landraces to Modern Cropping Systems: The Effects of Environmental Conditions and Management Practices on Long-Shelf-Life Tomatoes

The individual effects of biotic and abiotic factors on tomatoes have been widely reported. However, under commercial conditions, multiple interactions between factors occur, masking or even changing the direction of their effects in some cases. Here we report a comprehensive analysis of preharvest factors affecting yield, quality (soluble solids content, fruit color, and firmness), and shelf-life of long-shelf-life Mediterranean varieties of tomatoes. We studied five long-shelf-life genotypes under 16 growing environments, including tunnel and open-air systems and suboptimal to excessive fertigation (22–142% crop evapotranspiration). The results enabled us to classify traits into three groups according to the importance of the contributions of different types of factors: mainly genotype (ripening earliness and firmness), genotype plus environment (yield, fruit weight, water-use efficiency (WUE)), or genotype plus environment plus the interaction between genotype and environment (cracking, soluble solids content, and shelf-life). Under similar management practices, open-air conditions optimized yields, and high fertigation doses improved yield and marketability (firmness), but reduced quality (redness and soluble solids content). WUE was maximized under low-input cropping systems (comparable to traditional agrosystems), and the balance between WUE and yield was optimized when fertigation was adjusted to the requirements of the crop. Shelf-life was negatively correlated with high-yielding environments, and day–night amplitude in relative humidity was strongly correlated with the incidence of fruit cracking. The present study sheds light on the contributions of environment and management practices on tomato yield and quality, and provides a basis on which to select better management practices for the novel commercial group of European long-shelf-life tomato landraces.

Formation of Microgrooving on C110 Casing Steel After Sulfide Stress Cracking Test

NACE TM0177 is a commonly used materials qualification standard specifying how sulfide stress cracking (SSC) tests must be conducted and interpreted to verify the suitability of material application in sour service. This standard specifies through the so-called method A test (a tensile uniaxial environmental cracking test) that a material could be considered acceptable for sour service as long as no failure is evidenced after 720 h of exposure, and no initiation of environmental cracking is observed on the reduced length of the specimen after macrographic observations. After cross-sectional observations, so-called “microgrooves” can sometimes be evidenced on the surfaces of nonfailed specimens. Such features can hardly be interpreted as SSC crack initiation sites considering their shape and depth. Experience, however, shows that the formation of these microgrooves appears to be dependent on test conditions and type of load. This paper presents the results of investigations on the parameters influencing the microgroove formation on C110 steel after the method A uniaxial tensile SSC test. Test parameters influencing the groove formation are studied, and the results suggest that grooving is not SSC initiation for the testing conditions used in this work.

Environmental control of crack propagation in polymer hydrogels

Hydrogels are highly hydrated polymer networks. The synergistic association of a fluid and an elastic phase is the key of numerous applications of hydrogels as food or cosmetic products, drug delivery vectors, wound dressings, scaffolds for tissue regeneration... Since the natural environment for many of these applications is a wet or liquid one, exchange of fluid or solute may occur via the liquid continuum which exists between the environment and the constitutive solvent. In addition to purely osmotic forces, stresses acting on the network are able to drive solvent flow. This is the basis of poroelasticity, initially studied within the framework of consolidated, fluid saturated rocks. The specificity of hydrogels lies on their high stretchability, which makes extended non-linear elasticity the rule rather than the exception when dealing with fracture mechanics. The association of poro- and non-linear elasticity brings the study of rupture of hydrogels at the forefront of research in mechanics. Along this review, we intend to explore the various ways the environment may affect the nucleation, growth and path stability of a crack in a hydrogel. This goal is pursued from a physicist and experimentalist point of view, with special emphasis on dimensionless relevant parameters and order-of-magnitude estimates. A substantial part of the paper is devoted to an introduction to the specific features of soft gel fracture mechanics. We then try and put forward the wide variety of theoretical and experimental issues relevant to environmental crack control with some tentative insight into tissue engineering and living tissue biomechanics.

Development of new performance indices to evaluate the fatigue properties of asphalt binders with ageing

This work presents the development of new fatigue performance indices for asphalt binders based on viscoelastic continuum damage (VECD) theory and failure energy. Five plant-produced asphalt mixtures were subjected to three different conditioning levels (short-term ageing during production and loose mix ageing for 5 and 12 days at 95°C in the laboratory) and the corresponding binders were extracted and recovered. Direct Tension Cyclic Fatigue (DTCF) tests were performed on the mixtures to characterise the mixture fatigue properties using the simplified viscoelastic continuum damage (S-VECD) analysis approach. Frequency and temperature sweep tests and the Linear Amplitude Sweep (LAS) test using a Dynamic Shear Rheometer (DSR) were conducted on the recovered binders to evaluate the binder rheological and fatigue properties. Three new performance indices are explored from the LAS test: Strain Tolerance (εT ), Strain Energy Tolerance (Εf ), and Average Reduction in Integrity to Failure (IR ). These indices were used to track the evolution of binder fatigue properties with ageing. A unique aspect of these indices is that they capture the failure point of the binder during the LAS test and combine the stress and strain histories of the material. Compared with the traditional A and B parameters from the LAS test, the new indices show a consistent decrease in the fatigue properties of the binders with ageing. The newly proposed parameters show improved correlations with mixture fatigue performance index (DR ) from the DTCF test, indicating their potential for evaluation of asphalt mixture fatigue properties. In addition, the new indices developed from this study have been shown to effectively capture the ageing gradient within the pavement structure and can also be used together with the binder rheological indices (e.g. G-R parameter and ΔTc) to evaluate both environmental and fatigue cracking of asphalt pavements at the same time.