Four-point Bending Fatigue Tests Research Articles

Sustainable asphalt: self-healing and its impact on fatigue life and damage model

ABSTRACT Asphalt mixtures are frequently used for highway pavements, with fatigue damage occurring over time. Although numerous fatigue damage models have been proposed in academia, none account for the influence of asphalt mixtures’ self-healing characteristics on their fatigue processes. The present paper examines the self-healing effect of multi-factor asphalt mixtures on the fatigue process from a mechanical perspective. The original model is revised, and the influence of the correction coefficient is introduced, leading to the proposal of a fatigue model of asphalt mixtures that considers multi-factor self-healing effects. The model’s accuracy is verified through four-point bending fatigue tests on various grades of asphalt mixtures. The findings demonstrate that the self-healing properties of asphalt blends have a distinct positive impact on fatigue progression and endurance when considering temperature, strain strength, initial damage rate, and healing time. Furthermore, after experimental validation and model analysis, the adjusted model, which includes the self-healing effect, provides a more precise account of the fatigue life of asphalt blends. Furthermore, the experimental analysis yielded the performance characteristics of asphalt mixtures with varying coarse and fine aggregate gradations.

Investigation of Fatigue Life by Four Point Bending Test of Recycled Asphalt Pavements

The performance of added 50% reclaimed asphalt (RAP) mixtures was investigated by four-point bending fatigue tests (FPBT). Mixtures with 50% RAP were modified with SBS polymer, diatomite (D) and hydrated lime (HL). Ten specimens were produced and fatigue of specimens was evaluated with FPBT. Some samples give the fatigue breaking cycle compatible with each other. In some samples, the number of cycles is much higher than the average breaking load. Some samples may deteriorate in a short time before the end of test. Although the briquettes are mixed homogeneously for longer mixing times and produced with great care, inconsistent results can be obtained. If water damage is applied to briquettes due to the presence of HL, more compatible results can be obtained. The use of SBS-HL and rejuvenating oil at high RAP ratios will provide more compatible results. As a result of 50% stiffness reduction, the difference in the remaining stiffness values is usually 2-3 times, while there are huge differences between the cycle numbers that cause this. In terms of sustainable and long-term performance, the homogeneity of the pavement composition appears to be essential, having a much more pronounced effect than the number of loadings.

Fatigue life analysis based on the groove angle reduction in the butt welding of excavator booms

This study analyzes the effect of changes in groove angle on the fatigue strength of the V-groove butt weld joint made of SM490A steel used in excavators. Butt-type specimens with different groove angles of 40° and 30° were manufactured by CO2 welding at a speed of 300 mm/min on a 13.5 mm thick steel plate. Four-point bending fatigue tests were conducted at room temperature with a frequency of 5 Hz and stress ratio of R = 0.1, and fatigue limits were set to 2 × 106 cycles. The high-cycle fatigue life of VG40 was approximately 7% higher than that of VG30. The stress concentration coefficient calculated using the effective notch stress method was 1.62 for the VG40, and 1.78 for the VG30, with an approximate difference of 9%. This decrease in fatigue life was caused by stress concentration due to the notch effect at the weld root, which was attributed to the adjacent backplate. Although the fatigue life decreased slightly owing to the improvement angle of the welded part, no difference was observed in microstructure and hardness. Therefore, it was confirmed that a sound weld was formed. The results of this study can be used as important basic data for determining the V-groove angle.

Infrared imaging surface roughness criticality assessment of Wire Arc Additive Manufactured specimens

Infrared imaging surface roughness criticality assessment of Wire Arc Additive Manufactured specimens

Characterizing fatigue damage evolution in asphalt mixtures using acoustic emission and Gaussian mixture model analysis

The identification and investigation of fatigue crack evolution and damage modes in asphalt mixtures are crucial for understanding the corresponding mechanisms and characteristics of fatigue failure. In this study, the four-point bending fatigue tests were performed on the asphalt mixture specimens with precast joints using the acoustic emission (AE) technique to analyze the damage evolution. The failure modes of the asphalt mixtures were identified using the Gaussian mixture model (GMM). The results revealed that the fatigue damage of the asphalt mixtures can be categorized into four stages: Stage I (void compaction), Stage II (microcrack initiation and stable propagation), Stage III (crack aggregation and unstable propagation), and Stage IV (complete fracture). This division was defined based on the inflection points of the axial displacement curves, the cumulative number of AE events, and the cumulative ringing counts. The evolution of the AE b value was found to be correlated with the crack propagation. The rapid decline in the b value in Stage III was considered a harbinger of the eventual complete fracture in the asphalt mixtures. The GMM clustering analysis indicated that the fatigue damage of the asphalt mixtures primarily involved tensile damage (90%), and shear damage made a small contribution of 10%. Existing AE studies have focused on the quantitative evaluation of AE parameters, while research on clustering identification algorithms for these parameters is scarce. The analytical methods and findings of this study enable an effective identification of fatigue damage in asphalt mixtures at the laboratory scale and offer insights into the fatigue damage mechanisms of asphalt mixtures.

Investigation on fracture and fatigue performance of cold recycling emulsified asphalt mixture based on acoustic emission parameters

Cold recycling technique of asphalt reduces the demand for building materials, saves resources and costs, and meets the requirements of low-carbon and high-quality development. The purpose of this study is to improve the fracture and fatigue performance of cold recycling emulsified asphalt mixture. In this paper, cold recycling ordinary, basalt fiber (BF) emulsified asphalt mixture and cold recycling styrene butadiene rubber (SBR) modified emulsified asphalt mixture were taken as the research objects. Four-point bending strength and fatigue tests of specimens with and without prefabricated cracks were carried out respectively, and acoustic emission (AE) was used for real-time monitoring during these tests. The fracture mechanics method was used to study the fracture strength of cold recycling ordinary, BF and SBR modified emulsified asphalt mixtures. The phenomenological theory and energy analysis method were adopted to research their fatigue performance. The characterization parameter analysis method was employed to analyze the AE parameters. Furthermore, the effect of BF and SBR on the performance of the mixture was compared and analyzed. The test results show a significant improvement in the fracture energy and stress intensity factor of cold recycling BF and SBR modified emulsified asphalt mixtures, indicating that both BF and SBR can reduce the cracking risk of cold recycling emulsified asphalt mixture, of which BF is more effective compared with SBR. The dynamic modulus and cumulative dissipation energy attenuation law of cold recycling emulsified asphalt mixture during the fatigue process were revealed. Based on AE technique, a nondestructive test method for the fatigue damage of cold recycling emulsified asphalt mixture was established. This study expands the application scope of cold recycling emulsified asphalt mixture, which has good energy-saving, economic and environmentally friendly benefits.

Tensile Fatigue Properties of Ordinary Plain Concrete and Reinforced Concrete under Flexural Loading.

Many bridge structural components are subjected to repetitive vehicle load and temperature gradient action. The resulting cyclic tensile stresses within the structures could cause premature fatigue failure of concrete, dramatically impairing structural components' durability and sustainability. Although substantial knowledge of fatigue properties on low-strength pavement concrete and high-strength structural concrete has been obtained, research on the most widely used normal-grade ordinary concrete in bridge engineering is still ongoing. Therefore, a four-point bending fatigue test of 97 C50 concrete specimens under a constant amplitude sinusoidal wave was conducted in the laboratory, the flexural fatigue behavior of plain and reinforced concrete specimens was studied, and the cyclic deformation evolution of concrete under fatigue loading was obtained. The empirical fatigue S-N equations of concrete with a failure probability p of 0.1~0.5 were derived through statistical analysis of the test results. The fatigue life of the tested specimens exhibited a two-parameter Weibull distribution. In addition to the maximum stress level Smax, the stress ratio R is also a key factor affecting the flexural fatigue life of concrete N. The semi-logarithmic and logarithmic equations were almost identical at the tested stress levels, the latter predicting longer fatigue life for Smax < 0.70. The restraining effect from steel reinforcement slightly lengthened the concrete's fatigue cracking initiation life. The insight into concrete flexural fatigue properties from this study not only contributes to a better understanding of structural concrete, but also provides a basis for the practical evaluation of concrete or composite bridge decks.

Evaluating the use of different fillers and Kaowax additive in warm mix asphalt mixtures

The existing concerns about the global warming have prompted many researchers to study the warm mix asphalt (WMA) mixtures. Although WMA enjoys several advantages over the hot mix asphalt (HMA), it suffers from certain flaws such as moisture susceptibility and low temperature cracking. Therefore, it is important to enhance the performance of WMA, and one way of doing it is to use suitable fillers in the asphalt mixtures. The study aim is to evaluate the impact of the Portland cement type-II, fly ash, and the calcium carbonate as filler, on the WMA performance that made with Kaowax additive. We performed the semi-circular bending (SCB) test at low temperature, the four-point bending fatigue test, the indirect tensile strength (ITS), resilient modulus tests at medium temperature, and the dynamic creep test at high temperature. According to the obtained results, the presence of Kaowax increased resilient modulus and the rutting strength of the asphalt mix. The WMA samples containing the fly ash filler had good moisture susceptibility. The use of cement filler in the WMA resulted in improved rutting resistance. The calcium carbonate filler increased the performance of the WMA mixtures at all temperatures.

The Properties of Modified Bagasse Fiber/Nano-TiO2 Composite Asphalt in a High-Temperature and High-Humidity Salt Environment.

The southern tropical coastal areas of China are high-temperature and high-humidity salt environments, which hinder the durability and service life of ordinary asphalt pavement. To enhance the durability of asphalt pavement in these areas, modified bagasse fiber combined with nano-TiO2 was used to improve the corrosion resistance of asphalt pavement in high-temperature and high-humidity salt environments. The micro-morphology, high-temperature oil absorption, high-temperature heat resistance, and hygroscopicity of bagasse fiber modified using three silane coupling agents combined with NaOH were compared, and the best silane coupling agent/NaOH modification scheme for bagasse fiber was found. Based on conventional physical tests (penetration, softening point, ductility), rheological property tests (rotational viscosity, dynamic shear rheological test, multi-stress creep recovery test, linear amplitude scanning test), and a four-point bending fatigue test of the asphalt mixture, the properties of modified bagasse fiber asphalt binder and mixture after cyclic dry-wet erosion under pure water and salt solution (NaCl, Na2SO4) were determined, and the effects of the erosion environment and fiber ratio on the basic physical and rheological properties of the asphalt were clarified. Compared with the silane coupling agents KH550 and KH590, the bagasse fiber modified with KH570/NaOH had a better high-temperature oil absorption capacity, heat stability capacity, and matrix asphalt compatibility. The worst erosion environment was Na2SO4, but the increase in test temperature and fiber content weakened the sensitivity of the asphalt binder performance in different erosion environments. The erosion capacity order was as follows: Na2SO4 > NaCl > pure water. In the worst erosion environment, 0.5% modified bagasse fiber/Nano-TiO2 asphalt binder (Bn-570-0.5) had the best corrosion resistance in a high-temperature and high-humidity salt environment. The penetration, softening point, creep recovery rate R3.2, non-recoverable creep compliance Jnr3.2, and fatigue life after long-term aging (with 5% strain) of Bn-570-0.5 were, respectively, increased by -16.9%, 37.5%, 37.95%, -27.86%, and 38.30% compared with unblended base asphalt binder (B). In addition, the four-point flexural fatigue life of Bn-570-0.5 was 169.2% higher than that of the unblended base mixture.

Experimental study of epoxy asphalt binder and porous epoxy asphalt concrete

Epoxy asphalt binder offers a promising solution for road material due to its low environmental impact and potential to reduce carbon emissions. In this paper, hot-mix epoxy asphalt binder (HEAB) and warm-mix epoxy asphalt binder (WEAB) were prepared firstly. The curing conditions of the binders were determined through viscosity and tensile tests, and their low-temperature properties were evaluated through bend creep stiffness tests. Furthermore, hot-mix porous epoxy asphalt concrete (HPEC) was designed with target void ratios ranging from 16% to 24%. Control groups included warm-mix porous epoxy asphalt concrete (WPEC) and high-viscosity modified porous asphalt concrete (HPAC) with a 20% target void ratio. The road performance of these various porous asphalt concrete was evaluated through multiple tests, including wheel tracking, low-temperature beam bending, dynamic modulus, four-point bending fatigue, freeze-thaw splitting, and Cantabro loss tests. The results indicate that HEAB follows a two-stage curing method of “160 °C, 2 h + 60 °C, 4 d”, while WEAB adopts a one-stage curing method of “120 °C, 5 h”, both of which demonstrate favorable properties. Moreover, HEAB exhibits better low-temperature properties compared to WEAB. The study also found that increasing the void ratio can reduce the high-temperature performance, freeze-thaw resistance, hydrothermal resistance, and dynamic modulus of HPEC. The low-temperature performance of HPEC reaches an inflection point at a target void ratio of 20%. Under the same target void ratio, HPEC exhibits the best high-temperature performance, dynamic modulus, fatigue resistance, freeze-thaw resistance, and hydrothermal resistance, followed by WPEC and HPAC. However, the low-temperature performance of both the HPEC and WPEC is lower than that of the HPAC. Overall, the use of epoxy asphalt binder in the preparation of porous asphalt concretes shows great potential for enhancing road performance.

Study on fatigue damage evolution and model prediction of asphalt pavement in the end-stage of service

Through the use of the material test system (MTS), bending fatigue tests are conducted in this work in order to investigate the attenuation law of fatigue performance of asphalt pavement in the end-stage of service. Response surface methodology (RSM) is used to analyze the effects of strain, frequency, and temperature on the asphalt surface layer's initial stiffness, fatigue life, phase angle, and cumulative dissipated energy when there is a 50 % reduction in the initial stiffness. Through multi-factor coupling analysis, the optimal combination is found and verified by the MTS-810 test system. Based on this, the data of the initial stiffness declining to 20 % was used for analysis on the AC-13C asphalt surface mixture of the APT full-size test road in the laboratory. At 15 °C and 10 Hz, the evolution law of the flexural stiffness, the residual stiffness, phase angle, and cumulative dissipated energy of the asphalt mixture was investigated. Analysis of the asphalt mixture's damage evolution under the single stage of loading and various strain levels revealed changes in the fatigue cracking crack. Beam specimens were made from asphalt mixture field test beams of AC-13C (laboratory accelerated pavement test road), AC-20C, and AC-25C (Ji-Qing expressway) to conduct four-point bending fatigue test (4PB). According to the constant strain fatigue prediction equation, and the residual fatigue life of prediction localized model was established. The results show that the influence of frequency and temperature on the initial stiffness and phase angle is more significant than strain, and the influence of strain on number of fatigue is more significant. The flexural stiffness of the asphalt mixture shows an obvious S-curve, and larger the tensile strain at the bottom of the asphalt layer, shorter the time needed to reach the termination condition, that is, the faster the fatigue failure occurs. When the damage termination condition is reached, under the strain level of 200–300 με, 60 % of the number of loading produce about 35–40 % damage, and the remaining 20 % of the number of loading lead to 10–20 % damage.

Mechanical damage characteristics of CR/PPA composite modified asphalt pavement under multi-factor coupling effect in the seasonally frozen region

Asphalt pavements are inevitably affected by coupled effects of dry-wet/freeze-thaw cycles, UV radiation, temperature, and loading during service, resulting in degradation of their road performance and reduced service life. Therefore, this study used crumb rubber (CR) and polyphosphoric acid (PPA) as modifiers to prepare CR/PPA composite modified asphalt mixtures for testing. To investigate the mechanical properties of the composite modified asphalt mixtures under the action of multi-factor coupling. Meanwhile, the performance analysis of matrix asphalt and SBS modified asphalt mixtures were carried out as a comparison. Density and water penetration tests, splitting tests, beam bending tests, and four-point bending fatigue tests reveal the evolution of asphalt mixture road performance. Finally, regression fitting was performed on the test data to establish the mechanical damage model of each type of asphalt mixture. The results show that with the increase of wet-dry/freeze-thaw cycles and the increase of UV radiation time, the void ratio and water permeability coefficient increase and the splitting strength, bending and tensile strain, and fatigue life decrease for all types of asphalt mixtures. When the number of wet-dry/freeze-thaw cycles reached 8, the mechanical properties of the asphalt mixture decreased significantly, while the changes leveled off after the number of cycles reached 15. When the UV radiation time is less than 4 months, the mechanical properties of the asphalt mixture decay more slowly. However, with a further increase in radiation time, the mechanical properties decay rapidly. The water-saturated specimens have a more significant effect on the mechanical damage of each type of asphalt mixture. Compared with the other two mixtures, the composite modified asphalt mixtures have superior mechanical properties and fatigue life. The mixture performance damage model based on the least squares Levenberg-Marquardt method (L-M method) was able to simulate the experimental data well, with a minimum correlation coefficient R2 of 0.9285. In summary, the road performance of all types of asphalt mixtures under the coupling of multiple factors has deteriorated, while the composite modified asphalt mixtures have better anti-damage characteristics, with good prospects for promotion.

レーザピーニングが浸炭鋼の表面特性および曲げ疲労特性に及ぼす影響

To investigate the effects of laser peening (LP) on the surface and bending fatigue properties of carburized steel (JIS SCM420), surface roughness measurements, residual stress measurements, retained austenite measurements, and four-point bending fatigue tests were conducted. After LP, the compressive residual stress was introduced on the surface, with the effect extending to a depth of more than 1 mm. Due to the high compressive stress, the bending fatigue strength of LP specimen was 1.46 times higher than that of the as-heat-treated specimen even though the surface roughness was increased by LP. Notably, the amount of retained austenite was 10.9％ at the top surface of LP specimen, and high-density twins were observed in the lath martensite structure. This can be attributed to high strain rate deformation by LP.

The Effect of Microwave Radiation on the Self-Healing Performance of Asphalt Mixtures with Steel Slag Aggregates and Steel Fibers.

Self-healing in asphalt mixtures is a property that can be enhanced by external heating, which causes a thermal expansion that increases the flow of bitumen with reduced viscosity through the cracks. Therefore, this study aims to evaluate the effects of microwave heating on the self-healing performance of three asphalt mixtures: (1) conventional, (2) with steel wool fibers (SWF), and (3) with steel slag aggregates (SSA) and SWF. After evaluating the microwave heating capacity of the three asphalt mixtures with a thermographic camera, their self-healing performance was determined with fracture or fatigue tests and microwave heating recovery cycles. The results demonstrated that the mixtures with SSA and SWF promoted higher heating temperatures and presented the best self-healing capacity during the semicircular bending test and heating cycles, with significant strength recovery after a total fracture. In contrast, the mixtures without SSA presented inferior fracture results. Both the conventional mixture and that containing SSA and SWF presented high healing indexes after the four-point bending fatigue test and heating cycles, with a fatigue life recovery of around 150% after applying two healing cycles. Therefore, the conclusion is that SSA greatly influences the self-healing performance of asphalt mixtures after microwave radiation heating.

Multiscale Fatigue Performance Evaluation of Hydrated Lime and Basalt Fiber Modified Asphalt Mixture.

Long-life pavement construction is an important research direction for sustainable road development. Fatigue cracking of aging asphalt pavement is one of the main reasons that affects its service life, and improving the fatigue resistance of aging asphalt pavement has become a key factor in promoting the development of long-life pavement. In order to enhance the fatigue resistance of aging asphalt pavement, hydrated lime and basalt fiber were selected to prepare a modified asphalt mixture. The resistance to fatigue is evaluated by the four-point bending fatigue test and self-healing compensation test, based on the energy method, the phenomenon-based approach, and other methods. The results of each method of evaluation were also compared and analyzed. The results indicate that the incorporation of hydrated lime can improve the adhesion of the asphalt binder, while the incorporation of basalt fiber can stabilize the internal structure. When incorporated alone, basalt fiber has no noticeable effect, while hydrated lime significantly improves the fatigue performance of the mixture after thermal aging. Mixing both ingredients produced the best improvement effect under various conditions, with a fatigue life improvement of 53%. In the multi-scale evaluation of fatigue performance, it was found that the initial stiffness modulus was unsuitable as a direct evaluation index of fatigue performance. Using the fatigue damage rate or the stable value of dissipated energy change rate as an evaluation index can clearly characterize the fatigue performance of the mixture before and after aging. The self-healing rate and self-healing decay index clearly reflected the fatigue damage healing process under repeated loading and could be used as relevant indices for evaluating the new-scale fatigue performance of asphalt mixtures.

Investigation of the Effect of Combined Nanosilica and Iranian Natural Binder on the Rheological Behavior of Mastics and Performance of Asphalt Mixtures

The aim of this study was to evaluate the impact of nanosilica (NS) and gilsonite on the behavior of asphalt binders and stone matrix asphalt (SMA) samples. An asphalt binder with 60/70 penetration grade, 0%, 3%, 5%, and 7% gilsonite, and 0%, 2%, 4%, and 6% NS by the weight of the asphalt binder were used. The rotational viscosity (RV), linear amplitude sweep (LAS), bending beam rheometer (BBR), multiple stress creep recovery (MSCR), and dynamic shear rheometer (DSR) tests were applied to evaluate the physical and rheological behaviors of modified asphalt binders. Also, the wheel track, dynamic creep, indirect tensile strength (ITS), resilient modulus (Mr), and four-point bending (FPB) fatigue tests were utilized to examine the performance characteristics of mixtures. Moreover, a two-factor analysis of variance (ANOVA) was used to analyze the data. The rheological test results showed that gilsonite and NS enhanced the rutting and fatigue resistances of asphalt binders. Gilsonite also reduced the low-temperature resistance of asphalt binders, while NS improved that. The storage stability test showed that gilsonite enhanced the storage stability of asphalt binders. Also, adding NS led to an improvement in phase separation. MSCR test indicated an improvement in the high-temperature performance of base asphalt binder at different stress levels by the addition of gilsonite and NS. Based on the LAS test, gilsonite and NS enhanced the fatigue characteristics of asphalt binders. The sample test results also showed that gilsonite and NS improved the permanent deformation resistance, MR, ITS, fracture energy, and intermediate-temperature properties of samples.

An improved regression model to predict fatigue life of asphalt mixes incorporating low to moderate RAP contents

The research on the fatigue performance of recycled asphalt mixture and the establishment of its fatigue life prediction model is the key to its large-scale engineering application. The four-point bending fatigue tests of the fresh and recycled asphalt mixtures under the strain control of cyclic loading were conducted to investigate influencing factors on their fatigue performance and establish a new fatigue prediction model for RAP (recycled asphalt pavement). The hot recycled asphalt mixture samples of AC-16C were prepared by a uniform test design method, with the RAP content of 0%, 20%, 30%, and 40%. Through the fatigue test data of 20 groups of fresh asphalt mixture with 0% RAP and 40 groups of recycled asphalt mixtures with the contents of 20%, 30%, and 40% RAP, the simplified applicability of the fatigue prediction model in the current Chinese specifications for the design of highway asphalt pavement (JTG D50-2017, JTG model) and its parameters modification were studied, thereby an improved regression fatigue prediction model of recycled asphalt mixture is established on consideration of strain level, asphalt content, void ratio, and RAP mixing amount. This fatigue prediction model for recycled asphalt mixtures was proposed by modifying the parameters of the fatigue equation for new asphalt mixtures in the Chinese Highway Asphalt Pavement Design Code. (JTG D50-2017) and comparing the fatigue test data of the recycled asphalt mixture. The research results show that: The simplified JTG fatigue prediction model can effectively predict the fatigue life of fresh asphalt mixture with the content of 0% RAP, and the model parameter a is a constant of the order of 1016; The correction coefficients α and β of the initial bending stiffness modulus S0 and the Voids Filled with Asphalt (VFA) in the improved JTG model of the hot recycled asphalt mixture considering the RAP content are 0.006 and 0.0136, respectively; The model can accurately predict the fatigue life of recycled asphalt mixtures with the range of RAP content of 0–40%, with an average deviation of only 0.106, and has higher prediction accuracy for fatigue life measured close to or higher than 106 times. The average deviation of the predicted life of 20%, 30%, and 40 %RAP fatigue is only 0.057, 0.079, and 0.125. This paper’s indoor fatigue prediction model has higher accuracy for recycled asphalt mixture than the well-known traditional models.

Experimental study on the fatigue performance of emulsified asphalt cold recycled mixtures

With advantages such as energy saving, environmentally friendliness, green, low carbon emission, and high economic efficiency, emulsified asphalt cold recycled mixtures (CRM) have been used increasingly extensively, and their range of application has also extended from the base layer to the lower surface layer. Thus, studying their fatigue performance is particularly important. The inevitable secondary compaction in the construction process significantly affects the fatigue performance of emulsified asphalt CRM. However, relevant studies concerning the effect of secondary compaction on the fatigue performance of emulsified asphalt CRM are still lacking, and the conclusions of existing studies investigating the effect of emulsified asphalt CRM composition on its fatigue performance are inconsistent. In this study, the effect of emulsified asphalt content, cement type, cement content, and reclaimed asphalt pavement (RAP) content on fatigue performance was investigated through controlled strain four-point bending fatigue tests, and the effect of secondary compaction on the fatigue performance of CRM was comparatively studied by simulating the secondary compaction with indoor wheel rolling tests. The results showed that the fatigue performance of CRM increased significantly with the increase of emulsified asphalt content. With the increase of ordinary Portland cement content, the fatigue performance improved and then degraded. The fatigue performance peaked at the cement content of 1.5% and then decreased sharply. Mixing with high early-strength cement resulted in little improvement in fatigue performance but reduced it at the content of 3%. The fatigue performance increased with the increase of RAP content. Secondary compaction substantially improved the fatigue performance of CRM, and the fatigue performance was underestimated by the existing evaluation methods. This study could provide guidance and reference for the composition design of CRM and the objective evaluation of its fatigue performance.

Study of Fatigue-Damage Characteristics of Recycled Asphalt Mixture

To investigate the influence of methyl styrene block copolymers (SMC) modifier on the fatigue performance and damage evolution of recycled asphalt mixture (RAM), RAM with reclaimed asphalt pavement (RAP) ratios of 30%, 50%, and 70% and 90# asphalt mixture were used for four-point bending fatigue test. The fatigue performance and damage evolution process of RAM were analyzed using the stiffness attenuation rate and the relative change rate of dissipated energy (RDEC). Linear amplitude sweep (LAS) tests and atomic force microscopy (AFM) tests were carried out for mixed asphalt in the mixture. The results show that under the same test conditions, with the increase of RAP content, the damage development of RAM is faster, and the fatigue damage resistance is worse. Compared with 90# asphalt mixture, RAM has better fatigue resistance. The fatigue property of the mixed asphalt is better than that of the 90# asphalt. With different RAP contents, the modulus changes of RAM and mixed asphalt are almost the same on macro and micro scales, which proves that the difference of fatigue performance between 90# asphalt mixture and RAM probably is caused by asphalt. A fatigue failure criterion based on the peak dissipation energy is proposed for the LAS test, and the applicability and accuracy of the criterion were proved by grey correlation analysis. Under this criterion, the power function model is introduced to describe the development process of fatigue damage in LAS test, which has high fitting reliability.

Asphalt Mixtures Fatigue Life Considering Various Environmental Impacts.

The pavement structure during the colder seasons (winter) or in regions located above sea level is commonly affected and deteriorated by many environmental factors. Two prominent factors are water and frost (weather) or road salt (maintenance). According to the article's literature review, there are only a few studies related to water and frost or road salt impact on mineral asphalt mixes considering fatigue. Most of the tests were performed on mixes containing common road asphalt or only one binder content level was investigated. There are no articles that investigate this problem comprehensively including new asphalt, its content levels, or production technology. Based on the literature review, the main problem regarding degradation impact on mixtures fatigue life was stated. The investigation was performed using two proprietary experimental methods allowing approximates in situ conditions regarding environmental impacts. A dynamic four-point bending fatigue test was applied to evaluate degradation considering fatigue. The investigation was performed using four coarse-graded asphalt mixtures (asphalt concrete AC 22) which differed in binder type (35/50 WMA, 35/50, 25/55-60, and 25/55-80 HIMA), content level (4.24%, 4.03%, 3.82%), and production technology (hot and warm). Regarding the results obtained, the authors proposed a degradation ratio regarding fatigue life variability. Based on the obtained results and ratio used, it was found that both interactions caused a significant fatigue life decrease-in the worst case, over tens of percent. Furthermore, it was found that asphalt mixture resistance to environmental factors depends on binder type, its content level, air void content, and discussed impact. Moreover, asphalt mixtures' susceptibility to degradation (fatigue) is extreme at lower binder content levels and accelerates due to air void content increase. In the article, it was also stated that the highest resistance was reached by a mixture with highly modified asphalt (25/55-80 HIMA). It was also found that the SBS polymer dosage increase in the asphalt matrix enhances asphalt mixture resistance to environmental impacts. The least resistant to the environmental degradation mixture was WMA (35/50 WMA).