Asphalt Institute

Lexington, KY, United States

Asphalt Institute

Lexington, KY, United States
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Blankenship P.B.,Asphalt Institute | Zeinali A.,InstroTek Inc.
Asphalt Paving Technology: Association of Asphalt Paving Technologists-Proceedings of the Technical Sessions | Year: 2016

As the temperature of an asphalt pavement drops to below freezing point, the asphalt material starts to lose its ductility, and consequently, the asphalt mixture becomes more susceptible to cracking. The disk-shaped compact tension [DC(T)] fracture test has been used to quantify the fracture properties of asphalt concrete at subzero temperatures for more than a decade. The Asphalt Institute laboratory has successfully utilized the DC(T) test in several research studies. As a result of these studies, a valuable database has been gathered which represents the sensitivity of the DC(T) test, and exhibits how the test is capable of capturing the effects of various factors on the performance of asphalt mixtures at low temperatures. This paper briefly presents the findings from some of these studies. The paper presents the response of the DC(T) test to the variations in several factors relative to asphalt pavements including the crude source of the asphalt binder, aging of the asphalt mixture, deficiency in the in-place density, pavement temperature, using a warm-mix agent, using RAP and RAS materials, and chip sealing as a preservation method. The test proved to be well capable of capturing the variations in these factors; therefore, it can be utilized by pavement managers to assess changes in specimens from asphalt pavements over time to help determine if any maintenance or rehabilitation action is required. Furthermore, the test can be used to evaluate laboratory-made mixtures and ascertain if they would perform satisfactorily in their designated environmental conditions. © 2016 Taylor & Francis.


Gallivan V.L.,U.S. Federal Highway Administration | Chang G.K.,Transtec Group Inc. | Horan R.D.,Asphalt Institute
Asphalt Paving Technology: Association of Asphalt Paving Technologists-Proceedings of the Technical Sessions | Year: 2011

Intelligent Compaction (IC) is a major innovation in compaction technology that has been studied extensively in the US over the last five years. IC is defined as a process that uses vibratory rollers equipped with a measurement/documentation system that automatically records various critical compaction parameters in real time during the compaction process. The recorded information is then displayed for the roller operator and project personnel to improve the compaction process. Field studies by the authors and other researchers have shown that IC has many potential benefits that can result in better compaction processes and improved process/quality control/acceptance procedures. These benefits are likely to result in the construction of longer lasting asphalt pavements. Suppliers of IC technology have conducted extensive research and development and are geared up to make IC rollers commercially available. In short, the stage is now set for agencies that would like to implement the use of IC technology in a practical manner. It has been a well known fact for decades that effective compaction is a critical step in the construction of quality Hot Mix Asphalt (HMA) pavement. In recent years, the understanding has grown that pavement materials must be properly compacted in the field to obtain the desired long service lives. With this in mind, there have been many improvements and innovations in compaction equipment, as well as in situ test equipment and specifications related to compaction over the years. Manufacturers have been modifying their compaction equipment, State agencies have been modifying their specifications, and contractors have been modifying their processes over the years all in an attempt to improve the compaction of HMA pavements. This paper discusses the 21st century practical efforts to improve the compaction of HMA pavements by using " intelligent" equipment that provides the contractors and agencies real-time information regarding the effectiveness of their compaction operations. The results of multiple field demonstrations have shown that IC mapping of the underlying materials prior to paving can identify weak or non-uniform areas that affect the quality of the HMA pavement compaction efforts. The contractor can optimize rolling operations using IC with increased knowledge of the HMA surface temperatures and roller locations. Thus, IC is a technology that is increasingly being used nationally and internationally and has been shown to provide for greater control and oversight of the compaction process, resulting in improved and more uniform compaction.


Anderson R.M.,Asphalt Institute | King G.N.,GHK Inc. | Hanson D.I.,Amec Foster Wheeler | Blankenship P.B.,Asphalt Institute
Asphalt Paving Technology: Association of Asphalt Paving Technologists-Proceedings of the Technical Sessions | Year: 2011

Non-load related cracking of asphalt pavements is cracking that is associated with the development of thermal stresses - usually manifesting itself as transverse and block cracking. Transverse cracking is generally referred to as low temperature cracking since it is associated with cracking that develops as the asphalt pavement is subjected to low temperatures that approach the limiting stiffness of the asphalt binder. Block cracking, however, is usually associated with cracking that may happen as the asphalt pavement ages and loses durability. As part of a research project involving airfield asphalt pavements, a laboratory study was conducted to evaluate if there was any potential relationship between asphalt binder properties and non-load related cracking. The objective of the research was to identify one or more parameters that could be easily determined by testing that would allow an airport manager to monitor the loss of durability experienced with aging and to use the information to assess when the airfield asphalt pavement would need preventative maintenance to minimize the effects of non-load associated cracking. In the laboratory study, three asphalt binders were selected representing different expected aging characteristics. Testing was conducted on asphalt binders in their unaged condition, as well as on asphalt binders that had undergone long-term aging in the Pressure Aging Vessel (PAV) at 100C and 2.1 MPa pressure for 20, 40, and 80 hours. The purpose of the longer PAV aging times was not to correlate with any expected service life, but simply to create a more highly-aged sample. Past research indicated some relationship between ductility (conducted at an intermediate temperature) and the durability of an asphalt pavement. Using ductility as the hypothesized property related to flexibility, two parameters were identified that related well to ductility and the expected loss of flexibility with aging. The first is a parameter suggested by other researchers - G′(η′/G′) - as determined using the Dynamic Shear Rheometer (DSR). The second is a parameter that quantifies the difference in continuous grade temperature for stiffness and relaxation properties - referred to in the paper as ΔT c. In both cases, the parameters appear to quantify the loss of relaxation properties as an asphalt binder ages. Limited field testing from three general aviation airports generally validated the findings from the lab study, with the newer pavements having values of G′(η′/G′) and AT c that indicated less aging and more flexibility than the older pavements. Based on the study findings, values were identified for both parameters that could provide an indication of a loss of durability that could lead to an increased risk of non-load associated cracking.


Gierhart D.,Asphalt Institute
Asphalt Paving Technology, AAPT | Year: 2012

The Federal Highway Administration and Asphalt Institute conducted a cooperative study to identify the best methods for specifying and constructing longitudinal joints. The effort reviewed "best practices" for constructing asphalt longitudinal joints in four ways. The best method for constructing a longitudinal joint is to eliminate it by paving in echelon such that the lanes are rolled together while hot. However, the need to maintain traffic limits the opportunities for paving in echelon. This is an abstract of a paper presented at the Journal of the Association of Asphalt Paving Technologists Asphalt Paving Technology (Austin, TX 4/1-4/2012).


Clements T.M.,Kentucky Transportation Cabinet | Blankenship P.B.,Asphalt Institute | Mahboub K.C.,University of Kentucky
Asphalt Paving Technology: Association of Asphalt Paving Technologists-Proceedings of the Technical Sessions | Year: 2012

Recent improvements in warm mix asphalt technologies have spurred an aggressive adoption of these new practices within the asphalt paving industry. Concerns have arisen among federal and state agencies about the effects of this line of products on the performance of asphalt pavements. An investigation of the effects of lowering mixing, aging and compaction temperatures using Meadwestvaco's Evotherm 3G™ 09 chemical additive while varying the loose mix aging time was performed. Hamburg Wheel-Track Testing, Flow Number, Dynamic Modulus and Fracture Energy testing were used to evaluate mechanistic properties of the materials. It was found that lowering production temperatures has a significant influence on rutting related testing and a limited to negligible effect on dynamic modulus and low temperature fracture energy testing.


King G.,GHK Inc | Anderson M.,Asphalt Institute | Hanson D.,Amec Foster Wheeler | Blankenship P.,Asphalt Institute
RILEM Bookseries | Year: 2012

Asphalt aging is typically monitored through rheological changes at high pavement temperatures. Asphalt quality in laboratory aging experiments is then ranked using classic measures such as absolute viscosity ratios or changes in ring and ball softening point. However, this study [1,2] suggests that location on Black Space Diagrams at lower pavement temparatures is a better predictor for block cracking and related failure mechanisms associated with highly oxidized asphalt. Three unmodified asphalts were PAV aged for 20, 40, and 80 hours. Modulus and phase angle were determined using DSR for intermediate temperatures, while stiffness and m-values using BBR were measured at low temperatures. Proposed aging functions such as Glover-Rowe's Damage Parameter and Anderson's R-value were compared to lab results on Black Space Diagrams. The key finding from the binder phase of this study is that location in Black Space is an important performance measure for cracking. However, the initial quality of the asphalt as determined in Black Space is just as important to performance as rheological changes in modulus and phase angle occurring during aging. Aged mixtures were then tested in the BBR to determine whether binder aging trends would translate to mixture properties. One surprising finding was that microdamage forms in unconfined, highly aged mixture specimens as they cool. Findings from this study suggest that environmental effects models and timing strategies for pavement preservation should be revised to consider binder properties in Black Space, where both the initial asphalt quality and the effects of oxidation on key physical properties can be monitored. A new approach links initial binder quality with oxidative aging to propose a non-load induced cracking parameter for performance-related specifications. © RILEM 2012.


Blankenship P.B.,Asphalt Institute | Anderson R.M.,Asphalt Institute
Asphalt Paving Technology: Association of Asphalt Paving Technologists-Proceedings of the Technical Sessions | Year: 2010

One of the concerns that the Kentucky Transportation Cabinet (KYTC) would like addressed is to better understand the relation of field density to pavement durability. An investigation of the effect of density on asphalt mixture performance was performed. Various performance and performance-related tests such as the beam fatigue, dynamic modulus, and flow number were used to measure the effect of varying density. It was found that an increase in 1.5 percent density can increase the fatigue life by eight percent, dynamic modulus by 15 percent, and the Flow Number by 34 percent. This paper also compares the Flow Number to the cycles to five percent failure using the same test. The paper concludes by performing a "what-if" scenario and adding more asphalt binder to the lab design to further understand the mixture's potential performance and compactability in this higher than normal asphalt binder design scenario. It is found that a potentially more balanced mixture could be achieved by adding more asphalt and ultimately increasing the inplace pavement density. Adding asphalt and increasing pavement density should have a positive, compounding effect on overall performance if higher field density is achieved with the added asphalt cement content.


Zeinali A.,University of Kentucky | Mahboub K.C.,University of Kentucky | Blankenship P.B.,Asphalt Institute
Asphalt Paving Technology: Association of Asphalt Paving Technologists-Proceedings of the Technical Sessions | Year: 2014

Almost all of the current hot mix-asphalt (HMA) fracture tests are considered to be research tools. This paper describes the development of the indirect ring tension (IRT) fracture test for HMA, which was designed to be an effective and user-friendly test that could be used at the DOT level. Numerical modeling was utilized to calibrate the stress intensity factor formula of the IRT fracture test for various specimen dimensions. The results of this extensive analysis were encapsulated in a single equation. An experimental plan was developed to optimize the test parameters for HMA specimens. The experiment results revealed that the test is highly repeatable and capable of capturing the variations in the fracture properties of HMA. Moreover, the data from laboratory tests were utilized to estimate the maximum allowable crack lengths for the pavements based on a viscoelastic model. © 2014 Taylor & Francis.


Xu Q.,Transtec Group Inc. | Chang G.K.,Transtec Group Inc. | Gallivan V.L.,U.S. Federal Highway Administration | Horan R.D.,Asphalt Institute
Construction and Building Materials | Year: 2012

Conventional pavement analysis and design methods are based on the homogeneous or uniform material model such including the multi-layered analysis program and AASHTO design methods. With the Intelligent Compaction (IC) technology on hot mix asphalt (HMA) involved in recent years, the compaction uniformity of material property can be quantified. This paper intends to study the effects of compaction uniformity on pavement performances using the Bomag IC Evib - a measurement of elastic moduli with 100% coverage of the compaction area. The three dimensional (3-D) finite element (FE) model was built to simulate pavement responses with the heterogeneous HMA moduli derived from the field IC measurements. Then the Mechanistic-Empirical Pavement Design Guideline (M-E PDG) models were used to predict HMA performances of rutting and fatigue life. The geostatisical semivariogram model was studied to evaluate the uniformity of predicted performances. Different from conventional pavement analysis and designs, spatial-distributed heterogeneous moduli of the asphalt layer were considered in this work. Results show that spatial uniformity of material moduli affects pavement performances in terms of the distress severity and uniformity. Less uniform material moduli result in higher rutting depths and shorter fatigue lives. For the case study in this paper, the mean and peak values of fatigue lives for the heterogeneous model are 38.2% and 0.1% of those for the uniform model. A pavement section with overall lower material moduli does not necessarily correspond to inferior performances as the effects from uniformity of material property may dominate other factors. Therefore, it is recommended that the uniformity of pavement layer properties that emulate the typically more variable service condition be considered in future pavement designs and performance predictions. © 2011 Elsevier Ltd. All rights reserved.


Zeinali A.,University of Kentucky | Mahboub K.C.,University of Kentucky | Blankenship P.B.,Asphalt Institute
Road Materials and Pavement Design | Year: 2014

Almost all of the current hot-mix asphalt (HMA) fracture tests are considered to be research tools. This paper describes the development of the indirect ring tension (IRT) fracture test for HMA, which was designed to be an effective and user-friendly test that could be used at the Department of Transportation level. Numerical modelling was utilised to calibrate the stress intensity factor formula of the IRT fracture test for various specimen dimensions. The results of this extensive analysis were encapsulated in a single equation. An experimental plan was developed to optimise the test parameters for HMA specimens. The experiment results revealed that the test is highly repeatable, and capable of capturing the variations in the fracture properties of HMA. Moreover, the data from laboratory tests were utilised to estimate the maximum allowable crack lengths for the pavements based on a viscoelastic model. © 2014 © 2014 Taylor & Francis.

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