Ki Hoon Moon

Comparison of Thermal Stresses Calculated from Asphalt Binder and Asphalt Mixture Creep Tests

Low-temperature cracking is a significant distress in asphalt pavements built in the northern United States and Canada. As temperature decreases, thermal stresses develop in the restrained asphalt surface layer; and when the temperature reaches a critical temperature, cracking occurs. The current guides use thermal stress as a critical input parameter in the low-temperature performance model. In this paper, statistical and graphical analyses are performed to compare thermal stresses that develop in an idealized asphalt pavement calculated from mixture creep data obtained using indirect tensile test (IDT) and bending beam rheometer (BBR) test. In addition, the idea of obtaining thermal stresses from binder BBR creep data is further investigated. Thermal stresses calculated using IDT and BBR mixture creep data, respectively, are similar. Thermal stresses calculated from binder creep data are significantly different than thermal stresses calculated from mixture creep data. The effect of physical hardening is investigated for a limited number of materials, and the effect on thermal stresses is significant.

Micromechanical–analogical modelling of asphalt binder and asphalt mixture creep stiffness properties at low temperature

The Hirsch model and the ENTPE transformation are commonly used to predict low-temperature creep stiffness of asphalt binders from the corresponding asphalt mixture experimental data (forward problem) and vice versa (inverse problem). Nevertheless, the applicability of these models is affected by low accuracy and limited understanding of the model parameters, respectively. In addition, the transformation parameter, α, associated with the ENTPE equation, cannot be directly obtained without relying on both binder and mixture creep testing. This paper presents a comprehensive experimental and theoretical study to link model parameters and ENTPE transformation to the mixture microstructure. This is accomplished by three-point bending tests, performed on asphalt binders and mixtures, digital image processing and statistical evaluation of the mixture microstructure, together with a newly proposed micromechanical–analogical material model, called Moon Cannone Falchetto (MCF) model, used for deriving an explicit expression of the α parameter. The values of α obtained by fitting the Huet model to the asphalt binder and asphalt mixture laboratory results are compared with the values predicted by the newly proposed formulation based on microstructural and volumetric information. The results indicate that reasonable predictions of low-temperature creep stiffness of asphalt binder can be obtained from the corresponding mixture low-temperature creep properties when the new expression of α derived from the MCF model is used in the ENTPE transformation.

Low Temperature Fracture Properties of Polyphosphoric Acid Modified Asphalt Mixtures

AbstractThe low temperature fracture properties of polyphosphoric acid (PPA) modified mixtures are evaluated and compared with those of polymer modified mixtures. The main objective is to determine whether PPA can partially or completely substitute traditional polymer modifiers, without adversely affecting the mixture’s resistance to thermal cracking. Laboratory compacted and field cored test samples from the Minnesota Road Research Project (MnROAD) were tested using traditional methods as well as newly developed fracture testing protocols: indirect tensile test (IDT), semicircular bending test (SCB), and disk-shaped compact tension test (DCT). The effects of temperature, air-void content, comma and long-term aging on low temperature fracture properties were analyzed; and field performance observations of the test cells from MnROAD were discussed. On the basis of the analysis, the fracture resistance of the PPA modified mixture is less than that of the SBS modified mixture. However, when PPA is used to su...

Rheological modelling of asphalt materials properties at low temperatures: from time domain to frequency domain

The rheological model, Huet model, which is composed of one spring and two power function elements, has two expressions: one in time domain, which is used for creep compliance, and one in the frequency domain, which is associated with complex modulus. Previous research efforts showed that the Huet model provides a very good fitting of experimental results obtained from creep and complex modulus tests on asphalt materials. However, the potential use of this model as an inter-conversion tool between the data obtained in the time domain and those in the frequency domain, and vice versa, was never previously evaluated. In this paper, the possibility of using the Huet model for predicting the complex modulus of asphalt binders and asphalt mixtures from the experimental data obtained from creep tests, performed with the bending beam rheometer at low temperatures, was investigated. The predictions obtained with the Huet model were experimentally verified by a set of complex modulus tests performed on 2 asphalt binders and 20 asphalt mixtures with the dynamic shear rheometer. The good agreement between the predicted and the measured complex modulus of asphalt binders suggested that the Huet model can be used for inter-converting data obtained in time and frequency domains. This was not verified in the case of the asphalt mixtures complex modulus data due to experimental limitations.

Microstructural Analysis and Rheological Modeling of Asphalt Mixtures Containing Recycled Asphalt Materials

The use of recycled materials in pavement construction has seen, over the years, a significant increase closely associated with substantial economic and environmental benefits. During the past decades, many transportation agencies have evaluated the effect of adding Reclaimed Asphalt Pavement (RAP), and, more recently, Recycled Asphalt Shingles (RAS) on the performance of asphalt pavement, while limits were proposed on the amount of recycled materials which can be used. In this paper, the effect of adding RAP and RAS on the microstructural and low temperature properties of asphalt mixtures is investigated using digital image processing (DIP) and modeling of rheological data obtained with the Bending Beam Rheometer (BBR). Detailed information on the internal microstructure of asphalt mixtures is acquired based on digital images of small beam specimens and numerical estimations of spatial correlation functions. It is found that RAP increases the autocorrelation length (ACL) of the spatial distribution of aggregates, asphalt mastic and air voids phases, while an opposite trend is observed when RAS is included. Analogical and semi empirical models are used to back-calculate binder creep stiffness from mixture experimental data. Differences between back-calculated results and experimental data suggest limited or partial blending between new and aged binder.

Histogram testing for strength size effect in asphalt mixtures at low temperature

This paper presents a simple formulation to predict the size effect curve of mean structural strength of the asphalt mixture from the strength histogram obtained on single-size beam specimens under three-point bend tests. This method is based on the weakest link model (WLM), which relates the mean structural strength to the size dependence of the probability distribution of the material strength. The proposed formulation is verified by an extensive experimental work consisting of strength histogram and mean size effect tests on the asphalt mixture at low temperature. The mean strength size effect curve obtained from the WLM is found to be in very good agreement with the experimental mean strength results obtained on the asphalt mixture specimens of different sizes and geometries, providing evidence of the ductile to brittle transition (Type I size effect) of the asphalt mixture strength.

Correlation of low temperature fracture and strength properties between SCB and IDT tests using a simple 2D FEM approach

In this paper, the low temperature strength of asphalt mixture is investigated based on indirect tensile (IDT) and semi-circular bending (SCB) tests and on two-dimensional numerical simulation. The values of maximum stress at crack tip in SCB simulation are obtained using commercial finite element software and cohesive zone modelling. Then, a correlation between the numerically determined maximum SCB stress and the strength value experimentally measured on IDT specimens is derived. It is found that the newly proposed relationship can be used to predict the asphalt mixtures strength of IDT un-notched specimens-based SCB fracture tests and contribute to better understanding of the low temperature strength properties of asphalt pavements.

Pressure Aging Vessel and Low-Temperature Properties of Asphalt Binders

The oxidative aging during the service life in asphalt binders used in construction of asphalt pavements significantly affects the performance of these pavements. A study investigating the effect of the pressure aging vessel (PAV) laboratory aging procedure on low-temperature properties of asphalt binders is presented. Bending beam rheometer creep tests and direct tension fracture tests were performed on laboratory-aged binders as well as extracted binders. Significant differences existed between extracted binder and PAV binder behavior at low temperatures. PAV aging was not always detrimental for asphalt binder fracture properties compared with the aging from rolling thin-film oven testing.

Low-temperature performance of recycled asphalt mixtures under static and oscillatory loading

In this paper the effect of reclaimed asphalt pavement (RAP) on the low-temperature properties of asphalt mixture is experimentally investigated and modelled. Two test methods are used: bending beam rheometer (BBR) mixture creep test, which is based on static loading, and dynamic shear rheometer (DSR) mixture complex modulus test, which uses oscillatory loading. First, creep stiffness, m-value, thermal stress, critical cracking temperature and complex modulus are derived, and then, statistically and graphically compared. Then, the rheological Huet model is used to evaluate the experimental BBR measurements and to derive a simple relationship associating the characteristic time of mixtures to the RAP content. The statistical results indicate that most of the mixtures prepared with RAP have relatively poorer performance compared to virgin mixtures up to a RAP content of 25%. Based on rheological modelling, it appears that RAP and characteristic time are linked through an exponential relationship.

Simple Approach to the Investigation of Asphalt Mixture Strength on Small Beam Specimens at Low Temperature

AbstractIn this research, a simplified approach based on size effect theory is used to extrapolate the strength values obtained on small asphalt mixtures specimens at low temperature with a modified bending beam rheometer (BBR). First, nine asphalt mixtures having different mix designs are prepared. Then, Weibull statistics and factorial design are used to evaluate the statistical distribution of the BBR measurements and the effect of conditioning time, loading rate, and testing temperature on material response, respectively. Finally, the BBR strength measured at three different temperatures is compared to the corresponding values obtained from two conventional test methods: direct tension (DT) and indirect tension (IDT) tests. It is observed that BBR strength values are statistically equivalent to those of IDT and DT when the size effect theory and the weakest link model are used to take into account the difference in volume, geometry, and stress field across the three testing methods.