Behzad Behnia | University of Texas of the Permian Basin (original) (raw)

Papers by Behzad Behnia

NCHRP-IDEA Program Project Final Report, 2015

This project involved the development of an acoustic emission-based Asphalt Embrittlement Analyze... more This project involved the development of an acoustic emission-based Asphalt Embrittlement Analyzer (AEA) device as an advanced diagnostic tool to assess the degree of aging, crack resistance, and resiliency of near-surface properties in asphalt pavements. A sophisticated computer code was developed to analyze acoustic emission (AE) signals, to identify microcrack presence and location, and to produce a diagnostic schematic illustrating embrittlement temperature versus location (depth from surface of pavement). The AEA test offers: simplicity and portability; the ability to characterize the continuous and rapid change in surface properties as a function of depth from the surface; suitability for characterization of both binders and mixtures; relative insensitivity to sample size and fracture size effect; relative insensitivity to sample geometry; and suitability for determining the optimum timing and method(s) for preventive maintenance and rehabilitation. In addition, as a design to...

The project that is the subject of this contractor-authored report was a part of the Innovations ... more The project that is the subject of this contractor-authored report was a part of the Innovations Deserving Exploratory Analysis (IDEA) Programs, which are managed by the Transportation Research Board (TRB) with the approval of the Governing Board of the National Research Council. The members of the oversight committee that monitored the project and reviewed the report were chosen for their special competencies and with regard for appropriate balance. The views expressed in this report are those of the contractor who conducted the investigation documented in this report and do not necessarily reflect those of the Transportation Research Board, the National Research Council, or the sponsors of the IDEA Programs. This document has not been edited by TRB. The Transportation Research Board of the National Academies, the National Research Council, and the organizations that sponsor the IDEA Programs do not endorse products or manufacturers. Trade or manufacturers' names appear herein solely because they are considered essential to the object of the investigation.

<jats:p>Low-temperature cracking is a major form of distress in asphalt concrete pavements ... more <jats:p>Low-temperature cracking is a major form of distress in asphalt concrete pavements located in cold regions. A review of the background and fundamental aspects of the Acoustic Emission (AE) based approach with a brief overview of its application to estimate low-temperature performance of unaged, short-term, and long-term aged binders as well as asphalt concrete materials are presented. A comparison of the cracking temperatures estimated using the traditional rheological-based method and the embrittlement temperatures obtained using the proposed AE-based method is presented and discussed. In addition, embrittlement temperatures of asphalt concrete samples extracted from field cores are also presented and discussed. Results indicate that the AE-based method is faster and more accurate than the traditionally used methods. Moreover, results suggest that AE could be considered as a viable rapid, inexpensive, yet precise characterization approach for pavement materials, which could be effectively used towards enhancing pavement sustainability and resiliency.</jats:p>

Journal of Testing and Evaluation, 2017

This study presents an acoustic emission (AE)-based approach to assess low-temperature cracking b... more This study presents an acoustic emission (AE)-based approach to assess low-temperature cracking behavior of asphalt concrete materials, in which thermally induced damage within asphalt concrete is continuously monitored and evaluated when the material is exposed to decreasing temperatures from 20°C to approximately −50°C. Results of three different asphalt mixtures at three different aging levels (unaged [TANK], Short-term Aged [RTFO], Long-term Aged [PAV]) are presented. Two AE characteristic temperatures, i.e., the embrittlement temperature and the temperature corresponding to the maximum energy event, were sensitive to asphalt type as well as oxidative aging levels of the asphalt concrete materials. Low-temperature cracking performance of asphalt concrete materials was found to be better than what their low-temperature performance grades (PGLTs) suggest. X-ray microtomography (micro-CT) visualization of thermal damage within asphalt concrete showed the formation of microcracks in the mastic along with debondings at the interface of aggregates and mastic.

Construction and Building Materials, 2020

h i g h l i g h t s Block cracking formation in asphalt pavements due to thermal loads was invest... more h i g h l i g h t s Block cracking formation in asphalt pavements due to thermal loads was investigated. 2D viscoelastic heterogenous micromechanical discrete element models were developed. Various block cracking patterns, such as rectangular and hexagonal, were explored. In a symmetric or large pavement segment, cracks form a Y-junction pattern. Block cracking occurs in the upper one-to-two centimeters of the top material layer.

$Research paper thumbnail of Cohesive zone fracture modelling of asphalt pavements with applications to design of high-performance asphalt overlays$

International Journal of Pavement Engineering, 2017

Abstract Mechanism of fracture in a viscoelastic heterogeneous composite with thermo-rheological ... more Abstract Mechanism of fracture in a viscoelastic heterogeneous composite with thermo-rheological properties such as, asphalt mixture is quite involved and cannot be correctly simulated with simpler linear elastic fracture mechanics constitutive laws. Over the last decade and half, a number of researchers have adopted use of cohesive zone (CZ) fracture models for simulation of fracture in asphalt mixtures. CZ interface elements are utilised in finite element (FE) models for representation of crack path, these elements follow traction–displacement relationships that allow for gradually degrading traction capabilities along the crack path with increasing level of crack opening. This paper presents a review of CZ modelling approach for simulation of asphalt pavement and overlay cracking performances. Suitability of CZ modelling approach for capturing discrete fracture in asphalt mixtures at low temperatures is presented through simulation of lab scale test. An example is also presented to demonstrate applicability of CZ-based modelling effort in capturing the crack initiation and propagation in asphalt mixtures at low temperatures. Thereafter, an FE-based pavement simulation approach is discussed that can be utilised in design of asphalt overlays to lower the propensity of reflective cracking. A case study of designing asphalt overlay systems for four real-life pavements in Minnesota is presented to demonstrate the applicability of the CZ-based modelling approach in conducting mechanistic design of asphalt overlays.

Transportation Research Record: Journal of the Transportation Research Board, 2017

This study evaluated the oxidative aging of asphalt mixtures by both nondestructive and fracture ... more This study evaluated the oxidative aging of asphalt mixtures by both nondestructive and fracture performance tests and investigated the possibility of estimating the low-temperature fracture properties of aged mixtures by using a nonlinear ultrasonic approach. Asphalt mixture samples, oven aged for 12, 24, 28, 32, and 36 h at 135°C, were compacted, made into test specimens, and evaluated by using a noncollinear wave-mixing approach. In addition, the embrittlement temperature and fracture energy of the replicate samples were assessed by using the acoustic emission test and the disk-shaped compact tension test. Comparison of results from the three testing methods clearly showed similar trends. This finding suggests that the fracture properties of mixtures can be estimated by using the noncollinear ultrasonic wave-mixing approach, which is a nondestructive method which does not require core extraction in the field.

Construction and Building Materials, 2016

h i g h l i g h t s Acoustic emission approach allows to estimation of oxidative aging in asphalt... more h i g h l i g h t s Acoustic emission approach allows to estimation of oxidative aging in asphalt mixtures. Rapid estimation of embrittlement temperatures of asphalt mixtures. Provides source location of thermal cracks in asphalt mixtures. Acoustic emission approach has potential to evaluate rejuvenator's efficiency. Approach is portable and easy to operate when compared to traditional methods.

Materials & Design, 2017

• 3D spiral-shaped fracture pattern was discovered in a biaxially stressed layer of asphalt mater... more • 3D spiral-shaped fracture pattern was discovered in a biaxially stressed layer of asphalt material bonded to aluminum substrate. • A logarithmic spiral model was selected to mathematically represent three-dimensional spiral cracks. • The spiral tightness parameter, "b", was used in characterization of spiral cracks in different asphalt materials. • Shape of spiral cracks was independent of thickness and shape of samples and influenced by fracture properties of asphalt materials. • The embrittlement temperatures and fracture energies of asphalt materials were consistent with corresponding characteristic parameters of spiral cracks.

ABSTRACT An acoustic emission (AE) approach to estimate the embrittlement temperature of asphalt ... more ABSTRACT An acoustic emission (AE) approach to estimate the embrittlement temperature of asphalt binders is presented. Thin films of asphalt binders were bonded to various substrates and exposed to decreasing temperatures, starting at 20 °C and decreasing to approximately -50 °C. Differential thermal contraction between the substrate and asphalt binder sample under this cooling regimen induces thermal stress in the binder resulting in thermal crack formation, which is accompanied by a release of elastic energy in the form of transient waves. Using piezoelectric sensors (Digital Wave, Model B-1025), a four-channel acoustic emission system was used to record the acoustic emission activity during the cooling process. Assuming the embrittlement temperature to be the temperature at which the AE signal energy exceeds a pre-selected threshold energy level, this AE testing approach was found to be sensitive and repeatable for predicting this parameter for a wide range of asphalt binders. Unlike existing protocols for determining the low temperature cracking behavior of binders, the presented AE approach does not require the use of sophisticated software for predicting thermal stresses, and no assumption is required regarding the testing cooling rate and the binder coefficient of thermal contraction. The paper also explains how the procedure is being broadened to include asphalt mixture materials, and how the procedures developed may be used in a comprehensive pavement management system to accurately plan preventive maintenance and rehabilitation of asphalt surfaces to prevent propagating cracks and expensive repairs. The work is being conducted under the National Cooperative Highway Research Program (NCHRP) program titled Ideas Deserving Exploratory Analysis (IDEA).

$Research paper thumbnail of Compact tension test for fracture characterization of thin bonded asphalt overlay systems at low temperature$

Materials and Structures, 2012

Abstract Asphalt overlays provide an economical means for treating deteriorated pavements. Thin b... more Abstract Asphalt overlays provide an economical means for treating deteriorated pavements. Thin bonded overlay (TBO) systems have become popular options for pavement rehabilitation. In addition to functional improvements, these systems ensure a high degree ...

Materials and Structures, 2014

Journal of Materials in Civil Engineering, 2013

ABSTRACT

Insight - Non-Destructive Testing and Condition Monitoring, 2013

Asphalt concrete mixtures with different levels of oxidative ageing, prepared by oven-ageing the ... more Asphalt concrete mixtures with different levels of oxidative ageing, prepared by oven-ageing the mixture at 135ºC for different amounts of time, were used to study the effects of oxidative ageing upon the ultrasonic velocity and attenuation measurements. The embrittlement temperatures, ie low-temperature cracking, of the mixtures with different amounts of oven-aged times were also evaluated by monitoring the acoustic emission response of the specimens when cooled from room temperature to-50ºC. It was observed that the embrittlement temperature increases (ie the onset of embrittlement occurs at a warmer temperature) as the amount of ageing increases. However, the rate-ofchange of the embrittlement temperatures with ageing time increases gradually until 24 h of ageing, after which the rate of change significantly increases. It was also observed that both the dilatational and shear velocities increase up to approximately 24 h of ageing, after which they significantly decrease with ageing. Also, both the dilatational and shear attenuation decrease with ageing up to around 24 h of ageing, after which both attenuations strongly increase. The results from both ultrasonic and acoustic emission tests are consistent with results obtained using the mechanical discshaped compact tension (DC(T)) fracture tests.

Construction and Building Materials, 2014

The results supported the use of RAS modified mixtures in warm climates. The warmer embrittlement... more The results supported the use of RAS modified mixtures in warm climates. The warmer embrittlement temperatures due to RAS is critical in cold climates. Nodules of RAS form due to partial blending between the RAS and virgin binders. RAS nodules accumulate damage first and thus govern the embrittlement temperature.

Journal of Materials in Civil Engineering, 2017

An acoustic-emission approach to evaluate the low-temperature cracking performance of asphalt bin... more An acoustic-emission approach to evaluate the low-temperature cracking performance of asphalt binders is presented. The acoustic activity of a thin film of asphalt binder bonded to a granite substrate is monitored while the layer is exposed to decreasing temperatures from around 20°C to approximately −50°C. Results of eight different asphalt binders at three different aging levels, i.e., unaged (TANK), short-term aged (RTFO), and long-term aged (PAV), are presented. The acoustic emission (AE) embrittlement temperatures are found to be sensitive to binder type as well as binder aging level. Results show that for most binders, their AE-based embrittlement temperature is a few degrees lower than their bending beam rheometer (BBR) critical cracking temperatures.

2002 IEEE MTT-S International Microwave Symposium Digest (Cat. No.02CH37278), 2002

Abstract A new instrument for time-domain characterization of circuits is illustrated. We measure... more Abstract A new instrument for time-domain characterization of circuits is illustrated. We measure output waveshape and rise time of two high-speed digital circuits on wafer, using a 50 GHz prototype of the new instrument. It uses vector error-correction to de-embed the ...

IEEE Transactions on Microwave Theory and Techniques, 2002

We measure output waveshape and rise time of two high-speed digital circuits on wafer using a 50-... more We measure output waveshape and rise time of two high-speed digital circuits on wafer using a 50-GHz prototype of a new instrument. The instrument uses vector error correction to deembed the component under test like a network analyzer, but reads out in the time domain after the fashion of an equivalent-time oscilloscope. With the calibration plane of the instrument set at the tips of the wafer probes, errors arising from dispersion in the connection hardware are removed. We show that the random jitter in the measurement system is removed without the convolution penalty usually incurred by averaging so that anomalies such as pattern-dependent jitter are exposed. The system rise time is 7 ps, compared to a system rise time of 12-13 ps for a conventional equivalent-time oscilloscope of the same bandwidth in the presence of wafer probes, bias networks, and cables.