Modeling of the Rheological Properties of Asphalt Binder and Asphalt Mortar Containing Recycled Asphalt Material

Abstract The use of recycled materials in asphalt pavements increased significantly over the years, determining well known environmental and economic benefits. Many research agencies and road authorities evaluated the impact of Recycled Asphalt Pavement (RAP) on pavement performance. Nevertheless, the mechanism governing the interaction between virgin asphalt binder and aged RAP binder is not well understood. In this paper, the effect of RAP on the rheological properties of asphalt binders and mortars is experimentally evaluated, and theoretically modeled with the objective of defining a relationship between the linear viscoelastic (LVE) properties of binders and those of the corresponding mortars. Three asphalt binder types, obtained by blending a hard and a soft binder at three different percentages, were mixed with three different contents of a Selected fraction of Recycled Asphalt Pavement, called SRAP, for preparing the asphalt mortar samples. Dynamic Shear Rheomether tests were performed on binders and mortars to determining the complex modulus over a wide range of temperatures and frequencies. The rheological properties of the compound of virgin and RAP binder were evaluated by using a new approach based on a modified version of the Nielsen model, avoiding the extraction and recovery method. The results were then modelled by using the analogical 2S2P1D model, consisting of one spring, two parabolic and one-dashpot elements combined in series and then assembled together with a second spring in parallel. Based on test results, a simple experimental relationship between the characteristic times of the binder and the percentage of RAP in the mortar was found

Recommendation of RILEM TC237-SIB on cohesion test of recycled asphalt

This recommendation describes how to evaluate the presence of potentially active bitumen in recycled asphalt (RA) materials through the cohesion test. The experimental protocol is designed according to the research performed by the RILEM Technical Committee 237-SIB ‘‘Testing and characterization of sustainable innovative bituminous materials and systems’’ with the purpose, to develop a new, simple and fast method for the characterization of RA while limiting the need for conventional rheological tests. The guidelines in this recommendation focus on the testing procedure including specimen preparation, data analysis and provide information on the preparation of a tests report

Estimation of the SHStS transformation parameter based on volumetric composition

The Shift-Homothety-Shift in time-Shift (SHStS) transformation, derived from the 2S2P1D model, represents one of the most convenient and simple solution for describing the rheological behavior of asphalt materials, when the transformation parameter α is known. In this paper, a simple expression for predicting the SHStS transformation parameter α is proposed. First a set of binders and eighteen different mix designs are used together with the Hirsch model and the 2S2P1D model to derive a regression equation linking α to the binder content and to the fractal dimension of the aggregate gradation. Then, a second set of binders and mixtures is used to experimentally verify the prediction of the α parameter obtained with the newly proposed formulation. It is found that the values of the transformation parameter are in relatively close agreement

Microstructural and rheological investigation of asphalt mixtures containing recycled asphalt materials

Using increased proportions of Reclaimed Asphalt Pavement (RAP) in asphalt pavements construction has become a top priority due to significant economic and environmental benefits. A similar trend has also emerged in Recycled Asphalt Shingles (RAS), which represent the main roofing material in US. In this paper, the effect of adding RAP and RAS on low temperature properties of asphalt mixtures is investigated using microstructural analysis and modeling of rheological data obtained on eight asphalt mixtures. Detailed information on internal microstructure of asphalt mixtures is obtained from digital images of asphalt mixtures beams and numerical estimations of spatial correlation functions. It is found that that microstructure spatial distribution is not affected by RAP and RAS addition. Mechanical analog (Sharpe, 2008 [18]) 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 blending between new and old binder may be only partial

Fatigue comparisons of mortars at different volume concentration of aggregate particles

Fatigue cracking is one of the primary failure mechanisms in asphalt pavements and it predominantly occurs within the mortar phase. For this reason, in recent years, a number of studies were carried out by various researchers to better understand the fatigue mechanism in such a critical mixture phase. In the present work, time sweep tests were performed in strain control mode on asphalt mortars prepared with three volume percentages of fine aggregate at different aging conditions. In particular, two different asphalt mortars were used: one containing Recycled Asphalt Pavement (RAP) materials and the other one composed of the same RAP aggregate skeleton without the aged binder. The influence of the different aging conditions, the presence of the aged binder and the addition of fine aggregate particles on the fatigue resistance of the mortars were evaluated. Moreover, a relationship between the parameters of the obtained fatigue laws and the different aging and mix design conditions was found. The proposed relationship can be easily used to predict the fatigue resistance of a mortar composed of a specific volume concentration of aggregate particles and recycled material. The potential extension of the proposed relationship to mixtures may eventually result in the implementation of a simple analysis tool for practitioner limiting the need for more sophisticated and expensive fatigue tests on asphalt mixtures

Microstructural Characterization of Asphalt Mixtures Containing Recycled Asphalt Materials

Most 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 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 evaluation of 2- and 3-point correlation functions. No significant variations are found among the gradation curves and minimal differences were observed for 2- and 3-point correlation functions. This indicates the addition of the recycled materials does not significantly affect the aggregate spatial distribution of the asphalt mixtures. However, an increase in autocorrelation length was found for some of the mixtures containing recycled shingles

The Flexural Strength of Asphalt Mixtures Using the Bending Beam Rheometer

Asphalt mixture creep stiffness and strength are needed in the low temperature temperature algorithm of the AASHTO Mechanistic Empirical Pavement Design Guide to predict low temperature performance. A procedure for obtaining creep stiffness by testing thin mixture beams with a Bending Beam Rheometer was previously developed at University of Minnesota. Preliminary work investigating the possibility of also obtaining bending strength by testing thin mixtures beams is presented in this paper. Indirect Tensile (IDT), and Direct Tension (DT) strength tests are performed on eleven mixtures. The same eleven mixtures are used to perform three sets of tests using the proposed method named Bending Beam Strength (BBS). First set is performed to investigate the reliability and reproducibility of BBS testing method, and the validity of the measuring concept. Weibull modulus is calculated as part of the analysis. Second set of tests is done to investigate the effect of temperature, conditioning time and loading rate on the measured strength of three I1l1xtu:es. Third set consists of tests performed at three different temperatures on eight mixtures. IDT, DT and BBS experimental determined strengths are first compared without using any transformation, and results are found to be statistically different. The results are then transformed to take into account the size of the samples and the testing configuration. The statistical analysis indicates that BBS strength values are similar to the values obtained with IDT test method