Mihai Marasteanu

Effect of Reclaimed Asphalt Pavement (Proportion and Type) and Binder Grade on Asphalt Mixtures

Reclaimed asphalt pavement (RAP) has been used in the United States for more than 25 years because of the benefits in costs and environmental stewardship. The recent substantial increases in asphalt prices have led asphalt technologists to examine the increase in RAP use. The evaluation of the performance of the asphalt mixture containing RAP is therefore a priority for the asphalt materials community. This paper investigates the effect of RAP percentage and sources on the properties of asphalt mixtures. Ten asphalt mixtures, including two different RAP sources, three RAP content percentages (0%, 20%, 40%), and two different asphalt binders (PG 58-28 and PG 58-34) were investigated in this study. The complex dynamic modulus was performed on all mixtures at different temperatures and frequencies, and semicircular bend (SCB) fracture testing was performed for all mixtures at three low temperatures. Experimental results indicate that asphalt mixtures containing RAP have higher dynamic modulus values than the control mixtures containing no RAP. The stiffer asphalt binder was found to result in higher dynamic modulus values for both the control and the RAP-modified mixtures. Experimental data also show that the RAP source is not a significant factor for the dynamic modulus at low temperatures, although it significantly affects dynamic modulus values at high temperatures. In addition to test temperature, the RAP percentage was found to significantly affect the SCB fracture resistance of mixtures. However, for the dynamic modulus, values for the softer binder were higher than for the stiffer one at low temperatures. No significant statistical relationship between dynamic modulus and fracture energy was found.

Effect of Factors Affecting Fracture Energy of Asphalt Concrete at Low Temperature

ABSTRACT Low temperature cracking is considered one of the primary distress modes of asphalt pavements built in northern climates. The detrimental effects of low-temperature cracking of asphalt pavements have motivated new work in fracture testing of hot-mix asphalt (HMA). A comprehensive study was conducted to investigate the effect of various factors on the fracture resistance of asphalt mixtures at low temperatures. The Semi-Circular Bending (SCB) and Disc-Shaped Compact Tension Test (DCT) fracture tests were performed at three low temperatures to measure the fracture energy for 28 asphalt mixtures, which represent a combination of factors including binder type, binder modifier, aggregate type, asphalt content and air voids. In this study, the analysis from the experimental data indicates that fracture energy is strongly dependent upon temperature and significantly affected by type of aggregate and binder modifier. The results of the analysis show the significance of air voids in the SCB test, but no statistical difference was found for the DCT test data. The analysis also illustrates that richer mixtures, ones with more asphalt than the design optimum, are not necessarily more crack resistant.

Investigation of low temperature cracking in asphalt mixtures by acoustic emission

ABSTRACT This paper investigates the use of acoustic emission (AE) to characterize microstructural phenomena and the corresponding macroscopic behavior during the low temperature fracture of asphalt mixtures. An acoustic emission system with eight channels of recording was used to monitor the failure process during testing at low temperature using the semi circular bend (SCB) configuration in three Superpave mixtures used at MnROAD facility. Algorithms to automatically detect the relative arrival time of the AE signal and to locate the AE source were developed. The analysis of the accumulated AE events illustrated the relationship between the micro damage and macroscopic behavior at different loading levels. The damage level under certain loading conditions was evaluated and preliminary results showed that the load level corresponding to the localization played a critical role in the damage process of the material. As a first step, the fracture energy of asphalt concrete specimen was related to the accumulated AE energy. By observing the distribution of microcracks with different energy levels, it was reasonably assumed that 95% of the total AE energy before peak load corresponded to the process zone and this zone was determined to be around 3–6 mm in width and 20–30 mm in length for the materials tested in this research effort.

Effect of Binder Type, Aggregate, and Mixture Composition on Fracture Energy of Hot-Mix Asphalt in Cold Climates

Detrimental effects of low-temperature cracking of asphalt pavements and overlays have motivated new work in fracture testing of hot-mix asphalt (HMA). Recent work has indicated that the fracture behavior of asphalt concrete at low temperatures can be accurately predicted with a testing and modeling system that, along with viscoelastic bulk material properties, relies simply on fracture energy and material strength. In this study, the disk-shaped compact tension test is used to measure fracture energy of 28 HMA mixtures designed for cold climates. Four parameters are investigated: aggregate type (limestone and granite), temperature (three temperatures, encompassing the Superpave® performance graded binder low temperature grade for each binder tested), asphalt content (Superpave design asphalt content and Superpave design content plus 0.5%), and air voids (4% and 7%). A statistical analysis of results demonstrates the significance for fracture energy of binder content at higher temperatures, aggregate type, and temperature. The air void levels selected and binder content at lower temperatures, however, did not lead to a significant difference in fracture energy. An extrapolation technique is presented that was found to present a rational means for interpreting data from tests that were not finished because of equipment constraints.

Observation of Crack Propagation in Asphalt Mixtures with Acoustic Emission

Fracture in quasi-brittle materials is associated with the formation of microcracks, which release energy in the form of elastic waves called acoustic emissions. The use of acoustic emission (AE) in the characterization of the fracture behavior of asphalt mixtures at low temperatures is investigated, and a method that uses AE to locate the crack path is presented. An application of the method is detailed for fracture tests performed with the semicircular bend specimen on asphalt mixtures at low temperatures. A network of seven piezoelectric sensors was used to capture AE signals, and a nonlinear regression algorithm was employed to locate the AE events. The locations of microcracks were in good agreement with the crack path observed at the end of the test. When the load increased beyond 70% of the peak load, the rate of AE activity was significant, indicating the formation of microcracks, and the location of AE was concentrated in a distinct area called the process zone. Moreover, the location of AE in the postpeak load showed the movement of the process zone and identified the crack propagation in the macroscale.

Determination of Asphalt Mixture Creep Compliance at Low Temperatures by Using Thin Beam Specimens

The thermal cracking (TC) module (TCMODEL) of the recently developed Guide for Mechanistic–Empirical Design of New and Rehabilitated Pavement Structures (referred to as MEPDG) is used to predict thermally induced cracking in asphalt pavements over their service lives. The primary input to this model is the asphalt mixture creep compliance. The current standard test for determination of the creep compliance of asphalt mixtures is the indirect tensile test (IDT). This paper investigates the feasibility of using the bending beam rheometer (BBR) device to determine the low-temperature creep compliance of thin asphalt mixture beams (127 × 12.7 × 6.35 mm). The BBR device was used to evaluate 20 different asphalt mixtures, and the results were compared with the standard IDT results. Direct comparison of the BBR and the IDT results indicated that both methods produce slightly different creep compliance curves and that the relative ratio between the BBR and the IDT results varies with time and temperature. A simple phenomenological relation that gives good predictions of the IDT results on the basis of BBR creep compliance is proposed. The measured and predicted creep compliance curves were input into the MEPDG TC module, and the predicted depth of cracks and the amount of cracking were compared. The comparison showed that predicted creep compliance determined on the basis of the BBR results can be successfully used to estimate thermal cracking by use of the TCMODEL. It was concluded that the BBR device can be used for the practical and surrogate estimation of the creep compliance of mixtures. The proposed equation relating BBR and IDT creep compliances should be further validated with different types of mixtures.

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 creep compliance at low temperatures

ABSTRACT The creep compliance is one of the main material characteristics used to describe low temperature behavior of the asphalt mixtures. It also serves as a primary input to the current thermal cracking model in the US that is used to predict thermally induced cracking in asphalt pavements over their service life. The current standard method in the US to determine creep compliance of asphalt mixtures is the Indirect Tensile (IDT) test. This paper investigates the feasibility of using the Bending Beam Rheometer (BBR) device to determine the low-temperature creep compliance of thin asphalt mixture beams (127x12.7x6.35mm). The BBR was used to evaluate 20 different asphalt mixtures and the results were compared with the standard IDT results. Direct comparison of the BBR and the IDT results indicate that both methods produce slightly different creep compliance curves and the relative ratio between the BBR and the IDT results varies with time and temperature. A simple phenomenological relation was proposed that gives good predictions of the IDT results based on the BBR creep compliance. Furthermore, short-term aged asphalt binders used in the mixtures were also tested in the BBR. Modified Hirsch model was applied to the BBR results on both mixtures and binders and it was shown that this model is capable of producing quite accurate results in forward and inverse predictions using considered dataset. It was concluded that the BBR can be used in practical and surrogate estimation of the mixture creep compliance but proposed scheme requires validation on other mixture types.

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.

High-Temperature Rheological Properties of Asphalt Binders

Previous research efforts have shown that the rutting parameter used in the performance grade asphalt binder specifications, |G*|/ sin δ, does not reasonably predict the rutting potential of asphalt mixtures, especially when modified binders are used. A number of other parameters, such as the zero shear rate viscosity and the permanent strain accumulated under repeated creep and recovery, were investigated; however, no consensus was achieved. This paper investigates the use of zero shear rate viscosity and of repeated creep permanent strain as potential specification parameters and discusses the importance of temperature susceptibility and of strain tolerance to the rut resistance of asphalt binders.