Adam Zofka

Attenuated Total Reflection (ATR) Fourier Transform Infrared (FT-IR) Spectroscopy of Oxidized Polymer-Modified Bitumens

Oxidative age hardening of bitumen results in increasing fatigue susceptibility of bituminous mixtures, thus reducing the service life of asphalt pavements. Polymer additives to bitumen have been shown to improve its viscoelastic properties and, in some cases, reduce the level of bitumen hardening. Fourier transform infrared (FT-IR) spectroscopy enables evaluation of oxidation levels in bitumen by measuring the concentration of oxygen-containing chemical functionalities. This paper summarizes the results of the investigation of oxidative age hardening of polymer-modified bitumens (PMB) caused by accelerated aging in laboratory conditions. The PMB samples are prepared with different concentrations of styrene–butadiene-based co-polymers. Next, the PMB samples are aged using standard procedures that employ air blowing at 163 °C for 85 min followed by conditioning the samples at 100 °C and 2.1 MPa pressure for 20 to 48 hours. The resultant changes in their chemical composition are evaluated by portable attenuated total reflection (ATR) spectrometer. Measurements of ketone, sulfoxide, and hydroxyl content in PMB samples indicated similar oxidation pathways to those of non-modified bitumens. In addition, no evidence of polymer degradation due to accelerated aging of PMB was found in this study.

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.

Comparison of Low-Temperature Field Performance and Laboratory Testing of 10 Test Sections in the Midwestern United States

Current standards for evaluation of asphalt mixtures for low-temperature performance are based heavily on asphalt binder properties. These standards ignore the interactions between the binder and the aggregate, both chemically and physically. These interactions have been shown to have significant influence on the cracking resistance of asphalt mixtures. This paper investigates three laboratory tests that evaluate cracking resistance of asphalt mixtures at low temperatures. The first test is the traditional tensile strength test, the indirect tensile test (IDT). The two other tests are fracture tests: semicircular bending (SCB) and disk-shaped compact tension [DC(T)]. Field cores were obtained from 10 pavement sections in Minnesota and Illinois for testing in the lab. Results from the three laboratory tests were compared and correlated with field performance data. Results showed that the tensile strength from the IDT did not vary significantly for the 10 mixtures. The SCB and DC(T) correlated relatively well with each other depending on the test temperature. The SCB showed the best correlation and highest Spearmans rank correlation coefficient when compared with the observed quantity of cracking in the field. It was concluded that the laboratory fracture tests, SCB and DC(T), were better suited for qualitative cracking performance predictions at low temperatures than the IDT. For quantitative predictions, application of advanced analytical or numerical models (or both) that take into account material properties, environmental conditions, and loading conditions is recommended. Also recommended is that additional studies comparing laboratory fracture parameters with field performance be conducted.

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.

Evaluation of field aging effects on asphalt binder properties

ABSTRACT The oxidative aging that takes place in the asphalt binders used in the construction of asphalt pavements significantly affects the performance of the pavements during their service life. In this paper two issues that still generate a lot of debate in the research community are investigated: how far aging penetrates inside the asphalt layer and how reasonable laboratory aging tests simulate the aging occurring in the field. Cores were obtained from three cells at MnROAD facility and the binders were extracted and recovered from 25 mm slices cut along the depth of the cores. The properties of the recovered binders as well as the properties of the original binders aged in laboratory conditions were investigated, using standard testing procedures part of the current specifications as well as additional test methods. The results indicated differences in aging effects with location inside the asphalt layer and significant differences between the recovered and the laboratory aged binders.

Bending beam rheometer testing of asphalt mixtures

This paper provides a test protocol for performing creep tests on asphalt mixture beam specimens using the bending beam rheometer, and addresses the issues related to performing this test. First, a detailed sample preparation procedure is presented and the experimental data are provided to assess the consistency of this method. Then, three loading methods are investigated, and results are analysed and compared using statistical tools. Finally, a preliminary investigation on the representative volume element of asphalt mixtures at low temperatures is performed by testing beams of different sizes.

Evaluation of dynamic modulus of typical asphalt mixtures in Northeast US Region

This paper is based on the experimental results from the New England Transportation Consortium project titled “Establishing Default Dynamic Modulus Values for New England”. The dynamic modulus (|E*|) test results for 20 different dense-graded hot mix asphalt mixtures from five states in the Northeast US Region were compared with predicted |E*| values from Andrei-Witczak and Hirsch models as well as ENTPE transformation. The factors influencing measured |E*| values and prediction errors were also evaluated. The results showed that binder grade, air voids, and presence of reclaimed asphalt pavements (RAP) significantly affect |E*| values of asphalt mixtures. Statistical analysis of |E*| predictions revealed a similar level of underestimation produced by the three models over the high temperatures)>40°C). However, at medium and low temperatures (<25°C) the ENTPE transformation clearly outperforms two other models by yielding on average very small errors.

Advanced shear tester for evaluation of asphalt concrete under constant normal stiffness conditions

This paper presents motivation and details on the development of an advanced shear tester (AST) device capable of investigating the response of 150-mm cylindrical specimens under constant normal stiffness (CNS) conditions. Based on the laboratory experience and field observations from the soil and rock engineering, CNS conditions are particularly desirable when the normal stress changes considerably during the shearing process. Such situations occur in asphalt pavement structures especially under certain loading configurations. The CNS conditions are complementary to the constant normal load conditions that are applied in the current shear-mode devices incorporated in testing of asphalt concrete (AC) and pavement interface properties. This paper demonstrates the complex state of stress in the upper AC layer of a typical pavement under moving truck wheel and shows the need for the CNS device. In addition to outlining unique AST design features, this paper presents also the verification effort conducted on the solid Ultra-High Molecular Weight Polyethylene specimens. The AST results matched very well the reference data that were obtained under the elastic regime in the stress-controlled mode from the unconfined uniaxial compression and indirect tension tests. Finally, this paper demonstrates the example results collected on the solid AC specimens prepared with two different nominal maximum aggregate sizes. The analysis confirmed the ability of the AST device to capture both practical and fundamental phenomena occurring during the shearing process in the AC. It is believed that AST-type devices that are rather simple in design yet allow to induce complex state of stress in the AC specimens should be more recognised in the future research efforts.

Evaluating Applications of Field Spectroscopy Devices to Fingerprint Commonly Used Construction Materials

This report documents the results of the evaluation of practical portable spectroscopic equipment for in-situ analysis of a wide range of commonly used construction materials. The initial range of spectroscopic techniques evaluated by the project Team included Fourier-Transform Infrared (FT-IR) Spectroscopy, Size-Exclusion Chromatography (SEC), Nuclear Magnetic Resonance (NMR), X-Ray Fluorescence (XRF), and X-Ray Diffraction (XRD). The aforementioned techniques were applied to the following construction material categories: epoxy coating and adhesives, traffic paints, Portland cement concrete with chemical admixtures and curing membranes, asphalt binders, emulsions, and mixes with polymer additives. A series of laboratory and in-situ tests showed that the compact FT-IR spectrometer in the Attenuated Total Reflectance (ATR) mode, hand-held XRF instrument, and RTA’s Raman analyzer were successful in fingerprinting epoxy coatings and adhesives, curing compounds, and waterborne traffic paints. The ATR method also positively identified chemical admixtures in fresh mix samples and verified polymer presence in asphalt binders and emulsions. An electronic library of signature spectra of the materials tested in this project was created and submitted to SHRP 2 administration. Among other deliverables of this project are proposed AASHTO standards of practice for the analysis of titanium content in traffic paints by XRF, and identification of chemical admixtures by ATR.

Development of Double Edge Notched Tension (DENT) test for asphalt binders

This paper presents the experimental details of performing double edge notched tension (DENT) fracture tests on asphalt binders. The testing is performed using an existing direct tension (DT) test device and modificed molds for preparing the test specimens. The fracture toughness values obtained from DENT tests perfomed on nine different asphalt binders are in the reasonable agreement with the values published by other researchers. Further evaluation of the DENT and DT test results indicate that both produce similar trends in terms of failure strains. The KIC DENT results, however, have better repeatability compared to the DT results. The use of DENT test results to determine the critical cracking temperature in M 320-05 (former MP1a) AASHTO specification is discussed.