Yiqiu Tan

Application of Thixotropy to Analyze Fatigue and Healing Characteristics of Asphalt Binder

The fatigue performance of asphalt binder is critical to understanding the fatigue performance of asphalt mixtures, especially the effects of healing. Although research into the fatigue and healing characteristics of asphalt binder is found in numerous references, an efficient technique to evaluate these characteristics still does not exist. Thixotropy is a concept that may help explain the material behavior and provide an efficient evaluation technique. This property is related to the breakdown and buildup of microstructure that may cause the changes observed during fatigue and healing tests. Thus, tracking the thixotropy of asphalt binders may be a good method to study fatigue and healing. For this study, experiments were performed to characterize the fatigue and healing characteristics of three typical asphalt binders. Then a common thixotropic model was characterized with a relatively simple stepped-flow test and oscillation experiment. The resulting model shows good correlation with the measured fatigue and healing tests. This finding, though based on a limited number of binders, suggests that thixotropy may play a role in the fatigue and healing characteristics of asphalt binder.

Separation of thixotropy from fatigue process of asphalt binder

The fatigue performance of asphalt binder is critical to understanding the fatigue performance of asphalt mixtures. For the fatigue process to be modeled properly, the mechanism responsible for the fatigue behavior must be understood properly. In asphalt binder, it is widely accepted that the fatigue process is related to damage. However, some researchers have used the concept of thixotropy to describe the fatigue process in binder with equal success. If the real mechanism responsible for the observed reduction in modulus during a fatigue test is not properly understood, misinterpretation may occur. Such misinterpretation may lead to an improper assessment of a given materials quality and the acceptance of bad or rejection of good materials. This study attempted to separate the influence of thixotropy from other mechanisms during a fatigue experiment Tests were performed to characterize the exponential thixotropy model of four typical asphalt binders. The relationships between dynamic modulus and phase angle in a fatigue test and in a healing test were compared to determine the thixotropy-influence phase. According to the thixotropy model and fatigue test results, thixotropy is separated from the damage process for the entire fatigue test. A value of 50% |G*| after separation is put forward to evaluate the true fatigue characteristics of asphalt binder. The findings from this study, although based on a limited number of binders, suggest that thixotropy plays an important role in the fatigue characteristics of asphalt binder. The findings also provide a reasonable failure criterion for defining a fatigue evaluation index.

Diffusion of asphaltene, resin, aromatic and saturate components of asphalt on mineral aggregates surface: molecular dynamics simulation

In this research, the models of four asphalt components (asphaltene, resin, aromatics and saturate) and five minerals (SiO2, Al2O3, CaO, MgO and Fe2O3) were constructed individually, and then the interface models were constructed by adding the asphalt components and minerals together. The interfacial behaviour at molecular scale was simulated by setting boundary conditions, optimising the structure and canonical ensemble. The mean square displacement and diffusion coefficient of particles were selected to study the diffusion of asphalt components on the surface of different minerals. The results show that increasing the temperature can accelerate the diffusion of asphalt components. The diffusion speed of asphalt components on the surface of Al2O3 is faster than other mineral crystals. The temperature sensitivity of diffusion coefficient of asphalt components on the surface of CaO is the maximum. The diffusion speed of asphalt components ranked roughly as their molecular weight: saturate > aromatics > resin > asphaltene.

Development and Testing of Heat- and Mass-Coupled Model of Snow Melting for Hydronically Heated Pavement

Hydronic heating has been used to prevent ice formation and snow accumulation on road surface pavements with the aim of improving driver safety. A two-dimensional heat- and mass-coupled model for melting snow on a hydronically heated pavement is described. The extended Darcy law and continuity equation were adopted to describe water flow caused by moisture and temperature gradients. To solve the complex nonlinear equation set, an explicit finite difference method is used. The snow-melting model was evaluated with data measured from snow-melting experiments performed at the Harbin Institute of Technology in Heilongjiang, China. Results show that the model is capable of providing good simulations of the evolution of temperature and surface conditions during snowmelt. Simulation comparisons indicate that including the effects of melted snow on thermal properties is important in the simulation of temperature and surface condition during snowmelt.

Analysis of Linear Viscoelastic Response Function Model for Asphalt Binders

AbstractAsphalt binder properties play a significant role in the performance of asphalt pavement, but it is impossible to test the properties of asphalt binders under every condition. However, a suitable model that can be established using only a few tests can predict the behavior of asphalt binders under different conditions. Such models have received much attention over the last few decades. Many types of models are available, but most of them focus on only one kind of viscoelastic characteristic, whereas a good model should describe not only the dynamic viscoelastic characteristics of asphalt binders under cyclic loading but also their static viscoelastic characteristics. Based on this idea, the aim of this study is to compare the commonly used models and determine which one(s) can best describe both the dynamic and static viscoelastic characteristics of asphalt binders at intermediate temperatures and are suitable for establishing a fatigue damage model of asphalt binders. The dynamic viscoelastic cha...

Performance optimization method of composite modified asphalt sealant

AbstractCentral composite design-response surface methodology was used to determine the best content of raw materials and improve the performance of hot-poured bituminous sealant. Content range and process technology were studied through single factor analysis method. Cone penetration, elastic recovery, creep strength, and creep strain rate “m” were analyzed by central composite model testing. The response surface of the overall desirability was established and the optimal content of raw materials were determined and verified. Analyses of test results indicated that the optimal content of raw materials were as follows: rubber powder −25%, additive −7%, SBS −5%, and SBR −3%. This paper proposes the application of central composite design in the optimization of raw material dosage of hot-poured bituminous sealant.

Effect of Permeameter Size and Anisotropy on Measurements of Field Pavement Permeability

The permeability of hot-mix asphalt is important to a pavements durability. Measuring permeability along with density will give a better indication of a pavements durability than will density alone. The presence of water in the pavement for extended periods is directly linked to early deterioration. A modified field permeameter was developed for study of the water–pavement contact area (permeameter size) and anisotropy effect on field permeability measurements. A reliable sealing system was created to be consistent but not detrimental to the pavement surface. The results of the study showed that larger water–pavement contact areas yielded increasing influence on vertical flow, which better represented the one-dimensional flow conditions prescribed by the falling head method using Darcys law. Equations to calculate both vertical and horizontal permeability coefficients were developed with finite element (FE) simulations of the field tests as an axis-symmetric flow. Two permeability tests with two plate sizes were conducted with this approach to obtain both vertical and horizontal permeability coefficients. The FE simulations indicated that the nominal permeability calculation with one-dimensional assumptions was valid when the water–pavement contact area was large.

Investigation on the Mixing Stability of Asphalt Emulsion with Cement through Viscosity

AbstractCement asphalt emulsion (CA) mortar is a key material in the nonballast slab track. Its properties are largely dependent on the compatibility between asphalt emulsion and cement. The mixing stability of asphalt emulsion with cement is investigated by analyzing the viscosity of CA paste. Viscosity and the critical particle volume fraction of CA paste are proposed as indexes in evaluating the mixing stability of asphalt emulsion with cement, and factors influencing the mixing stability of asphalt emulsion are studied. Mixing stability is dependent on mixing method, superplasticizer, and emulsion type. The premixing cement method, superplasticizer, and good asphalt emulsion can increase the critical particle volume fraction of CA paste, which is helpful in achieving a low water–to–cement mass ratio (W/C). Anionic emulsion has much better mixing stability with cement than does cationic emulsion. The critical particle volume fraction of CA pastes with anionic emulsion increases stably with the mass rat...

Thixotropic Characteristics of Asphalt Binder

Asphalt binder has thixotropic characteristics that significantly affect its overall performance, but specifically fatigue performance, healing performance, and high temperature performance. Therefore, a clear understanding of the thixotropy of asphalt binder, together with proper modeling, is useful in researching the performance of the material. However, research in this area is still in the early stages of investigation. For the study reported in this paper, the thixotropy of four types of asphalt binder is examined by using various methods to establish corresponding thixotropy models. The results show that the exponential thixotropy model, the extended exponential function, and the structural kinetic model can be established by using different methods, and they all reflect the thixotropy of asphalt binder to some extent.

Performance evaluation of warm mix asphalt containing reclaimed asphalt mixtures

Abstract The objective of this study is to expose the effect of a variety of variables including three reclaimed asphalt pavement (RAP) contents, two warm mix asphalt (WMA) additives and a rejuvenating agent (or lack of) on the performance of WMA containing (WMA–RAP) materials. A laboratory study was conducted to evaluate the performance of WMA–RAP mixtures through rutting, bending and freeze-thaw splitting tests. Analysis of variance (ANOVA) was performed to analyse the significant effect of the variables on the performance. The tests results showed that the increased RAP content led to an increased rutting resistance and the decreased resistance to low-temperature cracking and moisture damage. The addition of the rejuvenating agent into the WMA–RAP mixtures can significantly improve the low-temperature cracking and moisture resistance. The ANOVA results showed that the RAP content had a significant effect on the rutting and low-temperature cracking resistance, and moreover, the rejuvenating agent (or lack of) had a large effect on the low-temperature cracking and moisture resistance.