Fatigue Life Of Asphalt Mixtures Research Articles

A new fatigue equation for asphalt mixtures considering loading sequence effects

The fatigue life of asphalt mixture has been found to significantly depend on loading sequences. However, the widely used traditional linear fatigue equations are difficult to determine the fatigue life of asphalt mixture subjected to different loading sequences. This study aims to improve these fatigue equations by establishing a fatigue equation considering loading sequence effects. First, the semi-circular bending (SCB) constant amplitude fatigue tests were conducted under the high loading amplitude (σhigh) and low (σlow) loading amplitude, respectively. Then, two of the loading sequences, namely the low-high stress (σlow-σhigh) and high-low stress (σhigh-σlow), were selected to carry out the SCB variable amplitude fatigue tests. Furthermore, the loading sequence effects on the life fractions and fatigue life of asphalt mixtures were analyzed. Finally, the damage equivalent criterion was successfully applied to establish the nonlinear fatigue damage accumulation model and fatigue equation considering loading sequence effects. It was found that the cumulative life fractions of asphalt mixtures under constant amplitude loading are equal to 1, indicating the linear fatigue damage accumulation. The cumulative life fractions corresponding to the σlow-σhigh and σhigh-σlow are greater than 1 and less than 1, respectively, indicating the nonlinear fatigue damage accumulation. The established nonlinear fatigue damage accumulation model can accurately characterize the dependence of fatigue damage accumulation on loading sequences. The established fatigue equations can improve the traditional linear fatigue equations to some extent and accurately predict the fatigue life of asphalt mixtures corresponding to the loading sequences of the σlow-σhigh and σhigh-σlow.

Evaluation of moisture‐induced damage on the fatigue life of asphalt mixtures using failure tests of asphalt binders, interfaces, and mixtures

AbstractFatigue cracking, a major distress in asphalt pavements, is worsened by traffic and climate conditions such as moisture effects on constituents and interfacial properties. However, investigation on fatigue's evolution in different scales under moisture effect is still scarce in the open literature. This work aims to assess moisture‐induced damage effects on asphaltic materials focusing on the failure of asphalt binders, the aggregate‐binder interface, and mixture. The methodology included tests under dry and wet conditions: linear amplitude sweep (LAS); asphalt bond strength (ABS) in different temperatures and pull rates for interfaces; indirect tensile strength (ITS), and tension‐compression fatigue on asphalt mixtures. Key findings were: (i) moisture damage presents growing effects from binders to mixtures; (ii) LAS test results were not sensitive to moisture; (iii) ABS tests require proper field temperatures for accuracy; (iv) ITS ratio provide reliable conditioned fatigue expectations; and (v) fatigue testing without conditioning to hydrodynamic effects or real moisture susceptibility might overestimate service‐life.

PINN-AFP: A novel C-S curve estimation method for asphalt mixtures fatigue prediction based on physics-informed neural network

The accurate prediction of fatigue life of asphalt mixture is the key to the design of long-lasting durable pavement. Currently, a critical aspect influencing the accuracy of life prediction methods for asphalt mixtures, based on Viscoelastic Continuum Damage Mechanics (VECD), is the precision of the damage characteristic (C-S) curve. Within the VECD framework, the C-S curve of asphalt mixture is regarded as an intrinsic material property. However, it has been observed in engineering applications that the C-S curve of the material exhibits notable sensitivity to varying loading conditions. The nonlinear fitting method based on a small number of experiments is difficult to fully characterize the fatigue performance of the material, while a large number of complete material fatigue tests are expensive in time and money. Based on the above problems, a physics-informed neural network embedded in VECD, PINN-AFP, is proposed. It can accurately predict the complete material C-S curve based on a small amount of pre-fatigue data of the material, thus achieving accurate prediction of the fatigue life of asphalt mixture. The case study uses the fatigue test data of AC-25 as an example, and the results demonstrate that the proposed PINN-AFP has strong generalization ability and prediction accuracy, achieving the state-of-the-art in the mainstream machine learning and deep learning methods with an average 5.2% fatigue life prediction error.

Predicting asphalt mixture fatigue life via four-point bending tests based on viscoelastic continuum damage mechanics

A more technically accurate approach to predict fatigue life of asphalt mixtures can enhance the precision of performance evaluation for asphalt pavements. This study applied the viscoelastic continuum damage mechanics (VECD) to investigate the fatigue behavior of asphalt mixtures. The fatigue life of typical asphalt mixtures was evaluated through four-point bending tests under various conditions. The strain-modulus empirical equation was firstly employed to fit the experimental data. However, it was noted that this equation was not entirely suitable for all conditions, as factors like temperature and loading frequency can influence fatigue life not only through the dynamic modulus but also via the damage properties of asphalt mixtures. To address this limitation and achieve a comprehensive fatigue life prediction equation, the Time-Strain Superstition Principle (TSSP) and Frequency-Strain Superstition Principle (FSSP) were introduced to characterize the impact of temperature and loading frequency on fatigue life, which can reduce fitting errors. Additionally, a mechanical prediction equation was also derived by the VECD approach, and its applicability under different conditions was explored. The results revealed that the damage characteristic curve (C-S curve) remained unaffected by loading frequency and strain level but was highly dependent on temperature. Significant fitting errors were observed in different temperatures when employing the VECD method for fatigue life prediction, as the VECD method did not account for the influence of temperature on the viscoelastic properties of asphalt mixtures, which in fact plays a critical role in fatigue life. In response, temperature adjustment coefficients were introduced into the derived equation. The predicted results demonstrated that the newly modified method significantly improved prediction precision, yielding an error of less than 20%.

Investigation of the Fatigue Performance of Sustainable Asphalt Pavement

Selecting suitable materials for sustainable asphalt pavement construction can be a challenging task, particularly due to the significant issue of fatigue damage in flexible pavement. The fatigue performance of gap-graded asphalt mixes (GGCP) was assessed through four-point bending beam fatigue testing, examining the impact of incorporating 6% Calcium carbonate (CaCO3) and 2% treated palm oil fuel ash (TPOFA) on fatigue cracking. The testing was conducted at various stress levels (800, 1000, and 1200 kPa) and a temperature of 5°C. Additionally, the asphalt mixtures underwent acceleration ageing and moisture conditions, which varied during the study. The experimental findings indicated that higher stress levels resulted in a decrease in the fatigue life of asphalt mixtures due to ageing effects. Moreover, moisture conditioning was found to diminish the fatigue life of the asphalt mixture. Comparatively, the fatigue model incorporating a plateau value and fatigue life demonstrated greater accuracy when compared to previous regression models.

Summarizing the Effect of Mixture Variables and Test Parameters on Fatigue Performance of Asphalt Mixtures

Abstract Fatigue cracking performance of asphalt mixtures is significantly affected by mixture variables and environmental and loading conditions in the field. Thus, there is a need to understand the effect of critical factors on the fatigue cracking resistance of asphalt mixtures through an extensive study. For this purpose, the present research is focused on characterizing fatigue cracking resistance of asphalt mixtures by considering different factors such as aggregate gradations (two dense and two gap gradations), binder types (two unmodified and three modified binder types), binder content (optimum binder content and optimum binder content ±0.5 %), test temperatures (15°C, 25°C, and 35°C), and three stress levels for different asphalt layer thicknesses (40, 80, 120, 160, 200, and 240 mm). An indirect tensile fatigue test was performed to characterize fatigue cracking resistance of asphalt mixtures, and a Kaplan–Meier survival analysis was carried out to examine whether the factors that were considered significantly affected the fatigue performance. Pavement sections with varying thicknesses of asphalt layers were analyzed using IITPAVE, a pavement analysis software, to compare the mixtures’ fatigue performance. All of the variables taken into consideration in this study were shown to have a statistically significant effect (p value < 0.05). However, the binder type had a stronger influence than the other variables on the resistance to fatigue cracking. Finally, a fatigue life equation (adjusted R2 = 0.77) was developed considering all the mixture combinations, which can be used for determining the laboratory fatigue life of asphalt mixtures.

Performance of hot-mix asphalt using polymer-modified bitumen and marble dust as a filler

Marble dust waste powder generated by the marble cutting industry has a high alkalinity. In this research, the use of marble dust (MD) as a mineral filler substitute in hot mixed asphalt (HMA) was evaluated. The Marshall mix design was used to determine the optimum bitumen content (OBC) for all of the mixtures. For each of the four MD contents, i.e., 0, 2%, 4%, and 6% by weight of the total aggregates, four different bitumen percentages were used. The results of the Marshall stability test showed that the optimum filler content was 4% MD. Samples were prepared with 0 MD in the control mix and varying percentages of MD as an alternate filler. In addition, MD aided in increasing the Marshall stability, rutting resistance, and permanent deformation and reduced the fatigue life of asphalt mixtures. As the percentage of MD increases, the rutting resistance and stiffness at high temperatures both increase. As the percentage of MD increases, the fatigue life reduces. Rut resistance in high-temperature conditions can be improved by using MD in HMA as a partial substitute for stone dust (SD). In areas where extensive MD waste is present, MD can be incorporated into HMA mixtures instead of conventional fillers.

Evaluating fatigue performance of Bailey asphalt mixtures containing natural river sand at varied strain and air void levels

This study aims to investigate the efficiency of Bailey method of optimizing the fatigue life of asphalt mixtures when natural sand is included in the mix at two coarseness levels of aggregate gradations: Fine-graded (FG) and coarse-graded (CG). Three mixes which varied with the percentage of the natural river sand were prepared at each coarseness level, namely: Coarse-graded with quarry sand only (CG-QS), coarse-graded with natural sands only (CG-NS), coarse-graded with quarry and natural sands (CG-QNS), fine-graded with quarry sand only (FG-QS), fine-graded with natural sands only (FG-NS), and fine-graded with quarry and natural sands (FG-QNS). The portions of the natural sand either in CG-QNS and FG-QNS mixes were minimized as possible without violating the Bailey ratios. The beam fatigue (BF) test was used to evaluate the performance of each mixture at strain levels of 800, 1000, and 1200 microstrain. Also, to further investigate the air voids influence on the performance of the asphalt mixes, each mix was prepared at two air void levels: 7 and 4%. The sensitivities of the volumetric measures with the number of cycles to failure (N f) were evaluated. The study’s findings indicate that N f was generally decreasing with the increase of the natural sand in the mix at any strain level. Also, the 7% air voids mixes provided a lower N f when compared to the 4% air voids mixes. The dust proportion (DP) was the most significant volumetric. The Bailey gradation method successfully provided a similar gradation coarseness for CG-QNS compared to CG-QS, which resulted in comparable N f and indicates a similar aggregate interlock. The percentage decrease of CG-QNS containing 4% air voids was minimal, ranging from 1.92 to 5.46%, and a little higher at 7% air voids where N f ranged from 11.48 to 13.23%.

Effect of mastic specifications on the fatigue and low-temperature performance of hot mix asphalt

ABSTRACT This study aimed to evaluate the effect of mastic specifications on the intermediate and low temperatures performance of hot mix asphalt. In this research study, four different asphalt mixtures were fabricated with two types of aggregate and bitumen at three different mastic densities (defined as F/B ratios). At intermediate temperature, Four-Point Bending (4PB) beam fatigue tests were carried out at 8 Hz frequency and the strain levels of 460, 750, and 1100 microstrain. Also, the low-temperature performance of mixtures was evaluated by using Semi-Circular Bending (SCB) tests at −6°C, −18°C and −12°C, −24°C for PG 64–16 and PG 58–22 fabricated mixtures, respectively. Fatigue test results showed that the fatigue life of asphalt mixtures was more influenced by the mastic density at the lower strain level. Moreover, a minimum mastic density was necessary for improving fatigue performance. The SCB test results revealed that increasing the mastic density makes higher values in the mixture’s fracture energy, fracture toughness, cracking resistance index (CRI), and tensile strength. Also, the low-temperature performance of asphalt mixtures containing aggregate with a high abrasion value (AAV) was more dependent on the mastic density.

Asphalt mixture fatigue damage and failure predictions using the simplified viscoelastic continuum damage (S-VECD) model

Fatigue cracking is a primary asphalt pavement distress and various models have been developed to predict the fatigue life of asphalt mixtures using laboratory tests. One such model is the simplified viscoelastic continuum damage (S-VECD) model, which has been implemented in the pavement performance prediction program, FlexPAVETM. The S-VECD model test protocols (AASHTO TP 133 and AASHTO T 400) and data processing tool (FlexMATTM) are widely used around the world. Over the past three decades, this model has been continuously improved and refined. However, questions remain on the model’s ability to predict the material response when stress or strain are used as the model input. Also, different fitting procedures for the model calibration were found to affect the model’s prediction accuracy. In this study, analysis was conducted using data for four typical North Carolina mixes based on single replicate tests and multiple replicate tests to compare the model’s prediction accuracy based on stress versus strain as the model input and by considering fitting errors in the different calculations. The results show that using strain as the model input, which automatically incorporates portions of permanent strain, yields more accurate predictions compared to using stress as the input, regardless of the fitting algorithm. Additionally, in the analysis of individual test data, which is not affected by replicate specimen variability, the model’s predictions match the measured data well, as long as the fitting errors of the damage characteristic curve are controlled. When the data from replicate tests are analyzed together, although specimen variability compromises the S-VECD model’s prediction accuracy, failure can still be reasonably determined when strain is used as the model input.

Performance characterization of asphalt mixtures under different aging levels: A fracture-based method

This paper proposes a straightforward approach to characterize the fracture properties and fatigue life of asphalt mixtures over the service time. Since the serviceability of flexible pavements varies as they age, assessing the performance of asphalt mixes under aged conditions is essential. To investigate the sensitivity of fracture-related parameters to aging, accelerated laboratory aging, which is conditioning asphalt concrete samples in a force draft oven for different aging times (0, 3, 5, 7, and 9 days), was used. The Semi-Circular Bending (SCB) test at 25 °C was carried out on neat and activated carbon-modified samples to examine the fracture responses of asphalt mixes. First, force–displacement curves at failure were plotted. Then, fracture-related parameters (e.g., peak load, fracture toughness, strain energy, and J-integral) and damage levels corresponding to each fracture criteria were measured versus aging levels. In addition, the fatigue life ratio was determined to measure the influence of aging on the long-term performance of asphalt mixtures. To incorporate the effect of aging on the overall cracking resistance of asphalt mixtures, different fracture-related parameters versus service time were studied. Experimental findings suggest that the area under the fracture property versus service time can provide a reliable index for evaluating the long-term performance of asphalt mixtures. In addition, statistical analysis was performed to assess the impact of aging on fracture-related parameters obtained from the SCB fracture test. The proposed method was able to simultaneously factor in the fracture resistance and the rate of damage development during flexible pavement service life.

Fatigue performance of graphene oxide modified asphalt mixture: experimental investigation and response surface methodology

Fatigue in asphalt pavements is a major deterioration caused by repeated traffic loading. The objectives of this research were to investigate the fatigue performance of graphene oxide (GO) modified asphalt mixtures and evaluate the influence of temperature and stress level on the fatigue life of GO asphalt mixtures using response surface methodology (RSM). For this purpose, an indirect tensile fatigue test was conducted. The results showed that the application of GO increased the fatigue life of the asphalt mixture. The RSM analysis proposed a quadratic model with a high determination coefficient (R2 = 0.9977) to fit the experimental data. The ANOVA test showed that temperature, stress level, and GO percentage had a pronounced effect on the fatigue performance of the mixture. Furthermore, multi-objective optimization was used to achieve an optimized mixture proportion and verify the model’s reliability by conducting validation experiments. The predicted and actual results were found to be in excellent agreement, with a variation of only 2.12%, suggesting that the model can accurately predict the fatigue life of the GO-modified asphalt mixture.

Laboratory Investigation on Pavement Performance of Basalt Fiber-Reinforced Asphalt Mixture Under the Coupling Effect of Freeze-Thaw Cycles and Aging

Due to the significant temperature difference and high solar radiation in high-altitude areas, the asphalt pavement has been in freeze-thaw cycles and radiation service conditions for a long time, resulting in a shorter service life. To extend the service life of asphalt pavement in high-altitude areas, this study uses basalt fiber to toughen the asphalt mixture, and the service characteristics of the asphalt pavement under the coupled effects of freeze-thaw cycles and aging were evaluated. First, the freeze-thaw cycles, aging time, and basalt fiber content were selected as independent variables to conduct the Box–Behnken design (BBD) test design. Consequently, the corresponding response surface model was established. Based on the rutting test, three-point bending test, and indirect tensile test, the optimum content of basalt fiber was obtained. Finally, the fatigue properties of the asphalt mixture by the four-point bending fatigue test were compared under the optimum content. The results showed the consequences of freeze-thaw cycles will reduce the road properties of asphalt and give rise to damage to the asphalt; among them, the indirect tensile strength was decreased by 21.7% at most (the number of freeze-thaw cycles from 10 to 30). Aging will reduce the fatigue life of the asphalt mixture, but its dynamic stability, flexural tensile strength, and slitting strength will be enhanced to a certain extent; among them, the dynamic stability can be improved by up to 28.1% (aging from 4 to 12 h). Basalt fiber can increase the flexural tensile strength, dynamic stability, and spitting strength; the optimum content is 0.35% of asphalt mixtures. Furthermore, the fatigue life of basalt fiber-reinforced asphalt mixture can be significantly improved, which can reduce the influence of freeze-thaw cycles and aging. In addition, the unit price of basalt fiber-reinforced asphalt mixture is only 6.9% higher than that of SBS-modified asphalt mixture, which has significant economic benefits. Under experimental conditions, the effect of aging on the properties of the asphalt mixture is greater than that of the freeze-thaw cycle. This research shows that careful consideration of the road behavior of basalt fiber-reinforced asphalt mixture under freeze-thaw cycles and aging is essential for the pavement durability design.

Evaluation the Effect of Different Kind of Waste and Mineral Filler on the Fatigue Life of Asphalt Mixtures with Dissipated Energy Method

In recent decades, with increasing in traffic load, a great portion of repair and maintenance budget is being spent on improving the pavement failure. Asphalt fatigue, which is due to traffic cyclic loading, is one of the most important failure in asphalt pavements, therefore, increasing fatigue life in pavement can lead to a decrease in repair and maintenance budget. As a result, replacing or adding some additives to improve the fatigue behavior of the asphalt mixture, can help to reduce the fatigue cracks and increase the mixture life. In this research, fatigue behavior of asphalt mixture has been analyzed by using four point bending beam test with constant strain method on control and modified specimens with cement, coal waste and lime as filler. Fatigue behavior has been assessed at 2 strain 400 and 600 with replacing cement, coal waste and lime as the filler in the mixture. Results show that using each of 3 fillers at both strain state, leads to an improvement in fatigue life of asphalt mixture. Analyzing the results show that using above fillers could be used as an approach to improve the pavement’s function. Quantitatively, the three fillers, cement, coal waste and lime improved the fatigue life compared to the witness specimen by 75%, 55% and 8.2% at strain state of 400 and 107%, 72% and 7.1% at strain state of 600, respectively. Using coal waste can reduce the environmental issues due to coal waste deposits in addition to improving the fatigue life of asphalt mixture.

Identification of parameter to assess cracking resistance of asphalt mixtures subjected to aging and moisture conditioning

This study comprehensively evaluated different parameters based on tensile strength testing to assess the cracking resistance of asphalt mixtures subjected to aging and moisture conditioning. For this purpose, two sources of aggregates were selected to produce hot and warm mix asphalt mixtures. Asphalt mixtures were subjected to short term and long term aging, three levels of moisture conditioning (freeze thaw cycles), and tested at two temperatures (15 °C and 25 °C). The load-displacement data was used to determine the fracture work density, fracture energy, toughness index, cracking resistance index, cracking tolerance index, and rate dependent cracking index. It was noticed that moisture conditioning increased the variability of the different parameters. The cracking tolerance index and rate dependent cracking index parameter had a much higher coefficient of variation (CoV) with a maximum value close to 50%. Indirect tensile strength, fracture energy, and fracture work density appropriately captured the effect of moisture on cracking resistance of mixtures. The cracking resistance index, cracking tolerance index, and rate dependent cracking index increased with an increase in the moisture conditioning level. The Statistical analysis showed that tensile strength, fracture work density, and fracture energy were significantly influenced by different aging and moisture conditions evaluated. Fracture energy showed better association with fatigue life of asphalt mixtures subjected to three freeze-thaw cycles compared to tensile strength. Further, the fatigue life prediction models showed that both indirect tensile strength and fracture energy significantly influence the fatigue life of asphalt mixtures subjected to aging and moisture conditioning.

Characterisation of cracking resistance in modified hot mix asphalt under repeated loading using digital image analysis

Laboratory determination of fatigue characteristics of asphalt mixtures is a vital step in evaluating and designing asphalt pavement. This study aims to provide a comprehensive analysis of the fatigue resistance of the modified asphalt mixtures containing plastic waste and crumb rubber. These dry process-modified mixtures have been presented in the road construction on the basis of the basic understanding of the mechanical properties and lack of intensive studies on fracture mechanics. In this study, a controlled-stress, repeated load semi-circular bending test under two load levels with the effect of ageing and moisture condition was used to characterise the three stages of fatigue life of asphalt mixtures. The fatigue life was characterised on the basis of the crack mouth opening distance assessment and image analyses of the crack patterns on the sample surface. Digital image correlation was used to capture the strain field that forms the plastic zone of mixtures under consideration. Results show that rubberised asphalt mixture promotes crack propagation and failure stages by increasing the plastic zone, whilst plastic waste-modified asphalt mixtures function to increase the bonding properties. Consequently, the cracking initiation and propagation stages increase. The digital image analysis of the sample surface of modified asphalt mixtures indicates higher values of crack tortuosity, crack density and fractal dimension due to the increase in the cracking resistance of asphalt mixtures. The extracted strain field has successfully captured the effect of modifiers on the size of plastic zones under the fatigue test.

Development of an analysis tool for deterministic and probabilistic viscoelastic continuum damage approach

Pavement industry concerns have been increasing in the past decades towards fatigue cracking due to its negative impact on asphalt pavement performance. Therefore, several studies were conducted to model and characterize asphalt mixture fatigue life and number of cycles to failure (Nf) to achieve the designer’s goal ensuring the asphalt pavement serviceability, durability and to reduce the cost. Viscoelastic Continuum Damage (VECD) approach with incorporating probabilistic analysis (P-VECD) was proposed by several researchers to characterize the fatigue cracking of asphalt mixtures reliably. Although the probabilistic VECD studies attract great attention for characterizing the fatigue crack of asphalt mixtures, the VECD-Nf model random variables (RVs) are defined by using many arbitrary assumptions. Furthermore, the proposed approaches are very complicated, which added computation complexity to the VECD mode. Therefore, the prediction of asphalt mixtures’ fatigue life is needed in a reliable and simple process. This study focuses on developing a user-friendly analysis tool that determines the Nf following the VECD approach with incorporating probabilistic analysis. To achieve this goal, the proper distribution function for each RV in the VECD-Nf model is defined, a simple analysis tool is developed using MATLAB App Designer, and previous studies data for Hot-Mix Asphalt (HMA) and Fine Warm-Mix Asphalt (F-WMA) mixtures are re-analyzed using the developed P-VECD analysis tool. By using the P-VECD analysis tool, deterministic VECD analysis, probabilistic VECD analysis, and the prediction of the fatigue life of asphalt mixtures will be possible for technicians and engineers in the asphalt community.

Evaluating the Effect of Plastomer Modified Asphalt Mixture on High/Low Temperature Performance

Asphalt pavement’s surfaces deteriorate over time due to combined effect of traffic and surrounding environment. Fatigue and rutting are the major distresses which cause failures in flexible pavements. Different temperature control computer operated equipment’s are being used worldwide to predict the performance of asphalt mixtures at approximately same condition to those in-service pavements. Similarly, different types of polymers such as elastomer and thermoplastic have been used all over the world in Hot Mix Asphalt (HMA) for the improvement of asphalt mixtures. But little attention has been taken to evaluate the effect of plastomer on hot mix asphalt performance. Moreover, the initial cost of elastomer is higher than other types of polymers such as plastomer. The aim of this research study is to check the effect of various plastomers on high/low temperature performance of asphalt mixture. Four performance tests like Cooper wheel tracker, dynamic modulus, uniaxial repeated load and four-point bending beam test are used to evaluate the effect of different type of plastomers such as polyethylene terephthalate, high density and low density polyethylene with limestone aggregate quarry and 60/70 pen grade asphalt binder. This research study concludes that plastomer increases flexibility and hardness of asphalt mixtures and improves the rut resistance, dynamic modulus and fatigue life of asphalt mixtures. Plastomer modification shows significant benefits as compared to neat binder for high/low temperature performance. Moreover, it can be concluded that plastomer provides an efficient and economical blend of asphalt mixture.

Pavement moduli back-calculation using artificial neural network and genetic algorithms

An Artificial Neural Network (ANN)-based back-calculating program combined with a Genetic Algorithm (GA) optimization algorithm was developed for the back-calculation of flexible pavement layer moduli. Deflections measured using geophones on a model pavement structure under accelerated pavement testing (APT) with the MLS30 were utilized for back-calculating the pavement layer moduli. As theoretically expected of visco-elastic materials that are temperature dependent, the back-calculated moduli of the asphaltic layers, namely the surfacing and base, exhibited a decreasing trend with an increase in the temperature and number of APT load cycles. By contrast, the moduli of the unbound base layer and subgrade exhited insensitivity to temperature changes and did not decay significantly as a function of the APT loading. Overall, the integrated GABP algorithm (based ANN formulation) exhibited potential in satisfactorily back-calculating the pavement layer moduli form geophone measured deflections with acceptable accuracy. The splitting fatigue test results show that the fatigue life of asphalt mixture decreases with the increase of loading cycles, which can verify the feasibility of back-calcultion model.

Impact of Aging and Moisture on Fatigue Life of Asphalt Mixture

Abstract In this study, the mechanical behavior of a dense-graded asphalt mixture subjected to unaged, short-term, and extended aged conditions along with one freeze-thaw moisture conditioning cycle was evaluated at two temperatures and three stress magnitudes. A stress-controlled repeated indirect tensile loading fatigue test with 0.1-s loading and a 0.4-s rest period was used for determining the fatigue life of asphalt mixture. Aging, moisture conditioning, and an increase in the test temperature adversely affected the tensile strength of the asphalt mixture. The reduction in stiffness modulus of asphalt mixture that was due to moisture conditioning increased with the increase in the level of aging. The ratio of conditioned to unconditioned stiffness modulus (stiffness modulus ratio) was noticed to be more sensitive to different aging conditions compared with the ratio of conditioned to unconditioned tensile strength (tensile strength ratio). The effect of aging on fatigue life of asphalt mixture reduced with the increase in stress from 450 kPa to 550 kPa and 650 kPa. Further, the fatigue life of asphalt mixture reduced with the increase in test temperature and moisture conditioning. The short-term and extended aged mixture had higher damage value at failure compared with the unaged mixture. The mean fatigue life represented by the scale parameter of Weibull distribution reduced with the increase in aging and moisture conditioning. Further, the reliability of fatigue life of short-term aged and extended aged asphalt mixture was lower than the unaged asphalt mixture. The fatigue model based on plateau value and fatigue life was found to be more accurate compared with other regression models considered. Statistical analysis showed that the critical combinations of factors that influenced the mechanical behavior of asphalt mixture were also dependent on the test type, which included the tensile strength test, stiffness test, and fatigue test.