Thermal Cracking Mechanism Research Articles

Effective optimization method of asphalt binders and asphalt mixtures based on the two-parameter of contraction and relaxation

Thermal cracking is one of the primary distresses of asphalt pavement which is a complex process. Evaluating the Low-temperature Performance (LTP) of asphalt mixtures accurately and conducting material optimization analysis is not only crucial for understanding the thermal cracking mechanism of asphalt mixtures but also serve as the basis for enhancing their thermal cracking resistance performance. However, current research has not sufficiently interpreted the mechanism of thermal cracking. It is segmentary that optimizes asphalt mixtures solely based on their ultimate strength, strain, and so on at certain low-temperature points. Therefore, this study closely integrated the thermal cracking mechanism and proposed a two-parameter optimization method. Firstly, clarifying the decisive role of the contraction and relaxation relationship in determining LTP through the Thermal Stress Restrained Specimen Test (TSRST), thermal contraction test, and low-temperature relaxation test. Secondly, quantizing the impact of the aggregates skeleton and then using a two-parameter method to analyze the comprehensive effects on LTP of asphalt mixtures. Finally, summarizing the material optimization method of asphalt binder-first, aggregates-second based on the multiple linear regression method. This paper simplified the evaluation method and provided a basis for material selection and design for improving the thermal cracking resistance of asphalt mixtures.

Research on the dynamics and mechanism of thermal cracking of coal-based endothermic hydrocarbon fuels

Thermal cracking of endothermic hydrocarbon fuels (EHF) plays an important role in the endothermic process when the fuel temperature exceeds the supercritical temperature. To gain a deeper understanding of the thermal cracking behavior of EHF, this work discusses the thermal cracking law and reaction mechanism of coal-based EHF at different temperatures through static thermal cracking experiments, and establishes a total molecular reaction dynamics model containing 34 species and 24-step reactions based on product distribution. The results show that in the temperature range of 450℃ to 500℃, the gas phase yield of the fuel increases linearly from 8% to 56%, and the conversion rate reaches up to 96.1%. The kinetic reaction of thermal cracking conforms to the primary kinetic equation, the cracking rate constant k is between 1.08×10-4~7.92×10-4s-1, the activation energy Ea=184.47±11.5kJ∙mol-1, and the precursor factor lnA=21.61±3.0. Gas phase products include hydrogen, methane, ethane, ethylene, propane and butane. Liquid phase products include paraffins, alkyldecahydronaphthalenes and aromatic hydrocarbons. As the cracking depth increases, the degree of fuel branching first increases and then decreases, up to 0.33. Paraffins and alkyldecahydronaphthalenes are gradually converted into olefins, cyclic olefins, benzene, naphthalene, indene, fluorene and pyrene and other compounds. Based on the product distribution, the reaction mechanism of thermal cracking of coal-based EHF is speculated to include single-molecule β-cracking, bimolecular F-S-S, intramolecular H-transfer, cyclization and isomerization mechanisms.

Study on thermal crack characteristics of granite in Shandong Province, China under different temperatures and heating/cooling treatments

The qualitative and quantitative analysis of crack initiation characteristics, extended procedure, and crack network morphology of rock under different temperatures and heating/cooling paths was conducted in order to delve deeper into the mechanism of thermal cracking, and the analytical perspectives mainly include microstructure, thermodynamics, and mineral crystal properties. Research results indicate that 200–300 °C and 600 °C are two obvious mutation points of water-cooled samples, while air-cooled samples show mutation points around 600 °C. The initiation positions of thermal cracking under all temperature paths are relatively similar, with intergranular crack located between particles at the edge of the sample or intercrystalline cracks in the middle of feldspar or quartz aggregates. Slow heating and rapid cooling contribute to the complexity of the thermal crack network, and rapid heating can form larger sized thermal cracks. The process of thermal cracking can be divided into three stages: initiation of small cracks, joint development of main cracks and small cracks, and interconnection of cracks to form a network structure. The thermal cracking mechanism is attributed to differences in expansion and thermal conductivity among various crystals.

The pyrolysis of 4,4,8,10-tetramethyl decalin and the influence of molecular structures on oil thermal cracking: A ReaxFF molecular dynamics simulation and DFT study

The molecular structure of different hydrocarbons in crude oil has a significant effect on the thermal cracking mechanism. This study delves into the thermal cracking mechanism, pyrolysis process, and kinetics of 4,4,8,10-tetramethyl decalin (a representative bicyclic sesquiterpane in crude oil) using reactive molecular dynamics simulation (ReaxFF–MD) at the temperature range from 2000 K to 3000 K. Interestingly, the major intermediate products from thermal pyrolysis simulation align closely with the main ion fragments in the mass spectrometry of 4,4,8,10-tetramethyl decalin. The results can be directly used to analyze the pyrolysis mechanism. It reveals five reaction pathways implicated in the initial pyrolysis of 4,4,8,10-tetramethyl decalin: three demethylation reactions (more likely to occur) and two ring-opening reactions. By employing first-order kinetic analysis based on ReaxFF–MD simulations within the temperature range of 2000 K to 3000 K, the apparent activation energies for 4,4,8,10-tetramethyl decalin are calculated and compared with our prior simulation results for n-tetradecane. The initial pyrolysis of 4,4,8,10-tetramethyl decalin predominantly entails the cleavage of C–C bonds in both branched chain and carbon ring systems, resulting in the generation of methyl and high molecular weight ring-structured radicals. Conversely, the initial pyrolysis of n-tetradecane yields low molecular weight straight–chain radicals by cleaving C–C bonds except for the terminal position. This implies that the bicyclic sesquiterpane 4,4,8,10-tetramethyl decalin serves as the favorable precursor for producing methane (CH4) and liquid hydrocarbons (C6–C13) during the primary formation stage of light oil. With an equivalent number of carbon atoms, n-tetradecane serves as the preferred precursor for generating wet gases (C2–C5) at the initial formation stage of wet gases. The insights derived from the ReaxFF–MD simulation offer valuable perspectives for comprehending the process of thermal cracking in crude oil under geological conditions.

Evaluating the low-temperature performance of asphalt mixtures based on the contraction and relaxation properties

The thermal cracking of asphalt pavement has been the focus of research in cold regions of the world. The contraction and relaxation properties of asphalt mixtures were crucial for investigating the thermal stress of asphalt pavement based on the thermal cracking mechanism. This paper proposed a novel evaluation index for characterizing the low-temperature performance of asphalt mixtures by considering their contraction and relaxation properties. Firstly, the rank during the evaluation indexes for low-temperature performance was determined by comparative analysis of method. Secondly, the thermal contraction coefficient was used to characterize contraction properties and cumulative stress at per unit strain rate (CSSR) was used to characterize relaxation properties in this paper. According to the cumulation process of thermal stress, a novel index was constructed based on the contraction and relaxation properties. Finally, considering the correlation between the failure temperature and the novel indexes, the prediction model of low-temperature performance consistent with the order of failure temperature was established based on the multiple linear regression method. Through the standardized analysis of the prediction model, the influence of novel indexes for the low-temperature performance of asphalt mixtures under different temperature conditions was clarified. A novel evaluation index provided a theoretical basis for unifying the evaluation indexes of asphalt mixtures.

Investigating the effect of fundamental properties of materials on the mechanisms of thermal cracking of asphalt mixtures

In most of tests and models to evaluate the thermal cracking of asphalt mixture, the consideration of different elements within the asphalt mixture has been neglected to provide a corrective solution. Accordingly, in this research, the evaluation of the mechanisms of thermal cracking involved assessing the impact of surface free energy (SFE) parameters and other fundamental properties of bitumen and aggregate. These parameters included the adhesion and cohesion free energy, the ratio of the base element to the acid element of the aggregate SFE (RBA), the creep stiffness of bitumen, the rate of changes in creep stiffness (m-value), and specific surface area (SSA) of aggregate. To this end, Wilhelmy plate (WP) test, universal sorption device (USD) test, the bending beam rheometer (BBR) test and the pull-off test were performed. In the following, models were presented to evaluate the effect of mentioned parameters as independent variables on the mechanisms of thermal cracking using an artificial neural network (ANN). The sensitivity analysis of the Artificial Neural Network (ANN) model revealed that in the status of adhesive failure, the cohesion free energy and m-value did not affect the Pull-off adhesion strength. On the other hand, the adhesion free energy, RBA, and the SSA were directly proportional and the creep stiffness was inversely proportional to the Pull-off adhesion strength. Also, in the status of cohesive failure, the adhesion free energy, the RBA, and the SSA did not affect the Pull-off cohesion strength. On the other hand, the cohesion free energy and m-value were directly proportional and the creep stiffness was inversely proportional to the Pull-off cohesion strength.

Evaluation index for the low-temperature performance of asphalt mixture based on relaxation characteristics of thermal cracking mechanism

ABSTRACT The thermal cracking behaviour of asphalt pavement is complex and includes thermal contraction, low-temperature relaxation, and low-temperature damage. However, using relaxation characteristics alone instead of low-temperature properties leads to an incomplete evaluation. In this paper, the relationship between viscoelastic properties and relaxation characteristics was analyzed. Based on the time domain characteristics of relaxation, the relaxation rate and cumulative stress at per unit strain rate (CSSR) were proposed as evaluation indexes corresponding to the long-term/short-term characteristics of the relaxation. By combining the relationship among the low-temperature performance obtained by Thermal Stress Restrained Specimens Test (TSRST) and relaxation characteristics, evaluation indexes for the low-temperature performance of asphalt mixture were preferably selected. The results show that asphalt binders dominate the relaxation characteristics of asphalt mixtures, but do not directly replace the low- temperature performance of asphalt mixtures. The relaxation characteristics expressed by the traditional viscoelastic indexes were insufficient to fully evaluate the low- temperature performance of asphalt mixtures. Furthermore, the results of the relaxation characteristic index for evaluating the low-temperature performance were different under different temperature conditions, indicating that performance at a single temperature cannot replace the low-temperature performance at all temperatures.

Managing Transport Processes in Thermal Cracking to Produce High-Quality Fuel from Extra-Heavy Waste Crude Oil Using a Semi-Batch Reactor

Soil pollution from waste crude oil in emergency pits is a major problem at petroleum industry sites. In this work, extra-heavy waste crude oil was recovered from emergency pits and underwent many pre-purification processes to remove water and impurities. This type of oil was subjected to thermal cracking reactions in a semi-batch reactor constructed from stainless steel, with a volume of 500 mL. The cracking reactions were tested at operating temperatures of 400, 425, and 450 °C, with operating pressures of 1, 3, 5, and 7 bar. The results indicated that during thermal cracking, the reaction mechanism was highly dependent on the heat and mass transfer processes that occurred in the reactor. It was noted that the interaction between the optimal reaction temperature and operating pressure enhanced the product distribution and formation of high-quality liquid fuel with low gaseous and coke formations. The highest API of 30.5 was achieved for the liquid product at an operating temperature of 400 °C and a pressure of 3 bar. Additionally, an evaluation of the thermal cracking mechanism found that the transport processes that occurred in the reactor were the chief factor in providing a high-performance thermal cracking process.

Predicting isotopologue abundances in the products of organic catagenesis with a kinetic Monte-Carlo model

Thermal cracking of complex organic matter can occur under many geological settings. However, the role of thermal cracking vs. other chemistries (e.g., metallic catalysis or Fischer-Tropsch-type reactions) in petroleum formation remains controversial. Realistic modeling of isotope effects in chemical reaction networks involving thermal cracking might shed light on this problem, especially given the recent progress on measurements of intramolecular stable isotope distributions in organic compounds. Previously published models of thermal cracking in petroleum formation are incapable of predicting the intramolecular isotope patterns of products because they do not incorporate realistic precursors, elementary reactions and patterns of inheritance. In this study, we develop a kinetic Monte-Carlo (kMC) model to address this problem. We simulate thermal breakdown of different types of organic matter that is represented by molecular models. At the onset of each simulation, we initialize the model parent organic molecules with isotopic substitutions, and then subject them to free radical chain reactions in a many-step process. Every simulation captures a possible route of thermal degradation and tallies the numbers of each unique isotopologue of all product molecules at the end. Although this model produces data that contain information for all molecules and isotopic forms, in this study we focus on the proportions of many of the isotopologues of all of the C1-C7n-alkanes. We use two chemistry schemes that differ in complexity. The basic scheme (scheme A) includes only homolytic cleavage and capping of metastable radicals by hydrogen atoms. The more sophisticated scheme (scheme B) includes most reactions of importance in the free radical chain mechanism of thermal cracking. We find significant differences between the schemes A and B in predicted molecular and isotopic compositions of products. Scheme B is more consistent with natural data than scheme A, suggesting that full radical mechanisms should be considered in models of thermal cracking in natural hydrocarbon formation. Our model is further validated by reproducing results from hydrous pyrolysis experiments. For simulating natural petroleum formation, we found that the kMC model is acceptable at low maturity, but cannot match compositions and time estimates of mature gas formation, suggesting the influence of alternative mechanisms in late-stage, high-thermal-maturity catagenesis. Using our model, we provide mechanistic explanations for some of the existing observations, such as the evolution of intramolecular and intermolecular carbon isotope compositions with thermal maturity. Our study also makes predictions of intramolecular isotope compositions for higher-order alkanes (C4+) that have been little studied to date but present attractive targets for future measurements.

Changes of pore structures and permeability of the Chang 73 medium-to-low maturity shale during in-situ heating treatment

To evaluate the thermally induced permeability enhancement potential and stress sensitivity during in-situ heating (ISH), real-time measurement of pulse-decay gas permeability (PDP) of medium-to-low maturity shale cores from Chang 73 sub-member shale oil reservoir was carried out in our self-developed high-temperature pseudo-triaxial core holder at different temperatures and effective stresses. Stereo light microscope (SLM), computerized tomography (CT) scan, and nuclear magnetic resonance (NMR) tests were conducted to quantitatively characterize the microstructure development in the shale cores. Based on the lithology and thermal analysis, the primary mechanisms of thermal cracking, nanopores evolution, and physical property improvement were discussed in detail. The experimental results show that the porosity and permeability can be effectively increased to 3.13 times and 624.09 times on average above the threshold temperature of approximately 400 °C, but this also results in a stronger stress sensitivity of permeability up to 30.21%. Furthermore, the coverage, density, complexity, and connectivity of the fracture network can be dramatically improved. A large number of secondary nanopores with diameters in the range of 2–50 nm dominate. There is a good correlation between microstructure development and physical property variation. We found that the kerogen pyrolysis was the most critical mechanism for the significant enhancement in microstructure and physical property.

Role of Cyclic Thermal Shocks on the Physical and Mechanical Responses of White Marble

Marble is a common rock used in many buildings for structural or ornamental purposes and is widely distributed in underground engineering projects. The rocks are exposed to high temperatures when a tunnel fire occurs, and they will be rapidly cooled during the rescue process, which has a great impact on the rock performance and the underground engineering stability. Therefore, the role of cyclic thermal shocks on the physical and mechanical properties of marble specimens was systematically investigated. Different cyclic thermal shock treatments (T = 25, 200, 400, 600, 800 °C; N = 1, 3, 5, 7, 9) were applied to marble specimens and the changes in mass, volume, density and P-wave velocity were recorded in turn. Then, the thermal conductivity, optical microscopy and uniaxial compression tests were carried out. The results showed that both the cyclic thermal shock numbers (N) and the temperature level (T) weaken the rock properties. When the temperature of a thermal shock exceeds 600 °C, the mass loss coefficient and porosity of the marble will increase significantly. The most noticeable change in P-wave velocity occurs between 200 and 400 °C, with a 52.98% attenuation. After three thermal shocks, the cyclic thermal shock numbers have little influence on the uniaxial compressive strength and Young’s modulus of marble specimens. Shear failure is the principal failure mode in marble specimens that have experienced severe thermal damage (high N or T). The optical microscopic pictures are beneficial for illustrating the thermal cracking mechanism of marble specimens after cyclic thermal shocks.

Optimization of the Evaluation Indexes for the Low-Temperature Performance of Asphalt Mixture Based on Relaxation Characteristics of Thermal Cracking Mechanism

Optimization of the Evaluation Indexes for the Low-Temperature Performance of Asphalt Mixture Based on Relaxation Characteristics of Thermal Cracking Mechanism

Role of microwave during microwave-assisted catalytic reforming of guaiacol, syringolbio-oil as model compounds

To better understand the role of microwave and the mechanisms of thermal cracking and catalytic reforming of lignocellulosic bio-oils, this study compares the difference in the reaction characteristics between microwave-assisted and conventional heating of representative bio-oil model compounds. Syringol and guaiacol were selected as bio-oil model compounds. The effects of the heating method on the conversion of the model compound and the yield and composition of products were systematically investigated in the temperature range of 600–700 °C. The results showed that high reaction temperature and microwave-assisted heating favoured the conversion of model compounds, and the conversions of syringol were generally higher than those of guaiacol under the same conditions (temperature, heating method). The heating method was found to greatly influence the yield and composition of products. The bio-oil obtained from conventional thermal cracking of model compounds contained phenolics, aromatic hydrocarbons, aryl alkyl ethers, and oxygen-containing heterocyclic compounds. In contrast, microwave-induced polarisation of poorly stable methoxy groups promotes the formation of phenolics, the concentration of the phenolic in the guaiacol and syringol bio-oil reached 62.5–66.17 area% and 85.18–87.65 area%, respectively, in the temperature range of 600–700 °C. Catalytic reforming of model compounds showed that activated carbon catalyst drastically promoted the phenol formation, particularly under microwave-assisted heating, the phenol concentration reached 93.9–97.97 area% in bio-oil during catalytic reforming of guaiacol. The formation of electron-hole pairs on the active metal sites induced by microwave radiation possibly enhanced the demethoxylation to selectively generate phenol due to the strong electron-donating ability of the methoxyl group. Microwave-assisted catalytic reforming of the model compounds was also beneficial for H2 formation because of the direct dehydrogenation of methyl radicals and the gas-phase reactions. The H2 concentrations of 81.07–82.41 vol.% and 75.2–79.16 vol.% were obtained during microwave-assisted catalytic reforming of guaiacol and syringol, respectively.

Simulation of the nonplanar three-dimensional thermal cracking using the finite element-meshfree method

Thermal cracking widely exists in nature and engineering practices, attracting more and more attention nowadays. Understanding the failure mechanism of thermal cracking is critical to improving the efficiency and safety of engineering applications. Despite great efforts have been performed on the numerical modeling of thermal cracking, accurately representing and tracking a nonplanar three-dimensional (3D) cracking pattern is still a challenge. In this work, a novel thermo-mechanical coupling model (FEMM-TM), combining a heat transfer algorithm and the finite element-meshfree method (FEMM), is proposed to simulate the nonplanar 3D thermal cracking problems, involving the temperature transfer, thermal stress distribution, as well as the crack propagation and coalescence. The performance of the proposed FEMM-TM model is validated by numerical tests with analytical or numerical solutions. The nonplanar 3D thermal cracking problems under different thermal loading conditions are further investigated. Results show that the proposed method can be effectively deployed in the analysis of nonplanar 3D thermal cracking problems.

Mechanical behaviour of Lac du Bonnet granite after high-temperature treatment using bonded-particle model and moment tensor

The thermal cracking mechanism has been increasingly investigated to analyse and solve the mechanical behaviour of rocks in deep underground engineering. Classic laboratory tests bear the intrinsic limitation of non-repeatability and lack of direct observation of the interaction effect between thermal stresses and thermal micro-cracks. In this paper, the bonded-particle model and moment tensor is used to simulate the process of thermally induced micro-and macro-cracks in Lac du Bonnet granite to help provide insight into the detailed influence temperature on mechanical properties and acoustic emission characteristic of granite. During modelling, macro- and microscopic responses are quantified and compared against other laboratory data in the literature. The results indicate thermal stresses and thermally induced micro-cracks increase with increasing temperatures during heating, and cooling generally reduces the thermal stresses and increases the micro-cracks slightly. Grain-size distribution has a significant influence on thermal micro-cracks, thermal stress and the mechanical behaviours of granite. The increase in thermally induced tensile intergranular micro-cracks density mainly contributes to reduction of mechanical properties in granite samples subjected to heating–cooling cycles. It is also observed that the nature of sources and the b-value are associated with temperature, which gives some light on underground engineering in high temperature environments.

ReaxFF Molecular Dynamics Simulation of the Cracking of Components of Vacuum Gasoil in the Presence of a Nickel Nanocluster

ReaxFF molecular dynamics simulation of the cracking of the paraffin, naphthene, and aromatic components of vacuum gasoil with and without a Ni468 nanoparticle is performed. It is found that the observed routes of destruction of hydrocarbons under thermal action do not contradict the real mechanisms of thermal cracking; the enthalpies of the thermal destruction reactions of the model components obtained in ReaxFF with the CHO and NiCH force fields correlate with those determined via quantum chemistry in the ub3lyp/6-31g(d,p) DFT approximation. The mechanisms of adsorption and destruction of the paraffin, naphthene, and aromatic components of vacuum gasoil on the surface of a Ni468 nanoparticle are studied, based on the results from ReaxFF molecular dynamics simulation. Their enthalpies of adsorption and dehydrogenation are calculated, along with the activation energies of dehydrogenation on the surface of a nickel nanoparticle. Cracking in a multicomponent system consisting of 93 hydrocarbon molecules and a Ni468 nanocluster is simulated, and all routes of the destruction of the initial hydrocarbons are determined.

Exploring free energy profile of petroleum thermal cracking mechanisms.

Understanding the mechanisms of petroleum thermal cracking is critical to develop more efficient and eco-friendly petroleum cracking processes. Asphaltenes are the main component of petroleum subjected to cracking processes. Thermal cracking mechanisms of petroleum were explored by computational methods using 1,2-diphenylethane (DPE) as a model molecule in this study. The overall mechanisms were divided into four steps including initiation, H-transfer reaction, H-ipso reaction, and termination represented by seven reactions. We carried out extensive quantum chemistry calculations at high levels of theory to accurately explore the minimum energy pathways as the mechanisms of the proposed reactions. The reaction energy and barriers in terms of enthalpy and free energy and their temperature dependence were calculated in the vacuum and in both polar and nonpolar solvents using the polarizable continuum model (PCM) method. The temperature dependence of the target reaction barriers are characterized in different environments and provides computational guidance for future development for petroleum thermal cracking. As the first reported systematic investigation of petroleum cracking mechanisms, this study provided a comprehensive theoretical description of petroleum cracking processes with valuable information about temperature and solvent dependence. Graphical abstract.

Morphology and Thermal Properties of Calcium Alginate/Reduced Graphene Oxide Composites.

Calcium alginate (CaAlg) is a kind of biodegradable and eco-friendly functional material, and CaAlg/reduced graphene oxide (rGO) composites are expected to be applied as new textile, heat-generating, and flame-retardant materials. In this paper, the CaAlg/rGO composites were prepared by a sol-gel method and their morphological and thermal properties were studied. The results showed that the introduction of rGO can efficiently improve the thermal stability of CaAlg. Further study showed that rGO increased the carbon formation rate by 4.1%, indicating that the thermal stability was improved by the promotion of carbon formation. Moreover, the weight loss rate of the composites was faster at 180–200 °C than that of CaAlg, after which the rate was less comparatively, suggesting the better thermal stability of the composite. This maybe because the high heat transfer efficiency of rGO allowed the material to reach the temperature of the thermal decomposition of the glycan molecule chain within a short time, and then promoted carbon formation. The thermal cracking mechanism of the composites is proposed based on the experimental data.

Thermophysical modeling of main-belt asteroids from WISE thermal data

By means of a varied-shape thermophysical model of Hanuš et al. (2015) that takes into account asteroid shape and pole uncertainties, we analyze the thermal infrared data acquired by the NASA’s Wide-field Infrared Survey Explorer of about 300 asteroids with derived convex shape models. We utilize publicly available convex shape models and rotation states as input for the thermophysical modeling. For more than one hundred asteroids, the thermophysical modeling gives us an acceptable fit to the thermal infrared data allowing us to report their thermophysical properties such as size, thermal inertia, surface roughness or visible geometric albedo. This work more than doubles the number of asteroids with determined thermophysical properties, especially the thermal inertia. In the remaining cases, the shape model and pole orientation uncertainties, specific rotation or thermophysical properties, poor thermal infrared data or their coverage prevent the determination of reliable thermophysical properties. Finally, we present the main results of the statistical study of derived thermophysical parameters within the whole population of main-belt asteroids and within few asteroid families. Our sizes based on TPM are, in average, consistent with the radiometric sizes reported by Mainzer et al. (2016). The thermal inertia increases with decreasing size, but a large range of thermal inertia values is observed within the similar size ranges between D ∼ 10–100 km. We derived unexpectedly low thermal inertias ( < 20 J m−2 s−1/2 K−1) for several asteroids with sizes 10 < D < 50 km, indicating a very fine and mature regolith on these small bodies. The thermal inertia values seem to be consistent within several collisional families, however, the statistical sample is in all cases rather small. The fast rotators with rotation period P ≲ 4 h tend to have slightly larger thermal inertia values, so probably do not have a fine regolith on the surface. This could be explained, for example, by the loss of the fine regolith due to the centrifugal force, or by the ineffectiveness of the regolith production(e.g., by the thermal cracking mechanism of Delbo’ et al. 2014).

Design parameter of low-temperature performance for asphalt mixtures in cold regions

The low-temperature performance of an asphalt mixture plays important roles in the thermal cracking mechanism of asphalt pavements in cold regions. However, the existing asphalt mixture design process does not involve a design parameter for low temperature performance as the asphalt content is determined. In this study, two types of asphalt mixtures are involved, Asphalt Concrete (AC) and Stone Mastic Asphalt (SMA), which are the most widely used materials for surface layer. The zone for low-temperature performance was defined on the basis of a survey of pavement distresses and numerical analysis. The design parameter was captured from an indirect tensile test by using Digital Image Correlation (DIC) analysis, considering the universalizability and simplification of the indirect tensile test. The selected indicators, such as tensile failure strain, validated that significant linear correlations existed between bending beam test and thermal stress restrained specimens test. Thus, the design parameter, which was defined as the tensile failure strain (εDIC), could characterize low-temperature property with asphalt content. Moreover, the critical strain of εDIC was proposed. The low-temperature design parameter (εDIC) was applied to the Marshall design method. The optimum asphalt content based on the new design method was slightly greater than that of the conventional Marshall design method. The evaluation methods used in this paper indicate that the low-temperature property of the asphalt mixture created by the new design method was better.