SUSTAINABLE ROADWAY CONSTRUCTION:
ENERGY CONSUMPTION AND MATERIAL WASTE
GENERATION OF ROADWAYS
John A. Gambatese1 and Sathyanarayanan Rajendran2
ABSTRACT
Sustainable roadway construction can be defined as the optimal use of natural and man-made
resources during the roadway lifecycle causing negligible damage to the environment. Two
means of improving the sustainability of roadways are to minimize the amount of energy
consumed for their construction and to efficiently use roadway materials to reduce waste.
This paper describes two separate studies conducted to estimate the amount of energy
consumed and the amount of waste generated in continuously reinforced concrete pavement
(CRCP) and asphalt pavement (AC) roadways from extraction of raw materials through the
end of construction. For CRCP, energy is primarily consumed during the manufacture of
cement and reinforcing steel, while for AC the majority of energy is consumed during asphalt
mixing, drying of aggregates, and the production of bitumen. With regard to material waste,
most of the waste generated from CRCP roadways occurs during extraction and production
of cement and aggregates. For AC, the extraction and production of aggregates produce the
majority of waste. The results indicate that the amount of waste generated is greater for
CRCP than for AC. The results of the two studies highlight where sustainable design efforts
to reduce energy consumption and waste generation can best be directed in the initial phases
of a pavement’s life cycle.
KEY WORDS
Asphalt, Concrete, Energy, Waste, Life cycle, Sustainability
INTRODUCTION
Presently, the U.S. national highway system requires the construction of new roads and the
widening, repair, and rehabilitation of existing roads to meet growing traffic demands. As
work to increase and improve the roadway system commences, the emergence of sustainable
development as a viable concept in civil engineering projects demands more attention to
incorporate the concept in roadway design and construction.
Sustainable development can be defined in general as “the development that meets the
needs of the present without compromising the ability of future generations to meet their own
needs” (WCED 1987). In their document titled “Agenda 21 for Sustainable Construction for
1
2
Asst. Professor, Oregon State Univ., Dept. of Civil, Constr, and Env. Engrg., Corvallis, OR 97331-2302.
Voice: (541) 737-8913; Fax: (541) 737-3300; E-mail: john.gambatese@oregonstate.edu
Graduate Student, Oregon State Univ., Dept. of Civil, Constr. and Env. Engrg., Corvallis, OR 97331-2302.
Voice: (541) 758-2712; Fax: (541) 737-3300; E-mail: rajendrs@engr.orst.edu
1
Developing Countries – A Discussion Document”, CIB and UNEP-ITEC provide the
following description of sustainable construction:
“Sustainable construction means that the principles of sustainable development are
applied to the comprehensive construction cycle from the extraction and beneficiation
of raw materials, through the planning, design and construction of buildings and
infrastructures, until their final deconstruction and management of the resultant waste.
It is a holistic process aiming to restore and maintain harmony between the natural
and built environment, while creating settlements that affirm human dignity and
economic equity.” (CIB & UNEP-IETC 2002)
Research questions arise from the sustainable development perspective as to whether energy
and materials are being optimally and efficiently used in roadway construction. Is a
significant amount of energy consumed and waste generated to construct roadways? What
phases of the roadway lifecycle from raw material extraction through construction consume
the most energy and create the most waste? Answering these questions provides direction for
where to focus sustainability efforts to have the greatest impact. This paper describes two
studies designed to address these questions by estimating the amount of energy consumed
and the amount of waste generated for the construction of continuously reinforced concrete
pavement (CRCP) and asphalt pavement (AC) roadways from extraction of raw materials
through the end of construction. The conduct and results of the studies are described, and
recommendations of where further efforts can be undertaken to minimize the energy
consumption and waste generation of each type of pavement are provided.
LITERATURE REVIEW
Traditional criteria held by the construction industry as project objectives are: cost, schedule,
quality, and safety. With the advent of the concept of sustainability, Kibert (1994) proposed
three additional project criteria for the construction industry related to sustainability: resource
depletion, environmental degradation, and healthy environment. Construction operations
consume energy, and can create substantial noise, cause significant environmental damage,
and produce large quantities of waste. Changes in construction processes may be needed to
protect the environment during construction operations. Excellence in design at all levels is
crucial; poor design can lead to unsustainable construction. Kibert suggests that materials
should be selected for either their recyclability or their ability to be composted and returned
to earth as biomass. To address these issues of sustainable construction, Kibert proposes six
principles for sustainable construction (Kibert 1994):
1.
2.
3.
4.
5.
6.
Minimization of resource consumption (Conserve)
Maximize resource reuse (Reuse)
Use renewable or recyclable resources (Renew/Recycle)
Protect the natural environment (Protect Nature)
Create a healthy, non-toxic environment (Non-Toxics)
Pursue quality in creating the built environment (Quality)
2
Kibert defined resource conservation as the first principle because it contrasts the major
problem that forces us to address sustainability in the first place: over consumption. He also
stressed the importance of reuse and recycling. It is highly desirable to reuse resources we
have already extracted. Reuse contrasts to recycling in that reused items are simply used
intact with minimal reprocessing, while recycled items are reduced to raw materials and then
used in new products. Considering the past negative effects on the natural environment,
perhaps it is time to do better than just sustain, but to restore the environment. The fifth
principle suggests the elimination of toxics in the indoor and exterior built environment.
ENERGY CONSUMPTION
Studies of energy consumption during the service life of asphalt and concrete pavements
have been conducted. Horvath and Hendrickson (1998) applied an “economic input-outputbased life-cycle analysis” (EIO-LCA) model in an attempt to compare the environmental
implications of asphalt and steel-reinforced concrete pavements. The study findings indicate
that for the initial construction of equivalent pavement designs, asphalt appears to have a
higher energy input, lower ore and fertilizer input requirements, and lower toxic emissions.
Asphalt, though, has higher hazardous waste generation and management than steelreinforced concrete. According to the study, the construction of a 1-km section of a typical
two-lane highway requires 7.0 x 106 MJ of energy in the case of AC pavement, and 5.0 x 106
MJ for CRCP pavement.
The Swedish Environmental Research Institute (IVL) performed a life cycle assessment
for road construction, road maintenance, and road operation (Stripple 2001). The
methodology used in this study follows an approach developed by the Society of
Environmental Toxicology and Chemistry (SETAC) and the U.S Environmental Protection
Agency (EPA). The SETAC-EPA technique divides each product or system into individual
process flows and attempts to quantify their environmental effects. This process-based
method traces back upstream the necessary process or activities to create a product or system.
Once the stages have been identified, the environmental inputs and outputs in each stage are
evaluated. The study analyzed three different road surface materials: PCC, hot-mix asphalt,
and cold-mix asphalt. In addition, two different engine alternatives for vehicles and machines
used in the process, conventional diesel engines and modern low emission diesel engines,
were studied. The study found that PCC pavements require more energy for their
construction and during their entire lifecycle than AC pavements.
The conclusions from the two studies presented above appear to be different. In Horvath
and Hendrickson’s study, asphalt pavement requires 30% more energy than concrete
pavement, while IVL reports that concrete pavement requires 37% more energy than asphalt
pavement. Horvath and Hendrickson acknowledge the difference of their study with the
findings of other researchers as being primarily due to significant system boundary
differences between the methods used. Although some of the results obtained in the two
studies have some similarities, there are important differences and contradictions that should
be studied in more detail. While the complexity of roadway systems presents difficulties for
their study, previous research indicates that asphalt and concrete are both energy-intensive
materials.
3
MATERIAL WASTE
A literature search uncovered little research on the sustainability of roadway construction and
material waste in the lifecycle of roadways. Sustainability of materials is affected by the
environmental impacts of mass materials movement throughout the material lifecycle. The
flow of materials has significant economic, environmental, and social impacts at each stage
of the lifecycle. Wagner (2002) suggests that the materials-flow cycle aids in the analysis of
the flow of materials through the environment and economy. The cycle is used to trace the
flow of materials from extraction through production, manufacturing, and utilization to
recycling or disposal. Throughout these processes, the potential for losses exist either through
the discarding of wastes or dissipation of materials to the environment. From this type of
analysis, particular processes can be identified for more efficient materials use.
The U.S. EPA (1998) conducted a major study on the characterization of building-related
construction and demolition (C&D) debris in the U.S., and estimated that 136 million tons of
building-related C&D debris was generated in 1996. The study did not include C&D waste
from transportation projects. The report cites “Road, bridge, and land clearing wastes
represent a major portion of total C&D debris, and some of the materials produced are
managed by the same processors and landfills that manage building-related wastes.”
However, estimates of material waste generated as part of roadway construction were not
available in the literature.
The recycling of reclaimed AC and PCC pavements is being practiced by the majority of
the State Highway Agencies in the U.S. (Ellis 1994; U.S. DOT 1993). With regard to the end
of service life stages, the majority of highway agencies recycle between 75% and 100% of
their asphalt surface (U.S. DOT/FHWA/U.S. EPA 1993). The remainder is reused except for
a small percentage of recycled asphalt pavement (RAP) that is disposed of because it was not
recoverable from the stockpile or was of poor quality. The U.S. Department of
Transportation estimates that 91 million metric tons (100.1 million tons) of asphalt pavement
are scraped or “milled” off roads during resurfacing and widening projects each year (U.S.
DOT 1993). Of that, 73 million metric tons (80.3 million tons) are reclaimed and reused as
part of pavements, roadbeds, shoulders, and embankments, giving a recycling rate of 80%.
RESEARCH METHODOLOGY
The Environmental Council of Concrete Organizations (ECCO) defines an environmental
LCA as a detailed, extensive tool used to systematically evaluate the environmental impacts
of a product or system (ECCO 1997). According to ECCO, an LCA considers environmental
impacts from all possible sources such as extraction of raw materials, manufacture, service
life, and disposal. An LCA involves quantification of the environmental burdens (lifecycle
inventory assessment or LCI), estimation of the impacts of these burdens on humans and
nature (impact analysis), and identification of areas where improvements are possible
(Horvath and Hendrickson 1998).
Using an abbreviated lifecycle inventory assessment, two separate research studies were
conducted to investigate the sustainability of roadways from energy and waste perspectives.
The studies attempted to estimate the amount of energy consumed and the amount of waste
generated for the construction of CRCP and AC pavement roadways from extraction of raw
4
materials through the end of construction. It should be noted that this paper presents the
results for only extraction of raw materials through the end of construction and does not
address the entire roadway lifecycle. Starting with a flowchart of the pavement lifecycles, the
researchers identified through reviews of literature and discussions with material trade
associations, possible points within the initial stages of the pavement lifecycles (extraction of
raw materials, manufacturing, and placement) where energy is consumed and waste
generated. This was followed by the: selection of the type and characteristics of the roadways
to be investigated, identification of energy use and waste generation data sources, collection
of data from the identified sources, and finally analysis of the data.
The two pavement structures used in the studies are designed for 10 million 80-kN (18
kip) equivalent single-axle loads, which is an estimate of 10 or more years of interstate
highway traffic. Both pavement sections are 720 cm wide and are assumed to sit on 15 cm of
high-quality cement-treated soil subbase [E = 6.9 GPa]. Because the base was designed to be
the same for both pavements, only the energy consumed and waste generated in the
manufacture and placement of course materials is compared. The type of PCC pavement
selected for the study is a 22 cm thick, continuously reinforced concrete pavement (CRCP),
with #4 longitudinal bars spaced 10 cm on center and #4 transverse bars spaced at 130 cm on
center. The PCC mix design includes the following percentages by weight: 12% cement,
43% coarse aggregate, 28% fine aggregate, and 17% water. The asphalt pavement design
selected is a 30 cm thick pavement, with 5% bitumen and 95% aggregate by weight. These
types of pavement are commonly used for roads with high traffic volumes traffic where
maintenance has to be kept to a minimum.
Life cycle inventory assessments of the energy consumed and waste generated by the
pavements were performed once the amount and type of materials needed for their
construction were established. Information about energy consumption was collected in two
ways. First, an extensive literature review of previous research and of the industries and
processes involved in the manufacture and construction of both pavement materials were
conducted. The second source of information was construction companies. Material
processing and energy consumption data was also collected through interviews with two
national heavy-civil construction contractors with offices located in the Pacific Northwest.
In the material waste study, an extensive literature review was initially conducted to
gather published information about waste sources and quantities. Additional data was
collected via surveys of construction industry firms. An on-line questionnaire was created
that solicited information about material waste causes and amounts in specific material flow
processes of different lifecycle phases. The questionnaire asked the respondents to provide
general demographic information and, for each individual material flow processes carried out
by the respondent, whether there was any waste and the approximate percent of material that
is wasted in the process. E-mails containing a link to the questionnaire and a request that the
questionnaire be completed and returned were sent to 163 construction contractors and
material producers and suppliers located in the Pacific Northwest and across the U.S. Thirty
of the contractors were taken from the list of Top 300 Federal Highway Contractors as
ranked by Transportation Builder Magazine (2003). Completed questionnaires were received
from 17 constructors, four aggregate producers, one cement producer, three asphalt binder
producers, and three steel rebar producers. In addition, ten ready-mix concrete producers and
5
five hot-mix asphalt producers were surveyed via the telephone. The questions asked during
the telephone interview were similar to those contained in the on-line questionnaire.
The most significant obstacle for the studies was a lack of existing and available
information regarding certain processes or activities. This barrier introduced limitations with
regards to some of the collected data in the studies and necessitated making several
assumptions. A limitation in the lifecycle assessment is the uniqueness of the conditions and
the design chosen for the studied road sections. There are many local factors that affect the
design of pavement structures, and it is impossible to develop a “standard” design that
accounts for all and dissimilar variables considered in roadway construction. As with all
assessments using a systems approach, the placement of the system boundary can also impact
the results. Both studies neglect the energy consumed and waste generated in the construction
of production plants, such as refineries and cement plants, as well as the manufacture and
maintenance of the equipment necessary for the construction of roads such as pavers,
concrete mixers, rollers, etc.
RESULTS
Energy use and material waste data collected from the literature and surveys was organized
according to the specific roadway material and different life cycle phases. Table 1 shows the
results related to energy consumption for the different materials at various stages of the
lifecycle for both CRCP and AC pavement. All of the values are taken from previous studies
and reports except the concrete mixing, PCC placement, and AC placement values are
calculated from fuel consumption information collected in the interviews of the two
construction contractors. No attempts were made to verify whether the values provided by
the contractors were an accurate representation of the actual consumption of energy. Some of
the materials exhibit a wide range of values. The wide range can be attributed to the
differences in study methodologies and system boundaries.
Results related to the percent of material wasted for different materials at various initial
stages of the lifecycle are provided in Table 2. The results come primarily from the survey of
construction industry firms. The values shown in the table are the mean values calculated
from the survey responses, and include waste generated from all different causes, e.g., poor
workmanship, procurement errors, spills, etc.
In the waste study, all of the data collected through the survey and interviews was in
terms of percent wastage of total materials. The percentages shown in Table 2 represent a
“waste factor” which has excluded the materials that were recycled from the total waste. For
example, in cement production waste, the percentage of cement kiln dust recycled has been
excluded from the total waste to get a net waste estimate.
ENERGY AND WASTE QUANTIFICATION FOR SELECTED ROADWAY DESIGNS
The total amounts of energy consumed and waste created for the specific pavement designs
being considered were then calculated as the sum of the expenditures of energy and waste
generated of the individual processes and subsystems, respectively. These values reflect the
specific mix design and physical characteristics of the roadways selected for the study. The
results of these calculations are shown in Table 3 for CRCP and in Table 4 for AC pavement.
6
Table 1: Energy Consumption of CRCP and Asphalt Materials
Process
Extraction of Aggregates
(coarse and fine
aggregate)
Energy Consumption
(J/Ton of Material)
53 x 106
22.2 x 106
74 x 106
24 x 106 (gravel)
52 x 106 (crushed aggregates
for asphalt)
38.18 x 106 (crushed
aggregates)
Steel Manufacturing
Concrete Mixing
PCC Pavement Placement
Production of Bitumen
NCSA, 1977
Berthiaume and Bouchard, 1999
Stammer and Stodolsky, 1995
Häkkinen and Mäkelä, 1996
Stripple, 2001
5.35 x 109 – 10.2 x 109
6.7 x 109
6.36 x 109
School of Resources, Environ.,
and Society (PCA 1990 data)
Berthiaume and Bouchard, 1999
Stammer and Stodolsky, 1995
Twinshare, 2003
5.35 x 109
4.77 x 109
1.90 x 1010
1.8 x 1010 – 2.3 x 1010
0.62 x 1010
2.53 x 1010
Häkkinen and Mäkelä, 1996
Stripple, 2001
Stubbles, 2000
Stammer and Stodolsky, 1995
Häkkinen and Mäkelä, 1996
Stripple, 2001
6.875 x 106
Contractor interviews
6.33 109
Cement Manufacturing
Data Source
107
3.40 x
(Concrete)
0 (Reinforcing steel)
0.63 x 109
0.42 x 109
6 x 109
2.93 x 109
Contractor interviews
Stammer and Stodolsky, 1995
NCSA, 1977
Häkkinen and Mäkelä, 1996
Stripple, 2001
Asphalt Storage
5.43 x 108
Stripple, 2001
Asphalt Mixing and Drying
of Aggregates
0.32 x 109 – 0.39 x 109 (per
ton of asphalt mixture)
Ang et al., 1993
AC Pavement Placement
1.34 x 107
Contractor interviews
Where multiple consumption values were found, as shown in Table 1, the mean of these
values was used in the energy calculations for Tables 3 and 4. For the waste quantities, the
values for manufacturing of the materials include the waste of PCC and AC in production
(mixing) plants. For placement of the PCC and AC, the percentage of waste is shown for the
material as a whole with the individual quantities obtained from the mix design.
From the results shown in Tables 3 and 4, the percent contributions of each life cycle
phase to the total energy consumption and waste generation were also calculated. These
results are presented in Figure 1 for both CRCP and AC pavement.
7
Table 2: Waste Generated for CRCP and Asphalt Materials
Waste
(% of Material)
Process
Data Source
Extraction and Processing of
Aggregates (coarse and fine
aggregate)
0.2 (Extraction)
11.5 (Processing-materials
remaining in wash ponds
and stockpiles)
Aggregate producer
interview
Cement Manufacturing
2 (Raw materials)
37.25 (Production)
0.3 (Finished product)
Cement producer survey
and PCA, 2003
Steel Raw Materials Extraction and
Manufacturing
0
Steel producer survey and
Trade Associations RFI
Concrete Production
0.173 (Concrete)
0.02 (Aggregates)
0.8 (Cement)
Ready mix concrete
producers interviews
Returned Concrete
0.393
Ready mix concrete
producers interviews and
Concrete Trade
Associations RFI
PCC Pavement Placement
2.5
Contractor survey
Production and storage of Bitumen
0.52
Asphalt producer survey
AC Production
0
HMA producers interviews
AC Pavement Placement
0.102
Contractor survey
Table 4 indicates that no energy is consumed for the extraction and initial transformation of
bitumen. In this process it is not easy to differentiate how much energy is used in the
distillation of each oil sub-product, and the consumption of energy is affected by the type of
petroleum and the conditions and location of the oil field. Hence, while some energy is
consumed for bitumen in this phase of the lifecycle, the amount consumed was not included
in the study because of the difficulties in accurately quantifying it during extraction,
transformation, and transportation.
ENERGY CONSUMPTION
CRCP and AC pavements consume 4.58 x 106 MJ and 3.78 x 106 MJ, respectively, in the first
three sub-phases of the roadway lifecycle (extraction, manufacturing, and placement). For
both types of pavement the consumption of energy for the extraction of aggregates and the
placement of course materials is almost negligible compared with the energy required for the
manufacture of concrete and asphalt. Figure 1 reveals that the extraction of raw materials and
the placement of concrete account for only 6% of the total amount of energy consumed in
CRCP pavement. The remaining 94% of the energy is spent in the manufacturing process,
where the production of cement makes up 65% of the energy consumed, while the production
of steel and concrete mixing process account for 34% and 1%, respectively.
8
Table 3: Energy Consumption and Waste Generation for Selected CRCP Pavement Design
Sub-step
Raw Materials
Extraction and
Initial
Transformation
Material or
Process
Energy
Consumed
(J/Ton)
Portland cement
Coarse aggregate
0
5.30 x 107
Total
Energy
Consumed
(MJ)
0
8.38 x 104
Fine aggregate
5.30 x 107
Reinforcing steel
5.30 x 107
Subtotal
Portland cement
Manufacturing
Placement
109
6.33 x
Waste
Generated
(%)
Total Waste
Generated
(Metric tons)
2
0.2
14.4
3.2
5.46 x 104
0.2
2.1
6.61 x 103
0
0.0
1.45 x
105
2.80 x
106
19.7
37.25
270.3
Coarse aggregate
0
0
11.5
214.9
Fine aggregate
0
0
11.5
140.0
Reinforcing steel
1.90 x 1010
1.48 x 106
0
0
Concrete mixing
106
104
--
--
2.5
1.79
625.2
77
1.39
Concrete
Rebar
6.875 x
2.53 x
106
Subtotal
3.40 x 107
0
4.31 x
1.25 x 105
0
Subtotal
1.25 x 105
78.39
Total
4.58 x 106
723.29
Table 4: Energy Consumption and Waste Generation for Selected AC Pavement Design
Sub-step
Raw Materials
Extraction and
Initial
Transformation
Material or
Process
Bitumen
Aggregates
0
5.30 x
107
Subtotal
Bitumen production
Manufacturing
Energy
Consumed
(J/Ton)
2.53 x
105
Waste
Generated
(%)
Total Waste
Generated
(Metric tons)
0
0
0.2
10
2.53 x 105
10
6.00 x 109
1.51 x 106
0.52
1.31
108
105
0
0
Bitumen storage
5.43 x
Asphalt mixing and
aggregate drying
3.62 x 108
1.82 x 106
0
0
0
0
11.5
619.4
Aggregates
Subtotal
Asphalt
Placement
Total
Energy
Consumed
(MJ)
0
1.34 x 107
1.36 x
3.46 x
106
6.70 x 104
620.71
0.102
5.11
Subtotal
6.70 x 104
5.11
Total
3.78 x 106
635.82
9
100%
3%
2%
90%
11%
1%
80%
70%
60%
50%
94%
91%
Placement
86%
97%
Manufacturing
Extraction
40%
30%
20%
10%
0%
3%
7%
3%
2%
CRCPEnergy
AsphaltEnergy
CRCPWaste
AsphaltWaste
Figure 1: Percent Contribution of Lifecycle Phases to Total Energy Consumption and Waste
Generation in CRCP and AC Pavements
From Figure 1 it can also be seen that the extraction of raw materials and the placement of
AC pavement account for 9% of the total energy consumption of the system. The remaining
91% of the energy is consumed in the manufacturing process, where the asphalt mixing and
drying of aggregates accounts for 53% of the energy consumed and the production of
bitumen and its storage account for 43% and 4%, respectively.
Since cement production consumes a significant amount of energy, an analysis was made
to test its impact on total energy consumption. It was found that if part of the cement in the
PCC mix design is replaced by fly ash, a byproduct of coal combustion, the consumption of
energy is dramatically reduced. When the content of cement is reduced from its original
value of 12% by weight to 8%, the consumption of energy will drop from 4.58 x 106 MJ to
3.64 x 106 MJ (20.5% reduction), the latter value being less than the energy required for AC
pavement.
WASTE GENERATION
CRCP and AC pavements generate 723 and 636 metric tons of waste, respectively, in the
first three sub-phases of the roadway lifecycle. Similar to energy consumption, for both types
of pavement the amount of waste generated in the extraction of aggregates and in the
placement of course materials is almost negligible compared with the waste created during
the manufacture of concrete and asphalt. Figure 1 shows that the extraction of raw materials
and the placement of concrete account for only 14% of the total waste generated from the
10
CRCP pavement. The remaining 86% of the waste comes from the manufacturing process
where the production of cement accounts for 43% of the materials wasted.
Figure 1 shows that the extraction of raw materials and the placement of AC pavement
account for a mere 3% of the total waste output from the system. The remaining 97% of the
waste is the result of the manufacturing process.
In order to further understand the relation between the materials and waste, additional
analyses of the data were made. First, to understand the impact of cement on the total waste
generated for CRCP pavement, the relationship between the percent of cement in the
concrete mix design and the total waste was studied. It was found that for every one percent
replacement of cement by fly ash, there was a decrease of rougly 25 metric tons in total
waste. A second analysis was made with respect to the size of reinforcing steel used. When
the steel rebar size was increased to the next larger size, the total waste increased
exponentially. It can be seen that the larger the bar size, the more waste will be generated.
CONCLUSIONS AND RECOMMENDATIONS
The two studies were successful in developing an estimate of the amount of energy
consumed and materials wasted for selected CRCP and AC pavement designs from
extraction of raw materials through placement on the project site. These assessments differ
from previous studies in that they attempt to quantify energy consumption and waste
generation using the collective findings of previous studies and incorporate actual values
experienced by the construction industry. This study is a starting point in the estimation of
waste quantities during the roadway lifecycle; no previous study results were available to
make a comparison. In the case of energy use, the results reflect that of previous studies
combined. Significant conclusions and recommendations from these studies are as follows
 A key aspect of the research is the application of the sustainability concept to the
roadway lifecycle from energy and material perspectives. The associated findings
enhance our understanding of the relationship between sustainability and roadways.
 Both studies indicate that material extraction and production are two critical stages where
optimization of energy and material is required. Use of recycled materials (e.g., fly ash,
RAP, and RCP) in the construction of roadways will eliminate the energy consumed and
waste generated during the production of virgin materials.
 The major consumption of energy in the production of AC pavement occurs during
asphalt mixing and drying of aggregates as opposed to during the extraction of crude oil
and the distillation of bitumen. Changes in the storage of aggregates and in their drying
process can substantially reduce the consumption of energy in the production of AC
pavement.
 Cement is the driving element in the consumption of energy and generation of waste for
PCC pavements. If low percentages of cement are replaced with industrial waste products
such as fly ash, the amounts of energy consumed and waste generated in the production
of concrete pavements will be substantially reduced.
 A large quantity of waste materials is created during the virgin aggregate production
processes. Use of recycled aggregates can significantly reduce this problem.
11


A preplanned material waste management plan should be developed and implemented on
projects. The plan should use the “principle of 4R’s” (Reduce, Recover, Reuse, and
Recycle) for the materials wasted during the roadway lifecycle. Incorporation of a
requirement for a waste management plan in contracts can help minimize waste during
the construction process.
To ensure that roadway construction is fully sustainable, other factors such as emissions,
noise levels, hazardous waste, and worker safety should be considered in addition to
energy and waste. Sufficient knowledge of all of these factors will help material
producers and suppliers, construction contractors, State Highway Agencies, and other
project stakeholders involved in the roadway lifecycle create sustainable roadways.
REFERENCES
Ang, B.W., Fwa, T.F., and Ng, T.T. (1993). Analysis of Process Energy Use of Asphaltmixing Pants. Department of Industrial and Systems Engineering and Department of
Civil Engineering, National University of Singapore.
Berthiaume, R, and, Bouchard, C. (1999). Exergy Analysis of the Environmental Impact of
Paving Material Manufacture. Canadian Society for Mechanical Engineering, CSME.
CIB & UNEP-TETC (2002). “Agenda 21 for Sustainable Construction for Developing
Countries – A Discussion Document.” International Council for Research and Innovation
in Building and Construction (CIB) and UNEP –IETC, Boutek Report No. Bou/E0204.
ECCO (1997). “Environmental Life-Cycle Assessment”. The Environmental Council of
Concrete Organizations, Skokie, IL.
Ellis, Ralph D., Jr. (1994). “Recent Success in Achieving Sustainable Construction in the
Highway Industry.” Sustainable Construction: Proceedings of the 1st Conference of CIB
TG 16, C. J. Kibert, ed., Center for Constr. and Envir., Gainesville, FL, pp. 591-598.
Häkkinen, T. and Mäkelä, K. (1996). Environmental Adaptation of Concrete; Environmental
Impact of Concrete and Asphalt Pavements. Technical Research Centre of Finland.
Horvath, A. and Hendrickson, C. (1998). “Comparison of Environmental Implications of
Asphalt and Steel-Reinforced Pavements”. Transp. Research Record, No. 1626, 105-113.
Kibert, Charles J. (1994). “Establishing Principles and a Model for Sustainable
Construction.” Sustainable Construction: Proceedings of the 1st Conference of CIB TG
16, C.J. Kibert, ed., Center for Construction and Environment, Gainesville, FL, pp. 3-12.
NCSA (1977). Flexible Pavement Cost Estimating Guide: Inflation/Energy Effects,
Worksheets, Spec Data. National Crushed Stone Association.
PCA (2003). “Cement Kiln Dust Production, Management, and Disposal.” Portland Cement
Association (PCA) Report Prepared by Hawkins, Garth J., Bhatty, Javed I., and Andrew
T. O’Hare. R&D Serial No. 2737.
Stammer, R.E. and Stodolsky, F. (1995). Assessment of the Energy Impacts of Improving
Highway-Infrastructure Materials. Center for Transportation Research, Energy Systems
Division, Argonne National Laboratory, Argonne, Illinois.
Stripple, H. (2001). Life Cycle Analysis of Road; a Pilot Study for Inventory Analysis.
Swedish Environmental Research Institute (IVL).
12
Stubbles, J.R. (2000). Energy Use in the U.S. Steel Industry – Historical Perspective and
Future Opportunities. Office of Industrial Technologies, U.S. Dept. of Energy,
Washington, D.C.
Transportation Builder (2003). “Eighth Annual Ranking of the Top 300 Federal Highway
Contractors.” Transportation Builder, Nov./Dec. 2003, pp. 10-20.
Twinshare (2003). http://twinshare.crctourism.com.au/cement_and_concrete.htm, Twinshare:
Tourism Accommodation & the Environment, Australia.
U.S. DOT (1993). “A Study of the Use of Recycled Paving Material: Report to Congress.”
U.S. Department of Transportation (U.S. DOT) and Federal Highway Administration
(FHWA), Report No. FHWA-RD-93-147; EPA/600/R-93/095, 1993.
U.S. DOT/FHWA/U.S. EPA (1993). “Engineering and Environmental Aspects of Recycled
Materials for Highway Construction - Final Report.” U.S. Department of Transportation
(U.S. DOT), Federal Highway Administration (FHWA), and U.S. Environmental
Protection Agency (U.S. EPA). Report prepared by D. Bloomquist, G. Diamond, M.
Oden, B. Ruth, and M. Tia, Report No. FHWA-RD-93-088.
U.S. EPA (1998). “Characteristics of Building-related Construction and Demolition Debris in
the United States.” U.S. Environmental Protection Agency. Report prepared by Franklin
Associates, Rep. No. EPA 530-R-98-010.
Wagner, Lorie (2002). “Materials in the Economy—Material Flows, Scarcity, and the
Environment.” U.S. Geological Survey circular #1221, U.S. Department of the Interior,
U.S. Geological Survey.
WCED (1987). Our Common Future, 1987. World Commission on Environment and
Development (WCED), Oxford University Press, Oxford, England.
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