HW

H. Wang

info

Please Note

45 records found

Journal article (2022) - H. Wang, H. Zhang, X. Liu, P. Apostolidis, S. Erkens, Athanasios Scarpas, Zhen Leng, G.D. Airey
Crumb rubber modified bitumen (CRMB) can be regarded as a binary composite system in which swollen rubber particles are embedded in the bitumen matrix. Previous study has successfully implemented the micromechanics models in predicting the complex moduli of CRMB binders using more representative constituent parameters. In the regime of master curves, while the micromechanics models used predicted well in the high-frequency range, they underestimated the complex modulus in the low-frequency range. The current study aims to further improve the prediction accuracy of micromechanics models for CRMB by considering the interparticle interactions. To accomplish this goal, a new reinforcement mechanism called chain entanglement effect was introduced to account for the interparticle interaction effect. Results show that the polymer chain entanglement effect accounts for the underestimation of complex modulus and lack of elasticity (overestimation of phase angle) for CRMB at high temperatures/low frequencies. The mechanical properties of bitumen matrix and entangled polymer network can be determined based on the rubber content. The introduction of the entangled polymer network to the generalized self-consistent model significantly improved the prediction accuracy for both complex modulus and phase angle in the whole frequency range. In summary, by incorporating the physio-chemical interaction mechanism into the currently available models, a new dedicated micromechanics model for predicting the mechanical properties of CRMB has been developed. The predicted viscoelastic behaviors can thereafter be used as inputs for an improved mix design. ...
Journal article (2021) - Cong Du, Guoyang Lu, Haopeng Wang, Yiren Sun, Pengfei Liu, Dawei Wang, Sabine Leischner, Markus Oeser
Porous asphalt (PA) pavements are widely employed in areas with wet climates. As particle enhancement inclusions in asphalt mastic, mineral fillers play essential roles in improving the performance of PA pavements. This study developed a coupled multiscale finite element (FE) model, involving the mesostructure of PA mixture and PA pavement. Four types of mastic properties were employed with four mineral fillers (Granodiorite, Limestone, Dolomite, and Rhyolite) in the mesoscale portion of the pavement model to analyse the effects of filler types on the performance of pavements. The performances (load-bearing capacity, rutting resistance, and ravelling resistance) of pavements with different fillers were identified and ranked, and their correlations with the chemical components of the four fillers were analysed. The computational results showed that pavements with Rhyolite and Granodiorite fillers have higher load-bearing capacities and rutting resistance, while the Limestone and Dolomite fillers can improve the ravelling resistance of the PA pavements. In the correlation analysis, the chemical components Al2O3 and SiO2 play dominant roles in improving the load-bearing capacities and rutting resistance of the PA pavements, and the fillers with high percentages of CaO can improve the ravelling resistance of the PA pavements. ...
Journal article (2021) - Guoyang Lu, Haopeng Wang, Yuqing Zhang, Pengfei Liu, Dawei Wang, Markus Oeser, Jürgen Grabe
The pore-water pressure generated by intermittent dynamic vehicle loading under various saturation states is recognized as a critical factor influencing the behaviour of permeable pavement structures, especially the behaviour of UGB layer. However, the underlying mechanisms of hydro-mechanical interaction in the UGB layer and the influence on the pavement structure are still unclear. This study aims to characterize the changes in dynamic response in permeable pavement structures under various saturation conditions by considering the hydro-mechanical interaction within the UGB layer. To achieve this objective, a full-scale test track with a PUPM wearing course was constructed. Pressures and water distribution were characterized by embedded sensors within different layers of the test track when subjected to the accelerating pavement test. Based on the coupled SAME model, the water distribution and the dynamic response of UGB in the rainfall events were both characterised and solved by FEM. The results predicted by the proposed SAME model correspond to the field measurements, and the influence of the water content on the resilient modulus distribution within the UGB layer was then estimated. Based on the predictions for the stress state of the UGB layer, the sensitivity analysis was also proposed. ...
Conference paper (2021) - M. Zhang, K. Zhong, M. Sun, H. Wang, X. Tian, Q. Huang
In order to evaluate the influence of different admixtures on the performance of cement stabilized macadam, the influence of fly ash, expansive agent, brucite fiber and alkali salt early strength agent on dry shrinkage, temperature shrinkage, compression and tensile properties of cement stabilized macadam mixture was studied by unconfined compressive strength test, dry shrinkage test, temperature shrinkage test and splitting test, respectively. The results show that the temperature shrinkage, dry shrinkage, unconfined compressive strength and Splitting strength of cement stabilized macadam with fly ash, expansive agent, brucite fiber and basic salt are greatly improved. ...
Journal article (2021) - Houzhi Wang, You Wu, Jun Yang, Haopeng Wang
Cracks are one of the main problems that plague road workers. A correct understanding of the internal crack propagation mechanism of asphalt pavement will help road workers evaluate the road’s working status more comprehensively and make more reasonable decisions in design, construction, and maintenance work. This paper established a three-dimensional asphalt pavement layered model using the software ABAQUS and fracture mechanics theory and the extended finite element method were used to explore the mechanical response of the pavement base layer’s preset reflective cracks. This paper investigated the influence of the modulus of each layer, vehicle load on the principal stress, shear stress, J-integral, and two stress intensity factors (K1, K2) during the pre-determined crack propagation process of the pavement base layer, and the entropy method was used to analyze the above-mentioned mechanical response. The results show that the main factor affecting the propagation of reflective cracks on asphalt pavements is the modulus of the bottom surface layer. However, from a modeling perspective, the effect of increasing load on crack growth is obvious. Therefore, in terms of technical feasibility, the prevention of reflective cracks should still be achieved by controlling the driving load and prohibiting overloading. ...
Journal article (2021) - S. Ren, X. Liu, P. Lin, H. Wang, W. Fan, S. Erkens
The chemo-rheological properties of crumb rubber modified bitumen are always unstable due to the mutable and uncontrollable swelling-degradation degree of crumb rubber in bitumen matrix. The study aimed at exploring the continuous swelling and degradation behaviors of crumb rubber modified bitumen (CRMB) considering the influence of rubber size through monitoring the dynamic viscosity changes of CRMB binders. Moreover, the synergistic effects of swelling-degradation degree and rubber size on the chemical and rheological properties of CRMB were investigated. The results revealed that the rubber size significantly influenced the swelling and degradation behaviors of CRMB. The reduction of rubber size shortened the equilibrium swelling and degra-dation time, while increased the related viscosity dramatically. Moreover, during the degradation process, the decrease of rubber size could accelerate the continuous swelling rate, increase the maximum viscosity and reduce the continuous swelling time of CRMB. Meanwhile, the high swelling degree and large rubber size were bene-ficial to enhance the high temperature properties, while the CRMB binder with high degradation degree showed the better low-temperature property, workability and wider Newtonian flow region. Furthermore, the degra-dation degree promoted the formation of free hydroxide groups, aldehydes, carboxylic acids and esters, while the swelling process increased the average molecular weight of whole liquid phase in CRMB binder. The outputs from this fundamental study are beneficial to provide the guidance to preparation conditions optimization of CRMB binders with different viscous property standards ...
Journal article (2021) - Liang Zhang, Pengfei Li, Guanfeng Hu, Sufeng Zhang, Bin Hong, Haopeng Wang, Dawei Wang, Markus Oeser
As an environmentally friendly alternative for the production of high-performance modified asphalt by chemical reactions, a liquid-state polyurethane-precursor-based reactive modifier (PRM) was developed and employed in the asphalt modification. In contrast to the traditional solid bitumen modifier, for example, rubber and thermoplastic elastomers, the PRM as a liquid modifier has more significant advantages in reducing energy consumption and improving asphalt performance, which has attracted widespread attention. However, the aging resistance and its mechanism are not clear. In view of this, the aging performance of two PRM-modified bitumen (PRM-70 and PRM-90), under the short-term thermo-oxidative aging, long-term thermo-oxidative aging, and ultraviolet (UV) aging conditions, was investigated through chemical and mechanical methods. The results show that the PRM-90 is more susceptible to the thermos-oxidative aging and UV aging. The use of low-penetration-grade bitumen and ensuring an adequate reaction are beneficial to enhance the aging resistance of PRM-modified bitumen. The impact of aging on high-temperature performance of PRM-modified bitumen is great, followed by the low-temperature performance and the anti-fatigue performance. The mechanic-relevant rheological aging index (RAI) and fracture energy index (FEI) are recommended to evaluate aging properties for PRM-modified bitumen. This study not only provides support for further research on the relationship between the aging properties and mechanical performance of PRM-modified bitumen, but also provides a reference for conducting mechanism analysis. ...
Conference paper (2021) - Guoyang Lu, Haopeng Wang, Pengfei Liu, Zhen Leng, Markus Oeser
Permeable pavements are often affected by pore clogging, which leads to their functional failure and reduced service life. However, the clogging mechanism and its impact on the permeability and complex pore microstructures in pervious pavement remains unclear. The aim of current study is to quantify the clogging behavior in pervious pavement materials and carry out investigations on the development of pore characteristics and permeability. Novel Polyurethane bound pervious mixture (PUPM) were adopted for comparative study in present research with conventional Porous Asphalt (PA). The Aachen Polishing Machine (APM) was selected to perfectly serve as a simulator for clogging process of pavement in the actual service condition. The development of pore characteristics in terms of clogging was experimentally illustrated. The developed experiments and analysis can further strengthen the understanding of the clogging mechanism within the porous pavement material. ...
Journal article (2021) - Haopeng Wang, Xueyan Liu, Panos Apostolidis, Di Wang, Zhen Leng, Guoyang Lu, Sandra Erkens, Athanasios Skarpas
Rubberized asphaltic materials have been frequently combined with warm-mix asphalt technologies to tackle the issues of high energy consumptions and emissions during construction. Effective and accurate characterization of binder properties is conducive to the improvement of long-term pavement performance. The current study aims to quantify the effects of rubber content and warm-mix additives on rutting and thermal cracking performance of crumb rubber-modified bitumen (CRMB), and explore the rubber and additives modification mechanisms and their impacts on the binder performance. CRMBs containing different rubber contents and warm-mix additives after long-term aging were subject to multiple stress creep and recovery (MSCR) tests and low-temperature frequency sweep tests using a dynamic shear rheometer (DSR) with 4-mm loading plate to investigate the high- and low-temperature performance, respectively. Rheological tests were also conducted on the bitumen and rubber phases of CRMB to understand the rubber modification mechanism. Results show that CRMB binders have superior rutting and thermal cracking resistance due to rubber modification. The improvement of high- or low-temperature performance is more prominent at higher rubber concentrations. The effects of warm-mix additives on the rutting and thermal cracking performance are different. Generally, the wax-based additive improves the rutting resistance but negatively affects the low-temperature performance. In contrast, the chemical-based additive has an opposite effect except for the high-temperature performance of neat bitumen. The stiffening of the bitumen phase and the contribution of swollen rubber particles in the bitumen matrix together contribute to the peculiar viscoelastic response of CRMB, i.e., stiffer/softer and more elastic at high/low temperatures. This modification mechanism explains the superior rutting and thermal cracking performance of CRMB. ...
Journal article (2021) - Rui Li, Zhen Leng, Haopeng Wang, Manfred N. Partl, Huayang Yu, Zhifei Tan, Christiane Raab
From the pavement construction emission perspective, bitumen emulsion is considered more environment-friendly than conventional bitumen because of its much lower construction temperature. However, bitumen emulsion faces the major concern of low mechanical strength especially at high service temperatures. To improve the mechanical performance of bitumen emulsion, waterborne epoxy resin can be used as a modifier. Nevertheless, there still lacks fundamental understanding on the effects of waterborne epoxy resin on the microstructure and rheological performances of the residual bitumen of the emulsion. To fill this gap, this study aims to investigate the microstructure and develop the constitutive model of the waterborne epoxy resin-modified bitumen emulsion residue (WEBER). To achieve this objective, a confocal laser scanning microscopy was first adopted to characterise the microstructure of WEBER. The frequency sweep tests were then conducted, and the ‘2S2P1D’ model was applied to simulate the WEBER’s dynamic response at different loading frequencies. The results indicated that the waterborne epoxy resin formed a polymer-rich film around the bitumen phase in the emulsion residue when its content reached 3 wt%, and the ‘2S2P1D’ model can well describe the WEBER’s dynamic response at different loading frequencies. ...

Experimental characterization and modelling

Doctoral thesis (2021) - H. Wang, S.M.J.G. Erkens, A. Scarpas, X. Liu
A sustainable pavement, which can minimize environmental impacts through the reduction of energy consumption, natural resources and associated emissions while meeting all performance conditions and standards, is in urgent need to combat the climate change. The current scenario of depleting crude oil, reduced quarry zones, and stringent environmental regulations has driven the use of waste materials and by-products in pavement applications. The utilization of crumb rubber from scrap tires for bitumen modification has become a common engineering practice since last century...
...
Journal article (2021) - Haopeng Wang, Hong Zhang, Xueyan Liu, Athanasios Scarpas, Zhen Leng
Crumb rubber modified bitumen (CRMB) can be regarded as a binary composite system in which swollen rubber particles are embedded in the bitumen matrix. The current study aims to further improve the prediction accuracy of micromechanical models for CRMB by considering the interparticle interactions. To accomplish this goal, two different strategies were used. Firstly, the (n+1)-phase model was applied to the CRMB system by considering the multilayer properties of swollen rubber particles. Secondly, a new micromechanical scheme called the J-C model was used to account for the interparticle interaction issue. Results show that the (n+1)-phase models slightly increase the prediction accuracy but the underestimation of complex modulus at lower frequencies remains unsolved. The J-C model remedies the underestimation of modulus in the low-frequency range by other models and provides an overall improvement for the relative prediction accuracy by properly addressing the interparticle interactions from the perspective of particle configuration. ...
Considering the application scenarios of rubber granules from waste tires in the bitumen modification process (wet or dry process), both aerobic and anaerobic aging of rubber may occur. The current study aims to investigate the thermal aging behavior of waste tire rubber samples using nanoindentation and environment scanning electron microscopy (ESEM) tests. Both aerobic and anaerobic aging tests with different durations were conducted on rubber samples. The complex moduli of aged rubber samples were measured by nanoindentation tests. The surface morphology and elemental composition of aged samples were obtained by ESEM tests together with the energy dispersive X-ray analysis. Results have shown that for both aerobic and anaerobic aging, the equilibrium modulus derived from the complex modulus curve first increases and then decreases with aging time. However, the time needed for the aerobically aged sample to reach the maximum equilibrium modulus is shorter than the anaerobic case. Aging results in crack propagation and an increase of sulfur content on the rubber surface until it reaches the peak. The degree of crosslinking reflected by sulfur content for anaerobic aging is higher than aerobic aging. The morphological change and elemental change of rubber correlate well with the change of mechanical properties. The aging of rubber from the waste truck tire at 180°C can generally be separated into two stages: crosslinking dominant stage and chain scission dominant stage. ...
Conference paper (2021) - M. Zhang, K. Zhong, M. Sun, Z. Qian, H. Wang, T. Gan
In order to study the maintenance strategy of Epoxy Asphalt Concrete (EAC) in low temperature environment, the similarity of four anti-cracking performance indexes (plane strain fracture toughness, bending stiffness modulus, ultimate tensile stress and ultimate elongation linear strain) of EAC were analyzed, and the mathematical model for investigating the relationship between the number of freeze-thaw cycles and the comprehensive evaluation index of the crack resistance of epoxy asphalt mixture (EAM) was established in this paper. At first, the weight of each index is determined by one-way ANOVA. Then the anti-cracking performance of EAC under freezing-thawing condition is evaluated by fuzzy comprehensive evaluation method. The results show that the pavement maintenance bureau needs to carry out the maintenance of epoxy asphalt pavement on steel bridge deck every 30 days (1 month) for ensuring the crack resistance of EAC in winter with low temperature. ...
Fundamental models should be developed and utilized in order to facilitate the chemo-mechanical design of modified binder systems for paving applications but not only. Especially, the fact that the incorporation of new chemical substances used as bio-based modifiers or alternative binders is attracting great interest to replace traditional technologies, the development of tools able to provide insight into the various physio-chemical phenomena is crucial. Among other polymer-bitumen interaction phenomena, the dissolution mechanism of polymers in bitumen is a significant aspect that should be considering in order to enhance binder properties through polymer modification. The current research gives emphasis on modelling the mechanism of dissolution for rubbery polymers in bitumen. ...
Recently warm mix asphalt (WMA) technologies have been introduced to rubberized asphalt mixtures to decrease the required construction temperatures and to alleviate the hazardous gas emissions. Rubberized asphalt pavements combining with WMA have the potential to improve the long-term pavement performance. This study aims to investigate the fatigue performance of crumb rubber modified bitumen (CRMB) containing warm-mix additives using different characterization methods. The effects of crumb rubber modifier (CRM) content (5%, 10%, 15% and 22% by weight of base bitumen) and warm-mix additives on the binder fatigue performance were investigated. Various laboratory tests, including frequency sweep tests, time sweep (TS) tests and linear amplitude sweep (LAS) tests, were conducted on the long-term aged binders to obtain indicators of fatigue performance. Results show that there is a good correlation between the measured fatigue life determined by TS tests using the dissipated energy concept and the predicted fatigue life determined by LAS tests using the simplified viscoelastic continuum damage (S-VECD) theory. However, the traditional Superpave fatigue parameter and the G-R parameter cannot characterize accurate enough the fatigue performance of modified binders. CRMB binders exhibit superior fatigue performance compared to the neat bitumen. The effects of warm-mix additives on the fatigue performance are different for neat bitumen compared to CRMB binder. Based on the findings in this study, rubberized asphalt mixture combining with WMA additives is expected to have a promising long-term fatigue performance. ...
Waste tire rubber has been incorporated into asphalt modification for decades due to its various benefits. There are two main mechanisms during bitumen–rubber interaction: rubber swelling and chemical degradation. This study surveys these two processes from the viewpoint of polymer science. The kinetics of rubber dissolution and thermodynamics of rubber swelling are discussed to provide a fundamental understanding of the interaction process and to demonstrate how optimisation of material selection and processing procedures can lead to the desired binder properties. Factors including the interaction conditions and raw material characteristics are analysed based on the previous theories and compared with experimental results. ...
Crumb rubber modified bitumen (CRMB) can be considered as a binary composite system where rubber particles are embedded in the bitumen matrix. The bitumen-rubber interaction process (mainly swelling) significantly changes the mechanical properties of both bitumen and rubber phases. This study aims to predict the complex moduli of CRMB binders with more representative constituent parameters using micromechanical models. To achieve this goal, frequency sweep tests using a dynamic shear rheometer were performed on the liquid phase of CRMB and swollen rubber samples to represent the essential properties of bitumen matrix and rubber inclusion. In addition, the numerical swelling model was developed to estimate the effective volume concentration of rubber after swelling. Results show that the liquid phases of CRMB are stiffer and more elastic than the neat bitumen while the swollen rubber is softer and more viscous than the dry rubber. The effective volume concentration of rubber can increase to 2.126 times as the blend percentage based on the finite element analysis. Using the liquid phase of CRMB binder and swollen rubber properties as the micromechanical model inputs yield more accurate predictions. The used four micromechanical models predict well at higher frequencies while underestimating the complex modulus at lower frequencies. ...
Rubber swelling in bitumen, which is a diffusion-induced volume expansion process, plays a dominant role in the design of crumb rubber modified bitumen binders and their properties development. This study aims to investigate the kinetics of bitumen diffusion into truck tire rubber, the equilibrium swelling characteristics of rubber, and the mechanical properties of rubber before and after swelling at different high temperatures. Fourier transform infrared spectroscopy results indicate that no rubber dissolution happens during the interaction in the temperature range from 160°C to 200°C. Aliphatic compounds from bitumen preferentially diffused into rubber during the swelling process. The diffusion coefficients of bitumen into rubber were determined by the sorption test using the gravimetric method. The diffusion coefficient increases with the increase of temperature in an Arrhenius form. The volume expansion of rubber during swelling was captured by the X-ray computed tomography scan images. Rubber swells faster at the earlier stages, then the expansion rate slows down. The swelling ratio of rubber increased from 1.97 at 160°C to 3.03 at 200°C after 36 h interaction. Mechanical tests by dynamic shear rheometer reveal that swollen rubber becomes softer compared with the dry rubber and exhibits obvious viscoelastic behaviors. With the increase of temperature, the softening and viscous effect are more significant. The obtained parameters can be implemented to swelling and micromechanical models to better predict the binder properties. ...
Oxidative aging is a complex phenomenon in bitumen and its fundamental understanding is needed to optimize paving materials with long-lasting characteristics. This research reports on a diffuse-reaction model for predicting the oxidation of bituminous binders over time and under different conditions. As known, the oxidation of bitumen is affected by the material chemistry, film thickness and temperature. Thus, these factors were considered in this research to simulate the oxidation of a thin bitumen film. Carbon compounds were assumed as the oxidation index of a model bitumen and analyses were performed enabling prediction of chemical compositional changes. In the future, the current model can be used to simulate the actual oxidative aging in (un)modified binders, such as epoxy modified asphalt, presented in a companion paper (Apostolidis et al., Kinetics of Epoxy-Asphalt Oxidation. AM3P). ...