A comparative study of the heterogeneous local mechanical response of two types of asphalt mixes

Two asphalt specimens featuring very different gradations, types of aggregates and binders are investigated in this study. A full-field measurement technique is used for this purpose: the grid method. Displacement and strain fields are captured during compression tests carried out on these specimens. The displacement and strain fields are analyzed and compared in light of the main characteristics of these materials. It is shown that a close relationship exists between gradation and ratio between local and global strain components. The strain recovery that follows the loading phase of the specimens is also analyzed and the difference between their mechanical response at the local level is also highlighted.     

Investigating the effect of nanoparticles on the rutting behaviour of hot-mix asphalt

Rutting is considered as one of the major damages in asphalt mixtures. In this study, different types of nanoparticles such as TiO₂, Al₂O₃, Fe₂O₃ and ZnO in different percentages were added to the base asphalt binder in order to decrease the rutting potential of hot-mix asphalt (HMA). In the first step, asphalt binder tests for characteristics such as penetration grade, ductility, softening point and viscosity were performed on the asphalt binder modified by the nanoparticles. Then, after preparing HMA samples, the static creep test was done at two stress levels at a specific temperature. Results of this study showed that using the nanoparticles improved the behavioural properties of the asphalt binder and decreased rutting in asphalt mix samples. Furthermore, scanning electron microscope images taken from the asphalt binder samples modified by the nanoparticles demonstrated that these nanoparticles were properly distributed in the asphalt binder space and had a positive effect on the rutting performance of the asphalt mixes.     

Effect of aggregate nature on the fatigue-cracking behavior of asphalt mixes

Fatigue cracking in asphalt mixes is one of the most common road pavement distresses. When mixes are designed in the laboratory, it is very important to select the most suitable materials to ensure a good performance against this phenomenon. The types of binder and mortar strongly influence mix cohesion by providing tensile and shear strength. The mineral skeleton supplies it with compressive strength and bearing capacity. In this sense, the grading curve and shape of the aggregate affect crack growth (because of the internal friction), whereas the nature of the aggregate plays an important role in mix behavior (because of its adhesion to the bitumen and its resistance to fragmentation). This paper analyzes the impact of the nature of coarse aggregate on the fatigue-cracking behavior of asphalt mixes, an aspect that until now has received little attention. The UGR–FACT test was used to evaluate the cracking behavior of two mixes by varying the load amplitude, frequency, and test temperature. The results obtained showed that the nature of the coarse aggregate has an important effect in the fatigue-cracking behavior of asphalt mixes, and could be as important as bitumen type or mineral skeleton in mix design.     

Viscoplastic modeling of asphalt mixes with the effects of anisotropy, damage and aggregate characteristics

This paper presents an approach for constitutive modeling of the viscoplastic behavior of asphalt mixes. This approach utilizes an anisotropic non-associated flow rule based on the Drucker–Prager yield surface. The selection of this yield surface is motivated by the field stress paths and material properties associated with permanent deformation at high temperatures. The efficacy of the model is demonstrated by analyzing data from compressive triaxial tests conducted at different confining pressures and strain rates for three different mixes. The model parameters are related to the experimental measurements of aggregate shape characteristics, aggregate surface energy, inherent anisotropic distribution of aggregates, and microstructure damage measured using X-ray computed tomography and image analysis techniques. Establishing the relationship between the model parameters and material properties is important in order to optimize the mix properties, and achieve desirable mix performance.     

Predicting the tensile relaxation modulus of asphalt mixes based on the mix design and environmental factors

The main objective of this study was to predict the tensile relaxation modulus of asphalt mixes, without having to perform the common relaxation modulus tests, by developing a predictive model based on the mix characteristics, ageing condition, temperature and loading time. To this end, cylindrical asphalt mixture specimens containing crushed stone aggregates with 60/70 penetration asphalt binder were fabricated using two aggregate gradations, two binder contents, two air void levels and three ageing conditions with four replicates. Uniaxial tensile relaxation modulus tests were conducted on the specimens at four temperatures using the trapezoidal loading pattern at a low level of strain. Tensile relaxation modulus master curves of all the experimental combinations were constructed by the sigmoidal model. Statistical analysis of variance and regression analysis was performed on the test data and a predictive model was developed. Finally, the predictive model was verified using a group of measured values other than those used for the development of the model, and it was found that the predicted values correlated well with the measured ones.     

Effect of waste plastic bottles on the stiffness and fatigue properties of modified asphalt mixes

Nowadays, the use of recycled waste materials as modifier additives in asphalt mixes could have several economic and environmental benefits. The main purpose of this research was to investigate the effect of waste plastic bottles (Polyethylene Terephthalate (PET)) on the stiffness and specially fatigue properties of asphalt mixes at two different temperatures of 5 and 20 °C. Likewise, the effect of PET was compared to styrene butadiene styrene (SBS) which is a conventional polymer additive which has been vastly used to modify asphalt mixes. Different PET contents (2–10% by weight of bitumen) were added directly to mixture as the method of dry process. Then the resilient modulus and fatigue tests were performed on cylindrical specimens with indirect tensile loading procedure. Overall, the mix stiffness reduced by increasing the PET content. Although stiffness of asphalt mix initially increased by adding lower amount of PET. Based on the results of resilient modulus test, the stiffness of PET modified mix was acceptable and warranted the proper deformation characteristics of these mixes at heavy loading conditions. At both temperatures, PET improved the fatigue behavior of studied mixes. PET modified mixes revealed comparable stiffness and fatigue behavior to SBS at 20 °C. However, at 5 °C the fatigue life of SBS modified mixes was to some extent higher than that of PET modified ones especially at higher strain levels of 200 microstrain.     

Influence of processed carbon black in the filler composition on the characteristics of baked carbon mixes

Several carbon products such as carbon brushes, special nuclear carbons, seal rings, etc. require carbon black in the filler composition. In the present study, the raw carbon black was mixed with a coal tar pitch and the resulting carbon mix was shaped, calcined and finally crushed into a fine powder for its subsequent use. The influence of this modified (processed) carbon black in the filler composition on the characteristics of the final calcined petroleum coke, processed carbon black and coal tar pitch-based carbon mixes has been investigated.     

Quantification of the inherent uncertainty in the relaxation modulus and creep compliance of asphalt mixes

Advanced material characterization of asphalt concrete is essential for realistic and accurate performance prediction of flexible pavements. However, such characterization requires rigorous testing regimes that involve mechanical testing of a large number of laboratory samples at various conditions and set-ups. Advanced measurement instrumentation in addition to meticulous and accurate data analysis and analytical representation are also of high importance. Such steps as well as the heterogeneous nature of asphalt concrete (AC) constitute major factors of inherent variability. Thus, it is imperative to model and quantify the variability of the needed asphalt material’s properties, mainly the linear viscoelastic response functions such as: relaxation modulus, \(E(t)\), and creep compliance, \(D(t)\). The objective of this paper is to characterize the inherent uncertainty of both \(E(t)\) and \(D(t)\) over the time domain of their master curves. This is achieved through a probabilistic framework using Monte Carlo simulations and First Order approximations, utilizing \(E^{*}\) data for six AC mixes with at least eight replicates per mix. The study shows that the inherent variability, presented by the coefficient of variation (COV), in \(E(t)\) and \(D(t)\) is low at small reduced times, and increases with the increase in reduced time. At small reduced times, the COV in \(E(t)\) and \(D(t)\) are similar in magnitude; however, differences become significant at large reduced times. Additionally, the probability distributions and COVs of \(E(t)\) and \(D(t)\) are mix dependent. Finally, a case study is considered in which the inherent uncertainty in \(D(t)\) is forward propagated to assess the effect of variability on the predicted number of cycles to fatigue failure of an asphalt mix.     

Estimating the moisture damage of asphalt mixture modified with nano zinc oxide

One of the main distresses of hot mix asphalt (HMA) is moisture damage. The most common method for decreasing this type of distress is using antistrip additives. In this study, the effect of nanoparticles was evaluated as an antistrip agent on the moisture damage of HMA. Two types of aggregates were evaluated in this study with different sensitivities against moisture damage (limestone and granite aggregate) and the asphalt binder with 60/70 penetration grade and nano zinc oxide (ZnO) in two different percentages by weight of the asphalt binder. The tests employed to evaluate the effects of modifying asphalt binder by nanomaterials on the moisture damage of asphalt mixture were surface free energy (SFE) and AASHTO T283. The results showed that the ratio of wet/dry values of indirect tensile strength for the mixtures containing nano ZnO for two types of aggregate were higher than the control mixtures. In addition, the results of the SFE method showed that adding nano ZnO increased the total SFE of the asphalt binder, which led to better coating of the aggregate with asphalt binder. Nano ZnO decreased the acid to base ratio of SFE of asphalt binder, while it led to improving adhesion between the asphalt binder and acidic aggregate that are prone to moisture damage.     

Investigating the effect of some operating parameters on phosphate flotation kinetics by neural network

Artificial neural network (ANN) was used to simulate the effect of feed mean size, collector dosage, and impeller speed on flotation kinetic. Simulation were conducted using multi layer feed forward neural network assuming that flotation is following first order kinetic model.Simulation results showed that flotation rate constant (K) exponentially increased with increasing particle size up to a certain limit where it then decreased sharply. On the contrary, flotation rate constant (K) was inversely proportional with collector dosage but gradually increased with increasing impeller rotational speed.     

Study on the optimization design of mixing moisture content in foamed asphalt mix

This research discussed the rational mixing moisture content (MMC) in foamed asphalt (FA) mix design. Sieve analysis was firstly used to study the bitumen dispersion and bitumen-aggregate coating and bonding action in FA mixes with three levels of MMC. Then, through variance analysis, the impacts of MMC, bitumen content and their interaction effect on the mechanical properties of FA mixes were studied. Indirect tensile strength test and dry density determination were carried out on FA mixes consisting of different gradings and material types to explore the rational MMC. On base of that, monotonic triaxial test was performed on two types FA mixes with various filler contents to further investigate the rational MMC for FA mix. The research results indicated that improper MMC led to bitumen clots and affected cohesion of FA mix. MMC and bitumen content had important impacts on mechanical properties of FA mix, while their interaction effect could be ignored in mix design. Optimal MMC increased to a certain extent with the increase of fine aggregates content, especially filler content in the grading. 70?C80% of the optimum moisture content (OMC) was recommended as rational range of MMC for FA mix with 5?C15% filler content and 75?C85% of OMC for mix with 15?C20% filler content, which offered a reference for easy and simplified MMC design for FA mix.     

Investigating the effect of chirality on structural parameters of chiral single-walled carbon nanotubes by molecular dynamics simulation

The structural parameters of thin single-walled carbon nanotubes (SWCNTs) vs. chiral angle were investigated using molecular dynamics (MD) simulation. A comparison was made between nanotube radius obtained from MD simulation and that obtained from ideal rolling graphene model. Brenner empirical bond order potential was used to describe the interaction between carbon atoms. SWCNTs (n, m) with n + m = 6, 8, 10 and 12 were considered. It was observed that chiral nanotubes have three unequal bond lengths and three unequal bond angles, while for armchair and zigzag SWCNTs there are two unequal parameters.     

Investigating the effect of moisture protection on solid-state stability and dissolution of fenofibrate and ketoconazole solid dispersions using PXRD, HSDSC and Raman microscopy

Enhanced dissolution of poorly soluble active pharmaceutical ingredients (APIs) in amorphous solid dispersions often diminishes during storage due to moisture-induced re-crystallization. This study aims to investigate the influence of moisture protection on solid-state stability and dissolution profiles of melt-extruded fenofibrate (FF) and ketoconazole (KC) solid dispersions. Samples were kept in open, closed and Activ-vials(?) to control the moisture uptake under accelerated conditions. During 13-week storage, changes in API crystallinity were quantified using powder X-ray diffraction (PXRD) (Rietveld analysis) and high sensitivity differential scanning calorimetry (HSDSC) and compared with any change in dissolution profiles. Trace crystallinity was observed by Raman microscopy, which otherwise was undetected by PXRD and HSDSC. Results showed that while moisture protection was ineffective in preventing the re-crystallization of amorphous FF, KC remained X-ray amorphous despite 5% moisture uptake. Regardless of the degree of crystallinity increase in FF, the enhanced dissolution properties were similarly diminished. Moisture uptake above 10% in KC samples also led to re-crystallization and significant decrease in dissolution rates. In conclusion, eliminating moisture sorption may not be sufficient in ensuring the stability of solid dispersions. Analytical quantification of API crystallinity is crucial in detecting subtle increase in crystallinity that can diminish the enhanced dissolution properties of solid dispersions.     

Investigating the effect of moisture protection on solid-state stability and dissolution of fenofibrate and ketoconazole solid dispersions using PXRD,HSDSC and Raman microscopy

Enhanced dissolution of poorly soluble active pharmaceutical ingredients (APIs) in amorphous solid dispersions often diminishes during storage due to moisture-induced re-crystallization. This study aims to investigate the influence of moisture protection on solid-state stability and dissolution profiles of melt-extruded fenofibrate (FF) and ketoconazole (KC) solid dispersions. Samples were kept in open, closed and Activ-vials^® to control the moisture uptake under accelerated conditions. During 13-week storage, changes in API crystallinity were quantified using powder X-ray diffraction (PXRD) (Rietveld analysis) and high sensitivity differential scanning calorimetry (HSDSC) and compared with any change in dissolution profiles. Trace crystallinity was observed by Raman microscopy, which otherwise was undetected by PXRD and HSDSC. Results showed that while moisture protection was ineffective in preventing the re-crystallization of amorphous FF, KC remained X-ray amorphous despite 5% moisture uptake. Regardless of the degree of crystallinity increase in FF, the enhanced dissolution properties were similarly diminished. Moisture uptake above 10% in KC samples also led to re-crystallization and significant decrease in dissolution rates. In conclusion, eliminating moisture sorption may not be sufficient in ensuring the stability of solid dispersions. Analytical quantification of API crystallinity is crucial in detecting subtle increase in crystallinity that can diminish the enhanced dissolution properties of solid dispersions.     

Evaluation of pore structure and its influence on permeability and moisture damage in asphalt concrete

This study evaluates the pore structure of asphalt concrete (AC) samples by measuring the different components of pore space and their contributions to permeability and moisture damage. Three components of the total pore space namely permeable, dead-end and isolated pores are quantified using tracer test, which is a combination of permeameter and salt concentration measuring meter. Permeable pores become impermeable if an AC sample is compacted below 5% air voids. Permeable pores increase with an increase in sample radius. It is observed from this study that the permeable pore has a good correlation with permeability, whereas total pore shows a poor correlation with permeability. The effects of permeable and dead-end pores on moisture damage of asphalt concrete are evaluated using a moisture induced sensitivity testing device and the AASHTO T 283 method. It is observed that permeable and dead-end pores do not contribute to moisture damage of AC samples.     

LSE investigation of the thermal effect on band gap energy and thermodynamic parameters of BInGaAs/GaAs Single Quantum Well

In this paper, we report on the experimental and theoretical study of BInGaAs/GaAs Single Quantum Well elaborated by Metal Organic Chemical Vapor Deposition (MOCVD). We carried out the photoluminescence (PL) peak energy temperature-dependence over a temperature range of 10–300 K. It shows the S-shaped behavior as a result of a competition process between localized and delocalized states. We simulate the peak evolution by the empirical model and modified models. The first one is limited at high PL temperature. For the second one, a correction due to the thermal redistribution based on the Localized State Ensemble model (LSE). The new fit gives a good agreement between theoretical and experimental data in the entire temperature range. Furthermore, we have investigated an approximate analytical expressions and interpretation for the entropy and enthalpy of formation of electron-hole pairs in quaternary BInGaAs/GaAs SQW.     

Effects of moisture absorption on the electrical parameters of embedded capacitors with epoxy-BaTiO3 nanocomposite dielectric

In this work the effects of moisture absorption on the electrical parameters of embedded capacitors is investigated. Capacitors of two different areas embedded inside a four-layered printed wiring board were selected for this work. The dielectric was a nanocomposite of epoxy and BaTiO₃ which is common dielectric material used in embedded capacitors. These capacitors were exposed to elevated temperature and humidity conditions (85?°C and 85% RH) and two parameters, capacitance and dissipation factor, were measured in situ. The diffusion of moisture in the dielectric was also modeled using the finite element method (FEM), and the changes in electrical parameters were calculated theoretically. The FEM methodology was then verified by applying it on capacitors of different dimensions.     

Effects of grain size and thermodynamic energy on the lattice parameters of metallic nanomaterials

A thermodynamic method based on surface thermodynamics and atomic bond energy was developed to accurately investigate the lattice distortion rates of metallic nanomaterials. The results indicated that the lattice distortion rates of nanomaterials follow an inverse proportional relationship with the size, in good agreement with the experimental results. In this method, the anisotropy of the lattice distortion was a considerable issue. We found that the surface tension and Young’s modulus of the nanocrystals, compared with those of the bulk materials, change because of the lattice distortion and exhibit a linear relationship at the nanoscale. By defining a shape factor (ξ), the lattice distortion rates of nanoparticles, nanowires, and nanofilms were calculated. This method provides a new approach for the evaluation of the lattice distortion rates in nanomaterials.     

The effect of document types and sizes on the scaling relationship between citations and co-authorship patterns in management journals

The aim of this paper is to explore the power-law relationship between citation-based performance (CBP) and co-authorship patterns for papers in management journals by analyzing its behavior according to the type of documents (articles and reviews) and the number of pages of documents. We analyzed 36,241 papers that received 239,172 citations. The scaling exponent of CBP for article papers was larger than for reviews. Citations to articles increased 2^1.67 or 3.18 times each time the number of article papers published in a year in management journals doubled. The citations to reviews increased 2^1.29 or 2.45 times each time the number of reviews published in a year in management journals doubled. The scaling exponent for the power-law relationship of citation-based performance according to number of pages of papers was 1.44 ± 0.05 for articles and 1.25 ± 0.05 for reviews. The citations to articles increased faster than citation to reviews. The scaling exponent for the power-law of citation-based performance to co-authored articles was higher than single-authored articles. For reviews the scaling exponent was the same for the relationship between citation based performance and the number of reviews. Citations increased faster in single authored reviews than co-authored reviews.