Friction Course Research Articles

Three-Dimensional Micromechanical Simulation and Evaluation of High-Toughness Ultra-Thin Friction Course with X-Ray Computed Tomography

As a novel pavement wear layer material, the micromechanical mechanisms of High-toughness Ultra-thin Friction Course (HUFC) have not been fully elucidated. This paper presents a new method for the three-dimensional micromechanical simulation of high-toughness asphalt mixtures based on a viscoelastic parameter calibration model. X-ray Computerized Tomography (CT) was employed to scan samples of high-toughness asphalt mixtures to obtain detailed information on the internal structure (aggregate, fine aggregate matrix FAM and voids), and a three-dimensional micromechanical model was constructed based on the real-scale distribution of these components. Aggregates in the high-toughness asphalt mixture were modeled as elastic bodies, while FAM was treated as a viscoelastic material characterized by the Burgers model. Using the Boltzmann linear superposition principle and Laplace transform theory, the viscoelastic properties of FAM were converted into Prony parameters recognizable by finite element software, and the viscoelastic parameters were calibrated. Micromechanical simulations were conducted for three different gradings of high-toughness asphalt mixtures, and the results show that the predicted deformation closely matched the measured deformation. This method accurately reflects the deformation characteristics of different gradings of high-toughness asphalt mixtures, overcoming the limitations of traditional numerical simulations based on homogeneous material models. It represents an advancement and refinement of micromechanical simulation methods for high-toughness asphalt mixtures.

Recycling steel slag as aggregate in developing an ultra-thin friction course with high comprehensive road performance

The demand for skid-resistant and wear-resistant alternative aggregates in the preparation of ultra-thin friction course (UTFC) asphalt mixtures is a key direction for achieving high durability and low-carbon development in pavement maintenance. As a typical industrial waste, steel slag with high alkalinity and strong adhesion can facilitate the mechanical property of asphalt mixtures. However, few researches focused on the impact of steel slag on the comprehensive road performance of UTFC mixtures. Hence, the issue merits systematic exploration. In this study, the chemical components, microstructure and morphological characteristics of three steel slags (GXSS, HBSS and IMSS) obtained from different sources were surveyed. Then the stone matrix asphalt (SMA)-5 and open-grade friction courses (OGFC)-5 mixtures with different steel slags were fabricated. And their comprehensive road performances were quantitatively explored via the improved radar chart. The results indicate that steel slag with approximately 40 % Ca content, about 20 % Fe content, irregular shapes and tiny pores endows its wear resistance and strong adhesion. IMSS demonstrates the largest average angularity and form 2D values of 3850 and 7.28, respectively, representing its significant crowding function and interlocking structure. Incorporating steel slag remarkably reinforces the rutting resistance, skid resistance and anti-interlayer shear performance of UTFC. While the effect of water stability and crack resistance of UTFC depend on the category of steel slag. All three steel slags manifest the improvement function on the comprehensive assessment indexes (CAI) of OGFC-UTFC. IMSS-OGFC reveals the optimal comprehensive road performance, achieving the highest CAI of 0.9909. It is inferred that steel slag is more suitable for OGFC-UTFC than SMA-UTFC due to its relatively high CAI and consistent performance regardless of the steel slag type.

Characteristics of Open-Graded Friction Course Macrotexture and Macrostructure and Its Effect on Skid Resistance under Rainfall.

An Open-Graded Friction Course (OGFC) presents a rough surface and a porous structure and provides skid resistance under wet conditions, differing from that of a dense graded mixture. This study explored the distribution of surface macrotexture with depth in OGFC. Using cross-sectional images and semantic image segmentation techniques, the internal structure, porosity, and void size distribution were analyzed to assess the effectiveness of rainfall drainage. Skid resistance was evaluated with a British Pendulum Tester, focusing on the influence of surface macrotexture and internal macrostructure, particularly with regard to contact depth. Results show that finer gradations increase surface roughness peaks, which are concentrated near the top surface. In contrast, coarser mixtures exhibit a greater effective contact depth and more peaks with higher curvature. Finer gradations also result in lower porosity, greater void dispersion, and smaller average void diameters. During heavy rainfall, OGFC-13 exhibits the highest friction coefficient due to its effective contact, surface roughness, and internal voids, which facilitate water expulsion. This research provides insights into the skid resistance mechanism of OGFC in wet conditions and offers practical guidance for selecting the optimal gradation.

Evaluation of the effect of binder type and layer thickness on the performnce of open graded friction courses

To improve the long-term durability and functionality of open graded friction courses (OGFC), the Florida Department of Transportation (FDOT) investigated the use of a highly modified asphalt binder and increased thickness using Accelerated Pavement Testing (APT). A total of six test sections with combinations of two modified binder types (PG 76–22 and PG 82–22) and three lift thicknesses of 0.75 (19.05 mm), 1.25 (31.75 mm) and 2 (50.8) inches were constructed at FDOT’s APT facility. Accelerated loading was performed using a Heavy Vehicle Simulator (HVS) to evaluate the relative rutting performance of the test sections. Supplementary field and laboratory tests to evaluate tensile strength, Cantabro loss, field permeability, surface characteristics, and asphalt binder properties were also conducted. Test results indicated that the use of PG 82–22 polymer modified asphalt (PMA) binder may be beneficial to improve long-term durability of the OGFC. Thicker layers of OGFC were found to have considerably lower durability. It is recommended that the use of a highly modified PMA asphalt binder in OGFC layers be considered when raveling and other durability issues are of concern.

Mechanical Analysis through Non-Destructive Testing of Recycled Porous Friction Course Asphalt Mixture

This study assessed the mechanical performance of porous asphalt mixtures, specifically the porous friction course (PFC), incorporating 10% Reclaimed Asphalt Pavement (RAP) and rubberized asphalt. Three different methods were investigated to evaluate the stiffness of the mixtures: the resilience modulus (RM) test at a single temperature and loading frequency, the complex modulus |E*| test from compressive loading conducted at various temperatures and frequencies, and the impact resonance (IR) tests performed at three temperatures with five impacts applied to the mixture. The results demonstrated that the RAP-containing mixture exhibited a higher resilience modulus at all tested temperatures, indicating greater stiffness compared to the mixture without RAP. Additionally, the IR and |E*| tests revealed similar behavior between the two evaluated mixtures. These findings suggest that both quasi-static and vibrational tests are suitable for characterizing the stiffness of porous asphalt mixtures due to the similarity in the viscoelastic parameters of the two investigated mixtures. This study provides important insights into the practical and scientific application of recycled and modified materials in porous asphalt mixtures.

Multi-scale FE analysis of coupled load-moisture mechanical behavior of saturated asphalt pavements considering transversely isotropic permeability

Assessing the collective impacts of external loading and void pressure on the mechanical behavior of porous media presents a significant challenge due to its inherent heterogeneity and complex multi-physical field coupling mechanisms. This study addresses this challenge by developing a novel multiscale hydraulic-mechanical modeling framework to investigate the structural response of water-saturated asphalt pavement under sequential coupling hydro-mechanical loading. The framework comprises three key components. Firstly, incorporating an upscaling homogenization approach to establish the linkage of material properties between different scales; secondly, developing a downscaling transfer procedure to transfer the structural response across scales for insight into its multiphysics mechanisms; and finally, proposing a new sequential coupling algorithm in multiscale simulations for comprehensive multi-field coupling calculations. The primary outcomes of this study demonstrate that asphalt concrete (AC)-graded pavements are susceptible to “down-top” cracks under hydro-mechanical loading, while open graded friction course (OGFC)-graded pavements have the potential to develop both “top-down” and “down-top” cracks. In AC-graded pavements, increasing the hydraulic head reduces stress concentrations, while in OGFC-graded pavements, changes in the permeability coefficient have a lesser impact on mechanical response. At the mesoscopic level, tensile stress concentrations in the asphalt mortar decrease significantly at higher temperatures. Furthermore, the OGFC-graded RVE model exhibits higher tensile stresses in the asphalt mortar compared to the AC-graded RVE model.

Effect of High Polymer, Crumb Rubber, and Epoxy-Modified Asphalt Binders on Laboratory Performance of Open-Graded Friction Course Mixtures

Open-graded friction course (OGFC) is a thin asphalt mixture surface layer. It is gap-graded with a high percentage of coarse aggregates that are nearly uniform in size, resulting in a high percentage of interconnected air voids and asphalt binder, which provides improved skid resistance, visibility, and decreased pavement–tire noise. However, construction personnel at the Louisiana Department of Transportation and Development reported that conventional OGFC mixtures have durability issues and shorter service life, compared with thin asphalt mixture lifts. Hence, effects of different asphalt binder types on the performance of OGFC mixtures were evaluated. Five types of asphalt binder were utilized: conventional styrene-butadiene-styrene (SBS) asphalt binder PG 76-22M; high SBS content asphalt binder PG 88-28; diluted epoxy asphalt (EA) binder with two different dosages (25% and 50%); and a hybrid modified asphalt binder prepared with SBS and crumb rubber modifier PG 76-22G. The optimal aggregate structures were determined based on minimum required air voids and voids in coarse aggregate. Physical and mechanical tests were conducted to assess the performance of OGFC mixtures, including draindown, permeability, loaded wheel track, and Cantabro abrasion loss. Results indicate that OGFC mixtures incorporating diluted EA binder exhibited lower draindown values than mixtures containing PG 76-22M and PG 88-28. Moreover, mixtures with PG 88-28 and 50% EA binders demonstrated improved resistance to rutting. Mixtures with 50% EA and PG 88-28 binders demonstrated improved durability, compared with mixtures with PG 76-22M for unaged and aged conditioning, as measured by Cantabro abrasion loss values.

Roadside Vehicle Particulate Vertical Dispersion Model for Friction Course Materials: A Case of Hong Kong

Roadside Vehicle Particulate Vertical Dispersion Model for Friction Course Materials: A Case of Hong Kong

Improving the Durability of 12.5 mm Open-Graded Friction Course using 9.5 mm Nominal Maximum Aggregate Size Gradation and High Polymer-modified Binder

Improving the Durability of 12.5 mm Open-Graded Friction Course using 9.5 mm Nominal Maximum Aggregate Size Gradation and High Polymer-modified Binder

Fracture properties of ultra-thin friction course mixture containing reclaimed asphalt pavement and glass fiber under monotonic and cyclic loading

Ultra-thin friction courses (UTFC) have demonstrated exceptional efficacy in the preventive maintenance of asphalt pavements. Despite this, research into the influence of reclaimed asphalt pavement (RAP) and glass fiber on the fracture behavior of UTFC mixtures under cyclic loading is sparse. In response, this study conducted both monotonic loading tests and tension cyclic loading tests on notched semi-circular specimens at a temperature of 25 °C to elucidate the impact of RAP and glass fiber on UTFC’s fracture resistance. The findings revealed that, during monotonic testing, the introduction of RAP appeared to bolster mechanical performance by increasing peak load and tensile stiffness index (TSI). However, RAP diminished the fracture energy, with the concurrent addition of RAP and glass fiber resulting in further compromise to fracture resistance. Conversely, in the cyclic loading tests operated under load control, the integration of RAP positively influenced fatigue life. Furthermore, the addition of 0.1 % glass fiber (identified as H-25R-0.1F) also improved fatigue life, highlighting its beneficial role in augmenting fatigue endurance. When compared to the mixture devoid of RAP, the inclusion of 25 % and 50 % RAP led to substantial increases in cumulative dissipated energy by 101 % and 398 %, respectively. These results suggest that both RAP and glass fiber have nuanced effects on the fracture and fatigue properties of UTFC mixtures, with potential implications for their application in roadway construction and rehabilitation. Minimum rate of cumulative dissipated energy change (RCDEC_min) could be used to characterize the fatigue performance. The lower the RCDEC_min, the larger the fatigue life. There existed a power law relationship between RCDEC_min and fatigue life, which was independent of the mixture type. Compared to the cumulative dissipated energy method, the maximum displacement method may be more suitable to characterize the damage evolution during the fatigue test.

Comparative evaluation of open graded friction course and stone matrix asphalt mixtures with modified binders and warm mix asphalt

Comparative evaluation of open graded friction course and stone matrix asphalt mixtures with modified binders and warm mix asphalt

Field Compaction Characteristics of Ultra-Thin Porous Friction Course Based on Laboratory Simulation

As a preventive maintenance treatment, the ultra-thin porous friction course (UPFC) has been widely recognized and used in road maintenance because of its excellent performance and cost effectiveness. The Marshall compaction method (MCM) has been adopted to design UPFC mixtures worldwide, particularly in China. However, there are few studies concerning the field compaction properties of MCM-designed UPFCs. The laboratory test results of this study from simulating on-site compaction showed that all UPFC specimens with thicknesses of less than 20 mm barely achieved the target compaction thickness, and all UPFC specimens with different thicknesses failed to meet the air void (AV) requirements of UPFC mixes designed using the MCM. According to the results of a virtual compaction test, and using the discrete element method, the strong force chains were strengthened as the UPFC thickness decreased inside the specimen, making it difficult to evenly diffuse and transfer inside the specimen and resulting in insufficient compaction of the UPFC. Furthermore, it was demonstrated that the MCM-designed UPFC specimens showed significant differences in the AV distributions along the vertical and lateral directions from those of the UPFC specimens that simulated field compaction. The UPFCs designed using the MCM had a poor correlation with field compaction.

Flexible Permeable-Pavement System Sustainability: A Methodology for Stormwater Management Based on PM Granulometry

Permeable-pavement design methodologies can improve the hydrologic and therefore the environmental benefits of rural and urban roadway systems. By contrast, conventional impervious pavements perturb the hydrologic cycle, altering the relationship between the rainfall loading and runoff response. Impervious pavements create a hydraulically conductive interface for the transport of traffic-generated chemicals and particulate matter (PM), deleteriously impacting their proximate environments. Permeable-pavement systems are countermeasures to mitigate hydrologic, chemical, and PM impacts. However, permeable pavements are not always equally implementable due to costs, PM loadings, and design constraints. A potential solution to facilitate environmental benefits while meeting the traffic load capacity is the combination of two filtration systems placed at the pavement shoulders and/or pedestrian sidewalks: a bituminous-pavement open-graded friction course (BPFC) and an aggregate-filled infiltration trench. This solution is presented in this manuscript together with the methodological framework and the first results of the investigations into designing and validating such a combined system. The research was conducted at the laboratories of the Polytechnic University of Bari and the University of Florida, while an operational and full-scale physical model was constructed in Bari, Italy. The first results presented characterize the PM deposition on public roads based on granulometry (particle size distributions (PSDs) and particle number densities (PNDs)). Samples (n = 16) were collected and analyzed at eight different sites with different land uses, traffic, and pavements from different cities (Bari and Taranto, Italy). The PM analysis showed similar distributions (PSDs and PNDs), except for two samples. The gravimetric-based PSDs of the PM had granulometric distributions in the sand-size range. In contrast, the PNDs, modeled by a Power Law Model (PLM) (R2 ≥ 0.92), illustrated an exponentially increasing number of particles in the fine silt and clay-size range, representing less than 10% of the PSD mass. Moreover, the results indicate that PM sourced from permeable-pavement systems has differing impacts on the pavement service life.

Exploring freeze-thaw damage distribution of asphalt mixture through DIC in combination with CT

Open graded friction course (OGFC) is highly susceptible to environmental impacts such as load and clogging, due to its rich void structure and exposure to environments. Especially in cold regions, freeze–thaw (F-T) damage is inevitable for OGFC. While the existing analysis methods cannot specifically describe the material's micro-response to load or environment. Therefore, the digital image correlation (DIC) in combination with computed tomography (CT) was applied to closely examine the intricate process of F-T damage of OGFC in this research. Principal strain and strain energy were used to describe the F-T damage process and distribution. In addition, the effects of initial void content and immersion conditions on the temporal and spatial distribution of damage were discussed. The data demonstrated that the spatial distribution of F-T damage strain was uneven. During F-T cycles, the principal strain inside the OGFC during F-T cycles was generally increased, and the deformation of the sample gradually accumulated. According to the strain energy growth rate variation, the F-T damage could be divided into two stages during the 18 F-T cycles, namely, the development stage and the deceleration stage. Moreover, the crucial parts of F-T damage were determined to be at the end of the voids connected with the outside or the void interface between the aggregates and asphalt mortar. The larger initial void content would increase the strain of OGFC during F-T cycles, as well as the inhomogeneity of the strain. Furthermore, the strain energy increased considerably, and the development of F-T damage of OGFC accelerated. Under partial immersion conditions, the immersed part has large strain and strain energy due to the direct effect of F-T, and the increase in immersion depth aggravates the F-T damage.

A multi-gradient analysis of microscopic void characteristics' influence on the mechanical properties of open-graded friction course bituminous pavement

The mechanical properties of the open-graded friction course (OGFC) bituminous pavement are tied to its microscopic void structure, but multiple void parameters influence void formation and distribution. Solely using air voids as an indicator of pavement stability is challenging. Thus, a multi-gradient analysis of void structure factors is vital for advancing OGFC pavement's mechanical property research. This study used computerized tomography (CT) and digital image processing (DIP) to gather data on void structure distribution, size, and complexity in OGFC bituminous mixtures. Mechanical experiments assessed high-temperature deformation, low-temperature cracking, and water damage resistance. Analysis of void parameters' influence led to a predictive model for mechanical property in OGFC mixtures. The study found that as air voids increase within the 18 %–24 % range, both equivalent void diameter and void fractal dimension increase, while void count decreases. Conversely, coarser gradation and a larger nominal maximum aggregate size (NMAS) lead to increased equivalent void diameter but decreased void fractal dimension, reducing void complexity. The mechanical properties of OGFC mixtures decline with rising air voids but improve with coarser gradation and larger NMAS. The predictive model highlights the void fractal dimension and NMAS as critical indicators, with other factors showing weaker influence or multicollinearity issues that are unfit for model fitting. The findings could provide useful references for the structural design, property evaluation, and quality control of OGFC bituminous pavements in actual road construction.

Improving skid-resistance durability of ultra-thin friction course in asphalt pavements through recycled steel slags as basalt replacements

The ultra-thin friction course (UTFC) has emerged as an effective solution for restoring skid-resistance on worn pavements. However, the scarcity and high cost of high-quality basalt aggregates pose challenges for UTFC implementation. This study explores the potential of utilizing recycled steel slags (blast furnace slag (BFS), basic oxygen furnace slag (BOFS), and electric arc furnace slag (EAFS) as alternatives to basalt aggregates in UTFC applications. The durability of skid-resistance and shear strength of these steel slag-UTFCs are investigated, and the chemical and mineral compositions of the steel slags are analyzed to assess their suitability. The findings reveal that EAFS-UTFC exhibits superior surface roughness, enhanced wear resistance, and comparable shear strength to Basalt-UTFC. The dynamic friction coefficient (μ) between EAF-UTFC and rubber at 120 km/h is 1.12 times higher than that of basalt at 0 wear cycles, and this advantage amplifies to 3.11 times higher after 400k wear cycles. However, BFS and BOFS are not suitable for direct use in UTFC, which have lower wear resistances and shear strengths compared to basalt, attributed to their poor bulk stability caused by high levels of free CaO and MgO. Consequently, a significant portion of their surface aggregates are dislodged under repeated wheel loading before sufficient polishing occurs. This study offers insights into sustainable solutions for improving skid-resistance on asphalt pavements.

Modification of High-Quality Porous Concrete Asphalt with Local Materials as an Alternative to Flexible Pavement

Environmental issues and a lack of attention to open space as rainwater catchment areas cause flooding problems in urban areas. Constructing environmentally friendly roads with permeable capabilities is one way to prevent waterlogging along the road in the rainy season. This study evaluated the type of porous asphalt concrete called Open Graded Friction Course specification Japanese standard. This study modified porous asphalt concrete using bamboo fiber and hydrated lime. Stability testing is conducted by the Marshall method, and the volumetric mixture is analyzed. Stability testing is carried out by the Marshall method and analysis of the volumetry of the mixture is carried out. The results showed that adding bamboo fiber and hydrated lime increased stability and maintained the porosity of the porous asphalt concrete.

Performance Evaluation on Open-Graded Friction Course Reinforced by Double-Adding Fibers Technology

The use of an open-graded friction course (OGFC) as a road surface demonstrates significant advantages in reducing driving noise and improving road drainage and safety. This study aims to enhance the overall performance of OGFC-13 by incorporating double-adding fiber technology. Laboratory tests were conducted on six OGFC-13 mixes modified with varying fiber ratios of lignin fibers (LFs) and glass fibers (GFs). Both GF and LF significantly improved high-temperature performance, with dynamic stability values increasing proportionally to GF content. The LF:GF = 0.15:0.15 ratio achieved peak shearing strength, demonstrating better improvement over single-fiber modification. Furthermore, both fibers effectively enhanced resistance to cracking, with GF-reinforced specimens excelling in bending stress and LF-reinforced specimens demonstrating the highest flexural strain. Water stability evaluations highlighted the substantial positive impact of LF and GF, with simultaneous addition resulting in superior moisture stability compared to single-fiber modifications. Anti-stripping performance assessments indicated that the LF:GF = 3:0 ratio exhibited the best performance. In fatigue performance, both LF and GF enhanced fatigue life, with GF outperforming LF. The LF:GF = 0.15:0.15 ratio achieved a balanced fatigue performance. Results from the radar evaluation method underscored a more comprehensive improvement in road performance achieved through double-adding technology. The LF:GF = 0.15:0.15 ratio emerged as the optimal choice for overall road performance.

The Consequences of Dimension Reduction for Open Graded Friction Course (OGFC) Asphalt Mixtures: Morphological Characteristics and Finite Element Model (FEM) Simulation

Asphalt mixtures exhibit complex mechanical behaviors due to their multiphase internal structures. To provide better characterizations of asphalt pavements under various forms of potential distress, a two-dimensional (2D) finite element simulation based on images of asphalt mixtures can be used to increase computational efficiency and reduce labor consumption. Nonetheless, using a representative image to eliminate the influence of dimension reduction from three dimensions to two dimensions is of great significance for attaining a reliable simulation result. Therefore, in this study, we investigated the consequence of dimension reduction for open-graded asphalt mixtures (denoted as OGFC-16), including a comprehensive characterization of these 2D models in terms of their morphologies and the similarities between them. This study aimed to reveal the variation in a 2D finite element simulation when applied to open-graded asphalt mixtures. Structural compositions, gradations, the aspect ratios of aggregates, and aggregate orientations were counted and calculated. In addition, the cosine similarity and structural similarity index measure (SSIM) were also calculated. Consequently, we performed a statistical analysis on the aforementioned indicators to quantitatively identify the discrepancy in the 2D images caused by dimension reduction. The results demonstrate that this 2D simulation might not be sufficient for representing the realistic mechanical performance of asphalt mixtures due to the remarkable variations in the image morphologies in different 2D images. However, the basic rules of stress behavior within structures can be accurately simulated. A compensative methodology for conducting a 2D simulation of open-graded asphalt mixtures should be based on a morphological characterization, considering structural compositions and the structural similarity index measure.

Investigation of energy-based interlayer debonding of open-graded friction course pavement under mode I fracture test

Layer bonding performance is essential for ensuring the longevity of open-graded friction course (OGFC) pavements. This study examined the interlayer bonding efficacy between OGFC and the underlying layer, considering variations in underlying layer types and the quantity of tack coat applied. To assess the bonding characteristics, three-point bending tests were performed at temperatures of 0 ℃ and 25 ℃. Parameters such as bonding stiffness, stress intensity factor, equivalent stress intensity factor, and energy parameters were determined to elucidate the fracture behavior between OGFC layers and their supporting layers. The total fracture energy (GF) was segmented into three components: plastic dissipation energy (Ud), elastic stored energy (Ue), and surface energy (Up), providing a comprehensive analysis of the energy dynamics during fracture. Results showed that at 0 ℃, the maximum bonding stiffnesses of OGFC-A and OGFC-B were obtained when the coat application contents were 1.0 kg/m2 and 0.5 kg/m2, respectively. With the increase of temperature, the bonding stiffness decreased significantly. At 0 ℃, the maximum value of KIC of OGFC-A was higher than that of OGFC-B by 7.1 %, which was attributed to the rougher surface of mixture A in terms of texture depth, average roughness and fractal dimension. At 0 ℃ and 25 ℃, the optimal tack coat application contents for fracture energy were 1.0 kg/m2 and 0.5 kg/m2 for OGFC-A and OGFC-B, respectively. At 0 ℃, the maximum value of GF of OGFC-B was higher than that of OGFC-A by 54.0 %; while at 25 ℃, the maximum value of GF of OGFC-B was lower than that of OGFC-A by 16.7 %. At both 0 ℃ and 25 ℃, the maximum values of Ud + Ue of OGFC-B were larger than that of OGFC-A, indicating that at both 0 ℃ and 25 ℃, the rougher interface of the underlying layer (mixture A) would not require more energy to initiate a crack. At 0 ℃, then energy required for crack propagation of OGFC-B was larger than that of OGFC-A; while at 25 ℃, opposite results were obtained, indicating a rougher interface (mixture A) helped delay the crack propagation. Temperature, underlying layer type, and tack coat affected the proportions of Ud, Ue and Up.