Mansour Solaimanian

Modelling linear viscoelastic properties of asphalt concrete by the Huet–Sayegh model

In order to seek an appropriate mechanical model to describe the complex modulus and characterise the linear viscoelastic property of asphalt concrete, the Huet–Sayegh model was studied in this research. Laboratory tests of complex modulus were conducted on 20 different mixtures. Several mechanical models (Maxwell, Kelvin, generalised Maxwell, generalised Kelvin and Huet–Sayegh) and the mathematical model of sigmoidal function were applied to establish master curves of dynamic moduli. Results indicate that the Huet–Sayegh model can describe complex modulus more accurately using fewer numbers of parameters compared with other mechanical models.

Measurement and Evaluation of Asphalt Concrete Thermal Expansion and Contraction

Thermal expansion and contraction (TE/TC) of asphalt concrete (AC) play a significant role in both the thermal fatigue and low-temperature cracking of AC pavements. This paper discusses a test method and procedure developed to determine the AC coefficients of thermal expansion and contraction (CTE and CTC, respectively). Cylindrical specimens were subjected to temperature variations in an environmental chamber and specimen deformations were measured using extensometers. Temperature was applied in the range of −5°C to 40°C during both expansion and contraction phases. A specimen made from ceramic with very low CTE/CTC was also tested so that the influence of the self TE/TC of extensometers could be accounted for, and therefore, the measured deformation of an AC specimen was properly adjusted. A finite element (FE) model was developed to simulate the thermal stresses and strains inside the specimen, and to provide means for reliable computation of CTE/CTC. For this FE model, required AC viscoelastic properties were determined from the dynamic modulus test. The CTE/CTC of AC were then determined by using the calibrated deformation-temperature relationship. The standard aluminum and rubber specimens were also tested for TE/TC within a temperature range to validate the developed test method and computation approach. It was found that the CTE/CTC of AC were nonlinear and temperature dependent. The CTE/CTC determined for the aluminum and rubber specimens were found to be close to the standard values, therefore, validating the proposed approach for determination of CTE/CTC of AC.

Optimization of Asphalt Pavement Modeling based on the Global-Local 3D FEM Approach

ABSTRACT This paper presents the use of three dimensional (3D) finite element modeling (FEM) techniques to determine asphalt pavement response to loading. In mechanistic-empirical pavement design, the properties of materials used in pavement layers must be specified before the pavement response to imposed loads can be determined. A numerical method is used to obtain the relaxation modulus of linear viscoelastic materials, such as asphalt concrete, from the dynamic modulus measured on specimens procured from the field. Linear elastic behavior is assumed for granular materials. In addition, regarding finite element modeling, key factors such as model geometry, material properties, load and boundary conditions, element type, and mesh refinement are discussed in detail. The adopted Global-Local (GL) FEM approach is capable of simulating pavement responses to multiple axle loads with different load configurations, speed, and temperatures.

Field Instrumentation and Testing Data from Pennsylvania’s Superpave In-Situ Stress/Strain Investigation

The Pennsylvania Department of Transportation (PENNDOT) is sponsoring the Superpave In-Situ Stress/Strain Investigation (SISSI), which will complete its firth year in May, 2006. The purpose of the SISSI project is to provide data essential to the validation and regional calibration of Superpave and the Mechanistic-Empirical Pavement Design Guide (MEPDG). SISSI is a unique, state-of-the-art instrumentation and analysis project that encompasses eight different Superpave pavement sections across Pennsylvania, including both new pavements and overlays. The uniqueness of the SISSI project is that the selected pavement sections were instrumented as-designed and as-constructed on full-scale public highways, to represent actual practices and materials, without modification for this research, and with minimal interruption to the construction process. The sections are exposed to normal traffic, but evaluated seasonally and yearly using a loaded test vehicle. The project also takes advantage of the latest developments and equipment in the field of instrumentation technology for the full-scale investigation of pavement performance. The project includes detailed monitoring of the construction process, intensive materials characterization, detailed load-response information, traffic and environmental data, and performance measures. This paper briefly reviews the instrumentation and data collection at the eight sites. Examples are provided of the data acquired from the instrumentation, and the interpretation of that data. Data examples are included from the dynamic gauge response under the controlled truck loading and corresponding WIM (weigh-in-motion) analysis, and from the subsurface environmental gauges

Results of integrating simple performance tests and environmental conditioning system

Under the guidance of the Strategic Highway Research Program, an environmental conditioning system (ECS) was developed to simulate field conditions to identify the moisture sensitivity of asphalt concrete mixes. However, the system was not included in Superpaver because of poor repeatability. Studies conducted at the University of Texas at El Paso improved the prediction capabilities of the conditioning system. The modified system uses resilient modulus as a moisture sensitivity indicator. Resilient modulus has been commonly used by highway practitioners as an indicator of hot-mix asphalt concrete performance. However, as an extension to the Superpave system, under NCHRP Project 9-19, researchers have proposed simple tests to evaluate the performance of asphalt concrete. These tests are referred to as dynamic modulus, flow number, and flow time. The objective of this study was to evaluate the potential of these tests, when integrated with an ECS, to predict moisture damage in lieu of the resilient modulus. Three mixes of known performance were selected and conditioned by using a conditioning procedure of the modified system. The simple performance tests were done on unconditioned as well as ECS-conditioned specimens. The integration results indicate that the flow number and flow time tests, as conducted during this study, do not have the potential to replace resilient modulus in ECS for identification of moisture-susceptible asphalt concrete in the present form. However, the dynamic modulus test demonstrated their potential as a performance indicator replacing the resilient modulus test. The results of the integration efforts are presented here.

The Effect of Aspect Ratio on the Frequency Response of Asphalt Concrete in Impact Resonance Testing

A comprehensive study was conducted to investigate the influence of aspect ratio (height/diameter) of laboratory specimens on the frequency response of asphalt concrete when tested with impact resonance (IR). Testing was conducted over a range of air voids and temperatures. The IR test, performed in longitudinal mode over 100 cylindrical asphalt concrete specimens, demonstrated that the test is repeatable and reproducible. It was observed that the test response was greatly dependent on the specimen length regardless of the aspect ratio, but the dependency was not noted for specimens with the same diameter of larger aspect ratios. Specimens with the same aspect ratio but different size delivered different resonant frequencies. The test results indicated that the frequency response increased as the aspect ratio increased approximately up to 0.7, and then it decreased with a nonlinear trend as the aspect ratio increased beyond 0.7, indicating the tendency of the frequency response reaching a plateau as the aspect ratio increased. It was inferred from test results that there was a threshold aspect ratio at which the fundamental longitudinal frequency mode was not the dominant frequency mode. Velocity calculations from measured resonant frequencies indicated that the true material properties could be attained at an aspect ratio of as low as 1. Based on the results of this study, testing specimens with a diameter of 150 mm and a height of 170 mm commonly used for producing dynamic modulus test specimens, provided proper size and aspect ratio for testing with IR.

COMPARATIVE ANALYSIS OF VOLUMETRIC PROPERTIES FOR SUPERPAVE GYRATORY COMPACTORS

The experience with the original Superpave gyratory compactors (SGCs) introduced into the paving industry in 1994 was very positive. Consequently, since 1995 several additional manufacturers have developed SGCs to meet the growing demand for such devices. Although these units generally meet the broad requirements of the original SGC specification developed by FHWA, their basic designs are somewhat different. To ensure a systematic means for evaluation of the compactors, FHWA developed a standard protocol, designated AASHTO PP35. This procedure was used to evaluate various gyratory compactors. By using the discriminating value of 0.010 for difference in bulk specific gravity (Gmb), the compactors were evaluated in terms of Gmb. The five gyratory compactors evaluated were the Rainhart, Test Quip, Troxler Electronic Laboratories, Inc. (Troxler), Model 4141, Pine Instrument Company (Pine) Model AFG1A, and Interlaken compactors. These compactors were compared with either Pine Model AFGC125X (Pine 1) or Troxler Model 4140 (Troxler 1) SGCs, which were used as reference compactors. In addition, the project included a comparison of two Pine compactors (Pine 1 and Pine 2) of the same model (AFGC125XS) with each other. A total of 336 specimens (48 specimens for each compactor) were prepared for all the compactors to fulfill the comparison. Eleven comparisons of each candidate compactor and the reference compactor were made during a 12-month period. All of the candidate compactors compared favorably with an existing SGC. It was found that all seven compactors would provide the same results within the given tolerance range under the rigid conditions of the AASHTO PP35 protocol.

Investigating the effect of rejuvenators on low-temperature properties of recycled asphalt using impact resonance test

ABSTRACT Use of recycled asphalt pavement (RAP) in highway construction is highly promoted due to recent awareness in sustainable construction practices. The concerns with material brittleness in utilising higher content of RAP are alleviated through addition of rejuvenators to some extent. Inclusion of rejuvenator to the aged binder improves its flexibility and lessens its cracking potential. A study was undertaken to investigate the effectiveness of the impact resonance (IR) testing in determining low-temperature binder properties through mixture testing. To this effect, the presented study consisted of two stages. In stage I, the IR test was conducted on mixes made with different low-temperature grade binders. Stage II consisted of testing pure RAP mixes treated with a rejuvenating agent at different levels using the IR as well as testing blends of recovered RAP binder and rejuvenator and virgin binder using bending beam rheometer (BBR). The IR test was performed at a range of temperatures between and . The results indicate that the IR test can successfully capture the low-temperature properties of binders in virgin mixes as well as RAP mixes incorporating rejuvenator. A very high linear correlation was observed between stiffness from IR testing of the RAP mix and stiffness from BBR testing of the blend of recovered binder and virgin binder and rejuvenator. A good correlation was also observed between phase angle of RAP mixes obtained from IR with the m-value, a relaxation index, from BBR at a range of temperatures for a given rejuvenator content. The results clearly demonstrate the potential of IR to be used for grading and optimisation for the asphalt binder of RAP and rejuvenator content in lieu of the binder recovery method.

Evaluation of Nondestructiveness of Resonant Column Testing for Characterization of Asphalt Concrete Properties

The resonant column (RC) test has been used as a nondestructive test (NDT) to study dynamic properties of soils for the past few decades. With some modifications, this test can also be employed to characterize properties of asphalt concrete, especially because these properties are strongly dependent on the loading frequency. A conventional RC apparatus was retrofitted to characterize asphalt concrete properties at a range of temperatures from 10°C to 45°C. The RC test is believed to be nondestructive for most soils; however, this must be verified in case of testing asphalt concrete, especially at elevated temperatures. For this purpose, the impact resonance (IR) test, as a purely NDT tool, was used to check the integrity of asphalt concrete specimens before and after RC testing. The modulus values measured before and after RC tests, at each of the testing temperatures, were compared to evaluate the nondestructiveness of RC testing. Strain levels were also monitored to ensure that the material remained within the linear elastic range through the tests. The results show that the specimens exhibited the same modulus before and after RC testing over the full range of temperature and frequency sweep tests.

Characterization of high RAP/RAS asphalt mixtures using resonant column tests

AbstractUsing recycled materials in construction of asphalt pavements yields both economic and technical advantages. Recycled asphalt shingles (RAS) and reclaimed asphalt pavement (RAP) are two major sources to serve this purpose for which proper design and characterization are key elements. In this study, engineering properties of asphalt concrete containing RAP and RAS under dynamic loading were investigated. Three asphalt mixes were designed and included in this research: a conventional mix with no RAP/RAS as a control, a mix with 35% RAP, and finally a mix with 35% RAP and 5% RAS. A conventional resonant column (RC) apparatus was retrofitted and used for testing the specimens in torsional mode. Testing was conducted at five temperatures ranging from 10 to 45°C. Damping ratios and moduli of the mixes were analyzed and compared to assess the effect of the recycled materials on dynamic properties of asphalt concrete. Results clearly show the impact of RAP and RAS in increasing the mix stiffness. The stud...