S. Ren
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60 records found
1
The transition to sustainable pavement materials requires innovative alternatives to traditional mineral fillers that can simultaneously deliver mechanical performance, durability, and reduced environmental impact. This study systematically investigates four geopolymer-based powders derived from fly ash (FAG), metakaolin (MKG), red mud (RM), and slag (S) as substitutes for conventional limestone fillers (WG and WG60K) in asphalt mastic. Rheological testing, chemical characterization, and microstructural analysis are conducted to evaluate their effects on the chemo-structural-mechanical behaviour of bitumen. Results show that FAG markedly enhances high-temperature performance, improving rutting resistance, thermal stability, and shear strength by up to 58%, 45%, and 62%, but exhibits poor fatigue resistance and limited stress-relaxation capacity. In contrast, slag and metakaolin powders offer a more balanced performance profile, with superior fatigue resistance, finer dispersion, and smoother surface morphology (Ra < 1.5 μm), making them promising candidates for durable pavements in warm and moderate climates. RM shows intermediate behaviour, providing good thermal stability but a rougher texture and stronger elastic stiffening. Although no chemical reaction is observed between powders and bitumen, physical interactions such as surface adsorption and alignment of aliphatic chains are found to stiffen the mastic and alter its temperature-dependent response. Surface roughness and dispersion quality are directly correlated with rheological performance, with coarser fillers (FAG, WG60K) enhanced rigidity but shortened fatigue life. Overall, Slag and metakaolin emerge as the most promising geopolymer fillers for durable asphalt pavements.
To increase the utilization of used tires, reduce carbon emissions and improve asphalt pavement performance, SBS/TB crumb rubber modified asphalt binder was designed, which was enhanced by SBS and terminal blend (TB) crumb rubber. SBS/TB crumb rubber modified asphalt binder was prepared by mixing 0 %, 10 %, and 15 % TB crumb rubber with 2 % and 3 % SBS, respectively. This study investigated the microstructure, thermal stability and rheological properties of SBS/TB crumb rubber modified asphalt binder. The Spearman correlation coefficient is introduced to analyze the correlation of microstructural, thermodynamic and rheological parameters. The results showed that SBS and TB crumb rubber were uniformly dispersed in asphalt binder without agglomeration phenomenon. In addition, the interaction between SBS and TB crumb rubber resulted in the formation of cross-links between the polymer and the asphalt binder, significantly improving the storage stability and the thermal stability of the modified asphalt binder. The pyrolysis mechanism of the modified asphalt binder is One-dimension diffusion or One-dimension phase boundary. With the addition of SBS and TB crumb rubber, the rheological, high-and-low temperature properties of modified asphalt binder are improved. Finally, microstructural, thermodynamic and rheological parameters have an extremely strong correlation by Spearman correlation coefficient analysis.
Low-carbon bio-recycled asphalt development
Insights into the rheological and chemical behaviour of bio-rejuvenated bitumen with warm-mix additives
This study investigates the effects of warm-mix asphalt (WMA) additives and bio-oil on the rheological and chemical properties of virgin bitumen (VB) and polymer-modified bitumen (PMB) under varying aging conditions. The workability, viscoelasticity, and chemical characteristic of warm-mix bio-rejuvenated bitumen are assessed using a rotational viscometer, dynamic shear rheometer, Fourier Transform Infrared Spectroscopy. Results show that PMB has superior aging resistance than VB. The wax-based additive exponentially reduces viscosity of VB, while the chemical-based additive decreases viscosity linearly and performs better in PMB due to improved polymer-bitumen interfacial lubrication. The wax-based additive enhances high-temperature elasticity and rutting resistance, whereas adding 0.9 wt% chemical-based additive declines the rutting failure temperature (RFT) of VB by 3.3°C and PMB by 2.3°C. However, the wax-based additive lowers the fatigue life of VB, while the chemical-based additive extends the fatigue life. The fatigue failure temperature (FFT) value increases by 2.3°C for VB and 3.4°C for PMB after adding 4 % wax-based additive. The optimal dosage of the chemical-based additive for PMB is determined to be 0.6 %. The bio-rejuvenator significantly enhances the fatigue performance of aged VB, but has limited impact on aged PMB. Both WMA additives reduce aromaticity and alter aliphatic content, with the chemical-based one showing a stronger dilutive effect, particularly in PMB. Additionally, a warm-mix bio-rejuvenated bitumen with higher aliphatic index (AII) and carbonyl index (CI) shows better deformation resistance and longer fatigue life.
A novel Visbreaking-Supercritical Fluid extraction (SFE) strategy for efficient upgrading of vacuum residue
Experimental optimization and molecular dynamics insights
The increasing demand for cleaner and more efficient refining processes has driven the development of advanced upgrading technologies for heavy crude residues. This study investigates a novel Visbreaking-Supercritical Fluid Extraction (SFE) approach to upgrade the Merey vacuum residue (VR), integrating experimental analysis with molecular dynamics (MD) simulations for atomic-level mechanism exploration. The Visbreaking process is optimized at 400 °C for 40 min, achieving a viscosity reduction of 89.0 % while minimizing coke formation. The SFE process fractionates the visbroken VR, with total extraction yields ranging from 70.1 wt% to 70.7 wt%, demonstrating remarkable efficiency. Higher extraction pressures enhance deasphalted oil (DAO) yield but compromise its quality with higher metal and sulfur contents, while lower temperatures improve extraction selectivity. The integrated process effectively removes Fe, Ni, V, and Na, with demetalization efficiencies exceeding 62 %, 75 %, and 95 %, respectively. Molecular dynamics simulations provide atomic-scale insights into solubility mechanisms, revealing that higher pressures and lower temperatures enhance solvent compatibility with lighter visbroken VR fractions. The extracted DAO meets marine fuel oil blending specifications, while raffinates show potential for bitumen production and modification. These findings highlight the Visbreaking-SFE combination as a promising and sustainable upgrading strategy for heavy crude residues.
detection studies. The findings of this study provide valuable insights and practical recommendations for selecting appropriate DP methods, thereby enhancing the classification accuracy and reliability of ATR-FTIR spectral analysis of bituminous binders. This contributes significantly to the design of experiments, reduces operational risks, and optimizes resource utilization in the field. ...
detection studies. The findings of this study provide valuable insights and practical recommendations for selecting appropriate DP methods, thereby enhancing the classification accuracy and reliability of ATR-FTIR spectral analysis of bituminous binders. This contributes significantly to the design of experiments, reduces operational risks, and optimizes resource utilization in the field.
Towards a Reliable Design of Geopolymer Concrete for Green Landscapes
A Comparative Study of Tree-Based and Regression-Based Models
This dissertation aims to develop a comprehensive and multi-scale approach for assessing the rejuvenation efficiency and mechanisms of various rejuvenator-aged bitumen blends. The combination of molecular dynamics (MD) simulations prediction and experimental validation is throughout the whole thesis to evaluate the compatibility potential and diffusive capacity of rejuvenators within aged bitumen, as well as their rejuvenation effectiveness in the chemo-thermodynamic-rheological performance. Additionally, the intermolecular interactions occurring between the rejuvenator and aged bitumen molecules are visualized and quantified by MD simulations.
The accurate construction of molecular models for aged bitumen is crucial for investigating the fundamental effects of aging on bitumen behavior at the molecular scale. To accomplish this, the long-term aging influence on the chemical characteristics of bitumen was assessed through Saturate, Aromatic, Resin, and Asphaltene (SARA) fractionation, Fourier Transform Infrared Spectroscopy (FTIR) test and element analysis method. The chemical information obtained served as a foundation for determining the molecular structures of bitumen models. Various thermodynamic parameters of both virgin and aged bitumen were predicted to fundamentally evaluate the aging effect on bitumen properties. Lastly, functional group and SARA-based long-term aging reaction kinetics models were proposed to anticipate the chemical characteristics of aged bitumen with different aging degrees, thereby establishing the corresponding molecular models without the need for additional experimental procedures.
Simultaneously, novel average and multi-component molecular models for various rejuvenators (bio-oil BO, engine-oil EO, naphthenic-oil NO, aromatic-oil AO) were established. The average models were based on the average chemical characteristics, such as functional group distribution, element component, and average molecular weight. On the other hand, multi-component models were derived from molecular component distribution in rejuvenators through Gas Chromatography-Mass spectrometry (GC-MS) analysis. Both models were validated by comparing MD outputs with experimental results. It was found that the average models provided more accurate predictions regarding the glass transition temperatures, especially for the aromatic-oil. Additionally, a range of thermodynamic parameters for the rejuvenators were predicted and compared. Finally, the average structures of rejuvenators were adopted to construct subsequent molecular models of rejuvenated binders.
The consideration of compatibility between the rejuvenator and aged bitumen is crucial due to the potential phase separation. In this thesis, different thermodynamic parameters, such as solubility parameter difference Δδ, Flory-Huggins parameter\chi, and mixing free energy ΔGm were predicted and calculated using MD simulations for various rejuvenated bitumen systems. The predicted compatibility ranking for four rejuvenators was AO > BO > NO > EO, aligned with the experimentally measured thermal stability results. Moreover, separation index (SI) parameters based on rheological and chemical indices were available to assess the thermal stability of rejuvenated bitumen.
Furthermore, a comprehensive investigation was implemented to explore the effects of rejuvenator type, temperature, and aging degree of bitumen on the diffusion behavior of rejuvenators in aged binders at multiple scales. The molecular dynamics (MD) simulation method was employed to detect the molecular-level diffusion characteristics of rejuvenators and predict their diffusion coefficient (D) parameters. At the atomic scale, it was observed that there was a mutual but partial interfacial diffusion feature between rejuvenators and aged bitumen molecules. Meanwhile, the concentration distribution of rejuvenator molecules in aged bitumen was well described by Fick's Second Law. The calculated D values for the four rejuvenators ranged from 10-11 to 10-10 m2/s, and the diffusive capacities followed the order of BO > EO > NO > AO. To verify the MD simulation outputs, diffusion tests and dynamic shear rheometer (DSR) characterizations were conducted. The experimental results regarding the magnitude and order of the D values were in good agreement with the MD simulation findings. Lastly, it was observed that an increased aging degree of bitumen had a negative impact on the molecular diffusivity of BO, EO, and NO rejuvenators, whereas the D value of AO molecules enlarged as the aging level deepened.
A series of measurements were conducted to estimate the combined effects of rejuvenator type/dosage and aging degree of bitumen on the rheological properties of rejuvenated bitumen. Importantly, several critical indicators were identified that effectively assess and differentiate the rejuvenation efficiency of different rejuvenators on aged bitumen performance. In terms of high-temperature performance, parameters rutting failure temperature (RFT) and zero-shear viscosity (ZSV) from the linear viscoelastic (LVE) and flow tests were found to be useful. Additionally, parameters R3.2, Jnr0.1 or Jnr3.2, and Jnrslope were recommended for estimating the elastic performance, creep potential, and stress sensitivity of rejuvenated bitumen. Among these, the RFT parameter played a crucial role in evaluating and distinguishing the rejuvenation effectiveness of various rejuvenators on the high-temperature performance of aged bitumen. For the low-temperature relaxation property, parameters τ50s, t25%, and A were proposed as critical indicators. Regarding fatigue life improvement, BO demonstrated the highest rejuvenation effectiveness, followed by EO, NO, and AO rejuvenators. The fatigue failure temperature (FFT) parameter was identified as an effective indicator for fatigue performance evaluation in LVE tests. In linear amplitude sweep (LAS) tests, the fatigue life (Nf5), peak strain (ɛsr), and elastic modulus (E) parameters were optimized as effective fatigue indicators. Nonetheless, crack width (C) results were consistent with conclusions drawn from LVE and LAS tests. Particularly, the crack width C500 parameter showed strong correlations with other critical fatigue indicators, and its prediction could be achieved using correlation equations without the need for time-consuming TS tests.
At the atomic-level evaluation, several key thermodynamic properties of variable rejuvenated bitumen models were outputted by molecular dynamics (MD) simulation. The rejuvenation effectiveness of different rejuvenators on the thermodynamic indices of aged bitumen was estimated and compared. Importantly, the potential connections between these essential nanoscale parameters and critical macroscale indicators in terms of high-and-low temperature performance and fatigue behaviors of rejuvenated binders were explored. It was revealed that the addition of rejuvenators inherently catalysed a restoration of density and cohesive energy density (CED) values toward those of virgin bitumen. A suite of indicators, including UVEP, UWEK, EN, UVET, UNED, and ECT, are introduced as critical energetic parameters, each reflecting rejuvenator efficacy on atomic-level energetic features, except for specific cases involving aromatic-oil rejuvenated binders. Meanwhile, it is recommended to predict the relaxation properties of different rejuvenated bitumen by the fractional free volume parameter from MD simulation. The surface free energy (γ) emerges as a dependable index for assessing the rejuvenation efficacy of the cohesive cracking potential of aged bitumen.
In summary, a multiscale evaluation framework of rejuvenated bitumen was proposed and developed in this dissertation, together with a full understanding of the difference in rejuvenation efficiency and mechanism between various rejuvenators on chemo-thermodynamic-rheological performance restoration of aged bitumen. The outcomes of this thesis would be beneficial to promoting the formation of classification standards of rejuvenator additives, development of advanced multifunctional rejuvenators, and improvement of all-round evaluation method on rejuvenated binder.
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This dissertation aims to develop a comprehensive and multi-scale approach for assessing the rejuvenation efficiency and mechanisms of various rejuvenator-aged bitumen blends. The combination of molecular dynamics (MD) simulations prediction and experimental validation is throughout the whole thesis to evaluate the compatibility potential and diffusive capacity of rejuvenators within aged bitumen, as well as their rejuvenation effectiveness in the chemo-thermodynamic-rheological performance. Additionally, the intermolecular interactions occurring between the rejuvenator and aged bitumen molecules are visualized and quantified by MD simulations.
The accurate construction of molecular models for aged bitumen is crucial for investigating the fundamental effects of aging on bitumen behavior at the molecular scale. To accomplish this, the long-term aging influence on the chemical characteristics of bitumen was assessed through Saturate, Aromatic, Resin, and Asphaltene (SARA) fractionation, Fourier Transform Infrared Spectroscopy (FTIR) test and element analysis method. The chemical information obtained served as a foundation for determining the molecular structures of bitumen models. Various thermodynamic parameters of both virgin and aged bitumen were predicted to fundamentally evaluate the aging effect on bitumen properties. Lastly, functional group and SARA-based long-term aging reaction kinetics models were proposed to anticipate the chemical characteristics of aged bitumen with different aging degrees, thereby establishing the corresponding molecular models without the need for additional experimental procedures.
Simultaneously, novel average and multi-component molecular models for various rejuvenators (bio-oil BO, engine-oil EO, naphthenic-oil NO, aromatic-oil AO) were established. The average models were based on the average chemical characteristics, such as functional group distribution, element component, and average molecular weight. On the other hand, multi-component models were derived from molecular component distribution in rejuvenators through Gas Chromatography-Mass spectrometry (GC-MS) analysis. Both models were validated by comparing MD outputs with experimental results. It was found that the average models provided more accurate predictions regarding the glass transition temperatures, especially for the aromatic-oil. Additionally, a range of thermodynamic parameters for the rejuvenators were predicted and compared. Finally, the average structures of rejuvenators were adopted to construct subsequent molecular models of rejuvenated binders.
The consideration of compatibility between the rejuvenator and aged bitumen is crucial due to the potential phase separation. In this thesis, different thermodynamic parameters, such as solubility parameter difference Δδ, Flory-Huggins parameter\chi, and mixing free energy ΔGm were predicted and calculated using MD simulations for various rejuvenated bitumen systems. The predicted compatibility ranking for four rejuvenators was AO > BO > NO > EO, aligned with the experimentally measured thermal stability results. Moreover, separation index (SI) parameters based on rheological and chemical indices were available to assess the thermal stability of rejuvenated bitumen.
Furthermore, a comprehensive investigation was implemented to explore the effects of rejuvenator type, temperature, and aging degree of bitumen on the diffusion behavior of rejuvenators in aged binders at multiple scales. The molecular dynamics (MD) simulation method was employed to detect the molecular-level diffusion characteristics of rejuvenators and predict their diffusion coefficient (D) parameters. At the atomic scale, it was observed that there was a mutual but partial interfacial diffusion feature between rejuvenators and aged bitumen molecules. Meanwhile, the concentration distribution of rejuvenator molecules in aged bitumen was well described by Fick's Second Law. The calculated D values for the four rejuvenators ranged from 10-11 to 10-10 m2/s, and the diffusive capacities followed the order of BO > EO > NO > AO. To verify the MD simulation outputs, diffusion tests and dynamic shear rheometer (DSR) characterizations were conducted. The experimental results regarding the magnitude and order of the D values were in good agreement with the MD simulation findings. Lastly, it was observed that an increased aging degree of bitumen had a negative impact on the molecular diffusivity of BO, EO, and NO rejuvenators, whereas the D value of AO molecules enlarged as the aging level deepened.
A series of measurements were conducted to estimate the combined effects of rejuvenator type/dosage and aging degree of bitumen on the rheological properties of rejuvenated bitumen. Importantly, several critical indicators were identified that effectively assess and differentiate the rejuvenation efficiency of different rejuvenators on aged bitumen performance. In terms of high-temperature performance, parameters rutting failure temperature (RFT) and zero-shear viscosity (ZSV) from the linear viscoelastic (LVE) and flow tests were found to be useful. Additionally, parameters R3.2, Jnr0.1 or Jnr3.2, and Jnrslope were recommended for estimating the elastic performance, creep potential, and stress sensitivity of rejuvenated bitumen. Among these, the RFT parameter played a crucial role in evaluating and distinguishing the rejuvenation effectiveness of various rejuvenators on the high-temperature performance of aged bitumen. For the low-temperature relaxation property, parameters τ50s, t25%, and A were proposed as critical indicators. Regarding fatigue life improvement, BO demonstrated the highest rejuvenation effectiveness, followed by EO, NO, and AO rejuvenators. The fatigue failure temperature (FFT) parameter was identified as an effective indicator for fatigue performance evaluation in LVE tests. In linear amplitude sweep (LAS) tests, the fatigue life (Nf5), peak strain (ɛsr), and elastic modulus (E) parameters were optimized as effective fatigue indicators. Nonetheless, crack width (C) results were consistent with conclusions drawn from LVE and LAS tests. Particularly, the crack width C500 parameter showed strong correlations with other critical fatigue indicators, and its prediction could be achieved using correlation equations without the need for time-consuming TS tests.
At the atomic-level evaluation, several key thermodynamic properties of variable rejuvenated bitumen models were outputted by molecular dynamics (MD) simulation. The rejuvenation effectiveness of different rejuvenators on the thermodynamic indices of aged bitumen was estimated and compared. Importantly, the potential connections between these essential nanoscale parameters and critical macroscale indicators in terms of high-and-low temperature performance and fatigue behaviors of rejuvenated binders were explored. It was revealed that the addition of rejuvenators inherently catalysed a restoration of density and cohesive energy density (CED) values toward those of virgin bitumen. A suite of indicators, including UVEP, UWEK, EN, UVET, UNED, and ECT, are introduced as critical energetic parameters, each reflecting rejuvenator efficacy on atomic-level energetic features, except for specific cases involving aromatic-oil rejuvenated binders. Meanwhile, it is recommended to predict the relaxation properties of different rejuvenated bitumen by the fractional free volume parameter from MD simulation. The surface free energy (γ) emerges as a dependable index for assessing the rejuvenation efficacy of the cohesive cracking potential of aged bitumen.
In summary, a multiscale evaluation framework of rejuvenated bitumen was proposed and developed in this dissertation, together with a full understanding of the difference in rejuvenation efficiency and mechanism between various rejuvenators on chemo-thermodynamic-rheological performance restoration of aged bitumen. The outcomes of this thesis would be beneficial to promoting the formation of classification standards of rejuvenator additives, development of advanced multifunctional rejuvenators, and improvement of all-round evaluation method on rejuvenated binder.
Elastomer/plastic compound-modified bitumen was created by adding reactive elastomeric terpolymer (RET) to plastic-modified bitumen, made of either high-density polyethylene (HDPE) or recycled polyethylene (RPE). The rheological properties of the modified bitumen were analyzed. The results indicated that RET elastomer improved high-temperature modulus, temperature insensitivity, anti-rutting properties, elastic recovery, and shear-resistance of both HDPE and RPE-modified bitumen. A high dosage of RET had a negative impact on the cracking resistance of plastic-modified bitumen, thus it is recommended to use 1wt% for optimal results. The increased elasticity in the bitumen was attributed to the creation of a polymer network by RET.
Developed by Delft University of Technology, the tri-component polyurethane modified cold binder (PMCB) displays impressive durability and strength in asphalt mixtures, showing promise as a reliable binder for cold in-place recycling. However, when applying PMCB for rapid, in-situ recycling, the presence of moisture in reclaimed asphalt pavement (RAP) poses a significant challenge. To address this, an innovative approach involving treatment of the wet RAP with Calcium dioxide (CaO) prior to the integration of PMCB was tested. Evaluation methods used included the Indirect Tensile Test (ITT), followed by the calculation of the Indirect Tensile Strength Ratio (ITSR) to assess moisture susceptibility. Furthermore, Cantabro tests were performed to determine the material loss under abrasion and weathering conditions. These assessments underscored the feasibility of this approach. The treatment of wet RAP with CaO has proven a viable strategy for rapid in-situ recycling with PMCB, contributing to sustainable pavement construction. In addition, the research identified that a 5.5% concentration of the PMCB binder maximizes structural integrity and performance in the considered RAP.
Mechanical Framework for Geopolymer Gels Construction
An Optimized LSTM Technique to Predict Compressive Strength of Fly Ash-Based Geopolymer Gels Concrete
Surface energy is a key material property and can work as a crucial parameter in various mechanical models to predict the moisture sensitivity and fatigue damage of asphalt mixtures. The calculated surface energy values of the aggregate minerals strongly depend on their surface roughness. Therefore, it is very relevant for accurate calculation of surface energy to study the relationship between roughness and surface energy. This study aims to investigate the relationship between surface roughness and surface energy of aggregate minerals. Two minerals—quartz and calcite—were used for this study. The surfaces of the mineral specimens were treated to achieve four levels of roughness. Their surface roughness was described by three roughness parameters. Based on the sessile drop method, an optical tensiometer with a 3D topography module was employed to measure the contact angle and the surface energy of the minerals with different roughness. The influences of surface roughness on the contact angle and the surface energy were then analyzed. The results showed that the contact angle for both quartz and calcite decreases with the increasing surface roughness when it is less than 90° and increases when it is greater than 90°. The Wenzel equation can remove the effect of surface roughness on the contact angles of the minerals. The surface energy of quartz and calcite in the presence of roughness at the microscale would be underestimated when using the measured (apparent) contact angle. The corrected surface energy based on the Wenzel equation must be applied to represent the real surface energy of the minerals.