sustainable roads

8/12/2019 Sustainable Roads

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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 energyconsumed 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 theend 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 wa ste generated is greater forCRCP 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 pavements life cycle.

KEY WORDSAsphalt, Concrete, Energy, Waste, Life cycle, Sustainability

INTRODUCTION

Presently, the U.S. national highway system requires the construction of new roads and thewidening, 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 conceptin 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

1Asst. 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:[email protected]

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: [email protected]


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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 beneficiationof 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 asignificant 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 forwhere to focus sustainability efforts to have the greatestimpact. This paper describes twostudies 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 materialsthrough 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) proposedthree additionalproject 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 materialsshould 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. Minimization of resource consumption (Conserve)2. Maximize resource reuse (Reuse)3. Use renewable or recyclable resources (Renew/Recycle)

4. Protect the natural environment (Protect Nature)

5. Create a healthy, non-toxic environment (Non-Toxics)

6. Pursue quality in creating the built environment (Quality)


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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 wehave 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 thenused 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 fifthprinciple suggests the elimination of toxics in the indoor and exterior built environment.

ENERGYCONSUMPTION

Studies of energy consumption during the service life of asphalt and concrete pavements

have been conducted. Horvath and Hendrickson (1998) applied an economic input-output-

based life-cycle analysis (EIO-LCA) model in an attempt to compare the environmentalimplications 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 steel-

reinforced concrete. According to the study, the construction of a 1-km section of a typical

two-lane highway requires 7.0 x 106MJ of energy in the case of AC pavement, and 5.0 x 10

6

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 ofEnvironmental 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 machinesused 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 Hendricksons study, asphalt pavement requires 30% more energy than concrete

pavement, while IVL reports that concrete pavement requires 37% more energy than asphaltpavement. Horvath and Hendrickson acknowledge the difference of their study with the

findings of other researchers as being primarily due to significant system boundarydifferences between the methods used. Although some of the results obtained in the twostudies 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.


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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. Theflow 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 theflow 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 wastefrom 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 aremanaged 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 endof 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 notrecoverable 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 environmentalimpacts 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 andnature (impact analysis), and identification of areas where improvements are possible

(Horvath and Hendrickson 1998).

Using an abbreviated lifecycle inventory assessment, two separate research studies wereconducted 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


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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, theresearchers identified through reviews of literature and discussions with material trade

associations, possible points within the initial stages of the pavement lifecycles (extraction ofraw materials, manufacturing, and placement) where energy is consumed and waste

generated. This was followed by the: selection of the type and characteristics of the roadwaysto 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 (18kip) 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 bethe 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 oncenter. 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. Thesetypes 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 thepavements 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 wereconducted. 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 createdthat 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 outby 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 thequestionnaire 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. Thirtyof 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 binderproducers, and three steel rebar producers. In addition, ten ready-mix concrete producers and


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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 availableinformation regarding certain processes or activities. This barrier introduced limitations with

regards to some of the collected data in the studies and necessitated making severalassumptions. 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 thedesign 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 impactthe 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.

RESULTSEnergy 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 studiesand 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 bythe 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 initialstages 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., poorworkmanship, 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 awaste 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 designsbeing 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.


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Table 1: Energy Consumption of CRCP and Asphalt Materials

ProcessEnergy Consumption

(J/Ton of Material)Data Source

53 x 10

6

NCSA, 197722.2 x 10

6Berthiaume and Bouchard, 1999

74 x 106

Stammer and Stodolsky, 1995

24 x 106(gravel)

52 x 106(crushed aggregates

for asphalt)Hkkinen and Mkel, 1996

Extraction of Aggregates(coarse and fineaggregate)

38.18 x 106(crushed

aggregates)Stripple, 2001

6.33 109 School of Resources, Environ.,

and Society (PCA 1990 data)

5.35 x 109 10.2 x 10

9Berthiaume and Bouchard, 1999

6.7 x 109


6.36 x 109

Twinshare, 20035.35 x 10

9Hkkinen and Mkel, 1996

Cement Manufacturing

4.77 x 109

Stripple, 2001

1.90 x 1010

Stubbles, 2000

1.8 x 1010

2.3 x 1010


0.62 x 1010

Hkkinen and Mkel, 1996Steel Manufacturing

2.53 x 1010

Stripple, 2001

Concrete Mixing 6.875 x 106

Contractor interviews

PCC Pavement Placement3.40 x 10

7(Concrete)

0 (Reinforcing steel)Contractor interviews

0.63 x 109


0.42 x 109 NCSA, 1977

6 x 109

Hkkinen and Mkel, 1996

Production of Bitumen

2.93 x 109

Stripple, 2001

Asphalt Storage 5.43 x 108

Stripple, 2001

Asphalt Mixing and Dryingof Aggregates

0.32 x 109 0.39 x 10

9(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 thematerial 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. Theseresults are presented in Figure 1 for both CRCP and AC pavement.


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Table 2: Waste Generated for CRCP and Asphalt Materials

ProcessWaste

(% of Material)Data Source

Extraction and Processing ofAggregates (coarse and fineaggregate)

0.2 (Extraction)11.5 (Processing-materialsremaining in wash pondsand stockpiles)

Aggregate producerinterview

Cement Manufacturing2 (Raw materials)37.25 (Production)0.3 (Finished product)

Cement producer surveyand PCA, 2003

Steel Raw Materials Extraction andManufacturing

0Steel producer survey andTrade Associations RFI

Concrete Production0.173 (Concrete)0.02 (Aggregates)0.8 (Cement)

Ready mixc oncreteproducers interviews

Returned Concrete 0.393

Ready mixc oncreteproducers interviews andConcrete TradeAssociations 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 thedistillation of each oil sub-product, and the consumption of energy is affected by the type ofpetroleum 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 106MJ and 3.78 x 10

6MJ, 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 themanufacture 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.


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Table 3: Energy Consumption and Waste Generation for Selected CRCP Pavement Design

Sub-stepMaterial or

Process

EnergyConsumed

(J/Ton)

TotalEnergy

Consumed

(MJ)

WasteGenerated

(%)

Total WasteGenerated

(Metric tons)

Portland cement 0 0 2 14.4

Coarse aggregate 5.30 x 107

8.38 x 104

0.2 3.2

Fine aggregate 5.30 x 107

5.46 x 104

0.2 2.1

Reinforcing steel 5.30 x 107

6.61 x 103

0 0.0

Raw MaterialsExtraction and

InitialTransformation

Subtotal 1.45 x 105

19.7

Portland cement 6.33 x 109

2.80 x 106

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 6.875 x 106 2.53 x 104 -- --

Manufacturing

Subtotal 4.31 x 106

625.2

Concrete 3.40 x 107

1.25 x 105

2.5 77

Rebar 0 0 1.79 1.39Placement

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-stepMaterial or

Process

EnergyConsumed

(J/Ton)

TotalEnergy

Consumed(MJ)

WasteGenerated

(%)

Total WasteGenerated

(Metric tons)

Bitumen 0 0 0 0

Aggregates 5.30 x 107

2.53 x 105

0.2 10

Raw MaterialsExtraction and

InitialTransformation Subtotal 2.53 x 10

510

Bitumen production 6.00 x 109

1.51 x 106

0.52 1.31

Bitumen storage 5.43 x 108

1.36 x 105

0 0

Asphalt mixing andaggregate drying

3.62 x 108

1.82 x 106

0 0

Aggregates 0 0 11.5 619.4

Manufacturing

Subtotal 3.46 x 106

620.71

Asphalt 1.34 x 107

6.70 x 104

0.102 5.11Placement

Subtotal 6.70 x 104

5.11

Total 3.78 x 106

635.82


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3% 7% 3% 2%

94% 91%86%

97%

3% 2%11%

1%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

CRCP-

Energy

Asphalt-

Energy

CRCP-

Waste

Asphalt-

Waste

Placement

Manufacturing

Extraction

Figure 1: Percent Contribution of Lifecycle Phases to Total Energy Consumption and WasteGeneration 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 remaining91% 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 ofbitumen 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 ofenergy 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 106MJ to

3.64 x 106MJ (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 thefirst three sub-phases of the roadway lifecycle. Similar to energy consumption, for both typesof 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 duringthe manufacture of concrete and asphalt. Figure 1 showsthat the extraction of raw materials

and the placement of concrete account for only 14% of the total waste generated from the


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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 pavementaccount 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 wastegenerated 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 totalwaste. 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 energyconsumed 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 valuesexperienced 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 studiescombined. Significant conclusions and recommendations from these studies are as follows

A key aspect of the research is the application of the sustainability concept to theroadway 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 duringasphalt 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 ACpavement.

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 productssuch as fly ash, the amounts of energy consumed and waste generated in the productionof concrete pavements will be substantially reduced.

A large quantity of waste materials is created during the virgin aggregate productionprocesses. Use of recycled aggregates can significantly reduce this problem.


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A preplanned material waste management plan should be developed and implemented onprojects. The plan should use the principle of 4Rs (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 materialproducers 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 Asphalt-

mixing Pants. Department of Industrial and Systems Engineering and Department ofCivil Engineering, National University of Singapore.

Berthiaume, R, and, Bouchard, C. (1999). Exergy Analysis of the Environmental Impact ofPaving Material Manufacture. Canadian Society for Mechanical Engineering, CSME.

CIB & UNEP-TETC (2002). Agenda 21 for Sustainable Construction for DevelopingCountries 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 ofConcrete 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. a nd Envir., Gainesville, FL, pp. 591-598.

Hkkinen, T. and Mkel, 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 1stConference 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. OHare. R&D Serial No. 2737.

Stammer, R.E. and Stodolsky, F. (1995). Assessment of the Energy Impacts of ImprovingHighway-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).


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