Search

The long-term aging of bitumens and its effect on low-temperature performance is a detrimental phenomenon. In order to investigate the effects of the aging phenomenon on the low-temperature performance of bitumens, it is very important to accurately simulate the behavior of bitumens in repeated aging cycles and to investigate related viscoelastic, chemical, and microstructural changes. In this research, three types of bitumen with penetration grades of 40/50 , 60/70 , and 85/100 were subjected to one to three cycles of pressure aging vessel (PAV) aging. Comprehensive data on the bitumen's behavior were obtained by conducting bending beam rheometer, Fourier transform infrared spectroscopy, and atomic force microscopy tests. Using the results of the conducted tests, an attempt was made to find precise relationships between different indicators of bitumen aging in terms of chemistry and viscoelasticity. The results revealed a linear correlation between the aging index and the ΔTc and dissipated energy ratio (DER) values, as well as the aging index and the vertical shift factor of the stiffness-time curve. The fitting coefficients of these linear relationships were R2=0.8 and above, indicating a strong linear relationship between these parameters. Furthermore, the viscoelastic indices DER and the derivation of creep compliance (J′) exhibited a fairly good linear relationship. [ABSTRACT FROM AUTHOR]

Acid sludge is an environmental pollutant that is produced daily in large amounts in used engine oil refineries. Recycling this waste is the primary goal of this paper. This study used 'washing with water' and 'neutralization with quicklime' methods to prepare acid sludge for use in bituminous materials as huge potential disposal. The neutralised sludge by the 'washing with water' method was added to bitumen in the wet blending process at 10, 20, and 30 wt%. This product is brittle without proper adhesion and cohesion and cannot meet the standard limits as an acceptable binder. It performs like long-term aged bitumen, reducing penetration and ductility and increasing the aging potential and viscosity. In another method, the neutralised sludge by adding quicklime was added to the asphalt mixture to replace fine aggregates in 50, 75, and 100 wt%. Using this product decreases the aging potential and moisture susceptibility up to 36.4, and increases rutting resistance up to 34.7%, indirect tensile strength up to 17.3%, and resilient modulus up to 17.3%. Despite the presence of large amounts of heavy metals in acid sludge, using this product in asphalt mixtures is an economical and completely hygienic solution for disposing of acid sludge. [ABSTRACT FROM AUTHOR]

Acid sludge is an environmental pollutant that is produced daily in large amounts in used engine oil refineries. Recycling this waste is the primary goal of this paper. This study used 'washing with water' and 'neutralization with quicklime' methods to prepare acid sludge for use in bituminous materials as huge potential disposal. The neutralised sludge by the 'washing with water' method was added to bitumen in the wet blending process at 10, 20, and 30 wt%. This product is brittle without proper adhesion and cohesion and cannot meet the standard limits as an acceptable binder. It performs like long-term aged bitumen, reducing penetration and ductility and increasing the aging potential and viscosity. In another method, the neutralised sludge by adding quicklime was added to the asphalt mixture to replace fine aggregates in 50, 75, and 100 wt%. Using this product decreases the aging potential and moisture susceptibility up to 36.4, and increases rutting resistance up to 34.7%, indirect tensile strength up to 17.3%, and resilient modulus up to 17.3%. Despite the presence of large amounts of heavy metals in acid sludge, using this product in asphalt mixtures is an economical and completely hygienic solution for disposing of acid sludge. [ABSTRACT FROM AUTHOR]

The objective of this study is to create explicit prediction models for the complex shear modulus (G*) and phase angle (δ) of bitumen mastic fabricated using an evolutionary machine learning approach. The dynamic shear rheometer (DSR) test in frequency sweep mode at seven test temperatures was performed to measure G* and δ. In order to create specific prediction models for each modifier, multigene genetic programming (MGGP) was employed. These models took into account various factors including the dosage of the additive, filler volume filling rate, loading frequency, temperature, as well as the G* and δ values of the neat bitumen. In general, six explicit prediction models are presented for different additives with R-squared values of more than 0.9. The results showed that the hybrid machine learning approach can effectively develop precise, meaningful, and yet simple formulas for calculating G* and δ of the bitumen mastic. To gain a deeper understanding of the developed models, a comprehensive parametric study and sensitivity analysis were carried out. [ABSTRACT FROM AUTHOR]

Three-dimensional numerical finite element (FE) biphasic models verified against the experimental data were developed aiming to study the accuracy of FE modelling in the prediction of viscoelastic properties of crumb rubber-modified asphalt binders. In the numerical models, crumb rubber-modified asphalt binders are considered as a heterogeneous composite material consisting of the original asphalt binder and rubber particles which respectively have viscoelastic and hyperelastic behaviours. Three different dosages of crumb rubber including 10, 15 and 20 wt% of the original asphalt are added. To capture rubber particles distribution within the bituminous matrix, a random generation method by using the MOA software (French acronym for random object modeller) was implemented based on rubber's minimum and maximum particle sizes. In order to determine the viscoelastic properties of the original asphalt binder as well as the crumb rubber-modified ones, the dynamic shear rheometer (DSR) was used. The excellent agreement between the numerical FE modelling and experimental results witnessed the capability of biphasic finite element models to predict the visco-hyperelastic behaviour of crumb rubber-modified asphalt binders having an error lower than 9%. [ABSTRACT FROM AUTHOR]

This study investigated the effect of waste toner as a cost-effective enhancement modifier on short-term aging and moisture resistance of asphalt binders and mixtures. Moreover, the mechanism of asphalt binder aging and moisture resistance was reviewed, aiming to provide promising evaluation methods for assessing short-term aging resistance of asphalt binders as well as moisture resistance of asphalt binders and mixtures. First, the aging resistance of neat and toner-modified asphalt (TMA) binders was evaluated using three approaches: rheological aging index (RAI), viscosity aging index (VAI), and chemical functional group indices based on data obtained from Fourier transform infrared spectroscopy (FTIR) analysis. To measure viscoelastic and viscosity characteristics of neat and TMA binders, a dynamic shear rheometer (DSR) and a viscometer were employed, respectively. Second, the moisture resistance of asphalt binders and mixtures were investigated based on analyzing the infrared spectrum and tensile strength ratio (TSR), respectively. The findings indicated that modifying binder with low percentages of waste toner enhanced the short-term aging resistance. Also, TMA binders containing 12% of waste toner presented a significant improvement in moisture resistance of asphalt binders and mixtures. [ABSTRACT FROM AUTHOR]

• Predicting J nr and %R of modified bitumens deterministically by using MGGP based on MSCR test results. • Predicting probability of different traffic levels by using logistic regression technique. • Determining the critical dosages of crumb rubber, SBS, and PPA modifiers that alter the traffic levels. This study aims to develop deterministic and probabilistic prediction models for the multiple stress creep and recovery (MSCR) test. For this purpose, crumb rubber, polyphosphoric acid, and styrene–butadiene–styrene bitumen modifiers have been used with different dosages to modify high-temperature performance of PG 58–28 and PG 64–22 base bitumens. The MSCR test has been performed at different temperatures. Deterministic models are developed by the multi-gene genetic programming technique for each modifier individually, and the non-recoverable creep compliance (J nr) and percent recovery (R) parameters are predicted. The accuracy of deterministic models is suitable and the performance of R models has been better than J nr models. Furthermore, a comprehensive probabilistic model has been developed by using the logistic regression technique to predict different traffic levels. The accuracy of the probabilistic model is 0.85. The sensitivity analysis has been performed on this model and the effect of changes in the modifier dosage and temperature on the traffic levels have been investigated. Results show that using the probabilistic model, it is possible to find a range of modifier's dosage in which the traffic level is desired. [ABSTRACT FROM AUTHOR]

Moisture damage is a major concern for evaluating the performance of asphalt mixtures. There are different types of experimental methods to determine the effect of moisture on mechanical and durability characteristics of asphalt mixtures. In this study, three different experimental approaches were implemented, including the boiling water test, the indirect tensile test, and the resilient modulus test, as well as the fracture energy analysis to evaluate moisture susceptibility of asphalt mixtures fabricated with different types of fillers including portland cement, limestone powder, and recycled concrete aggregates. Replacing the control filler material with these fillers resulted in improved fracture energy, which shows the stripping rate becomes slower by using them as fine aggregate. The fracture energy ratio of the asphalt mixture containing portland cement has the lowest rate of decrease for freeze-thaw cycles. Also, by applying a two-dimensional registration image-processing method as a low-cost soft-computing technique, an adhesion–cohesion index is introduced for determining the effect of moisture on adhesion between asphalt binder and aggregates as well as cohesion within asphalt mastic. Results have shown that there is a meaningful correlation between adhesion–cohesion index and number of freeze-thaw cycles, tensile strength ratio, resilient modulus ratio, and fracture energy ratio. To predict the adhesion–cohesion index of asphalt mixtures as an output of the image-processing method based on experimental results, a regression model was developed and verified in terms of the aforementioned parameters with an average prediction error of 4.46%. [ABSTRACT FROM AUTHOR]

This work focuses on the use of a heterogeneous generation method in order to develop a micromechanical model of Hot Mix Asphalt (HMA) that takes into account the effects of characteristics at the interfacial zone (IZ), where aggregate surfaces come into contact with the mortar matrix. Numerical calculations are conducted to investigate the effect of IZ mechanical characteristics on both the overall viscoelastic response of HMA and the local scale behavior. First of all, the HMA is treated as a biphasic material composed of mortar and granular inclusions. Next, a third phase is added between these two at each point of aggregate/mortar contact. Elastic and viscoelastic behaviors are assigned to the aggregates and mortar, respectively. The mechanical behavior of IZ varies between that of the inclusions and the matrix. At the global scale, these numerical results demonstrate that the use of triphasic micromechanical models improves the predictive accuracy of the dynamic modulus. At the local scale, a significant strain variation was found in each model. These results justify our triphasic modeling approach whenever local zone characteristics are the subject of interest. [ABSTRACT FROM AUTHOR]

Asphalt binder resistance to permanent deformation considerably influences total pavement resistance to rutting at the high service temperatures. To improve asphalt shear strength against rutting resistance, researchers have been used various modifiers and recently the use of waste materials as binder rheological enhancement agents is paid lots of attention. In this study, waste toner was adopted as an anti-rutting enhancement agent, and then neat asphalt binder was modified by waste toner at four dosages: 4, 8, 12 and 16% based on asphalt binder's weight. The effectiveness of binder modification by waste toner to improve asphalt binder and mixture's resistance to permanent deformation has been assessed by means of different methods: the Superpave specification parameter, G*/sinδ, and the multiple stress creep and recovery (MSCR) test for asphalt binder and wheel track test for asphalt mixture to determine the rut depth for a certain number of loadings. Results showed that adding toner to neat asphalt binder can meaningfully enhance the anti-rutting performance of asphalt binder and subsequently asphalt mixture. Moreover, increasing the dosage of toner up to 12% in the modified asphalt binder amplifies the trend of rutting resistance improvement. [ABSTRACT FROM AUTHOR]

Asphalt binders generally behave in a linear viscoelastic manner under conventional stress and strain level. There are several researches and technical protocols consistent with linear viscoelastic theorem. However, two main reasons can affect this well-known behavior of asphalt binders: 1) modification of asphalt binder with some additives causing a change in its microstructure and 2) higher order stress and strain level induced to asphalt binder under heavy traffic or climate loading. It is important to consider non-linear viscoelastic behavior of asphalt binder and its effect on conventional characteristics of asphalt especially two constitutive functions of creep compliance and relaxation modulus. In this research, nonlinear viscoelastic properties of asphalt binders modified with crumb rubber, styrene-butadiene-styrene and polyphosphoric acid are investigated to evaluate the variation in non-linear viscoelastic parameters due to addition of these modifiers. For this purpose, a specified research program was defined to consider non-linear behavior of one neat asphalt binder as well as nine modified ones. Based on a robust literature review and some prior experiences, three different extents selected for each modifier and then specimens were made. Implementing a simple creep-recovery test with creep loading time of 1 s and 100 s and 999 s unloading to simulate traffic load by using a dynamic shear rheometer at different stress levels of 0.1, 1, 10, 20 and 30 kPa, non-linear viscoelastic behavior of neat and modified asphalt binder was captured. The generalized fractional nonlinear viscoelastic model is introduced and successfully implemented to simulate creep and recovery behavior of neat and modified asphalt binders. Addition of all modifiers to the neat asphalt binder alters its non-linear viscoelastic behavior and properties. For short time creep loading, crumb rubber and polyphosphoric acid amplify non-linear behavior while SBS control it and for long creep loading time all asphalt modifiers increases non-linearity of asphalt binder’s viscoelastic behavior. [ABSTRACT FROM AUTHOR]

Predicting faulting failure is useful in the optimal concrete pavement design. In this study, artificial neural networks and the random forest method have been used to predict the amount of this failure. The general prediction model was created by inserting 32 available input variables into artificial neural networks. An integer two objectives optimisation problem was designed to select features that significantly affect the faulting. After applying this method, 19 important variables were identified and used to develop two simplified models based on artificial neural networks and the random forest method. It is shown that the simplified model developed by artificial neural networks is the best model to accurately predict the faulting considering the number of input variables. The cumulative number of days when the precipitation is more than 12.7 mm, the elastic modulus of concrete slab, the number of days passed since the pavement was built, base thickness, the cumulative ESALs in the traffic lane, and the annual average number of days when the temperature is more than 32°C were identified as the most important parameters in predicting faulting using the random forest method. A Sensitivity analysis has been then performed on these variables and optimal values were determined. [ABSTRACT FROM AUTHOR]

• High-strength fiber-reinforced concrete (HSFRC) was fabricated using polypropylene fibers. • The performance of the SCB setup in determining the fracture characteristics was evaluated. • Finite element simulation was carried out using concrete damaged plasticity (CDP) model in ABAQUS. Semi-Circular Bending (SCB) Setup is commonly used to investigate the fracture parameters of the road materials like asphalt mixtures. This paper examines the performance of the SCB setup in extracting the fracture characteristics of high-strength fiber-reinforced concrete (HSFRC). Monofilament and fibrillated polypropylene fibers with polyolefin coatings of 19, 30, and 50 mm length were added to a high-strength concrete mixture at three volume percentages of 0.5, 1, and 1.5 %. Standard cube and cylinder specimens were initially fabricated for conventional material properties tests. Subsequently, the three-point bending test specimens, i.e., intact rectangular beam, notched beam, and SCB, were made using the same concrete mix of different fibers lengths and percentages. A total of 36 beam and SCB tests with three replications was conducted to find the fracture energy and pick load of each specimen. Results showed that selecting the shortest fibers (19 mm) of 0.5 % and 1.5 % by volume increased the elastic modulus and the splitting tensile strength by 70.5 % and 43 %, respectively. Also, increasing the fiber length and volume enhanced the fracture energy of the notched beam and SCB specimens up to 90 times and 40 times, respectively. However, increasing the volume of the fibers was more effective than using longer fibers in fracture energy increase. For these three test setups, finite element models were generated and analyzed to develop a numerical framework capable of predicting the fracture characteristics of HSFRCs with acceptable accuracy (maximum error of 4 %). The concrete damaged plasticity (CDP) model in ABAQUS software package were adopted to simulate the damage initiation and progression in concrete using the material properties from the conventional tests. Comparing the results of beam setups with SCB tests, it was found that SCB can be a reliable and economical setup to find the fracture characteristics of the HSFRCs. [ABSTRACT FROM AUTHOR]

Physiochemical and rheological properties of asphalt binder are known to directly relate to asphalt pavement performance as it relates to fatigue and low temperature cracking. While other performance criteria such as rutting is also affected by binder properties, the latter is known to be also very sensitive to aggregate skeleton and mixture gradation. To enhance pavement performance, asphalt industry has commonly used various modifiers to improve binder rheological properties both before and after it is exposed to oxidative aging. Among those additives are polymers, ground tire rubber, as well as several organic and inorganic fillers. Inorganic fillers such as nano-clay and silica fume showed to be promising candidates to enhance asphalt rheology and aging behavior. Such enhancements are typically attributed to the presence of silicate platelet and silica particles. Accordingly, this paper investigates the merits of application of mesoporous silica nanoparticles in this paper referred to as nano-silica as an asphalt binder additive to enhance binder rheological properties and oxidative aging resistance. To do so, different percentages of nano-silica were added to neat asphalt binder. Asphalt binder was then exposed to short-term oxidative aging using a rolling thin film oven (RTFO). To study the distribution of nano-silica in binder as well as the change in the chemical, rheological, and morphological properties of asphalt binders due to the addition of nano-silica, the scanning electron microscopy (SEM), Superpave tests, and Fourier transform infrared spectroscopy (FTIR) were conducted. It was found that introduction of nano-silica to asphalt binder can improve the rheological properties and oxidative aging resistance of asphalt binder. [ABSTRACT FROM AUTHOR]

[Display omitted] Introducing waste plastics in bituminous composites can increase the composites' durability, provided that the waste plastics are compatibilized with bitumen to avoid phase separation. To enhance the compatibility of plastic particles with bitumen, various treatment methods were used to alter their physical and chemical characteristics. Considering the complex nature of bitumen, knowing the properties of isolated particles is not sufficient to indicate their performance in a bituminous composite. Therefore, there is a need to quantify the efficacy of each treatment method directly. While the plastic-bitumen interface can be examined via advanced characterization instruments such as atomic force microscopy, those methods are often relatively complicated and time consuming for formulators and designers. Here, we use a heterogeneous micromechanical model to calculate compatibility indicators; the model is tailored for viscoelastic bituminous composites containing waste-plastic particles. With experiments using a dynamic shear rheometer and a bending beam rheometer, data were generated on the bitumen with and without waste plastics having various surface treatments. The model was then used to calculate the Effective Volume Filling (EVF) ratio to indicate the interaction between plastics and bitumen as a measure of compatibility. A higher EVF ratio indicates greater compatibility. The corresponding EVF ratio was found to be higher for the oil-treated plastics compared to non-treated plastics, demonstrating higher compatibility of the oil-treated plastics with bitumen. This study promotes sustainability in construction by facilitating the use of waste plastics and enhancing the cracking resistance of bitumen. [ABSTRACT FROM AUTHOR]

• SBS and PPA with three different dosages are used to fabricate modified asphalt mastic. • Fractional viscoelastic model (FDM-4) is used to describe mechanical behavior of modified asphalt mastic. • The RSM is used to relate parameters of asphalt mastic models to parameters of asphalt binder models. • Additive's dosage, temperature, and filler volume filling rate are model inputs. The main aim of this study is to develop prediction equations of asphalt mastic fractional model parameters based on the fractional model parameters of asphalt binder, taking into consideration many parameters including, styrene–butadienestyrene (SBS) and polyphosphoric acid (PPA) modification, modifier's dosage, volume filling rate of siliceous filler, and test temperature. Experimental tests were conducted on original, SBS- and PPA-modified asphalt binders and asphalt mastics fabricated with these binders by using a dynamic shear rheometer device to achieve this aim. The asphalt mastic samples were fabricated considering a couple of volume filling rates of siliceous filler: 18 and 35%. Then, a fractional viscoelastic and the generalized Maxwell model were implemented and compared to describe the viscoelastic behavior of binder and mastic samples. The results showed that the fractional viscoelastic model could accurately predict the viscoelastic behavior of the original and modified asphalt mastic using fewer parameters compared to the well-known generalized Maxwell model so that the fitting accuracy of all samples is more than 0.99. In addition, the response surface methodology (RSM) was used to develop the prediction equation between the parameters of modified asphalt binders and the correspondent asphalt mastic fractional model. R2 values of SBS and PPA prediction models for fractional model coefficients are between 0.89 and 0.96. The predictive models presented a high accuracy so that mastic parameters with asphalt binder parameters, additive's percentage, temperature, and volume filling rate can be achieved. [ABSTRACT FROM AUTHOR]

This paper examines effects of a new biobased modifier, 'biobinder,' on low-temperature properties of asphalt binder and compares the results with those of conventional modifiers: crumb rubber, Gilsonite, styrene-butadiene-styrene (SBS), and polyphosphoric acid (PPA). Low-temperature characteristics of modified and nonmodified asphalts were studied using experimental and modeling approaches. A three-point bending beam rheometer was used to measure the stress-strain response of each specimen. A theoretical approach was used to determine stiffness and stress release rate; in addition, the Burgers model was implemented to predict the stored and dissipated energy ratio and quantity of derivation of creep compliance in each of modified and nonmodified asphalt specimens. Effects of various modifications were compared based on both the calculated stored and dissipated energy ratio and quantity of derivation of creep compliance. The proposed biobinder is produced from the thermochemical conversion of biomass (including animal waste, switch grass, and woody biomass). Biobinder is then blended with virgin binder to produce biomodified binder (BMB). This paper argues that the improved low-temperature rheological properties in biomodified binder is reflected in the enhancement in energy dissipation ratio and quantity of derivation of creep compliance. [ABSTRACT FROM AUTHOR]

Highlights: [•] Using the simple fractional model to characterize low temperature performance of asphalt binders. [•] Using derivation of creep compliance to estimate low temperature performance of asphalt binders. [•] Comparing performance of the crumb rubber and gilsonite modified asphalt binders. [Copyright &y& Elsevier]

• A new fracture resistantce indicator was developed accounting for the crack growth rate. • Increasing the polyphosphoric acid dosage increases fracture resistance at low temperatures. • Asphalt fracture resistance was the highest when 1 wt.% polyphosphoric acid was added. This paper examines the effect of polyphosphoric acid (PPA) on asphalt's fracture properties. While PPA has been commonly used in the asphalt industry to increase the elasticity and stiffness of asphalt binder, its effects on fracture properties are not thoroughly understood. Fracture as relates to thermal cracking is often associated with asphalt binder rather than a stone skeleton. However, because PPA not only interacts with molecules of asphalt binder but also strongly interacts with stone aggregates due to its highly polar molecules, we hypothesize that the presence of PPA in asphalt will change both bulk and interface properties in asphalt composites, which consequently alter asphalt fracture properties. To test this hypothesis, various PPA dosages (0.5–1.5% wt.) were introduced to the original asphalt binder, and thermo-mechanical and fracture properties of asphalt binder and asphalt mixture were examined. The study results showed that introducing up to 1% PPA enhances the asphalt resistance to fracture; however, excessive PPA weakens the asphalt against cracking. Considering that polar molecules of bitumen supersede others to adsorb to stone aggregate surfaces, the observed weakening effect could be attributed to PPA's preferential adsorption to stone aggregate surfaces compared to those of asphalt binder. The study outcomes provide insights pertaining to PPA's role and its interplay with other components in asphalt pavements. [ABSTRACT FROM AUTHOR]

This study exploits silica and polyphosphoric acid (PPA) synergistic effects to produce air-blown bitumen with desired stiffness and reduced carbon footprint. This in turn enhances the durability of the resulting air-blown bitumen while reducing gaseous emissions associated with its production. Here, we hypothesize that PPA-grafted silica made by adsorption of polyphosphoric acid to pristine silica nanoparticles promotes intermolecular interactions in vacuum bottom (VB), facilitating the production of air-blown bitumen. To test this hypothesis, laboratory experiments and modeling were used to determine the underlying molecular interactions determining PPA-grafted silica's role in facilitating the production of air-blown bitumen. Our molecular modeling showed PPA promotes the interaction between VB molecules by up to 10.28%; this combined with the increased polarity of VB molecules during the air-blowing process, leads to a significant increase in intermolecular interactions accelerating VB's stiffening. The latter was evidenced in our experiments showing that the required air-blowing time to reach desired stiffness measured by penetration and softening point was reduced up to 25% (time to reach required stiffness was reduced from 120 min to 90 min when silica-grafted polyphosphoric acid was used). Reduction of manufacturing time reduces VB's exposure to heat which leads to the formation of secondary organic aerosols. This promotes the economic and environmental sustainability aspects of the air-blowing process and contributes to resource conservation. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: In this research, the effects of four modifiers including crumb rubber, gilsonite, styrene–butadiene–styrene (SBS) and polyphosphoric acid (PPA) on the mechanical and rheological properties of asphalt binder at low service temperature are investigated. The main objective of this paper is to rank modifiers due to their effect on low service performance characteristics of asphalt binder for all type and extent of observed modified asphalt binders. For this purpose, the bending beam rheometer (BBR) test is performed on different extent of modifiers at five temperatures: −6°C, −12°C, −18°C, −24°C and −30°C. Asphalt binder is categorized as a viscoelastic material. Among several linear viscoelastic models, the Burgers model is selected for describing the mechanical behavior of modified asphalt binders. Four Burgers parameters are calculated by means of the principle of multiple non-linear regression and then these parameters are used for comparing the performance of asphalt binders by these three approaches: SuperPAVE Performance Grading (PG) protocol, dissipated energy ratio and derivation of creep compliance. Utilizing these three approaches, modified asphalt binders are ranked based on higher quantity of low temperature, dissipated energy ratio and derivation of creep compliance for all type and extent of modifiers alongside. Results show that each approach produces a particular grading which is not same as another one. In spite of variation of rankings, among the all evaluated modified asphalt binders, crumb rubber modified asphalt binder totally shows superior performance on low service temperature in all three methods. [Copyright &y& Elsevier]

• Prediction models were developed for viscoelastic behavior of modified bitumen. • G* and δ of the original bitumen, temperature and frequency were the model inputs. • Among the six different methods, the Ensemble Regression method showed the highest performance. Additives are commonly used in pavement engineering to improve the original bitumen's rheological and mechanical characteristics to meet severe loading and climatic condition requirements. To select the optimum dosage of an additive for modifying the original bitumen, it is essential to predict the viscoelastic behavior of modified bitumens, which can be performed by implementing the constitutive viscoelastic parameters of the complex shear modulus (G*) and phase angle (δ). In this work, a comprehensive experimental database consisting of the results of the frequency sweep mode of a dynamic shear rheometer (DSR) at seven test temperatures (−22 ~ 22 °C) was used. Prediction models for the viscoelastic behavior of bitumen modified with different dosages of crumb rubber, styrene–butadienestyrene (SBS), and polyphosphoric acid (PPA) were developed by optimizing and applying different machine learning approaches, including Artificial Neural Networks (ANN), Robust Linear Regression, Linear Support Vector Regression, Decision Tree Regression, Gaussian Process Regression (GPR), and Ensemble Regression, on the data. By comparing the various studied model outputs in terms of performance measurements, such as the correlation of coefficients, relative root mean square error, scatter index, relative error, and Nash-Sutcliffe efficiency coefficient, it was determined that the Ensemble Regression method has the highest performance in predictions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Three types of additives were used at three different dosages: crumb rubber, SBS, and PPA to modify bitumen. • Genetic programming based closed-form equations are developed for G* and δ of modified bitumens. • G* and δ of original bitumen, test temperature and frequency were considered as model inputs. • The performance of models were successfully verified using statistical indices and external data validation. The objective of this research was to develop prediction models for complex shear modulus (G*) and phase angle (δ) of bitumens modified with crumb rubber, styrene-butadiene styrene, and polyphosphoric acid at low and moderate temperatures. The experiments consisted of three different dosages of each modifier added to the original bitumen followed by measurement of G* and δ of the original and modified bitumen using the dynamic shear rheometer (DSR) test in frequency sweep mode (21 loading frequencies from 0.1 to 100 Hz) at seven test temperatures: −22, −16, −10, 0, 10, 16 and 22 °C. Having the experimental database, a robust genetic programming (GP) method was used to develop an individual prediction model for each modifier based on temperature, loading frequency, the G* and δ of the original bitumen, and the dosage of the modifier. Results showed that GP successfully developed accurate and meaningful expressions for calculating G* and δ of the modified bitumen as two main constitutive components of the viscoelastic behavior of bituminous composites. Then, a parametric study and sensitivity analysis were performed on the developed models to better understand the effect of variables on the trend of the models. The modifier dosage is the most effective input variable of the model and the amount of G* and δ of the original bitumen accurately reflect the effect of temperature and loading frequency on viscoelastic behavior of the modified bitumen, as they behave linearly at the considered test temperatures. [ABSTRACT FROM AUTHOR]

In this study, the mutual effect of polyphosphoric acid (PPA) and ethylene bis(stearamide) (EBS) modification was examined on the high and low service temperatures and viscosity of a performance grade (PG) 58-22 asphalt binder as a conventional neat bitumen widely used for paving applications. Three different dosages of PPA, including 0.5%, 1.0%, and 1.5% were used to modify the neat asphalt binder, and 3% of EBS as a selected percentage was added to PPA-modified samples. The dynamic shear rheometer was used to evaluate the high-temperature properties of the neat and modified bitumens based on standard Superpave protocol parameter (G*/sinδ) and multiple stress creep and recovery test. The low service temperatures of the samples were determined using the bending beam rheometer test. Also, the high-temperature ranges viscosities of the samples were evaluated using a series of rotational viscometer tests. The results have shown that increasing the PPA dosage up to 1.5% enhances the high service temperature of the neat asphalt binder 20.4°C and 14.7°C based on Superpave protocol and multiple stress creep and recovery test, respectively. However, it deteriorates the low-temperature performance of modified binders from −24.3°C to −16.9°C. The EBS can significantly compensate for the negative effect of PPA modification on the low-temperature behavior of modified bitumens. The optimum combination was 1% PPA+3% EBS as it provides a similar low-temperature grade to the neat asphalt binder having a significant two grades enhancement of high service temperature. Modifying a PPA-modified asphalt binder with EBS can reduce its viscosity at high temperatures, leading to saving energy of mixing and compaction. [ABSTRACT FROM AUTHOR]

• Performing temperature sweep test to generate master curves for viscoelastic properties of bitumen. • Optimizing the number of frequencies and temperatures to develop master curves of asphalt mortar and mixture. • Reducing the time and cost of dynamic modulus test without missing the accuracy of master curves. This study aimed to assess the feasibility of substituting temperature sweep tests for frequency sweep tests and explore the potential of utilizing fewer temperatures and frequencies in dynamic modulus tests to formulate viscoelastic properties master curves. The results indicated that master curves derived from temperature sweep tests mirrored the trends and values obtained from frequency sweep tests, presenting a viable alternative for constructing viscoelastic properties master curves of bitumen. Furthermore, models fitted to dynamic modulus test results at three temperatures and three frequencies exhibited comparable primary parameters, values, and trends to those derived from the complete dataset. The model fitted on reduced data demonstrated robust performance with correlation and R-squared values exceeding 0.95. Considering a marginal increase of about 5% in Residual Standard Error (RSE) values when using the reduced dataset, generating master curves with fewer test results underscored the feasibility and reliability of the original master curves. [ABSTRACT FROM AUTHOR]

• A biphasic random generated model was introduced to simulate microstructure of modified bitumen. • Using 2D or 3D heterogeneous viscoelastic FE models of the BBR test resulted in identical outputs. • Addition of crumb rubber having lower modulus than bitumen improved critical cracking temperature. This paper uses a heterogeneous micromechanical model to evaluate the resistance to thermal cracking in bituminous composites containing granular particulates. Thermal cracking is mainly caused by temperature fluctuations leading to accumulated stress that exceeds the strength of the materials. The presence of various granular particulates significantly affects a material's strength and capacity to release stress. Here, we use a two-dimensional heterogeneous numerical finite element model to evaluate and predict the thermal cracking characteristics of bitumen containing granular particulates such as crumb rubber and taconite. To develop the model, randomly distributed polygons using the Delaunay triangulation method were used to represent taconite and crumb rubber inside a bitumen matrix. The elastic properties of taconite and crumb rubber were assigned to the particulates, and the viscoelastic properties of the bitumen were modeled using a Prony series by implementing a simple fractional viscoelastic model. The study results showed that the flexural creep stiffness and creep rate calculated by the model were in good agreement with the measurements of experiments: the maximum errors were 6.15% for bitumen containing crumb rubber and 13.72% for bitumen containing taconite. Considering that flexural creep stiffness and creep rate are commonly used as indicators of thermal cracking resistance, the newly developed heterogeneous micromechanical model can be used to evaluate the thermal cracking resistance of bituminous matrices containing granular particulates. The model was further used to study the effects of temperature, elasticity, and concentration of particulates on the cracking resistance of the bituminous matrix. For instance, it was found that introducing 16% particulates with an elasticity of 1.02 MPa (representing crumb rubber) to bitumen improves its critical cracking temperature from −25 °C to −29.3 °C. This model provides insights to help the design of bituminous composites with desired cracking resistance properties by incorporating the proper particulates. [ABSTRACT FROM AUTHOR]

In this study, the efficacy of the extended oven aging procedure outlined in NCHRP 973 for generating laboratory-produced reclaimed asphalt pavement (RAP) was explored. The study also sought to establish a correlation between the results obtained from the aged bitumen extracted from oven-aged asphalt mixture and PAV-aged bitumen. Both aging techniques, with varying durations, were applied, and a series of tests, encompassing penetration, softening point, rotational viscosity, bending beam rheometer, temperature sweep using dynamic shear rheometer, and FTIR, were conducted for comprehensive comparison. The outcomes revealed that the oven aging procedure has limited applicability for simulating the long-term aging of asphalt mixtures. At the temperature of 95°C, an increase in the oven aging duration had minimal impact on the degree of aging, especially beyond five days, as evidenced by various parameters such as penetration, softening point, viscosity, master curves of viscoelastic properties, aging index, and low-, intermediate-, and high-temperature characteristics of the different aged bitumens. Furthermore, a comparative analysis between PAV and bitumen extracted from oven-aged asphalt mixture indicated that bitumen aged for five days in the oven exhibited analogous properties to bitumen subjected to 1 cycle of PAV aging, encompassing chemical, rheological, and physical test results. In conclusion, while some researchers have suggested that performing 2 or 3 cycles of PAV aging may be necessary to simulate long-term aging, the findings indicate that oven aging of asphalt mixture cannot effectively simulate aging characteristics beyond 1 cycle of PAV aging. • Changing the oven aging duration beyond 5 days does not affect asphalt mixture aging. • The PAV aging method, with varying cycles, effectively achieves higher levels of bitumen aging. • A single PAV aging of bitumen yielded results identical to five days of aging the asphalt mixture in an oven. [ABSTRACT FROM AUTHOR]

• Fractional viscoelastic model can characterize low-temperature mechanical behaviour of bio-modified bitumen. • Bio-modifiers effects on bitumen's properties is highly source dependent. • Bio-modifiers have positive effect on bitumen performance at low service temperatures. • Bio-modifiers enhance bitumen behaviour during both creep-loading and relaxation. Cracks associated with large temperature fluctuation especially in cold regions are among prevalent pavement distresses. Binder rheology is typically found to the key factor affecting low temperature cracking resistance. Recognizing the importance of binder properties, many road authorities are requiring the use of special additives to enhance low temperature properties of binder to alleviate low temperature cracking problems. However, most of these modifiers are petroleum-based products with unstable price and depleting resources. Therefore, the asphalt industry is looking for renewable alternatives for modifying bitumen and improving its low temperature performance. Accordingly, this paper incorporates laboratory experiments and modeling to study merits of modifying bitumen with several bio-binders to enhance low temperature properties of bitumen. To investigate rheological properties at low temperatures, an extended bending beam rheometer test was used incorporating a simple fractional viscoelastic model based on the general power law. The data collected during loading and unloading portion of the test was used to evaluate the effect of introduction of bio-modifiers on low temperature properties of bitumen. The experimental results showed that introduction of bio-modifiers to bitumen significantly enhanced bitumen behavior both during creep loading and relaxation. The results of finite element modeling based on the extended bending beam rheometer geometry and boundary conditions proved that the simple fractional viscoelastic model can accurately characterize low-temperature mechanical behavior of bio-modified bitumen. [ABSTRACT FROM AUTHOR]

This paper evaluated the effect of a biobased polyurethane modifier on the moisture resistance of asphalt binder. Biomodifiers with high acid values have been implicated in moisture damage to asphalt. Here, castor oil with a relatively high acid value of 190 mg KOH·g−1 was used to produce biobased polyurethane. Biobased polyurethane was produced by combining castor oil, toluene diisocyanate (TDI), and diethylene glycol (DEG) at a molar ratio of 1∶2∶1. Asphalt binder was modified with 3%, 6%, or 9% of the biobased polyurethane (by weight of asphalt binder), and the moisture susceptibility of the modified asphalt was evaluated with a comprehensive laboratory experiment plan using the boiling water test, the indirect tensile strength test, the bitumen bond strength test, the water contact-angle moisture-susceptibility test, and the moisture-induced shear-thinning index test. Study results showed that the introduction of biobased polyurethane enhanced the bond between the aggregate and asphalt, thereby increasing the asphalt mixture's resistance to moisture damage. Consequently, the resistance of asphalt binders to cohesive failure and adhesive failure was enhanced in biobased polyurethane, as evidenced by respective increases of 19%, 40%, and 49% in tensile strength ratio for dosages of 3%, 6%, and 9% biobased polyurethane. Compared with neat asphalt, the asphalt blend containing 9% polyurethane had the highest bond-strength increases, 55.73% and 37.93%, for dry and wet conditions, respectively. This improvement is attributable to the phenol and amide components in biobased polyurethane, which increase the polarity of asphalt binder and increase the affinity of asphalt binder to siliceous aggregate. In addition, the moisture-induced shear-thinning index and the contact-angle moisture-susceptibility index showed that increased doses of biobased polyurethane resulted in increased resistance of asphalt to moisture damage. The study outcomes promote the sustainability of asphalt construction by introducing biobased polyurethane as a sustainable modifier for asphalt. [ABSTRACT FROM AUTHOR]

• NaCl has the most negative effect on K 1c parameter among other deicers. • CMA causes additional stress and reduces J c parameter. • KAc has no significant statistical effect on both K 1c and J c. • Zycotherm reduces the J c parameter in all asphalt mixture samples. Winter maintenance of roads with inappropriate deicers causes much damage to road infrastructures. Researchers have always looked for suitable alternatives to salts or methods to increase the resistance of asphalt mixtures against chloride-based deicers. In this research, an accelerated laboratory method was used to investigate the effect of different deicers on nano-modified silane-based asphalt mixtures. Asphalt mixture samples were made by gyratory compaction method, and after core extraction, they were exposed to moisture and a solution of salt, Calcium Magnesium Acetate (CMA), and Potassium Acetate (KAc) for 96 h at 60 °C. Afterward, their fracture characteristics were measured at low and intermediate temperatures, and the results were statistically analyzed using two-way ANOVA and Tukey test. Statistical analysis showed that although there is no significant difference between the fracture toughness of asphalt mixtures at 0 °C in the presence of distilled water, CMA, and KAc, the reduction in the fracture toughness of samples is much greater in the presence of brine solution so that the fracture toughness of this mixture experienced a 30% reduction compared to the dry sample. Submerging the specimens in the brine solution reduces the resistance of asphalt mixture to cracking at both low and intermediate temperatures, while KAc has the least damaging effect on the fracture toughness of asphalt mixtures. Based on visual inspection and test results, CMA causes additional stress and cracking in asphalt specimens and reduces their resistance to fracture at intermediate temperatures. The silane-based anti-stripper, maintains the fracture toughness of asphalt mixture samples submerged in distilled water and the deicers at 0 °C at almost constant levels but reduces the J c parameter in all samples. Also, conditioning in the deicers has a greater effect than binder type on the fracture toughness of asphalt mixtures at 0 °C. Besides, there is a strong interaction between binder and deicer type on stress intensity factor, K 1c , of asphalt mixtures. [ABSTRACT FROM AUTHOR]

• MOEA/D method has the best performance to select 17 features affecting faulting. • ANN- SAA with R2 value of 0.976 has been the best model for predicting faulting. • Pavement age, cumulative average precipitation, and elasticity modulus of concrete slab are the most important variables. This study aims to predict faulting failure of jointed plain concrete pavement (JPCP) using different variables. For this purpose, four feature selection methods were developed by combining the artificial neural networks (ANN) and four multi-objective metaheuristic optimization algorithms, namely, the Pareto envelope-based selection algorithm II (PESA-2), the strength Pareto evolutionary algorithm 2 (SPEA-2), multi-objective particle swarm optimization (MPSO), and multi-objective evolutionary algorithm based on decomposition (MOEA/D). The MOEA/D showed better performance compared to the other models, which identified 17 input variables affecting faulting failure. In the next step, the classic back-propagation (BP), Biogeography-based optimization (BBO), invasive weed optimization (IWO), and simulated annealing algorithm (SAA) were combined with the ANN to develop three prediction models for faulting failure. Modeling with metaheuristic optimization algorithms showed better performance than the ordinary ANN. The pavement age, cumulative average precipitation, and elasticity modulus of the concrete slab have the most significant impact on the formation and increase of faulting. [ABSTRACT FROM AUTHOR]

Low-temperature cracking in pavement is a common distress in cold regions especially in North America; such distresses are shown to be highly related to binder low-temperature properties. To reduce the low-temperature cracking, several state departments of transportation are requiring the use of polymer-modified asphalt. However, polymer modification tends to be costly and in some cases led to phase separation in asphalt. Therefore, the current paper implements a fractional viscoelastic approach to study the effectiveness of several bio-based modifiers on improving asphalt binder's low-temperature characteristics. As such, implementing the bending beam rheometer (BBR) test, low-temperature rheological characteristics of asphalt binders, which are modified by four different bio-oils including biobinder from swine manure, corn stover, wood pellet, and miscanthus pellet are investigated. For this purpose, the BBR test was performed on asphalt binder samples containing 10% modifier at three temperatures of -12, -18, and -24°C. In order to analyze results of the BBR test, a fractional viscoelastic model is used to describe the relation of creep compliance and time. Utilizing the simple fractional model, relaxation modulus, storage modulus, and loss modulus are derived. In addition to the Superpave performance grading (PG) protocol, parameters of the simple fractional viscoelastic model are used to evaluate the performance of asphalt binders at low service temperatures through damping ratio and dissipated energy ratio. While biobinder from swine manure has the best performance by Superpave PG protocol analysis, corn stover shows the highest values for damping ratio and dissipated energy ratio among all modified asphalt samples. [ABSTRACT FROM AUTHOR]

• Adding fibers significantly enhances ductile behavior of high strength concrete. • Steel fibers resulted in different fracture behavior in comparison to glass and PP fiber. • Increasing the loading rate affects steel FRC samples more than samples with other fiber types. • SCB can be used as a reliable test for evaluating fracture behavior of concrete. Adding different types of fiber is one of the most common ways to enhance high strength concrete's mechanical behavior. In this paper, the effect of the loading rate and different type of fibers including glass, polypropylene, and steel were studied using the semi-circular bending (SCB) test method. It was evaluated that the SCB test can be used as a rapid and simple method to measure fracture properties of fiber reinforced high strength concrete (HSC) including ductility, energy absorption, and loading capacity by considering the effect of the loading rate on the parameters mentioned above. Specimens with glass fibers showed the most ductile behavior among all specimens with different types of fiber. On the other hand, steel fibers provided higher strength and higher energy absorption among the specimens. While specimens with steel fibers are highly sensitive to the loading rate in terms of peak load, this effect is not significant for specimens with glass and polypropylene fibers. [ABSTRACT FROM AUTHOR]

In this research, the effect of adding SBS and vacuum bottoms residue on 60/70 neat asphalt binder have been carried out using classic and superpave testing methods. Adding SBS led to increase of softening point, elastic recovery and viscosity of asphalt binder. Besides, SBS reduced the penetration and ductility of specimens. Results of dynamic shear rheometer indicated that G and G sinδ reduced by adding the SBS content before and after aging while δ and G /sinδ parameters increased. Therefore, adding SBS improves the permanent deformation and fatigue resistance of neat asphalt binder. [ABSTRACT FROM AUTHOR]

• Measuring LVE properties of bituminous composites through a multiscale simulation. • Multiscale simulation has more accuracy than the generalized self-consistent scheme. • 3.35 mm is the best mortar cutting size to find mixture behavior with NMAS of 19 mm. Viscoelastic properties of asphalt mixture were studied through a multi-scale approach, including bitumen, mastic, mortar, and mixture length scale. Biphasic and triphasic finite element modeling were employed to construct the heterogeneous models of bituminous composites, including matrix, inclusions, and air voids. The 2S2P1D model consisting of two springs, two parabolic creep elements, and one dashpot was fitted on the output of the numerical model, i.e., dynamic modulus (E*) and phase angle (δ), to accurately determine the Prony series. Then, the data of each scale was utilized as a matrix for the next scale's model. Three cutting sizes, including 3.35, 2.36, and 1.7 mm were selected based on the previous experimental study of Khodadadi et al. (2021) to generate the mortar model and find the best length scale of the matrix. In addition, the numerical results were compared with the results of the generalized self-consistent scheme model as an analytical approach. Both numerical and the generalized self-consistent scheme models yield adequate results; nevertheless, the numerical solution has more accuracy than the analytical model. The cutting size of the mortar scale had a considerable effect on the LVE properties of the mixture. The result showed that a cutting size of 3.35 mm is more suitable for a mixture with a nominal maximum aggregate size of 19 mm. These findings were consistent with the experimental results. [ABSTRACT FROM AUTHOR]

Asphalt binder resistance to permanent deformation at intermediate temperature significantly affects overall pavement resistance to rutting. To enhance asphalt resistance to permanent deformation, researchers have used various modifiers and additives such as styrene butadiene styrene (SBS) block copolymer, ethylene vinyl acetate (EVA), polyvinyl acetate (PVA), styrene butadiene rubber (SBR), and natural rubber latex. In this paper, the effectiveness of modification of asphalt binder by styrene-ethylene/propylene-styrene (SEPS) in order to enhance asphalt binder's resistance to permanent deformation has been investigated using two different evaluation methods: the Superpave specification parameter, , and the cross model for calculating zero shear viscosity (ZSV). The experiments were conducted using dynamic shear rheometer (DSR) frequency sweep test performed on both the neat sample and modified ones at 40, 50, and 60°C. Utilizing these two approaches, rutting resistance of modified asphalt binders are determined and then normalized using the rutting resistance of the neat asphalt binder as the control data in order to calculate the rutting resistance improvement ratio. The research results showed that regardless of the evaluation method, SEPS can significantly improve anti-rutting performance of asphalt binder. However, it was found that ranking of modified asphalt binders according to the two approaches is different. [ABSTRACT FROM AUTHOR]

• Using a multi-scale approach to find viscoelastic properties of three scales: mastic, mortar, and mixture. • Threshold stress is evaluated to characterize linear viscoelastic properties of the mortar scale. • Mortar with the cutting size of 3.35 mm has the closest behavior to the asphalt mixture with an NMAS of 19 mm. The mortar component plays an essential role in forming different asphalt mixture distresses. The fine aggregate size affects the viscoelastic behavior of mortar. In this study, three cutting sizes of 3.35, 2.36, and 1.7 mm, on the aggregate grading curve were considered to construct the mortar scales, namely mortar (I), (II), and (III), respectively. With a unique loading mode, a frequency sweep test was performed on four different length scales, including bitumen, asphalt mastic, mortar, and asphalt mixture, to make a direct comparison through a multi-scale approach. Also, a stress sweep test was conducted to find the mortar scale's linear viscoelastic domain. The results indicate that different mortar types have variable linear viscoelastic domains. The master curves of dynamic modulus (E*) and phase angle (δ) show that adding filler to bitumen has more effect on the E* than the δ. Although scaling up from the mastic to mortar (II) causes a significant difference between the viscoelastic parameters, the results remained approximately the same. The main gap between the mixture and mentioned sub-scales is filled with mortar (I). While the Cole-Cole diagrams demonstrate that the bitumen to mortar (II) scales have the same behavior, the closest scale to the mixture is the mortar (I). Therefore, using a cutting size of 3.35 mm is recommended to fabricate mortar (for asphalt mixture with a nominal maximum aggregate size of 19 mm) instead of 2.36 mm, which was suggested in previous studies. [ABSTRACT FROM AUTHOR]

Based on full-scale experiments on steel tubular T/Y-joints wrapped with FRP, nonlinear finite element (FE) models were verified and calibrated for prediction of the static load-bearing capacity (SLC) of FRP-strengthened joints. The verified FE methodology was utilized to perform parametric studies. Due to the fact that local buckling of the chord member is the governing mode of failure in tubular joints capacity, FRP strengthening on the chord is determining while brace strengthening showed negligible effects. Increasing the brace-to-chord diameter ratio (β), chord diameter-to-thickness ratio (γ), and brace inclination angle (θ) enhanced the joint capacity but decreased the FRP effectiveness on the joint capacity improvement. Based on the results of the experimentally-verified numerical analyses and parametric studies, three indices ψ , λ and δ were introduced as strengthening index, FRP fibers orientation and the stacking sequence, to represent the effective parameters respectively. Multiplying these indices by the unstrengthened joint capacity constitutes a practical and efficient formulation for estimating the SLC of FRP strengthened joints. Since a large number of FE models were generated and analyzed, the presented formulas can be employed for FRP optimal application on tubular joints, while providing a guideline for the assessment of the strengthened joint SLC. [ABSTRACT FROM AUTHOR]