Papers by mehdi shishehbor
Infrastructures
The interfacial adhesion between asphalt binder and carbon nanotubes (CNTs) depends on many nanos... more The interfacial adhesion between asphalt binder and carbon nanotubes (CNTs) depends on many nanoscopic properties such as diffusion of SARA molecules on CNTs surface. Functionalization of CNTs with Oxygens (O=CNTs), hydroxyl groups (HO–CNTs), and hydrogens (H–CNTs) has been an effective way to modify the surface properties of CNTs and ultimately the macroscopic properties of the CNT-composites. This paper presents the effect of different dosages of oxygenated and hydrogenated CNTs on the adhesion and diffusion of SARA molecules on CNTs’ surfaces. First, reactive molecular dynamics simulation is used to oxygenate and hydrogenate CNTs up to a certain dosage. Next, it is employed to model the interaction and diffusion of SARA molecules with the functionalized CNTs. We employ the steer molecular dynamic (SMD) and Einstein formula to calculate the adhesion and diffusion properties. The results demonstrate that hydrogenation has little effect on the adhesion energy, while oxygenation can ...
Nanomaterials , 2020
Improving the adhesion properties of carbon nanotubes (CNTs) at the molecular scale can significa... more Improving the adhesion properties of carbon nanotubes (CNTs) at the molecular scale can significantly enhance dispersion of CNT fibers in polymer matrix and unleash the dormant extraordinary mechanical properties of CNTs in CNT-polymer nanocomposites. Inspired by the outstanding adhesion, dispersion, mechanical, and surface functionalization properties of crystalline nanocellulose (CNC), this paper studies the mechanical and adhesion properties of CNT wrapped by aligned cellulose chains around CNT using molecular dynamic simulations. The strength, elastic modulus, and toughness of CNT-cellulose fiber for different cellulose contents are obtained from tensile and compression tests. Additionally, the effect of adding cellulose on the surface energy, interfacial shear modulus, and strength is evaluated. The result shows that even adding a single layer cellulose wrap (≈55% content) significantly decreases the mechanical properties, however, it also dramatically enhances the adhesion energy, interfacial shear strength, and modulus. Adding more cellulose layers, subsequently, deceases and increases mechanical properties and adhesion properties, respectively. In addition, analysis of nanopapers of pristine CNT, pristine CNC, and CNT-wrapped cellulose reveals that CNT-wrapped cellulose nanopapers are strong, stiff, and tough, while for CNT and CNC either strength or toughness is compromised. This research shows that cellulose wraps provide CNT fibers with tunable mechanical properties and adhesion energy that could yield strong and tough materials due to the excellent mechanical properties of CNT and active surface and hydrogen bonding of cellulose.
Powder Technology, 2020
In this study, the effect of coarse aggregate shape characteristics on the compactability and mic... more In this study, the effect of coarse aggregate shape characteristics on the compactability and microstructural properties of asphalt mixtures was virtually investigated using a discreet element method (DEM). Results reveal there is a statistically significant correlation between coarse aggregate flatness, elongation, roundness, and sphericity as shape descriptors and initial asphalt mixture density, as a compaction parameter. Analyses indicate that among all particle shape descriptors, only roundness and regularity had a statistically significant relation with compaction slope, and as the amount of roundness and regularity increase, the compaction slope decreases. Additionally, flatness and elongation values greater than 0.75 result in lower average coordination number values compared to those values less than 0.75. Results also indicate that although the probability density function (PDF) of low contact force highly depends on flatness, elongation and sphericity of particles, the PDF of high and very high contact forces is independent of the particle shape.
Construction and Building Materials , 2020
Introducing crumb rubber (CR) into asphalt binder can both provide environmental benefits such as... more Introducing crumb rubber (CR) into asphalt binder can both provide environmental benefits such as conservation of natural resources and conservation of landfill space and significantly improve rheological and mechanical performance characteristics of asphalt binders. Incorporation of CR into asphalt binder demands some amount of kinematic energy to make modified asphalt binder sufficiently fluid for mixing and compaction purposes that liberates some greenhouse and fume emissions. By taking advantage of warm mix additives (WMA), it is possible to effectively reduce the production temperature of hot-mix asphalt mixtures to mitigate such environmental concerns. This study, fFirstly, aims to investigate the CR dosage effect on the properties of asphalt binder containing different non-foaming warm mix additives: Sasobit and Evotherm M1. Secondly, the environmental concerns regarding CR inclusion into asphalt binder are evaluated by implementing gas chromatography-mass spectrometry (GC–MS) test. Rheological and mechanical tests have provided deep insight into the effects of such combinations of WMA and CR in asphalt binders and results indicated that a crumb rubber modified (CRM) asphalt binder with 15-20% CR yielded optimum performance concerning rutting, fatigue, and cracking performance. Furthermore, while both WMA additives can significantly improve the workability and enhance the rutting performance of CRM asphalt binders, they have a slightly negative effect concerning fatigue and cracking performance of CRM asphalt binders. From the environmental aspect, application of WMA additives also could potentially result in a 63-75% reduction in total emission of CRM asphalt mixtures containing 10-25% CR. Relationship between temperature and the total emission of CRM binders is not linear and it is more than likely a second-order polynomial relationship. Moreover, the results of emission analysis showed that CRM binders deliberate some hazardous fumes due to high temperature, which can be alleviated by incorporating WMA additives into the modified blend.
Construction and Building Materials, 2019
A finite element-based multiscale model is employed to examine the early-age mechanical behavior ... more A finite element-based multiscale model is employed to examine the early-age mechanical behavior of cementitious composites under a mode-I loading condition. The mechanical response of early-age mortar and concrete are influenced by the time-dependent development of mechanical properties of the cement paste as well as the mechanical and morphological properties of the aggregate phase. A competing mechanism exists in the fracture process (i.e., crack propagation) of the aggregate and cement paste phases. This paper investigates the distinct role played by the properties of each phase. This paper addresses the problem through a two-step homogenization approach that first starts at the meso-level of the mortar, where the fine aggregates are embedded within the cement paste. The second step considers the homogenization of concrete composed of the mortar matrix resulting from the first homogenization step, and coarse aggregate particles. For the purpose of computational homogenization, the continuous scheme for bulk modeling combined with the discontinuous scheme for modeling the transition of mesoscopic diffusive damage to macro-crack are employed. Inter-and intra-phase cohesive zone elements are utilized to represent the fracture process. The results indicate the relative significance of elastic and cohesive properties of composite constituents for the development of tensile stiffness and strength, damage evolution, and macro-crack patterns. A competing mechanism was observed for early-age cracking of the cementitious composites. When the tensile strength of the cement paste is lower than the tensile strength of aggregate phase, the crack propagates across the paste. When the tensile strength of the cement paste exceeds that of the aggregate, the cracks begin to deflect and propagate through the aggregates. As such, a critical degree of hydration (associated with a certain time) exists below which the cement paste phase is weaker than aggregate phase at the onset of hydration. This has implications on the inference of kinetic based parameters from mechanical testing (e.g., activation energy). Our results show a promising quantitative agreement with experimental observations.
Environments, 2019
During recent decade, the pavement sustainability has received much attention by road agencies, c... more During recent decade, the pavement sustainability has received much attention by road agencies, companies, governments and research institutes. The aim of this paper is to introduce and evaluate the sustainability of the technologies developed or underdeveloped to address environmental issues of asphalt mixtures, and the waste materials and by-products that can be recycled and reused in asphalt production. Warm Mix Asphalt (WMA) technology, the most popular waste materials to substitute neat binder (crumb rubber modifier (CRM), recycled plastic (RP), vacuum tower bottoms (VTB)) and/or virgin aggregates (reclaimed asphalt pavement (RAP), reclaimed asphalt shingles (RAs), construction and demolition (C and D) wastes, steel and copper slags), and bio-binders were evaluated with respect to their environmental and economic benefits and engineering performance as the main components of pavement sustainability. The performance evaluation was carried out by examining rutting, moisture susceptibility, thermal and fatigue cracking resistance. Two main environmental impacts, greenhouse gas (GHG) emission, and energy consumption were considered to study the environmental effects of these technologies and materials. Additionally, the economic effect was investigated considering initial cost and long-term benefit. Results of investigation illustrated that although each individual technology and waste material is valuable in terms of performance and/or the environment, specific combinations such as WMA + RAP, WMA + CRM, RAP + CRM, and WMA + CRM + RAP lead to further benefits. Notably, these combinations suffer from a lack of comprehensive economic analysis, thus, their sustainability cannot be fully assessed and is prone to future studies.
Journal of the Mechanics and Physics of Solids, 2019
Cellulose nanocrystals (CNCs) is a new family of cellulose materials with outstanding mechanical ... more Cellulose nanocrystals (CNCs) is a new family of cellulose materials with outstanding mechanical and chemical properties that have been successfully demonstrated to have potential for many applications. Understanding the mechanical behavior of individual CNCs and their interaction at nanoscale is very important for improving the manufacturing process and mechanical performance of the resulting materials at macroscale. However, due to time and length scale limitations for both, experimental observations and atomistic modeling, predicting the mechanical performance of a system consisting of many CNCs is still challenging. We present a coarse-grained model of CNCs based on both mechanical properties and crystal-crystal interactions to overcome this limitation. Parametrization of the model is carried out in comparison with all-atom (AA) molecular dynamics and experimental results of some specific mechanical and interfacial tests. Subsequently, verification is done with other independent tests. In particular, we note that the parameters of the model can be calibrated to capture the properties of both twisted and untwisted CNC interface without sacrificing the mechanical properties of the individual particle. Finally, we analyze the effect of interface properties on the mechanical performance of CNC-based materials including, bending test of a crystalline bundle, tensile test and fracture in two representative bioinspired architectures. The results revealed different failure mechanisms depending upon the interfacial configuration. For instance, well-aligned CNCs lead to a more brittle and catastrophic failure mechanism, whereas naturally twisted interfaces promote toughening mechanisms that helps attained optimal mechanical performance.
Journal of the Mechanics and Physics of Solids , 2018
We present a continuum-based structural model to study the mechanical behavior of cellulose nanoc... more We present a continuum-based structural model to study the mechanical behavior of cellulose nanocrystals (CNCs), and analyze the effect of bonded and non-bonded interactions on the mechanical properties under various loading conditions. In particular, this model assumes the uncoupling between the bonded and non-bonded interactions and their behavior is obtained from atomistic simulations. Our results indicates that the major contribution to the tensile and bending stiffness is mainly due to the cellulose chain stiffness, and the shear behavior is mainly governed by Van der Waals (VdW) forces. In addition, we report a negligible torsional stiffness, which may explain the CNC tendency to easily twist under very small or nonexistent torques. In addition, the sensitivity of geometrical imperfection on the mechanical properties using an analytical model of the CNC structure was investigated. Our results indicate that the presence of imperfections have a small influence on the majority of the elastic properties. Finally, it is shown that a simple homogeneous and orthotropic representation of a CNC under bending underestimates the contribution of non-bonded interaction leading up to 60% error in the calculation of the bending stiffness of CNCs. On the other hand, the proposed model can lead to more accurate predictions of the elastic behavior of CNCs. This is the first step toward the development of a more efficient model that can be used to model the inelastic behavior of single and multiple CNCs.
8 Performance of the nanoparticle-modified asphalt binder are greatly influenced by adhesion 9 pr... more 8 Performance of the nanoparticle-modified asphalt binder are greatly influenced by adhesion 9 properties between asphalt binder and nanoparticle. In this work the adhesion properties of crude 10 oil fractions (e.g. Saturate, Asphaltene, Resin and Aromatic components of asphalt binder), 11 graphene and mineral aggregates (silicon dioxide) at various temperatures are investigated through 12 molecular dynamic simulation and REAXFF force field. The results from SARA-graphene 13 interface demonstrations that aromatic and asphaltene have 30% higher adhesion properties than 14 saturate and resin. Also, the strength and work of adhesion for graphene-SARA interface is 150% 15 and 133% more than those values in graphene-SiO2 respectively. Finally, the results show that 16 using graphene is more beneficial for the properties of the binder and has no significant advantage 17 over binder in binder-aggregate interactions. 18 19 20
Understanding the structure-property relationships of the binder-aggregate interface at the molec... more Understanding the structure-property relationships of the binder-aggregate interface at the molecular level provides insights into the nature of their adhesion and could pave the way for better asphalt mixtures. In this study, molecular dynamic simulation and reactive force field (REAXFF) were employed to investigate the adhesion properties of Saturate, Asphaltene, Resin and Aromatic (SARA) components of asphalt binder on silicon dioxide (SiO2) aggregates at different temperatures (-12℃-160℃). The result showed that Aromatic and Resin had their maximum adhesion properties around 80℃, while Saturate had the minimum work of adhesion. Also, due to hydrogen bonding and covalent bond breaking, the adhesion properties of Asphaltene molecule was 300% higher than the other components.
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Papers by mehdi shishehbor