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Papers by Salman Hakimzadeh

Journal of Testing and Evaluation, 2015

Asphalt concrete is commonly used as the surface layer in many pavement structures. One of the mo... more Asphalt concrete is commonly used as the surface layer in many pavement structures. One of the most important characteristics of asphalt concrete is its cracking resistance. At present, the conventional engineering material parameters such as tensile strength and dynamic modulus are the parameters used in the process of flexible pavement designs. In order to improve the design process, development and use of mechanistic-based design methods are necessary. These methods require characteristics that accounts for fracture resistance of asphalt concrete materials such as fracture energy. Thus, the use of a fracture mechanics approach and the development of valid fracture tests which are able to extract fundamental fracture properties of asphalt concrete are crucial. The goals of this research were to first introduce and evaluate a new and more practical fracture test, called single-edge notched disk (SEND) test, that can be easily used to characterize fracture properties of asphalt concrete, and second, to describe testing and analysis technique used in this investigation. As compared to other available fracture tests, the SEND test had several advantages, including capability of using field specimens, easy specimen preparation and test procedure, simple load configuration and test fixtures, big fractured surface area, and capability to induce cracks to propagate across the pavement thickness. Since the SEND test combined materials’ visoelastic deformation with fracture, it was able to simulate real life failure in pavements more accurately as compared to other existing fracture tests. The scope of this study was on laboratory and field compacted, dense graded asphalt mixture specimens. The results of the study clearly showed the ability of the SEND test to characterize fracture properties of various types of asphalt concrete mixtures at different testing temperatures, loading rates, and air void levels.

International Journal of Pavement Research and Technology, 2017

In the present work, three different asphalt binders were studied to assess their fracture behavi... more In the present work, three different asphalt binders were studied to assess their fracture behavior at low temperatures. Fracture properties of asphalt materials were obtained through conducting the Compact Tension [C(T)] and Indirect Tensile [ID(T)] strength tests. Mechanical fracture tests were followed by performing Acoustic Emissions test to determine the "embrittlement temperature" of binders which was used in evaluation of thermally induced microdamages in binders. Results showed that both nondestructive and mechanical testing approaches could successfully capture low-temperature cracking behavior of asphalt materials. It was also observed that using GTR as the binder modifier significantly improved thermal cracking resistance of PG64-22 binder. The overall trends of AE test results were consistent with those of mechanical tests.

7th RILEM International Conference on Cracking in Pavements, 2012

Road Materials and Pavement Design, 2012

The behavior of the interface between adjacent pavement layers is one of the most important facto... more The behavior of the interface between adjacent pavement layers is one of the most important factors affecting pavement performance. Despite the importance of interface behavior between different pavement layers, there are few guidelines that can be used for construction, and the selection of tack coat type, application rate, and placement is usually based on empirical judgment. This paper presents a

Transportation Research Record: Journal of the Transportation Research Board, 2012

Asphalt mixture low temperature cracking performance has investigated. A new thermal cracking mod... more Asphalt mixture low temperature cracking performance has investigated. A new thermal cracking model was proposed. The effect of non-linear thermal contraction coefficient was investigated. The importance of cooling rate and creep compliance parameters was studied. This extended model can evaluate the low temperature cracking performance.

Transportation Research Record: Journal of the Transportation Research Board, 2012

41 42 43 Word Count: 4409 + 7 figures (1750) + 3 tables (750) = 6909 44 45 46 1 2 In asphalt conc... more 41 42 43 Word Count: 4409 + 7 figures (1750) + 3 tables (750) = 6909 44 45 46 1 2 In asphalt concrete, warm mix asphalt (WMA) has become one of the most popular methods 3 used to meet sustainability demands. Researchers have determined that WMA use can lead to 4 reductions in fuel consumption and emissions. Early literature hypothesized that an additional 5 benefit arising irrespective of the WMA additive/process used was decreased thermal cracking 6 susceptibility. The current study examined this hypothesis through laboratory testing involving 7 the use of four WMA mixtures produced at a reduced production temperature and a reference 8 hot-mix asphalt (HMA) mixture. 9 10 The Disk-Shaped Compact Tension [DC(T)], Indirect Tension (IDT) and Acoustic Emission 11 (AE) tests were used to characterize the mixture low temperature properties. DC(T) fracture 12 energy results showed that the chemical additives improved fracture energy in comparison to 13 HMA while the organic and foaming additives reduced fracture energy. The IDT creep 14 compliance results produced similar results, where the two chemical additive modified WMA 15 systems increased mixture creep compliance, while the other two systems did not significantly 16 alter creep compliance as compared to the control HMA mixture. 17 18 AE testing provided further information regarding the low-temperature behavior of WMA 19 mixtures. The foaming additive displayed an embrittlement temperature similar to HMA while 20 the organic additive increased the embrittlement temperature. Furthermore, the two chemical 21 additive modified mixtures produced differing embrittlement temperatures. Upon completion of 22 this study, researchers concluded that thermal cracking resistance is not ensured by virtue of 23

Journal of Testing and Evaluation, 2015

Asphalt concrete is commonly used as the surface layer in many pavement structures. One of the mo... more Asphalt concrete is commonly used as the surface layer in many pavement structures. One of the most important characteristics of asphalt concrete is its cracking resistance. At present, the conventional engineering material parameters such as tensile strength and dynamic modulus are the parameters used in the process of flexible pavement designs. In order to improve the design process, development and use of mechanistic-based design methods are necessary. These methods require characteristics that accounts for fracture resistance of asphalt concrete materials such as fracture energy. Thus, the use of a fracture mechanics approach and the development of valid fracture tests which are able to extract fundamental fracture properties of asphalt concrete are crucial. The goals of this research were to first introduce and evaluate a new and more practical fracture test, called single-edge notched disk (SEND) test, that can be easily used to characterize fracture properties of asphalt concrete, and second, to describe testing and analysis technique used in this investigation. As compared to other available fracture tests, the SEND test had several advantages, including capability of using field specimens, easy specimen preparation and test procedure, simple load configuration and test fixtures, big fractured surface area, and capability to induce cracks to propagate across the pavement thickness. Since the SEND test combined materials’ visoelastic deformation with fracture, it was able to simulate real life failure in pavements more accurately as compared to other existing fracture tests. The scope of this study was on laboratory and field compacted, dense graded asphalt mixture specimens. The results of the study clearly showed the ability of the SEND test to characterize fracture properties of various types of asphalt concrete mixtures at different testing temperatures, loading rates, and air void levels.

International Journal of Pavement Research and Technology, 2017

In the present work, three different asphalt binders were studied to assess their fracture behavi... more In the present work, three different asphalt binders were studied to assess their fracture behavior at low temperatures. Fracture properties of asphalt materials were obtained through conducting the Compact Tension [C(T)] and Indirect Tensile [ID(T)] strength tests. Mechanical fracture tests were followed by performing Acoustic Emissions test to determine the "embrittlement temperature" of binders which was used in evaluation of thermally induced microdamages in binders. Results showed that both nondestructive and mechanical testing approaches could successfully capture low-temperature cracking behavior of asphalt materials. It was also observed that using GTR as the binder modifier significantly improved thermal cracking resistance of PG64-22 binder. The overall trends of AE test results were consistent with those of mechanical tests.

7th RILEM International Conference on Cracking in Pavements, 2012

Road Materials and Pavement Design, 2012

The behavior of the interface between adjacent pavement layers is one of the most important facto... more The behavior of the interface between adjacent pavement layers is one of the most important factors affecting pavement performance. Despite the importance of interface behavior between different pavement layers, there are few guidelines that can be used for construction, and the selection of tack coat type, application rate, and placement is usually based on empirical judgment. This paper presents a

Transportation Research Record: Journal of the Transportation Research Board, 2012

Asphalt mixture low temperature cracking performance has investigated. A new thermal cracking mod... more Asphalt mixture low temperature cracking performance has investigated. A new thermal cracking model was proposed. The effect of non-linear thermal contraction coefficient was investigated. The importance of cooling rate and creep compliance parameters was studied. This extended model can evaluate the low temperature cracking performance.

Transportation Research Record: Journal of the Transportation Research Board, 2012

41 42 43 Word Count: 4409 + 7 figures (1750) + 3 tables (750) = 6909 44 45 46 1 2 In asphalt conc... more 41 42 43 Word Count: 4409 + 7 figures (1750) + 3 tables (750) = 6909 44 45 46 1 2 In asphalt concrete, warm mix asphalt (WMA) has become one of the most popular methods 3 used to meet sustainability demands. Researchers have determined that WMA use can lead to 4 reductions in fuel consumption and emissions. Early literature hypothesized that an additional 5 benefit arising irrespective of the WMA additive/process used was decreased thermal cracking 6 susceptibility. The current study examined this hypothesis through laboratory testing involving 7 the use of four WMA mixtures produced at a reduced production temperature and a reference 8 hot-mix asphalt (HMA) mixture. 9 10 The Disk-Shaped Compact Tension [DC(T)], Indirect Tension (IDT) and Acoustic Emission 11 (AE) tests were used to characterize the mixture low temperature properties. DC(T) fracture 12 energy results showed that the chemical additives improved fracture energy in comparison to 13 HMA while the organic and foaming additives reduced fracture energy. The IDT creep 14 compliance results produced similar results, where the two chemical additive modified WMA 15 systems increased mixture creep compliance, while the other two systems did not significantly 16 alter creep compliance as compared to the control HMA mixture. 17 18 AE testing provided further information regarding the low-temperature behavior of WMA 19 mixtures. The foaming additive displayed an embrittlement temperature similar to HMA while 20 the organic additive increased the embrittlement temperature. Furthermore, the two chemical 21 additive modified mixtures produced differing embrittlement temperatures. Upon completion of 22 this study, researchers concluded that thermal cracking resistance is not ensured by virtue of 23