Augusto Cannone Falchetto

Microstructural Characterization of Asphalt Mixtures Containing Recycled Asphalt Materials

AbstractMost studies addressing the use of recycled asphalt materials in asphalt paving mixtures are based on experimental tests and performance evaluation. Investigating the effect of adding recycled materials to the microstructure of asphalt mixtures has received little consideration. For example, higher-order microstructural information can be used in place of simple volumetric information as input in micromechanical models that can more accurately predict the effective properties of asphalt mixtures. In this paper, the influence of adding three different recycled materials, reclaimed asphalt pavement (RAP), manufacturer waste scrap shingles (MWSS), and tear-off scrap shingles (TOSS), on the microstructural distribution of the aggregate phase is investigated using digitally processed images of asphalt mixtures and numerical evaluations of two- and three-point correlation functions. No significant variations are found among the gradation curves, and minimal differences were observed for two- and three-p...

Investigation of asphalt mixture strength at low temperatures with the bending beam rheometer

A new strength test method for asphalt mixture at low temperatures is presented in this paper. The method uses a modified bending beam Rheometer (BBR), capable of applying loads at different rates. Two major factors, that can significantly affect strength, were analysed: cooling medium and specimen size. Similar strength values were obtained in air and potassium acetate and significantly lower values were obtained in ethanol. Preliminary investigation with sodium fluorescein (FL) indicates the fluorescing marker diffused in mixtures when ethanol was used. The failure distributions of BBR mixture beams and of larger beams (LBs) were analysed using histogram testing and size effect theory. Different Weibull moduli were obtained for BBR and for the LB, which indicates that BBR beams may be too small to capture the representative volume element of the material.

Investigation on asphalt binder strength at low temperatures

A new strength test method for asphalt binders at low temperatures is investigated in this paper. A modified Bending Beam Rheometer (BBR), capable of applying loads at different rates, is used to obtain asphalt binder flexural strength. Strength values obtained from the BBR test are compared with strength values obtained from the Direct Tension Tester (DTT) test and significant differences are found between the two tests. Additional BBR strength tests are run on asphalt binder beams after replacing the ethanol used in the cooling bath with potassium acetate, similar to DTT testing conditions, and flexural strengths significantly larger than those obtained with ethanol are obtained. Weakest link theory is used to convert three-point bending strength to direct tension strength and to perform volume correction of DTT values. Based on the corrected values, the BBR and DTT strength measurements are similar, when the same cooling medium is used. The effect of the cooling medium on BBR creep stiffness is also evaluated. From the limited experimental tests, it appears that there are no significant differences in stiffness and m-value after 1 h of isothermal storage.

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.

From Mixtures to Binders: Can the Inverse Problem be Solved?

ABSTRACT This paper investigates the inverse problem of obtaining asphalt binder properties from asphalt mixture properties. First, the forward problem of predicting the mixture properties from binder properties is investigated using several micromechanical and phenomenological models and asphalt binder and mixture creep stiffness data obtained with the Bending Beam Rheometer. Next, Hirsch model was selected as most promising and its capability in providing the binder properties from the mixture properties was evaluated. Digital Image Processing techniques are also used to obtain additional information on the microstructure of the mixture and to improve the performance of the models.

Comparison of rheological parameters of asphalt binders obtained from bending beam rheometer and dynamic shear rheometer at low temperatures

In this paper, an investigation was performed to determine if the complex modulus obtained from frequency sweeps performed with the dynamic shear rheometer (DSR) can be used to accurately predict the creep compliance obtained experimentally using the bending beam rheometer (BBR). Two sets of asphalt binders were tested at low, intermediate, and high temperatures and the results were analysed using 2S2P1D and DBN rheological models. DSR and BBR testing was performed in two different laboratories using different equipment manufacturers. It was found that significant differences are observed between the creep stiffness obtained with DSR and BBR devices, most likely due to the different preparation and conditioning of the test specimens in different cooling media.

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.

Development of simple relationship between asphalt binder and mastic based on rheological tests

The relationship between the different phases of asphalt materials, from asphalt binder to mastic and mixture, has received significant interest over the years. The Shift-Homothety-Shift in time-Shift (SHStS) transformation developed by the research team of the École Nationale des Travaux Publics de l’État has been found to provide a very effective tool to relate the rheological properties of binders to those of the corresponding mixtures. In this paper, the possibility of using the SHStS transformation to link the behaviour of asphalt binder to that of mastic is investigated with the objective of proposing a simple expression of the SHStS transformation parameter, α, as function of the filler content in the mastic. First, an experimental campaign consisting of dynamic shear rheometer tests is conducted on a set of binders and mastics to obtain the material response at different temperatures and frequencies. Then, the rheological 2S2P1D (2 springs, 2 parabolic elements, 1 dashpot) model is used to evaluate the experimental measurements. Finally, a simple relationship associating the characteristic times of asphalt binder and mastic as function of the filler content is developed. The proposed expression allows to easily and efficiently predict the complex modulus of mastics from the binder complex modulus and vice versa.

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.