Analysis of the Role of Recycled Material Agglomerations on the Location of Fracture in Asphalt Mixtures
01 Jun 2022-Journal of transportation engineering-Vol. 148, Iss: 2
About: This article is published in Journal of transportation engineering.The article was published on 2022-06-01. It has received 5 citations till now. The article focuses on the topics: Urban agglomeration & Asphalt.
TL;DR: In this paper , the authors make use of a sieve analysis method and tracer-based microscopy analysis to quantify recycled binder availability and design asphalt mix design procedures to account for partial availability.
Abstract: The use of reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS) in asphalt mixtures is a routine process. Recycled binder availability reflects the proportion of the total recycled binder in a given recycled asphalt material (RAM) that is available to blend with the virgin binder. Studies show that agglomerations of adhered RAM particles preclude complete availability. However, the Superpave volumetric mixture design methods adopted by the majority of state agencies assume complete availability. This study makes use of a sieve analysis method and tracer-based microscopy analysis to quantify recycled binder availability. Revisions to asphalt mix design procedures to account for partial availability are proposed, including consideration of the unavailable binder as part of the bulk aggregate volume and the use of the RAM gradation (i.e. black curve) rather than the recovered aggregate gradation (i.e. white curve) to design the mixture’s aggregate structure. Three high RAM content ‘control’ mixtures that were originally designed under the assumption of complete recycled binder availability are redesigned according to the proposed approach. The redesigned mixtures had notably higher virgin binder content than the control mixtures. The redesigned mixtures also had significantly better cracking resistance than the control mixtures while still meeting permanent deformation requirements.
TL;DR: In this paper , a method to quantify the extent of RAP agglomeration and, in turn, RAP binder availability by comparing the gradation of recovered RAP aggregates with that of the RAP itself is presented.
Abstract: One of the challenges of engineering asphalt mixtures containing reclaimed asphalt pavement (RAP) is uncertainty in the proportion of the total recycled asphalt binder that is available to interact and blend with the virgin asphalt, referred to as the recycled binder availability. The industry presently lacks a practical method to quantify RAP binder availability. Research has shown that the primary source of unavailable recycled binder is agglomerations of adhered RAP particles. The binder bound within the agglomerations is unavailable to contact and therefore blend with virgin asphalt. Building on this knowledge, this study establishes a practical method to quantify the extent of RAP agglomeration and, in turn, RAP binder availability by comparing the gradation of recovered RAP aggregates with that of the RAP itself. A size-exclusion method and corresponding predictive equation to estimate RAP binder availability from the high-temperature performance grade of recovered RAP binder and mixing temperature were also assessed. Four RAP sources were evaluated. Each RAP stockpile was paired with virgin aggregates from the same plant that the RAP was sourced at to produce eight mixtures. Tracer-based microscopy measurements within the eight mixtures were generally in good agreement with the estimations of recycled binder availability using sieve analysis. Implementing the size-exclusion method was challenging with local aggregate, and estimates using the predictive equation yielded in some cases good but overall poorer agreement with the measurements of recycled binder availability from tracer-based microscopy compared with the sieve analysis approach.
TL;DR: In this article , the authors investigate the effects of asphalt mixture constituents on the RBC in asphalt mixtures using energy-dispersive x-ray spectroscopy (EDS) tracer-based microscopy analysis.
Abstract: Reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS) are incorporated into some asphalt mixtures produced today. The use of recycled asphalt materials (RAM) in asphalt mixtures encompasses engineering challenges pertaining to uncertainty in the proportion of the recycled binder that is in contact with and blends with the virgin binder in the asphalt mixture, termed recycled binder contribution (RBC) here. Recent research shows that agglomerations of RAM particles are the main cause of partial RBC. These agglomerations prevent recycled binder from interacting with the virgin binder. However, current practices generally assume complete RBC and a detailed understanding of the role of asphalt mixture constituents on RBC does not at present exist. The use of softer binders, extenders, and recycling agents has been proposed in high-RAM-content mixtures to restore recycled binder stiffness and embrittlement. However, the effects of asphalt binder variables as well as RAM type, source, and content on RBC is at present poorly understood. This paper aims to investigate the effects of asphalt mixture constituents on the RBC in asphalt mixtures using energy-dispersive x-ray spectroscopy (EDS) tracer-based microscopy analysis. It is found that the virgin binder, RAM type, and source significantly influence RBC in asphalt mixtures. However, RAP age level and content as well as additives are found to have only marginal impacts on RBC.
TL;DR: In this paper , three different preheating procedures were used to fabricate samples of four asphalt mixtures from different sources in the laboratory and quantified recycling contribution in the fabricated mixtures using tracer-based microscopy.
TL;DR: The use of reclaimed asphalt pavements or RAP has been around for more than half a century as mentioned in this paper , and there have been notable advances that require a renewed examination of the state of the art with respect to recycling agents (RA) usage.
TL;DR: In this paper, a multi-scale approach using the dynamic shear rheometer (DSR), electron microscopy and computer tomography (CT) was used to visualize the blending of virgin materials with reclaimed asphalt pavement (RAP).
Abstract: The nature of blending of virgin materials with reclaimed asphalt pavement (RAP) has been investigated using a multi scale approach using the dynamic shear rheometer (DSR), electron microscopy and computer tomography (CT). In order to simplify the visualization of the blending of the virgin and reclaimed materials five specially engineered hot asphalt mixtures were produced incorporating large mineral fraction (8/11 mm) of virgin aggregates and small fraction (2/4 mm) from RAP mixed with virgin bitumen. The complex modulus and phase angle of reclaimed binder from the blended mixtures were found to be between that of RAP and virgin binder. The CT slices of compacted cylindrical samples (150 mm diameter × 120 mm height) could incorporate the effect of compaction on the blending. They show lumped regions with virgin large aggregates as well as lumped regions of RAP aggregates. Using micro CT the spatial distribution of the different binders was investigated at the micro-scale. Millimeter size distinct clusters of virgin binder and clusters of RAP binder could be distinguished. The existence of RAP binder next to large virgin aggregates indicated the migration of the old RAP binder from the RAP aggregates to the virgin aggregates. From these CT images, it was not possible to verify if blending between the virgin and old binders occurred. Using electron microscopy micro-crack formations in the zone between old and new binder were identified suggesting weak spots that could lead to larger crack formation and propagation. However, using energy-dispersive X-ray spectroscopy good qualitative distribution of titanium dioxide tracer in the virgin binder in the mixture could be seen, indicating good blending at the investigated location. Hence, the results show that blending is not homogeneous throughout the sample. Some locations show good blending whereas other locations appear non-blended with micro-cracks forming at the binder boundaries.
TL;DR: In this paper, two types of mixtures containing virgin aggregates, bitumen and 50% and 90% RAP were investigated at different mixing temperatures and the formation of clusters in the mixture was verified using rheological properties (DSR) and imaging (ESEM, EDX).
TL;DR: In this paper, the authors measured the RAP binder film thickness at micro-scale and subsequently statistically analyzed showing that along the surface of the aggregate it is not homogenous; it depends on the local curvature of the aggregates, with positive curvature resulting in a smaller film thickness and negative curvature in larger film thickness.
TL;DR: State highway agencies recognize the environmental and economic benefits of utilizing reclaimed asphalt pavement (RAP) in asphalt mixes as discussed by the authors, and most agencies assume all of the RAP binder conten...
Abstract: State highway agencies recognize the environmental and economic benefits of utilizing reclaimed asphalt pavement (RAP) in asphalt mixes. Currently, most agencies assume all of the RAP binder conten...
TL;DR: In this article, microscopic technique tests were carried out to observe and evaluate the degree of blending between reclaimed asphalt pavement (RAP) binder and virgin binder in hot mixed asphalt mix.
Abstract: In this paper, microscopic technique tests were carried out to observe and evaluate the degree of blending between reclaimed asphalt pavement (RAP) binder and virgin binder in hot mixed asphalt mix...