| 1. |
- Birgisson, Björn, et al.
(författare)
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A new algorithm for determination of crack growth path in HMA materials
- 2007
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Ingår i: International Journal on Road Materials and Pavement Design. - 1468-0629 .- 2164-7402. ; 8:1, s. 47-60
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, a new algorithm is presented for determination of the crack growth path in hot mix asphalt (HMA) materials. In a newly developed fracture simulator, the pavement structure is modeled with a viscoelastic boundary element method, which provides an attractive alternative to finite element-based methods for modeling crack initiation and growth. According to the HMA fracture mechanics, a fundamental energy-based threshold is used to determine crack growth and the direction of crack growth, and viscoelastic mixture properties are used to determine the rate of crack growth. To determine where a crack propagates, a grid in the critical zone is defined to cover a range of possible crack growth directions and locate the direction of the maximum dissipated creep strain energy (DCSE). The crack will propagate in the direction of the maximum DCSE when the DCSE in this direction reaches the damage threshold. The fracture simulator is shown to predict top-down crack growth patterns in hot mix asphalt pavements observed in the field.
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| 2. |
- Birgisson, Björn, et al.
(författare)
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A viscoelastic displacement discontinuity method for analysis of pavements with cracks
- 2006
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Ingår i: International Journal on Road Materials and Pavement Design. - 1468-0629 .- 2164-7402. ; 7:4, s. 417-455
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a development of the displacement discontinuity boundary element method for modeling the linear viscoelastic behavior of asphalt mixtures and simulating crack propagation in asphalt pavements. The viscoelastic formulation is based on the correspondence principle, involving Laplace transformation of the constitutive equations and the associated boundary conditions. The time-dependent behavior of the asphalt mixtures is characterized by the Burger's or power law model. The associated transformed problem is solved in an analogous way to using the linear-elasticity-based displacement discontinuity method. The corresponding time-dependent viscoelastic solution is obtained using an efficient and robust algorithm for numerical Laplace inversion. A substructuring approach is employed to construct the layered formulation and higher order elements are used to capture the bending effect in the pavement structure. With incorporation of the hot mix asphalt (HMA) fracture mechanics, which is based on the concept that there is a dissipated creep strain energy (DCSE) threshold to cracking, the numerical framework can efficiently simulate crack onset and growth in asphalt pavements. Several examples are presented to verify the accuracy and efficiency of the numerical method and to demonstrate its application in modeling pavement cracking.
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| 3. |
- Birgisson, Björn, et al.
(författare)
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An optical strain measurement system for asphalt mixtures
- 2009
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Ingår i: Materials and Structures. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873. ; 42:4, s. 427-441
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Tidskriftsartikel (refereegranskat)abstract
- Knowledge of the conditions governing the initiation and propagation of cracks in hot mix asphalt (HMA) mixtures is a prerequisite for a comprehensive understanding of HMA cracking mechanisms. Traditional strain measurement sensors have proved to be not completely adequate in the sense that they do not provide pointwise measurements, thus not pinpointing the location of crack initiation, and not accounting for non-uniform strain distributions. This paper presents a digital image correlation (DIC) system for non-contact and full strain field measurements, conceived for the purpose of investigating the cracking behavior of HMA mixtures. The whole system was developed so as to account for the special nature of typical HMA testing configurations. An image matching technique (least squares matching) was employed for providing matches with sub-pixel accuracy. The performance of the method was investigated by several tests. The DIC system was shown to overcome the shortcomings of traditional on-specimen strain measurement devices achieving satisfactory accuracy compared to strain gauges.
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| 4. |
- Birgisson, Björn, et al.
(författare)
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Development of new moisture-conditioning procedure for hot-mix asphalt
- 2007
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Ingår i: Transportation Research Record. - : SAGE Publications. - 0361-1981 .- 2169-4052. ; :2001, s. 46-55
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Tidskriftsartikel (refereegranskat)abstract
- The presence of pore water in mixtures can cause premature failure of hot-mix asphalt pavements. The processes typically associated with moisture damage are complex and occur over a long period of time in the field. Short of being able to simulate each of the possible mechanisms of moisture damage directly, the ideal laboratory-based conditioning system should accelerate the penetration of moisture through the asphalt film and at the same time minimize complicating effects. This paper presents the results of an experiment conducted to determine whether it was possible to use cyclic pore pressures to induce enough damage to distinguish between mixtures known to be highly resistant from mixtures known to be susceptible to moisture damage. Experimental constraints included requirements that conditioning be accomplished within a reasonable length of time and that typical laboratory equipment be used. Evaluation of the resulting effects of moisture damage included the use of the Superpave (R) indirect tension test and the energy ratio parameter. Findings show that cyclic pore pressures can be used to accelerate moisture damage enough to distinguish between mixtures known to be strippers and those known to be highly resistant to moisture damage. The use of cyclic pore pressures to accelerate moisture damage in mixtures may minimize the introduction of other confounding damage effects on the mixtures.
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| 5. |
- Birgisson, Björn, et al.
(författare)
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Influence of Mixture Properties on Fracture Mechanisms in Asphalt Mixtures
- 2010
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Ingår i: International Journal on Road Materials and Pavement Design. - : Informa UK Limited. - 1468-0629 .- 2164-7402. ; 11, s. 61-88
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Tidskriftsartikel (refereegranskat)abstract
- This paper reports a research study aimed at providing insight into key mechanisms and mixture properties that influence fracture in asphalt concrete. The experimental analysis was based on the Hot Mix Asphalt (HMA) Fracture Mechanics visco-elastic crack growth law. HMA cracking mechanism was investigated using multiple laboratory test configurations on both unmodified and polymer modified mixtures. A Digital Image Correlation (DIC) was employed to more accurately capture localized or non-uniform stress distributions in asphalt mixtures and as a tool for detecting first fracture. Crack initiation and crack growth were predicted effectively using a Displacement Discontinuity (DD) boundary element method.
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| 6. |
- Birgisson, Björn, et al.
(författare)
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Numerical implementation of a strain energy-based fracture model for HMA materials
- 2007
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Ingår i: International Journal on Road Materials and Pavement Design. - 1468-0629 .- 2164-7402. ; 8:1, s. 7-45
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Tidskriftsartikel (refereegranskat)abstract
- This work combines a new strain energy-based fracture criterion with a viscoelastic displacement discontinuity boundary element method to investigate crack growth in hot mix asphalt (HMA) materials. The study employs a fundamental crack growth threshold and simulates crack growth by accumulation of the dissipated creep strain energy (DCSE) below this threshold, only healable micro-damage develops, and non-healable crack initiation or growth occurs, otherwise. A critical zone is introduced ahead of the crack tip to represent the portion of the material being damaged. Once the cumulative micro-damage inside the critical zone reaches the cracking threshold, the crack extends by the length of the critical zone. An HMA fracture simulator is developed by incorporating the DCSE threshold concept into a numerical framework based on a viscoelastic displacement discontinuity method, which has proven its convenience and efficiency in crack modeling. Numerical analyses are performed to predict piecewise crack propagation in asphalt mixtures using the HMA fracture simulator, and laboratory experiments are also conducted to verify and validate the numerical model.
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| 7. |
- Drakos, Christos A., et al.
(författare)
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Identification of a physical model to evaluate rutting performance of asphalt mixtures
- 2006
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Ingår i: Performance Tests for Hot Mix Asphalt (HMA) Including Fundamental and Empirical Procedures. - 0803134959 ; , s. 156-176
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Konferensbidrag (refereegranskat)abstract
- The objective of this study is to identify a physical model that can provide reliable predictions about a mixture's ability to resist permanent deformation under realistic stress states. Key differences were identified between stress states under the existing Asphalt Pavement Analyzer (APA) loading device (hose) and stress states under radial truck tires, which may indicate potentially different rutting mechanisms. It was shown that the APA hose was not capturing the critical lateral stresses found to be detrimental to rutting and cracking of HMA pavements. A new loading device (rib) was designed and constructed for use in the APA that more closely represents stress states found under radial tires. Contact-stress measurements under the two loading devices - hose and rib - showed that the rib was able to reproduce the lateral stresses found under individual ribs on a radial-tire tread. Subsequent finite element modeling also showed that the rib appeared to generate similar shear stress patterns to those found under the modeled radial-tire load. A new method was developed to measure deformations on the surface of APA specimens, where a contour gauge was used to record and store the entire surface profile of the sample throughout the progress of the test. An area-change parameter, which reflects volume change, was introduced to calculate the volumetric changes in the specimen. The area-change parameter can be used to determine whether specimen rutting is primarily due to shear instability or consolidation. Two mixtures of known field performance - poor and good - were tested to evaluate the test's ability to predict performance with the new loading device and the new measurement and interpretation system. Results showed that the new system (loading strip and profile measurement method) appears to have greater potential of evaluating a mixture's potential for instability rutting than the original (hose and single rut-depth measurement) configuration.
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| 8. |
- Kim, Sungho, et al.
(författare)
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Identification and Assessment of the Dominant Aggregate Size Range (DASR) of Asphalt Mixture
- 2006
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Ingår i: Journal of Asphalt Paving Technologists. - : ASSOCIATION ASPHALT PAVING TECHNOLOGISTS. - 0270-2932. ; 75, s. 789-814
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Tidskriftsartikel (refereegranskat)abstract
- Coarse aggregate structure or interlock is critical for resistance to rutting, and recent work has shown that it can also play a significant role in resistance to damage and fracture. Therefore, large enough aggregates should engage dominantly in the structure for good mixture performance. This study focused on the development of a conceptual and theoretical approach to evaluate coarse aggregate structure based on gradation.In soil mechanics, it has been well established that the porosity of granular materials in the loose state is approximately constant between 45% and 50%, regardless of size or gradation. This implies that one can use porosity as a criterion to assure contact between large enough particles within the mixture to provide suitable resistance to deformation and fracture. Calculations performed for gradations associated with typical dense graded mixtures indicated that the porosity of particles retained on any single sieve was significantly greater than 50%, even for gradations associated with the maximum density line. Since many dense graded mixtures are known to provide suitable resistance to deformation and fracture, then there must be a range of contiguous coarse aggregate particle sizes that form a network of interactive particles with a porosity of less than 50%.A theoretical analysis procedure was developed to calculate the center to center spacing between specific size particles within a compacted assemblage of particles of known gradation. Calculations performed with this procedure indicated that the relative proportion of two contiguous size particles, as defined by the standard arrangement of Superpave sieves, can be no greater than 70/30 in order to form an interactive network. Thus, the 70/30 proportion can be used to determine whether particles on contiguous Superpave sieves can form an interactive network of particles in continuous contact with each other. The range of particle sizes determined to be interactive was referred to as the dominant aggregate size range (DASR) and its porosity must be no more than 50% for the particles to be in contact with each other.It was concluded that porosity of the DASR may provide a good criterion for determining the suitability of gradation for dense-graded asphalt mixture.
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| 9. |
- Kim, Sungho, et al.
(författare)
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Laboratory evaluation for rutting performance based on the DASR porosity of asphalt mixture
- 2008
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Ingår i: International Journal on Road Materials and Pavement Design. - Cachan, France : Lavoisier. - 1468-0629 .- 2164-7402. ; 9:3, s. 421-440
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Tidskriftsartikel (refereegranskat)abstract
- Research has shown that gradation characteristics determine whether the aggregate structure in asphalt mixture results in good performance. A recent study indicated that large enough aggregates should engage dominantly to form an aggregate structure that can resist deformation; also, a new approach identified the porosity of the Dominant Aggregate Size Range (DASR) as the key parameter that determines whether or not a particular gradation results in a suitable aggregate structure. This paper presents a laboratory experiment to evaluate the DASR porosity in terms of its ability to identify unsuitable aggregate structures. Fight dense-graded Superpave mixtures were designed using two aggregate types (limestone and granite). For each aggregate hype, mixtures with varying DASR porosity were produced and tested to evaluate laboratory rutting resistance. Test results indicated that the new approach successfully, separated mixtures according to their observed laboratory rutting performance, indicating that DASR porosity can serve as an effective parameter to evaluate aggregate structure.
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| 10. |
- Kim, Sungho, et al.
(författare)
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Porosity of the Dominant Aggregate Size Range to Evaluate Coarse Aggregate Structure of Asphalt Mixtures
- 2009
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Ingår i: Journal of materials in civil engineering. - : American Society of Civil Engineers (ASCE). - 0899-1561 .- 1943-5533. ; 21:1, s. 32-39
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents the results from an evaluation of a new gradation-based framework developed for identifying and assessing the coarse aggregate structure of dense-graded mixtures for resistance to rutting. A theoretical packing-based analysis procedure was used to evaluate the coarse aggregate structure for hot mix asphalt mixtures. This procedure was applied to an extensive range of mixtures. A key feature of this new framework is the concept of the existence of a dominant aggregate size range (DASR). The porosity of the DASR is calculated based on an interaction diagram to evaluate the degree of particle-to-particle interaction of coarse aggregates between contiguous sieve sizes. In addition, an interaction diagram-based criteria for dense-graded Superpave mixtures are determined, as well as criteria for the porosity of the DASR. Based on the field and laboratory-based rutting performance of the mixtures evaluated in this paper, it was concluded that DASR along with the porosity of the DASR may provide a framework for evaluating the gradation of dense graded mixtures for their likely rutting potential.
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| 11. |
- Wang, Jianlin, et al.
(författare)
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Windows-based top-down cracking design tool for Florida : Using energy ratio concept
- 2007
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Ingår i: Transportation Research Record. - : SAGE Publications. - 0361-1981 .- 2169-4052. ; :2037, s. 86-96
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Tidskriftsartikel (refereegranskat)abstract
- Top-down cracking has been found to be a predominant mode of distresses of asphalt pavements in Florida. Therefore, it is important to accommodate top-down cracking in the design of asphalt mixtures and pavement structures. After a multiyear study on top-down cracking supported by the Florida Department of Transportation, the University of Florida developed a top-down cracking model based on hot-mix asphalt fracture mechanics. This paper presents the implementation of the Florida cracking model into a mechanistic-empirical (M-E) flexible pavement design framework. Based on the energy ratio concept, a new M-E pavement design tool for top-down cracking has been developed. In the Level 3 M-E design, a series of semiempirical models were developed for estimation of time-dependent material properties. With incorporation of the material properties models, the design tool is capable of performing pavement thickness design as well as pavement life prediction for top-down cracking in Florida. The thickness design is optimized for different traffic levels, mixture types, and binder selections, and the optimization is an automated process. This design tool has been packed into Windows-based software, making it convenient to use for pavement design engineers.
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