Development of the fracture-based flexibility index for asphalt concrete cracking potential using modified semi-circle bending test parameters

The focus in recent years has been to make asphalt mixes more affordable, and this has led to the increased use of recycled materials and binder modifications. Consequently, one often-heard complai...

Development of an IDEAL Cracking Test for Asphalt Mix Design and QC/QA

Crack resistance of hot mix asphalt containing different percentages of reclaimed asphalt pavement and glass fiber

Evaluation of fracture resistance of asphalt mixes involving steel slag and RAP: Susceptibility to aging level and freeze and thaw cycles

For performance-based specifications and design processes, a number of cracking-related index parameters have been proposed for asphalt mixtures in recent years. A number of these parameters have b...

Comprehensive evaluation of low-temperature fracture indices for asphalt mixtures

The use of reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS) in asphalt concrete (AC) mixtures can reduce demand for virgin aggregates and asphalt binder, bringing environmental and economic benefits. However, replacing virgin asphalt binder in AC mixtures poses challenges in terms of mixture volumetrics and low-temperature cracking, fatigue cracking, and other deterioration related to cracking. To counter these effects, softer virgin asphalt binder grades or modifying agents are used to improve production consistency. The purpose of this study was to develop and evaluate protocols, procedures, and specifications for testing engineering properties and performance of AC mixtures with high amounts (up to 60%) of RAP and RAS. The criteria for selection of the test method were (1) statistically significant spread in test outcome, representing a mix’s cracking resistance; (2) applicability and seamless implementation; (3) correlation to other independent test methods and engineering intuition; and (4) correlation to field performance. A practical test method, the Illinois modified semi-circular bending test (IL-SCB) was developed that can be readily implemented to quantify AC mixture’s cracking potential. In addition, a flexibility index (FI) was introduced to determine cracking resistance in a consistent way. The IL-SCB showed consistent and repeatable trends for changes in AC mix design properties. The developed FI was shown to provide greater separation between AC mixes to capture some of the changes that could not be captured by fracture energy alone. This approach does not enforce any limits on any AC mixture design characteristics, such as RAP and RAS content, or other alternative materials or technologies. Instead, it categorizes AC mixes based on their performance index. Hence, this approach encourages innovation and sustainability at the same time.

Testing Protocols to Ensure Performance of High Asphalt Binder Replacement Mixes Using RAP and RAS

Using reclaimed and recycled materials in asphalt mixtures is one of the most commonly used sustainable strategies, which results in cost savings and environmental benefits because they replace virgin materials. Commonly used recycled, reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS) can pose challenges because their inclusion in the asphalt mixture may adversely affect pavement performance. This paper presents the recently developed fracture testing method, the Illinois semicircular bending (IL-SCB) fracture geometry at 25°C with a displacement rate of 50 mm/min. The flexibility index (FI), derived from the IL-SCB test results, was introduced to rank the potential cracking resistance of mixes. The developed testing protocol provides a practical and reliable approach to screen the capacity of mixes to resist cracking. An application of the IL-SCB test method and FI is presented using laboratory-prepared and compacted mixes with varying proportions of RAP and RAS. The mixes were designe...

Fracture Characterization of Asphalt Mixtures with High Recycled Content Using Illinois Semicircular Bending Test Method and Flexibility Index

Damage zone development in heterogeneous asphalt concrete

In this work we have studied the fracture behavior of asphalt mixtures, a heterogeneous mix of hard aggregates (usually in the form of crushed quarried rock) with a petroleum based asphalt binder, used in paving applications. Specifically, we studied the dependence of asphalt mixes’ fracture response on loading rate, temperature, and recycled content—the latter used primarily to replace virgin materials like aggregates and binder. Fracture tests were conducted on semi-circular bend edge cracked specimens obtained from mixes with different compositions, and the fracture event was recorded with a camera to allow for digital image correlation (DIC) measurements. DIC, with a spatial resolution of about 40 
 $$\upmu $$
 m/pixel, measured the far-field strain and displacement fields developing around a preexisting notch tip. Our focus here is on characterizing the material behavior by quantifying its viscoelastic response and fracture properties. The elastic–viscoelastic correspondence principle was used to extract viscous and elastic components from the full-field DIC-measured strain and displacement fields. Various energy dissipation mechanisms other than the fracture itself were evaluated. Stress–strain response and energy dissipated in the far-field regions were quantified. The pseudo-elastic stress intensity factor was then used to study the fracture properties, and quantify the effects on fracture properties of loading rate, temperature, and recycled content in the binder. It was seen that the viscoelastic characteristics of the material were a dominant factor in the material behavior obtained at room temperature. In general, the elastic component of the displacement was only up to about 30% of the total displacement, indicating a strong influence of viscoelasticity in this state. Loading rate, temperature and recycled asphalt shingles (RAS) content all affected the viscous response by introducing more elastic response when loading rate or recycled content increased or when temperature decreased. It became clear from these macroscopic measurements that the increase of RAS content considerably embrittles the material producing less viscous effects and less energy dissipated in the far-field, almost comparable to reductions associated with the loading rate increase (from 6.25 to 50 mm/min) or the temperature change (
 $$-12$$
 to $$25\,{^{\circ }}$$
 C).

Jose Rivera-Perez

Papers

Testing Protocols to Ensure Performance of High Asphalt Binder Replacement Mixes Using RAP and RAS

Fracture Characterization of Asphalt Mixtures with High Recycled Content Using Illinois Semicircular Bending Test Method and Flexibility Index

Damage zone development in heterogeneous asphalt concrete

Investigation of viscoelastic fracture fields in asphalt mixtures using digital image correlation

Fracture Characterization of Asphalt Mixtures with RAP and RAS Using Illinois Semicircular Bending Test Method and Flexibility Index