Annales de Chimie - Science des Matériaux
Vol. 48, No. 2, April, 2024, pp. 233-250
Journal homepage: http://iieta.org/journals/acsm
Framework for the Innovative Use of Recycled Materials in Pavement Structures: A
Canadian Case Study
Hanaa Khaleel Al. AL-Bayati1* , Abimbola Grace Oyeyi2 , Susan L. Tighe3
1
Department of Civil Engineering, Faculty of Engineering, University of Tikrit, Tikrit 34001, Iraq
Department of Civil and Environmental Engineering, University of Windsor, Windsor N9B 3P4, Canada
3
Office of the Provost & Vice-President (Academic), McMaster University, Hamilton L8S 4L8, Canada
2
Corresponding Author Email: dr.hanaa.khaleel@tu.edu.iq
Copyright: ©2024 The authors. This article is published by IIETA and is licensed under the CC BY 4.0 license
(http://creativecommons.org/licenses/by/4.0/).
https://doi.org/10.18280/acsm.480210
ABSTRACT
Received: 22 October 2023
Revised: 6 March 2024
Accepted: 22 March 2024
Available online: 30 April 2024
The availability of high-quality aggregate for infrastructure development in Canada has
significantly decreased. This reduction has posed significant challenges, particularly in
large urban areas across Canada. Moreover, exploring the potential of incorporating
innovative by-products into pavement structures has displayed potential advantages in
technical, economic, and environmental aspects. The methodology presented in this
paper is based on several research projects from over the past twenty years. This case
study is based on the several research projects that have been conducted at the Centre for
Pavement and Transportation Technology (CPATT) in Canada. The focus of this paper
is developing a framework that can be used to evaluate the use of recycled materials in
asphalt pavement. These include recycled concrete aggregate (RCA); recycled asphalt
roof shingles (RAS); recycled crumb rubber (RCR); and recycled asphalt roof shingles
(RAS) in asphalt pavement. In addition, the use of RCA in concrete pavement will also
be evaluated. In addition, the use of RCA in concrete pavement will also be evaluated. A
methodology and strategy for implementing these materials and designs into
specifications, while also managing risk, are outlined. Finally, the work presents a life
cycle assessment analysis, including the analysis of cost and sustainability. Overall, the
paper illustrates the process of evaluating products, technologies, and designs from
technical, economic, and environmental viewpoints, and then implementing them in a
robustly engineered way. Generally, the collected data results from the lab, field
performance of the test sites, and sustainability and Life Cycle Cost Assessment (LCCA)
analyses are very promising. For example, the Hot Mix Asphalt (HMA) pavement design
with a 40% RAP was the most environmentally friendly. Meanwhile, it was determined
that the HMA mix comprising 20% RAP and 20% Crumb Rubber Modifier (CRM) was
found to be the most creative and environmentally friendly option. According to another
study, higher storage durations were shown to improve RAP and virgin binders' blending,
thereby raising the general quality of HMA and RAP mixtures. Furthermore, the study
discovered that mixtures containing various types of untreated CRCA in different
amounts had higher Indirect Tensile Strength (ITS), rutting resistance, and stiffness
modulus than the control mix, which contained 0% coarse recycled concrete aggregate
(CRCA). This suggests that the effective utilization of recycled materials is a viable
approach with the capacity to significantly enhance the adoption of recycled components
in asphalt pavements.
Keywords:
recycled pavement materials, management
framework,
life
cycle
assessment,
microstructure of pavement materials,
pavement mixtures
alternatives that will solve numerous problems, ranging from
the development of replacements for raw materials that are
increasingly difficult to extract, to ways to cut back on waste
that ends up simply being dumped in landfills, and developing
more efficient ways to use materials in order to decrease waste
and environmental impact [1].
In Canada and around the world, the pressure to build
infrastructure in urban areas over the past century has resulted
in the challenge to find economical and high-quality materials
for road construction. This is practically related to the fact that
the good quality aggregate is located far away from urban
areas where the demand is high, and this subsequently results
1. INTRODUCTION
Globally, transportation agencies find themselves
progressively more concerned with environmental questions.
These agencies were increasingly aware that transportation
infrastructure and systems needed to be developed with
environmental sustainability in mind. The asphalt industry has
recognized that finding solutions to the problems of resource
depletion, waste generation, and environmental sustainability
is essential. Consequently, the industry has been
experimenting with new technological approaches and new
materials. The industry aims to develop sustainable
233
in the high costs associated with trucking the materials to the
sites. The outcome of the Ontario Stone, Sand & Gravel
Association's (OSSGA) recent (March 2022) survey found
how unpopular quarries are as community development
initiatives. Because of this, high-quality aggregate is located
particularly far from cities. This has prompted many Canadian
Departments of Transportation (DOT's) to evaluate the role of
recycling and the opportunity to evaluate alternative materials
in our traditional road-building projects. In practice, several
barriers must be addressed before recycled materials can be
accepted. Initially, there can be a high investment cost required
by the private and/or public sector to process the materials.
Physical and behavioral barriers, lack of knowledge, and
attitudes and perceptions represent some of these barriers [2].
The concept of 'recycling' encompasses nearly any
procedure involving the reuse of waste materials instead of
their disposal in landfills or destruction. These materials,
frequently of excellent quality, hold the potential to diminish
the need for other finite resources. As a result, the quest for
greater value in terms of technology, economics, and
environmental considerations emerges as a fresh challenge.
While the reasons for recycling may vary, the recognition of
the necessity for sustainable development has significantly
shaped the practice of materials recycling [2].
Therefore, this study presents recommendations for
improving the sustainable use of recycled concrete aggregate
(RCA); recycled asphalt pavement (RAP); recycled crumb
rubber (RCR); and recycled asphalt shingles (RAS) in rigid
and flexible pavement construction. These recommendations
include the best way to incorporate RAP, the type of binder to
use, how to integrate crumb rubber, how much RCA is the
right amount, treatment techniques that have been proven to
improve the quality of recycled materials before applying
them to the pavement, the pertinent tests that should be
initiated for each type of recycled material, and the right
amount of each material for typical asphalt mixtures in Ontario.
To help engineers and managers assess creative designs
involving material modifications, a framework has been
developed to improve sustainability and make and effectively
use recycled materials above and beyond current industry
norms. There are advantages to this framework; it can be
applied and modified for use in colder nations.
as compounds of sulphur, nitrogen, and carbon dioxide, are
produced. These emissions cause substantial pollution in the
environment [5]. As an example, according to the
manufacturing process, creating one tonne of PC can cause
almost one tonne of carbon dioxide to be released into the
atmosphere [6].
Simultaneously, large volumes of construction and
demolition (C&D) waste are generated from various human
endeavours, including but not limited to construction,
renovation of existing ones, and the demolition of old
buildings and civil engineering works. In recent years, it has
been estimated that the annual global production of
construction and demolition (C&D) waste amounts to 1,183
million tonnes [7].
Crushed concrete debris from building and demolition sites
is used to make RCA. This procedure produces a useful
product out of waste material. As shown in Figure 1, RCA is
primarily used in pavement subbase materials, but it has also
been applied in other paving applications.
In base and sub-base construction purposes, the use of RCA
has become an appealing and effective choice of materials due
to its attributes of strong durability and non-expansive
properties [8], but at the same time, it has also been used in
other paving applications as presented in Figure 1. Strength,
durability, cost-effectiveness, waste reduction, and
environmental sustainability are some of the advantages of
using RCA. The main challenges facing RCA were limited
applications, transportation costs, the presence of
contaminants, and quality variability, all occurring at the same
time.
Figure 1. Crushed cement concrete's final applications [9]
2. LITERATURE REVIEW
Asphalt pavement meets the definition of a renewable
resource because it can be recycled for use in new construction
projects, road maintenance, and rehabilitation. With respect to
recycled asphalt pavements, RAP stands out as the most
frequently recycled product in North America. It comprises
well-graded aggregates coated with asphalt cement or binder
[10]. RAP is the substance left over after asphalt pavement
layers are removed or milled. This procedure is used in
projects involving road reconstruction, resurfacing, or
demolition. Usually, it is made up of asphalt binder and
aggregates, like sand and gravel. RAP is a sustainable
pavement construction method that balances economic
advantages and environmental benefits, but it also presents
some technical and regulatory issues that require careful
handling. While the use of RAP is widespread in Canada,
particularly in Hot Mix Asphalt (HMA) mixtures for surface
courses, it is restricted to 20%. This approach is viewed as
cautious when contrasted with the abundance of RAP
available in the province. Figure 2 illustrates the findings of
The ever-growing worldwide demand for the raw materials
used for constructing transportation infrastructure and systems
is complicated by the fact that the non-renewable resources
and natural aggregates (NAgs) essential for construction are
diminishing quickly [3].
An estimated 3 billion tonnes of raw materials are needed
each year by the construction industry worldwide, which is
twice the amount needed by any other industry [3]. In Ontario,
Canada, from 2000 to 2009, aggregate usage averaged about
179 million tonnes per year, and between 2020 and 2029, this
is expected to rise to approximately 191 million tonnes per
year, according to the Ontario Ministry of Natural Resources
[4]. Hence, this high demand has the potential to create a
significant shortage of NAgs in Ontario and may pose similar
challenges in other Canadian provinces and around the globe.
Furthermore, during the industrial production of concrete
mixtures, in which Portland cement (PC) is the main
component, significant emissions of various pollutants, such
234
the survey carried out by the Subcommittee on Materials under
AASHTO (American Association of State Highway and
Transportation Officials) [11]. The outcomes represent the
maximum allowable RAP percentage for different pavement
courses.
recycling rates employed in different Canadian provinces as of
1991 [16].
Used rubber tires represent another recyclable commodity.
With various uses, including rubberized asphalt, playgrounds
and sports fields, and building materials, crumb rubber offers
a helpful way to dispose of tire waste. Crumb rubber provides
several advantages, including reduced noise, costeffectiveness, durability, safety features, and environmental
benefits. But it also has to contend with issues like market
acceptability, processing complexity, and environmental and
health safety. Ontario has gathered more than sixty million
discarded rubber tires since the Ontario Used Tires Program
began in 2009 [17]. The Government of Ontario initiated this
program, which is managed by Ontario Tire Stewardship
(OTS). At present, the discarded tire inventory in Ontario
undergoes recycling processes to produce top-notch items like
crumb rubber, tire-derived aggregates (TDA), and
manufactured goods. Table 2 furnishes information about the
characteristics and applications of each product within Canada.
Used rubber tyres are broken down and ground into particles
ranging in size from 3.36 mm (No. 6 mesh screen) to 0.075
mm (No. 200 mesh screen) to produce rubber crumbs. While
integrating crumb rubber into HMA can be advantageous and
has the capacity to utilize significant quantities of discarded
rubber tires, its utilization in Canada is restricted due to a lack
of experience, early failures in pilot projects, difficulties in the
blending process, and limited cost-effectiveness [2].
Figure 2. Histogram of maximum permissible percentage of
RAP for various pavement layers [11]
Moreover, in Canada, the desire to utilize RAP is primarily
motivated by rising expenses related to substances and
conveyance. The charges associated with producing asphalt
pavement are included in this., the scarcity of high-quality
aggregates accessible locally, and the shift towards ecofriendly pavement maintenance, preservation, rehabilitation,
and reconstruction methods that prioritize low energy
consumption and reduced emissions. In 1980, the Ontario
Ministry of Transportation commissioned a task force to study
recycling practices in the United States, which impacted the
province's first concerted efforts to recover and reuse asphalt
pavement materials [12]. This initiative set a maximum
recycling threshold of 70%, and it was found to be effective in
producing economic benefits by avoiding the need for about
126,000 tonnes of new aggregate materials that would have
been required in the absence of RAP [12, 13].
In 1982, Alberta Province initiated its recycling initiative
through a laboratory study that explored various mix
formulations incorporating RAP ranging from 50% to 75%
[14]. In New Brunswick, the utilization of 40% RAP in base
courses during the period of 1985 to 1987 resulted in savings
of nearly forty thousand metric tonnes of asphalt binder, as
shown in Figure 2 [15]. Table 1 provides an overview of
Table 1. The RAP percentages incorporated into new HMA
in 1991 [16]
Province/Territory
British Columbia
Alberta
Saskatchewan
Manitoba
Ontario
Quebec
Prince Edward Island
New Brunswick
Nova Scotia
Newfoundland
Yukon
Northwest Territories
RAP
Integrated
(Yes/No)
Yes
Yes
Yes
Yes
Yes
Yes
No (Trial)
Yes
Yes
No
Yes
No
Percentage of
RAP Usage
20% to 40%
Up to 40%
30% to 70%
30% to 50%
15% to 50%
15% to 30%
Up to 45%
Up to 35%
Not known
-
Table 2. Recycled products from scrap tires and their applications across Canada [2, 18]
The Production
Description of the Product
Crumb Rubber
Discarded tires that undergo processing and are
subsequently crushed into various dimensions to
create a coarse sand or a product resembling small
gravel.
Tire Derived Aggregate
(TDA)
Discarded tires are sliced into dimensions that span
from 25 mm to 300 mm.
Fabricated products
Items are created by sectioning different segments of
the discarded tire and repurposing them.
235
Uses
- Playgrounds instead of sand
- Mulch in landscaping applications
- After blending the product with epoxy,
install it directly on-site.
- Raw materials are the primary constituents in
molded items such as engine components.
- Asphalt road mixtures
- Fill material for the subgrade and
embankments
- Filling materials that are used to support
walls and bridge abutments
- Projects of landfill
- Filling is light in weight.
- Drainfields for septic systems.
- Base of traffic cones
- Blasting mats
Centre for Pavement and Transportation Technology in
Canada over the past twenty years. The current study is
primarily concerned with the development of the assessment
framework for using different types of recycled substances
like RCA, RAP, RCR, and RAS either in asphalt pavement or
concrete pavement. To achieve this goal, a wide range of data
has been used such as recycled material properties,
characterization, benefits, and challenges for each recycled
material; mix design requirements; performance tests
requirements and life cycle assessment. This research
attempts to enhance existing knowledge by providing an
assessment methodology and developing a strategy related to
how these designs and materials can be utilized to meet
specifications and, at the same time, manage risk. Lastly, the
paper presents a life cycle assessment that encompasses both
a cost analysis and a sustainability analysis.
Asphalt shingle roofs, for both residential and commercial
use, are produced in Millions of tonnes every year.
Unfortunately, once their intended 15 to 20-year lifespan is
over, most of these shingles are disposed of in landfills [19].
An estimated 1.5 million tonnes of waste shingles for
roofing are produced in Canada each year, according to a 2007
study by Natural Resources Canada titled "Enhancing the
Recovery of End-of-Life Roofing Materials." These are wellmade shingles that hold value as a secondary product, even
though they might eventually need to be replaced as roofing
materials. When these shingles are processed and undergo
quality testing, they can be incorporated into asphalt
pavements.
For over twenty years, newly manufactured shingles have
been employed in asphalt pavements. These shingles are brand
new but have been deemed unsuitable for use on roofs due to
defects. Nonetheless, they are able to be broken down and
classified for utilization on asphalt roads [20].
As is commonly known, there are several environmental
advantages to using recycled materials when constructing
pavement, including decreased waste in landfills, preservation
of natural resources, decreased energy use, reduced
greenhouse gas emissions, and mitigation of resource
depletion. There are also some possible trade-offs, including
issues with durability and quality, costs associated with the
economy, obstacles to regulations and standards, and technical
difficulties [1].
After a thorough analysis of the literature, it was discovered
that most earlier studies on integrating various recycled
materials into concrete and asphalt pavements had focused on
the consequences of distinct recycled materials on the
pavement's properties. A few studies have examined the
effects of combining two various materials that have been
recycled. Based on the authors' knowledge, none have
thoroughly explored a framework similar to this case study,
which looks at these combinations in detail. Therefore, a
framework has been created to assist engineers and managers
in evaluating innovative designs concerning material changes,
aiming to enhance sustainability and efficiently utilize
recycled materials beyond the existing industry standards.
Therefore, this paper presents a methodology that has been
established based on several research projects conducted at the
3. METHODOLOGY
This research's main goal is to create an assessment
framework for adding different recycled materials to
pavements made of both concrete and asphalt. This framework
is derived from several research projects carried out at the
Centre for Pavement and Transportation Technology (CPATT)
in Canada during the past two decades. This goal is
accomplished by gathering engineering and performance
information on the recycled materials (RAP, RCA, RCR, and
RSP). The physical, mechanical, and microstructure properties
are among the engineering attributes of recycled materials. In
the meantime, performance tests, mixed design, and LCCA
serve as representations of the performance attributes.
Presenting the experimental findings and the engineering and
performance data tests that were completed is another aspect
of the research. Furthermore, one of the most important
components of this study was the guidelines and
recommendations for using recycled materials. The
framework for critical actions in using recycled materials is
established at the conclusion. The research approach is
detailed in Figure 3. Furthermore, the following sections
provide a detailed description of the methodology.
Figure 3. Methodology for the research
236
4. FRAMEWORK
FINDINGS
IMPLEMENTATION
required tests for each recycled material could be considered
as a guideline to help future studies, as seen in Table 3.
For the evaluation of the consensus properties of the
aggregate combination in RAP materials, the asphalt cement
was extracted from the RAP, and the aggregates recovered
were then utilized.
The outcomes of the studies demonstrated that there was a
strong connection between various engineering properties.
Figure 4 illustrates a network of interactions between the
characteristics of RCA.
The results obtained also suggested that recycled materials
exhibit lower physical and mechanical characteristics in
comparison to NAg. For example, RCA displays reduced Bulk
Relative Density (BRD), elevated absorption of water, and
increased porosity when contrasted with NAg. Therefore, to
improve the mechanical and physical characteristics of various
types of RCA before utilizing them in pavement construction,
multiple treatment approaches have been utilized to improve
the structural performance of both concrete and asphalt
pavements.
Figure 5 depicts a chronological representation of treatment
techniques sourced from literature that have been used to
improve the attributes of RCA. The results showed that
incorporating RCA following various treatment approaches
has been highly effective in meeting all the stipulated Ministry
of Transportation criteria, or the required specifications of
given province. In the next section, the effect of the utilization
of different types of recycled materials on the mechanical
performance properties of pavement mixtures will be
discussed.
AND
Using recycled materials in pavement mixtures goes beyond
simply incorporating lower-quality materials. Achieving
successful utilization involves considering various factors.
Some of these factors pertain to the recycled material itself,
including its physical, mechanical, and microstructural
characteristics, while others are associated with pavement
mixtures such as asphalt cement type, W/C ratio, Portland
cement type, NAg types, and volumetric properties of the
recycled pavement mixtures.
This part offers the outcomes of ten case studies conducted
using different recycled materials. The methodology proposed
for assessing the appropriateness of using RCA, RAP, RCR,
and RAS in pavement and the results are documented herein.
5. DATA COLLECTION
5.1 Engineering properties of recycled materials
It is well known that most of the pavement mixture's volume
is composed of aggregate particles. In asphalt mixtures, the
aggregate particles act as the mixture’s skeleton, whereas the
asphalt binder functions as an adhesive substance. Therefore,
the physical and mechanical properties of both coarse and fine
aggregates significantly influence the performance of the
pavement. The same behavior was registered for the aggregate
particles in the concrete pavement mix. Therefore, based on
previous research, the framework or the summary of the
Table 3. Framework' summary of the engineering properties tests of recycled materials of some studies
Aggregate Physical Properties
Test
Coarse
Aggregate
Angularity
(ASTM, 2006)
Uncompacted
Void Content of
Fine Aggregate
(ASTM, 2006)
Flat or
Elongated
Particles in
Coarse
Aggregate
(ASTM, 2010)
Properties
The percentage of
particles with at
least one crushed
face in the
aggregates
retained on the
No. 4 (4.75mm)
sieve
Measures the
angularity in the
portion of
aggregates that
passes the No. 8
(2.36 mm) sieve
The particles'
shapes
RAP Material [2, 21, 22]
Rheological and Physicochemical Properties of
Binder
Test
Properties
Direct Tension Test
(DTT)
To predict at what
temperature Thermal
Cracking would occur
Bending Beam
Rheometer (BBR)
Dynamic Shear
Rheometer (DSR)
At an intermediate
temperature for Fatigue
Cracking,
-Evaluate high temperature
performance permanent
deformation (rutting)
Pressure Aging Vessel
(PAV)
Simulate the extended-term
aging of the asphalt
Aggregate
Gradation
The proportion of
clay in the
aggregate passing
the No. 4 (4.75
mm) sieve.
Quality of the mix
(meet the mix
design gradation)
The Rolling Thin-Film
Oven (RTFO)
Simulate the asphalt's shortterm ageing
Dust Proportion
(DP)
Dust to binder
ratio
Rotational
Viscosity (RV)
Evaluate the workability
during construction (select a
binder that is sufficiently
stiff to resist rutting, but not
Sand Equivalent
Test (ASTM,
2009)
237
Binder Microstructure
Test
Properties
Environmental
Scanning
Electron
Microscope
(ESEM).
The composition and
microstructure of the
blending regions. The
purpose of this study is to
investigate the kinematics of
combining aged and virgin
binders by taking into
account the timetemperature impact that
occurs during handling and
storage in silos
too stiff to contribute to
fatigue cracking)
Asphalt binder
recovery, using
trichloroethylene
(TCE). (ASTM
D2172), (ASTM
D1856), X-ray
Fluorescence
spectroscopy
Aggregate Physical Properties
Asphalt binder recovery
from RAP samples and silostored samples
RCA Material [23-25]
Aggregate Mechanical Properties
Microstructure Properties
To find the bulk,
apparent specific
gravity and
absorption of
water
Abrasion resistance
ASTMD6928-10
The aggregate's resistance to
abrasion and degradation
-Scanning
Electron
Microscopy
(SEM)
-The microstructure surface
morphology
-Interfacial transition zone
(ITZ) microcracks (Interface
Gap)
-The size of pores on the
mortar's surface
-Matrix crack width and
length
-Matrix (Macro) cracks
density
Porosity [26]
Porosity of RCA
-Aggregate crushing
value (ACV) British
Standard (BS) (812110
Evaluating the aggregate's
relative durability
Assess the typical stressstrain reaction of loosely
compacted bulk aggregate
Dispersive X-ray
Analyzer
(EDAX)
Chemical and mineral
composition of RCA
Ratio of calcium to silicon
(Ca/Si)
Fractured
Particles, %,
(ASTM D5821)
Determines the
amount (percent)
of fracture faced
rock particles
Adhered Mortar Loss
[27]
Determine the quantity of
attached mortar in Recycled
Concrete Aggregate (RCA)
X-Ray
Diffraction
Analysis (XRD)
Evaluation of Calcium
silicate hydrate (CSH)
Compounds
Flat &
Elongated, %,
(LS-608)
The shape of the
particles
-Freezing and Thawing
(LS-614, 2012)
The ability of coarse
aggregate to withstand
deterioration due to
repetitive freezing and
thawing impacts
Aggregate
gradation
Quality of the mix
(meet the mix
design gradation)
Water
Absorption &
specific Gravity
(ASTM C127)
Aggregate Physical Properties
Quality of the mix
Aggregate
(meet the mix
gradation
design gradation)
RAS Material [19]
Binder Properties
Asphalt cement content
Shingle asphalt content
The asphalt hardness
Viscosity/penetration
Figure 4. The aggregate properties' relationships [23]
Figure 5. Schematic diagram depicting a range of treatment
methods aimed at improving the characteristics of RCA [25]
238
(MTO) for several reasons such as: engineering, economic,
and environmental reasons. In an effort to provide a
comprehensive program for individuals engaged in the
production, management, and use of recycled aggregates,
Aggregate Recycling Ontario (ARO) was established in 2011.
This initiative seeks to reduce the mounting debris piles and
increase the amount of old concrete that can be recycled [28].
To promote the adoption of recycled materials in Ontario,
the CPATT at the University of Waterloo has emerged as a
prominent institution in researching and implementing various
recycled materials in new pavement construction, conducting
numerous successful studies. Table 4 outlines the structure of
several literature reviews concerning the application of
recycled materials in asphalt and concrete mixtures.
5.2 Engineering performance properties of recycled
materials mixtures
This study is presented to provide more knowledge, solve
the technical challenges related to recycled pavement mixtures,
and advance the current state-of-the-art practice while leading
the paving industry towards improved sustainability and
effective usage of recycled materials and designs. This
research comprised an extensive program of laboratory and
field tests conducted to assess the behavior and mechanical
attributes of the mixtures that include various recycled
materials with different proportions.
Recycled materials have been used in highway projects
since the 1970s by the Ontario Ministry of Transportation
Table 4. Structure of existing literature reviews on the use of recycled materials in pavement mixtures
RCA Materials in Pavement Mixtures
Ref.
[29]
[23]
Type of RCA
and % Application
Type
The Properties of RCA
Treatments
of RCA
Test
Results and Notes
-The findings indicated that concrete
mixtures incorporating RCA perform
similarly to or outperform conventional
concrete in categories such as flexural and
compressive strength, freeze and thawing
(0%, 15%, 30% and
durability
and
thermal
expansion
BRD= 2379Kg/m3
50%) coarse RCA
coefficient.
W. A%= 4.41
(Lab work and field
-Visual surveys revealed that every test
Moisture content%=1.4
case study)
segment was in perfect condition, with a
pavement condition index (PCI) value
higher than (85). This examination took
place following two years of service and
approximately 300,000 ESXLs.
Twelve initial blends use three different cementitious content levels in total (315, 330, and 345) kg per m3 were developed. These
were used to identify four suitable mixes with RCA contents of varying coarseness, specifically 0%, 15%, 30%, and 50%. to place at
the CPATT test track. On the 28-day, the preliminary mixes exceeded the 30 MPa design strength. In June 2007, four testing segments
were constructed, each with a different proportion of coarse recycled concrete aggregate (RCA) materials, specifically 0%, 15%, 30%,
and 50%. The sections all had identical cross-sections which consisted of a mix of (250) mm Portland cement concrete (PCC), (100)
mm asphalt stabilized OGDL and a (450) mm granular base.
A.M %= (20.4, 32.1,
36.1) % for RCA*#1,2, &3
-Compressive
A.M %= (29.6, 41.1,
strength,
24.5) % for RCA**#1,2, &
Slump,
The results obtained suggested that concrete
-Tensile
3
incorporating pre-soaked RCA might exhibit
strength
A.M%= (46.4 ,55.7, &
-Nitric acid
higher compressive strengths when
splitting,
49.6) % for RCA***#1,2,
dissolution
compared to regular concrete with
The
elasticity
&3
Three types of
method*
equivalent
water-cement
ratios.
modulus,
BRD = (2.66,2.37, 2.31, &
coarse RCA with
-FreezeAdditionally, the findings indicated that it is
-Poisson's ratio,
2.23) for NA, RCA#1,2,
100% replacement
thaw
feasible to use 100% RCA in concrete
-linear
by volume of virgin &3
**
method
production throughout the manufacturing
coefficient
of
W.A5 = (1.52,4.66, 6.15,
coarse aggregate
-Thermal
process to achieve changing compressive
thermal
& 7.81) % for NS,
(lab work)
treatment
strengths within the range of 30–60 MPa
expansion
RCA#1,2, &3 Resp
method***
while keeping slump values from 75 to 125
(LCTE),
A.R%= (11.9, 15.1, 22.1,
mm by modifying water content, cement
- The energy of
&
25.0)
for
NA,
content, and the ratio of water to cement.
fracture and the
RCA#1,2,3 Resp.
modulus
of
Mean ACV= (18.2, 23.1,
rupture
26, 28.5) for NA,
RCA#1,2,3 Resp
24 mixtures of concrete were developed. These were classified into three groups: control, direct replacement, and strength-based
mixtures. The combinations (mixtures) assigned control were designated with proportions having slump values between (75 -125)
mm and compressive strengths of 30 MPa, 40 MPa, 50 MPa, and 60 MPa. These mixtures were used as a reference to compare the
mixtures that included RCA. The mixes classified under the "direct replacement" category were utilized to investigate the results
attainable through the complete substitution of virgin coarse aggregate with RCA. Virgin coarse aggregate was entirely substituted
with RCA, representing a 100% replacement by volume, to evaluate the effect on the concrete's hardened and fresh properties. In the
third group, the study used strength-based blends to examine the effect of aggregate properties on the bonding of reinforcement in
concrete mixture with identical compressive strength. Furthermore, there were two distinct experimental phases. These tested
-Compressive
and
flexural
strength,
-Freeze-thaw
durability,
coefficient
of
thermal
expansion
- visual surveys
for the field
section
239
[24]
[1]
concretes with varying ranges of compressive strength, different sources for the RCA
same kind of GU cement.
-Aggregate
Saturation
-At different
-Air content
A. M %= (40.3, 44.3) %
proportions,
-Slump
RCA#1,2
including
-Fresh density
W.A %= (1.53, 4.72,
0%, 60%,
- Compressive
6.9) %
and 100%,
strength,
For (NA, CRCA#1&2)
the internal
Two RCA types
Tensile
BRD= (2.66, 2.36, 2.28)
curing
30% to 100%
strength
For (CNA, CRCA#1&2)
capacity of
CRCA by volume
splitting
BRD (FNA)= 2.51
recycled
of coarse NA
-Linear
A.R %= (10.8, 16.1,
concrete
(Lab work)
Coefficient of
23.4) %
aggregates
Thermal
For (CNA, CRCA#1&2)
(RCA)
in
Expansion
ACV%= (17.9, 25.8,
concrete
Modulus
28) %
was
For (CNA, CRCA#1&2)
elastic,
&
evaluated.
Permeable
porosity
Two RCA types (0,
15, 30, & 60) %
CRCA by weight of
coarse CNAg
(Lab work)
A.M %= (20.4, 32.1,
36.1) % for RCA1#1 & 2
A.M %= (29.6, 41.1,
24.5) % for RCA**#1,2,
&3
A.M%= (46.4 ,55.7, &
49.6) % for RCA***#1,2,
&3
BRD = (2.66,2.37, 2.31, &
2.23) for NA, RCA#1,2,
&3
W.A5 = (1.52,4.66, 6.15,
& 7.81) % for NS,
RCA#1,2, &3 Resp.
A.R%= (11.9, 15.1, 22.1,
&
25.0)
for
NA,
RCA#1,2,3 Resp.
Mean ACV= (18.2, 23.1,
26, 28.5) for NA,
RCA#1,2,3 Resp.
-Heat TRE.
@
(250,350,50
0, & 700°C)
-Presoaking
TRE. with
(HCl
&
C2H4O2)
-Mechanical
TRE.
240
-The test of
Indirect tensile
strength
test
(ITS),
-Tensile
Strength Rati
-Dynamic
modulus test,
-Rutting
-Shear
Flow,
and
-Thermal stress
restrained
specimen
test
(TSRST)
materials used, and various providers of the
The study's results revealed that a fully
saturated mixture containing RCA leads to
higher early-age compressive strength when
compared to NA mixtures. Additionally, the
findings showed that including 30% RCA in
the mix had no substantial impact on the
tensile strength values, permeable porosity,
and modulus of elasticity of the concrete
mixtures. Porous porosity was higher in
concrete with RCA than the concrete with
NA; conversely, RCA concrete mixes had a
lower elastic modulus and tensile strength
than NA concrete mixes.
The study's results indicated that:
-The incorporation of CRCA (Coarse
recycled concrete aggregate) in different
proportions has proven incredibly effective
for CRCA that has been treated and
untreated, as it complies with all
requirements set by the MTO regarding the
volumetric properties of HMA. On the other
hand, applying treated CRCA using a variety
of treatment techniques seems to produce
even better outcomes than using untreated
CRCA.
-Adding different types of CRCA that has
not been treated
in varying ratios results in improved
resistance to rutting and greater stiffness
modulus compared to the control mixture.
The kind of CRCA used the asphalt
mixtures' permeate deformation properties.
Utilizing CRCA after applying various
treatments, such as thermal, soaking, and
short-mechanical ones, enhances rutting
resistance, reduces total rut depth, and
slightly increases the stiffness modulus of
asphalt mixes based on the type of CRCA.
-The results revealed that the mixes
incorporating CRCA that had not been
treated exhibited significantly higher ITS
(Indirect Tensile Strength) than the control
mixture.
-The TSR (Tensile Strength Ratio) values
for all mixtures containing different types
and percentages of CRCA that have not been
treated exceed the minimum value specified
in MTO regulations.
-The approach of combining prior to soaking
technique with a weak acid treatment,
subsequently to a brief mechanical
treatment, proved to be notably effective in
improving the moisture resistance of asphalt
mixtures, surpassing the performance of
other combination methods.
-According to the TSRST test results, adding
CRCA reduces the fracture temperature
compared to the control mixture.
-Moreover, implementing a combination of
different treatment methods results in a
notable decrease in the fracture temperature,
signifying the effective use of CRCA that
has been treated in Hot Mix Asphalt mixes,
particularly in colder climates.
[2, 21]
[22]
Designs for fourteen HMA Superpave mixes were developed in conformity with AASHTO R 30-2 (2006). The design equivalent to
a single-axle load varied from 10 to 30 million. The design gyration level (Ndes) was set at 100, while the maximum gyration level
(Nmax) was established at 160. To specify the temperatures of both compaction and mixing, viscosity values of 1.7 Poises and 2.8
Poises were determined, respectively.
-The results from the Rheological analysis of
binders demonstrated that the influence of
RAP variation is significantly influenced by
the
original
asphalt
binder's
PG
(performance grade).
-The experimental findings also indicated
that, apart from the recovered binders from
20% and 40% RAP (Reclaimed Asphalt
Pavement) in HMA mixtures with PG 52-40
and 52-34 asphalt cement types, all other
recovered asphalt binders from various PG
types and different RAP proportions
exhibited greater flexibility at lower and
moderate temperatures. This characteristic
-Rheological
contributes to enhancing the resistance
Characterization against fatigue failure in RAP HMA.
of
Asphalt -The results indicate that there were
-DGAC with (15, -Crushed faces %= (99.1,
Binders
significant enhancements in both the
20, & 40%) RAP
98.5, 97.8%) two crushed
-Shear Modulus complex shear modulus (G*) and phase
-DGAC
RCR faces for (0, 20, 40%) RAP
(DSR)
angle (δ) parameters of the binder when
terminal-blend
-Uncompacted
Voids=
-Tensile
modified with CRM (Chemical Recycling
HMA
mix (44.5, 45.8, 44.7%) for (0,
Strength Rati
Method). Consequently, the use of CRMcontaining
20% 20, 40%) RAP
-Dynamic
modified binder helps in achieving a balance
RAP
-F&E= (0.2, 0.1, 0.4%) for
modulus,
between the asphaltenes and maltenes
-GGAC RCR field- (0, 20, 40%) RAP
- Rutting
components in the aged-RAP (Reclaimed
blend with 20% Sand Equivalency%= (67,
-Flow Number, Asphalt Pavement) binder, leading to a
RAP
73.5, 90.5%) for (0, 20,
and
substantial impact on the resistance to
(Field & lab)
40%) RAP
-Thermal stress rutting and thermal cracking in the evaluated
restrained
Hot Mix Asphalt (HMA) mixtures.
specimen
test -The experimental findings showed that
(TSRST)
increasing the RAP (Reclaimed Asphalt
Pavement) content or incorporating CRM
into HMA (Hot Mix Asphalt) led to mixtures
that were more rigid and had greater
elasticity. These mixtures also demonstrated
improved resistance to low-temperature
cracking, fatigue cracking, and permanent
deformation impacts.
-In conclusion, it was established that the
performance of recycled HMA regarding
issues like low-temperature cracking,
rutting, stiffness, and susceptibility to
fatigue was influenced by both the RAP
content and the PG of the virgin asphalt
binder concurrently.
-The results indicated that longer interaction
periods and higher temperatures between the
aged and virgin asphalt binders result in
more effective mixing and blending.
-The results reveal that RAP-HMA samples
obtained after 12 hours of storage in a silo
-Dynamic
exhibited decreased stiffness, which was
modulus,
attributed to enhanced blending between the
-Rutting
aged and virgin binder.
-Thermal stress
-The experiential results indicated that an
20% & 40% RAP
restrained
increase in the silo-storage time leads to a
(Lab work)
specimen
test
slight reduction in VMA and Vbe of all
(TSRST), &
RAP-HMA samples.
-Four-point
-According to data collected, RAP-HMA
bending test
mixture stiffness significantly decreased
following 8 and 12 hrs of storage. In
addition, the findings demonstrated that silostorage duration of up to 4 hrs did not
significantly influence the RAP-HMA
stiffness.
The asphalt mixtures were manufactured and gathered from two distinct asphalt plants. Various times were used to gather the mix
samples to investigate the impact of storage duration on the blending process and achieve a cohesive outcome. (0, 4,8, 12, and 24) hrs
241
[14]
[30]
of storage in the silo. To reduce any additional blending between the virgin and aged binder, all the RAP HMA samples were stored
in a particular chamber at (7˚C) till the compaction day of the samples.
RAS & RAP Materials in Pavement Mixtures
-Surface distress
evaluation
–
visual analysis
-Surface texture -The field assessments indicated that the
– sand patch road surfaces remained in satisfactory
method
condition during the research monitoring
-Friction
– period, the study, which ended up lasting for
-(1.5, 3, 6) % RAS
British
four years for all three of the residential
-(12, 13.5, 25) %
pendulum tester streets used in Markham (town) and lasted
RAP in all HL3,
-Deflection
for two years on the CPATT Test Track
SP12.5 FC1 &2, &
measurement – -The structural analysis data, executed using
SP19
PFWD
MEPDG, showed Mix 3 as the highest
(laboratory & field
-Friction
– performer in terms of Life-Cycle
work)
British
Assessment, followed by Mix 2. Mix 3
pendulum tester consists of 3% RAS and 25% RAP, while
-Dynamic
Mix 2 is comprised of 6% RAS and SP19
Modulus
and asphalt binder.
properties
of
binders
(MEPDG)
This study aimed to assess the incorporation of discarded shingles into six standard Hot Mix Asphalt (HMA) mixtures commonly
used in Ontario; firstly, (5 and 13.5) % RAS and RAP, respectively, make up HL 3. The two mixtures, SP19 with 6% RAS and SP19
with 3% RAS and 25% RAP, comprise the binder layer. Two mixes are also present in the surface layer: SP12.5 FC1 with 3% RAS
and 17% RAP and SP12.5 FC2 with 6% RAS and 3% RAS along with 12% RAP. The six HMA formulations were also crafted to
incorporate RAP, adding complexity to the study as RAP and RAS were presented.
The outcomes of the research found that:
-The dynamic modulus and TEST testing
-Dynamic
indicated that Mix 3-SP12.5 FC2, which has
modulus,
3% RAS with 12% RAP, performed better.
-Resilient
-Mix 1(HL 3), which included 1.5% RAS
modulus,
with 13.5% RAP, exhibited the highest
-Flexural
-(1.4, 3, 6) % RAS
fatigue, and - resilient number, whereas Mix 2 (SP12.5
-13.5, 17, 25) %
Thermal stress FC1), comprising 3% RAS with 17% RAP,
RAP
displayed superior performance in the
restrained
(laboratory & field
specimen
test flexural fatigue test.
work)
-In general, the findings from laboratory
(TSRST)
-Portable falling experiments and field performance tests
provided strong encouragement for the
weight
incorporation of RAS into HMA, provided
deflectometer
that it is appropriately integrated into the
(PFWD)
mixture.
The six distinct asphalt mixture types included in this study were designed to be used in pavements' surface and binder courses. The
following are the formulations for Surface Layer HMA:
13.5% RAP and 1.4% RAS are combined with HL 3 to make Blend 1.
Blend 2 contains SP12.5 FC1 with 17% RAP with 3% RAS.
Blend 3 consists of SP12.5 FC2, 12% RAP, with 3% RAS.
SP12.5 FC2 with 6% RAS make up Blend 4.
The formulations for the Binder Layer HMA are as follows: Blend 1 is SP19 E and contains 25% RAP and 3% RAS.
Blend 2, which is SP19 E, contains 6% RAS.
BRD = Bulk Relative Density; W.A = Water absorption; ESXLs = Equivalent Single Axle Loads; A.M = Adhered mortar; * Nitric acid dissolution method; **
Freeze-thaw method; *** Thermal treatment method; A.R = Abrasion resistance; CAN = coarse natural aggregate; FNA = fine natural aggregate; ACV = Aggregate
crushing value; TRE = Treatment; HCl = Hydrochloric acid; C2H4O2 = Acetic acid; DGAC = Dense-graded Asphalt Concrete Mixtures; GGAC = Gap-graded
Asphalt Concrete Mixtures; F&E= Flat and Elongated Particles.
Consequently, the key criteria for assessing the sustainability
of a pavement should encompass the following aspects [2]:
• Reduce the utilization of the natural resources;
• Minimize consumption of energy;
• Reduce emissions of greenhouse gases (GHG);
• Reduce pollution in the environment (noise, water, air,
etc.);
• Improve safety, health, and risk reduction; and
• Ensure that user comfort and safety are held at a high level.
Applying crumb rubber (CR) to pavements' surface layer,
for example, demonstrates energy requirements that are
comparable to those of conventional pavements. However,
compared to standard mixes, it produces fewer greenhouse gas
5.3 Sustainability and cost assessment
“A sustainable pavement is one that achieves its specific
engineering goals, while, on a broader scale, (1) meets basic
human needs, (2) uses resources effectively, and (3)
preserves/restores surrounding ecosystems” [31].
The central agreement concerning sustainability primarily
pertains to its interconnection and advantages concerning the
economy, the environment, and society. Taking these elements
into account in the context of constructing a sustainable
pavement necessitates that the road is long-lasting, economical,
environmentally efficient, and demonstrates performance that
is equal to or better than one constructed using new materials.
242
GreenPave, Sustainable Highways Self-Evaluation Tool, and
Envision [2].
Life Cycle Cost Assessment (LCCA) is an analytical
method built upon established economic analysis principles,
used to evaluate the long-term economic viability among
different competing investment alternatives [35]. Table 7
provides a summary of the six primary components affecting
pavement life cycle costs and their respective degrees of
impact.
LCCA proves highly advantageous in cases where project
options meet similar performance standards but exhibit
variations in costs relevant to the agency, owner, and
pavement users. It allows for a comparison aimed at selecting
the project that optimizes net savings.
To increase the usage of recycled materials in the Province
of Ontario and to remove hesitation from using them. The
University of Waterloo's CPATT had worked on adopting the
responsibility of studying HMA LCCL with different types of
recycled materials in the new pavement through many
successful investigations. Table 8 reveals the framework of
some literature studies involving the use of recycled materials
in pavement mixtures.
emissions. Based on these initial findings, adding CR to the
surface layer of pavement may be a more environmentally
friendly option. It provides a workable way to dispose of old
tires while enhancing pavement performance [32]. The results
indicate that a large amount of steel slag (SS) is substituted for
natural aggregates in pavement concrete and blocks. The fact
that this substitution uses a lot less cement means that it is
better for the environment overall. Unfortunately, there are
adverse environmental effects from the increased use of
asphalt and the heavier transportation weight of SS during the
mixing process. However, using SS greatly lowers the risks
related to landfill overflow and stops the environmental
damage caused by exploitation. These benefits are significant,
albeit difficult to measure exactly [33].
Tables 5 and 6 summarize some general approaches to
improving sustainability concerning pavement recycling at the
end of its life & Concrete Materials Production, alongside the
related environmental advantages and trade-offs [34].
Various assessment tools have been created to evaluate the
sustainability of different options for pavement design, for
example: Leadership in Energy and Environmental Design
(LEED), GreenLITES, GreenGuide, INVEST, GreenRoads,
Table 5. Strategies for increasing pavement sustainability through the production of concrete materials [31]
Concrete Materials
Objective
Reduce non-renewable
energy consumption and
GHG emission in cement
manufacturing
Reduce energy
consumption and
emission in concrete
production
Approach to Sustainability
Improvement
Increased efficiency of
cement plants through
improved energy harvesting
and grinding
Utilization of renewable
energy including wind and
solar
Utilization of more efficient
fossil fuels
Economic Effects
Impact on the
Environment
Impact on Society
High capital cost but
lower cost of
manufacturing
Decreased energy use and
GHG emissions
Less fuel is used,
and fewer emissions
are produced
High capital cost but
lower cost of
manufacturing
lower manufacturing
costs
lowers manufacturing
costs
Reduced non-renewable
energy consumption and
GHG emissions
Reduced emissions per unit
of energy used
Beneficial use of waste
material
Utilization of biofuels
Reduces cost to cost
neutral
Reduced GHG emissions
Minimize clinker content in
portland cement through
allowable limestone additions
and inorganic processing
additions
Reduces cost to cost
neutral
Reduced GHG emissions
and consumption on fuel
Increased output of blended
cements containing SCMs or
limestone
Reduce cost
Significant reductions in
energy use and greenhouse
gas emissions. takes
RCWMs away from the
landfill
Increase concrete mixing
plant efficiency and reduce
emissions
Increased capital cost
but decrease production
costs
Reduce emissions
Utilization of renewable
energy
Cost neutral to increase
cost
Depends on proximity
to grid; should save
cost
Utilization of waste fuels
Use electrical energy from the
grid
Use less cement in concret
mixtures without
compromising performance
Use more blended cements
without compromising
performance
Increase addition rate of
SCms at concrete plant
Reduces
dependency on
fossil fuels and
lowers emissions
Reduces
dependency on
fossil fuels and less
material sent to
landfill
Reduced local
emissions including
noise and
particulate
Reduced emissions
Reduced emissions
Reduced emissions, better
emission controls
Reduced local
emissions
Reduce cost of concrete
Reduced emissions and
energy
No impact on cost
Reduce emissions and
energy
Reduce cost of concrete
Reduced emissions and
energy
243
Less non-renewable
fuel consumed and
GHG generated
Cleaner buming
fuel
Reduces materials
in landfills
Reduces
dependency on
fossil fuels
Longer lasting
pavements; less
delays
Longer lasting
pavements; less
delays
Longer lasting
pavements; less
delays
without compromising
performance
Recycle washout water
Reduce water use in
concrete production
Increase use of RCWMS
and marginal materials as
aggregate in concrete
Improve the durability of
concrete
Recycle water used to process
aqqreqates
Change specifications to
allow greater amounts of
RCWMS to be used in
concrete without
compromising performance
Use RCWMS and marginal
aggregate in lower lift of twolift pavement
Lower w/cm through
admixture use
Utilize an effective QA
program throughout material
production phase
Cost neutral to slightly
added cost
Cost neutral to slightly
added cost
Reduced cost
Cost neutral to slightly
added initial cost;
potential for reduced
life cycle costs
Cost neutral to slightly
added cost
Slightly added initial
cost; save cost on
litigations
Improved water
quality
Improved water
quality
Use less water resources
Use less water resources
Less landfill material, less
transportation
Less landfill material, less
transportation
Longer lasting pavements
Less delays over
life cycle
Longer lasting pavements
Less delays over
life cycle
Table 6. Strategies to enhance the sustainability of asphalt pavement recycling within the context of pavement sustainability [34]
Objective of Recycling
Asphalt Pavement
Increase central plant
recycling rate of
pavements
Increase the rate of inplace recycling for
paving
Approach to Sustainability
Improvement
Enhance plant technology through
the improvement of elements like
heating effectiveness, positive dust
control, dual-barrel mechanisms,
and other pertinent features.
Economic Effects
Impact on the
Environment
Impact on
Society
Requires the producer to
make an initial capital
investment. can possibly
lower the price of making
pavement
If the burden of
transport is not offset,
can reduce GHG
emissions.
Protects pristine
natural resources.
Decreases the
need for landfills
Can use more energy
during material
production, but overall
life-cycle energy and
emissions may
decrease.
Improved pavement
quality can lower GHG
emissions over the
course of a project.
Can use more energy
during the production
of materials, but
overall life-cycle
emissions and energy
use could go down.
Improve the initial quality of the
materials and construction of the
pavement.
Might lower life-cycle
costs while increasing
initial costs.
Use softening agents or
rejuvenators.
Can increase material
production costs.
Maintain and manage RAP
stockpiles (reduce moisture,
fractionation).
Can slightly raise the cost
of producing materials,
but life-cycle costs could
go down.
Use the proper type and amount of
additive or stabilizers.
To increase weathering, cracking,
and fatigue resistance, use structural
asphalt overlays.
Can raise material
production costs while
possibly lowering lifecycle costs.
Life-cycle energy and
emissions could be
reduced.
No costs.
As a result of the
higher quality, lifecycle energy and
emissions could be
reduced.
To increase quality, create
standards for mixture design and
QA.
Decline in natural
resources.
Protects pristine
natural resources.
Lessens the need
for landfills
Protects pristine
natural resources.
Lessens the need
for landfills
Protects pristine
natural resources.
Lessens the need
for landfills
Table 7. Pavement cycle cost components [2]
Initial costs
Maintenance costs
Rehabilitation
costs
User costs
Residual value
Salvage value
The Six major Life-Cycle Cost Components
-Design, build and construct.
-Cost of hot mix (standard mixes or enhanced pavement designs like stone mastic
asphalt or modified / engineered asphalt)
Routine maintenance such as crack sealing and patching to extend pavement
service life
Influence on Life-Cycle Costs
Moderate to high
Moderate
Resurfacing and reconditioning to restore pavement to acceptable service levels
Moderate
Cost of delays due to construction and maintenance
Value of the remaining service life of the road (the economic analysis may cover
40 years compared to the road’s expected life of 50 years)
Value of reusable components at the end of the analysis period
Low to moderate
244
Low
Low
Table 8. Framework of available literature studies of sustainability and LCCA for recycled materials application in pavement
mixtures
RAP & RCR Materials in Pavement Mixtures (2)
Sustainability Assessment
Tools
Results & Conclusions
Tools
GreenPave
This simple sustainability analysis
-Mechanisticassessment
registered a scorecard of 13.2 points
empirical
for Case A - Rubberized-RAP, so it is pavement design
awarded a GreenPave “Silver”
guide (MEPDG).
certification. Based on points earned
-PaLATE
for
and GreenPave rankings, Case B environmental
20% RAP and Case C – 40% RAP are analysis
awarded the “Bronze” certification,
respectively, while Case D – Control
Mix is certified unsustainable.
LCCA
Results & Conclusions
-Case
A
–
-The results indicate that building a 1Rubberized
kilometer pavement section using Case
RAP: 20% RAP
A (Rubberize-RAP HMA) is costlier in
+ 20% CRM in
comparison to Case D (Control HMA)
surface course
mix or mixtures involving Case B (20%
-Case B - 20%
RAP HMA) and Case C (40% RAP
RAP in surface
HMA). Nevertheless, Case C and Case
course
B appear to be more economical than
- Case C - 40%
Case A, in terms of initial pavement
RAP in surface
construction cost.
course
-Also, the outcomes showed that Case A
- Case D (Rubberized-RAP HMA) consistently
Control Mix with
returned the least expensive total
no
recycled
maintenance and rehabilitation cost
components in
throughout the analysis period for all
the surface and
discount levels considered.
binder course
-The analysis for Case A (RubberizedRAP) is seen to return salvage values
higher than Cases B, C and D across all
discount levels considered
-In conclusion, Case A (RubberizedRAP HMA) registered a reduction of
8% of the total cost than the Control
HMA (Case D) over the 20 years of
analysis. While Case B (20% RAP
HMA) and C (40% RAP HMA)
respectively are approximately 2% and
3% less expensive compared to Case D
(Control HMA) over the same period.
In terms of an average relative
environmental percentage savings
(RPS), the obtained analysis results
show that the Case C mix has the highest
RPS of 26.7% compared to the control
mix (Case D). Then followed by Case Bmix with 12.6%, and Case A with 3.4%
in total environmental savings compared
to the control mix (Case D).
-Green Pave evaluates the sustainability of pavements in four categories. These categories are; pavement design technologies, materials &
resources, energy & atmosphere, and innovation & design process with a point for each category (9, 11,8, & 4) respectively, up to a total of 32
points.
-The GreenPave framework, which divides assessments into four categories: Bronze (7–10 points), Silver (11–14 points), Gold (15–19 points),
and Trillium (20 or more points), has been used to evaluate the sustainability of pavements.
-Assessments were carried out for a 20-year anticipated lifespan in the context of maintenance and rehabilitation design strategies.
-Using discount rates of 3%, 4%, 5%, and 7%, the preliminary costs for constructing the pavement as well as the schedules for maintenance
and rehabilitation were calculated and then annualized over the 20-year analysis period.
-Excavation expenses were omitted from calculating the initial pavement construction expense because their inclusion is not consistently
essential in a Life Cycle Cost Analysis (LCCA).
-Initial pavement construction cost was determined at year zero for all case designs.
-Based on the outcomes of the evaluated HMA mixtures in this study, it is considered reasonable and practical to conclude that RAP and CRM
are valuable components of typical Ontario Superpave HMA mixtures
RCA Materials in Pavement Mixtures [29]
Sustainability Assessment
LCCA
Mix Types
Tools
Results & Conclusions
Tools
Results & Conclusions
-According to the results of the life cycle
cost analysis (LCCA), recycled concrete
The ME-PDG analysis results showed
aggregate (RCA) can be used to achieve
that the long-term performance
Mechanistic –
cost-effective measures as the supply of
Test section with
Mechanistic –
modelling of percent cracked slabs,
empirical
new aggregate resources decreases.
(0%, 15%, 30%,
empirical
joint faulting, and pavement roughness
pavement
-There is no substantial gap between the
and 50% coarse
pavement design
registered an improvement in the
design
coarse RCA amounts observed for each
RCA)
MEPDG
performance with increased coarse
MEPDG
scenario on a per-kilometer basis;
RCA percentage for all measures.
nonetheless, the savings become
substantial over the length of the whole
roadway.
Mix Types
245
-The pavement configuration included a 250 mm Jointed Plain Concrete Pavement (JPCP) with various percentages of Recycled Concrete
Aggregate (RCA), a 100 mm Open-Graded Drainage Layer (ODGL) stabilized with asphalt, then, a 450 mm-sized granular base substance
rests on a subgrade consisting of clay. The analysis covered fifty years.
-In the context of LCCA, three different pricing scenarios were implemented to model the cost fluctuations of virgin aggregate as its availability
diminishes. In Scenario One, costs rise as the quantity of RCA increases, while Scenario Two maintains uniform costs for all RCA mixtures.
Third Scenario, on the other hand, sees costs decreasing as the amount of RCA in the mix grows.
-A probabilistic LCCA was conducted to assess these scenarios, using Latin Hypercube sampling (LHS) to determine the Present Worth (PW).
RAS Material in Pavement Mixtures [20]
Sustainability Assessment
LCCA
Mix Types
Tools
Results & Conclusions
Tools
Results & Conclusions
-Based on the PaLATE outcomes, Mix
3: SP19 3% RAS and 25% RAP had a
lower quantity of environmental
emissions as well as consuming less
water and energy.
-In terms of an average relative
-Mix 1: HL 3
environmental percentage savings
1.5% RAS and
(RPS), the finding indicated that Mix 3:
Overall, the results indicate that Mix 2
13.5% RAP.
SP19 3% RAS, 25% RAP had the
(SP 19 6% RAS), the binder layer,
- Mix 2: SP 19
highest average percentage savings of
6% RAS.
performed better in all analyses of
18% followed by Mix 4: SP12.5 FC1
- Mix 3: SP 19
distress resistance, followed by Mix 5
3% RAS, 17% RAP (11.3%) when
3% RAS and
(SP 12.5 6% RAS), the surface layer.
compared to Mix 1.
25%RAP.
- While, the analysis results revealed
MEPDG
PaLATE
-Overall, the optimal sustainable Mix
- Mix 4: SP12.5
that the performance properties of Mix
Software
from PaLATE analysis was registered
FC1 3% RAS
3 (SP 19 3% RAS, 25% RAP), Mix 4
for Mix (3), the specifications include
and 12%RAP.
(SP 12.5 3% RAS, 17% RAP) and Mix
(3%) (RAS) and (25%) (RAP) intended
- Mix 5: SP12.5
6 (SP 12.5 3% RAS, 12% RAP) were
for application in HMA pavement, in
FC2 6% RAS.
similar to Mix 1: HL 3 1.5% RAS,
contrast to Mix (1).
- Mix 6: SP12.5
13.5% RAP.
-In conclusion, the structural analysis,
FC2 3% RAS
life-cycle assessment, and field and
and 12% RAP.
laboratory studies collectively suggest
that RAS can be a valuable supplement
in HMA mixtures, provided it is
integrated correctly into the mixture.
Moreover, this integration has the
potential to result in cost savings.
-This study was conducted to assess the potential utilization of discarded shingles in six typical HMA mixtures commonly used in Ontario.
The compositions that are discussed are as follows: HL 3, which has 1.5% and 13.5% Recycled Asphalt Shingles (RAS); binder layer mixes
SP19 with 6% RAS or a mix of 3% RAS and 25% RAP; and surface layer formulas SP12.5 FC 1, which has 3% RAS and 17% RAP, and
SP12.5 FC2, which has 6% RAS and, in another variation, 3% RAS with 12% RAP. It's important to note that all six HMA mixtures were
also designed to incorporate RAP, which added complexity to the research, given that RAP and RAS were both present.
- In this study, only the construction phase was examined within the context of LCCL.
-Employing life-cycle assessment (LCA), an assessment was conducted to analyze the environmental and economic benefits over a 20-year
evaluation timeframe for all blends that contain RAP and/or RAS. The aim was to identify the most economically efficient mixture.
-To gauge the cost reductions, two standard mixtures were employed: Control Mix, representing the typical HL 3 combination, and Mix 1,
consisting of HL 3 with 1.5% RAS with 13.5% RAP. Mix 1 was used to evaluate the effects of a higher RAS percentage in Hot Mix Asphalt
(HMA), and Control Mix was used to evaluate the long-term viability of adding recycled material to HMA.
➢ Examining the volumetric properties of HMA mixtures
containing recycled materials is highly recommended.
It's crucial to emphasize that these mixtures must satisfy
all specification criteria before assessing their
performance properties.
➢ It is advisable to subject the CRM employed in standard
Ontario rubberized mixtures to both cryogenic and
ambient grinding techniques.
➢ The dynamic modulus test offers a better way to test the
performance of asphalt mixtures with RCA added.
Crucial information can either be directly found or
estimated from this comprehensive test. The TSRST test,
specifically in terms of the temperature at which failure
occurs, was the sole test capable of detecting distinctions
in both aspects: the performance grade and the quantity
of recycled material in all mixtures.
➢ We highly recommend the utilization of blending charts
to assess the performance grade of the combined binder.
➢ When incorporating recycled materials like RAP and/or
RAS into asphalt mixtures, it is recommended to decrease
5.4 Recommendation and guideline for recycled materials
application
Derived from the findings of this study, here is a valuable
set of suggestions that can provide assistance in the
incorporation of recycled materials into road pavement.
➢ Regarding RCA, it is crucial to ascertain its source,
whether it originates from deteriorated or robust older
structures.
➢ Before using RCA, it is appropriate to evaluate its
strength using the ACV test.
➢ Techniques like SEM, EDAX, and ESEM have the
ability to accurately identify the microstructure,
morphological features, and mineralogical characteristics
of recycled materials.
➢ RCA's mechanical, microstructural, and physical
qualities can all be improved by applying various
treatment techniques.
246
dry-freeze, dry no-freeze, etc.) and various severity levels
using the ME-PDG to estimate pavement performance.
Generally, the recommendations and guidance herein are
designed to do the following:
The provisions of guidelines for how recycling can
potentially be applied. Assistance in the preliminary analysis
of how recycling can be used as an alternative mode of
pavement rehabilitation, as well as in setting methodology that
is convenient. The provision of guidelines and standards that
can be applied when making a detailed analysis of cost, energy,
materials design, structural design, construction specifications,
and quality control. A recommended methodology for the
evaluation of project results in order to compare recycling
alternatives with conventional methods of rehabilitation [36].
Figure 6 demonstrates the framework of the guidelines.
the PG Asphalt Binder grade by 60°C. This adjustment is
necessary because the final asphalt mixture tends to
become more rigid due to the inclusion of stiff RAS.
Reducing the grade of the binder and causing it to be less
stiff helps balance the impact of adding RAS. Since the
characteristics of HMA change when RAS and/or RAP
are introduced, this adjustment is instrumental in
achieving a well-suited field mix.
➢ Utilize the AASHTO TP-60 procedure to reexamine
RCA cylinders for the purpose of comparing and
confirming the outcomes. These results may allow one to
conclude that the simplified method is appropriate for
computing CTE. (Coefficient of Thermal Expansion) for
its application within the ME-PDG.
➢ Evaluate the suitability of pavements containing recycled
materials in all climatic zones (including wet no-freeze,
Figure 6. Schematic diagram of essential steps for the application of recycled materials in the pavement
creating traditional asphalt or concrete mixtures in Ontario that
incorporate different recycled materials while maintaining
pavement performance. The aim is to inspire Ontario's paving
sector to progress toward a more sustainable and economically
viable path, particularly by enhancing pavement recycling
methods.
The experimental test results and the test sites' field
performance are generally very positive. This indicates that
RAS, RAP, RAC, and RCA can serve as effective supplements
in concrete and asphalt pavement blends for roads with low to
6. CONCLUSIONS
This research briefly summarizes the guidance of the
utilization of recycled materials in pavement. This research
has been established based on the obtained results and
recommendations of several case studies presenting various
innovative research projects that have been conducted at the
Centre for Pavement and Transportation Technology in
Canada with the utilization of recycled materials over the past
20 years. This endeavor has examined the possibility of
247
moderate traffic volumes, provided it is integrated into the
mixture correctly.
The physical properties, mechanical properties, and
microstructural characteristics of recycled materials should be
taken into account before using them in pavement mixes and
field applications. Additionally, work on treatment methods
for enhancing the properties of inferior quality materials
should be encouraged. Consequently, the selection of a
suitable performance test regarding the type and proportion of
recycled materials can be made. Finally, a comprehensive
study of sustainability and LCCA for each recycled material
should be conducted before real application.
Regarding which non-Canadian regions that are best suited
for using recycled materials in pavement, there is no
universally applicable solution. Thus, it depends upon a
thorough evaluation of the local environment, the
characteristics of the materials, and the particular project needs.
However, the application of recycled materials can be
appropriate for a variety of regions with proper quality control
and design, supporting resource efficiency and sustainable
building methods. The summary tables in this study
illustrating pavement performance using various recycled
materials show that a range of temperatures and environmental
factors were used during the experimental tests. These tests
evaluated performance in a range of scenarios that simulated
different environmental conditions, including higher and
lower temperatures.
Appropriate material characterization, quality control and
testing, as well as design and engineering modifications, are
essential to efficiently using recycled materials in any traffic
situation. Therefore, areas with low to moderate traffic loads
are the best places to use recycled materials because hightraffic areas require materials with high durability, strength,
and resistance to deformation. To ensure they can handle the
demands, recycled materials are used in these situations after
thoroughly and accurately evaluating their performance
characteristics.
The main conclusions are shown below:
1. The experimental and field results indicated that the
utilization of untreated RCA in concrete mixtures was
promising in terms of performance (flexural and compressive
strength, freeze and thawing durability, thermal expansion
coefficient, and PCI).
2. The outcomes revealed that using pre-soaked RCA in
concrete mixtures shows higher compressive strengths when
compared to regular concrete mixes with equivalent water to
cement ratios.
3. In terms of the HMA's volumetric characteristics, the
incorporation of CRCA (coarse recycled concrete aggregate)
in various proportions has shown to be extremely effective in
varying amounts for both untreated and treated CRCA.
However, treating CRCA appears to produce even more
favorable results than using untreated CRCA when using a
variety of treatment techniques.
4. Adding various kinds of both treated and untreated
CRCA in varying ratios results in enhanced rut resistance and
increased stiffness modulus, ITS, and TSR than the control
mixture.
5. The kind of CRCA used influences the HMA
characteristics.
6. combining the pre-soaking treatment technique with a
weak acid treatment and then a short mechanical treatment
worked better than other combination methods to increase the
moisture resistance of asphalt mixtures.
7. The findings of the rheological analysis of binders
showed that the original asphalt binder's performance grade
(PG) significantly impacted the influence of RAP variation.
8. It was found that the RAP content and the virgin asphalt
binder's PG simultaneously affected recycled HMA's
performance, with problems like low-temperature cracking,
rutting, stiffness, and susceptibility to fatigue.
9. The findings showed that more effective mixing and
blending occurs when the aged and virgin asphalt binders are
exposed to longer contact times and higher temperatures.
10. As long as RAS is appropriately mixed into the mixture,
the results of field performance tests and laboratory
experiments generally strongly supported the addition of RAS
to HMA.
11. Regarding initial pavement construction, the case study
results (20% RAP HMA and 40% RAP HMA) were more
economical than the control mix (0.0% RAP).
12. Throughout the analysis period, for all discount levels
considered, the results demonstrated that Rubberized-RAP
HMA consistently returned the least expensive total
maintenance and rehabilitation cost.
13. According to the case study findings, Rubberized-RAP
HMA saw an 8% decrease in overall costs during the 20-year
analysis compared to Control HMA. In contrast, 20% and 40%
of RAP HMA over the same period are roughly 2% and 3%
less expensive than Case-Control HMA.
14. The findings of life-cycle assessment, structural analysis,
and field and laboratory studies suggest that RAS can be a
valuable addition to HMA mixes when properly incorporated.
This integration may also result in cost savings.
7. FUTURE RESEARCH
The following are potential areas for further research based
on the research work presented in this study.
-Examining how the use of recycled materials in asphalt
pavements influences the frequency and practices of
maintenance and rehabilitation, as well as the efficacy of
standard repair methods on these pavements.
-Evaluating the obstacles posed by policy and public
perception of using recycled materials in asphalt pavements.
Identifying and resolving issues with performance, safety, and
environmental effects could be the main goals of research.
-Investigating the foundation of various recycled material
kinds (such as broken electronics, glass, brick, and ceramic
waste, etc. Think of the data as more international and
worldwide).
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AASHTO
OTS
TDA
DTT
BBR
DSR
PAV
RTFO
DP
RV
SEM
ITZ
ACV
EDAX
XRD
CSH
BRD
CPATT
ARO
MTO
PCI
LCTE
ITS
TSRST
CRCA
GHG
MEPDG
NOMENCLATURE
LCCA
RCA
RAP
RCR
RAS
Nags
PC
life cycle cost assessment
recycled concrete aggregate
recycled asphalt pavement
recycled crumb rubber
recycled asphalt shingles
natural aggregates
Portland cement
250
construction and demolition
hot mix asphalt
American association of state highway and
transportation officials
Ontario tire stewardship
tire-derived aggregates
direct tension test
bending beam rheometer
dynamic shear rheometer
pressure aging vessel
the rolling thin-film oven
dust proportion
rotational viscosity
scanning electron microscopy
interfacial transition zone
aggregate crushing value
dispersive x-ray analyzer
x-ray diffraction analysis
calcium silicate hydrate
bulk relative density
pavement and transportation technology
aggregate recycling Ontario
ministry of transportation
pavement condition index
linear coefficient of thermal expansion
indirect tensile test
thermal stress restrained specimen test
coarse recycled concrete aggregate
greenhouse gases
empirical pavement design guide