life cycle assessment of asphalt pavement product -...

Sustain. Environ. Res., 25(5), 275-281 (2015) 275

*Corresponding authorEmail: [email protected]

Life cycle assessment of asphalt pavement product

Murat Özgür Polat and Nihal Bektaş*

Key Words: Life Cycle Assessment (LCA), asphalt production, CO2 emissions

ABSTRACT

Life Cycle Assessment (LCA) can be used to quantify the environmental impacts of materials, processes, products or systems during their entire lifetime from creation to disposal. The objective of the present study was to examine and compare the environmental impacts of different asphalt products by means of LCA. The functional unit selected was one ton asphalt production. The comparative LCA was performed using LCA software SimaPro® with Impact2002+ database. The guidelines from ISO 14040:2006 was used throughout the analyses. Results from the software underline the estimated environmental performance of asphalt production in terms of a number of choices such as carbon footprint, resource and energy consumptions and various environmental impacts. According to the comparisons, between three different types of asphalt products, it was found that average 10% decrease of environmental effects can be achieved when the less bitumen was used in the asphalt production. At the same time carbon emission was also 5% higher in the binder type asphalt production where bitumen needs to keep warm. Therefore it can be said that LCA can provide a useful comparison between products and helpful in decision making.

INTRODUCTION

Life-cycle assessment (LCA) is a methodical tool to evaluate all potential environmental impacts over the entire life cycle of product, materials and processes [1-3]. LCA quantifies all environmental impacts from raw material extraction, manufacturing and use to ultimate disposal. This is a useful tool if one needs to evaluate or find an alternative product, process or activity. Therefore it can be a valuable decision-support tool for both policy makers and industry. LCA results are also used in marketing or environmental labelling as well as getting information on environmental performance. The term of system boundaries can usually be used to define types of LCA. All relevant stages of the life of a product and LCA boundaries are given in Fig. 1.

International Organization for Standardization (ISO) produced series of LCA standards in 1997 which were then revised in 2006. ISO 14040:2006 provides a description of principles and framework whereas ISO 14044:2006 outlines requirements and guidelines for LCA [4,5].

The LCA process can be divided into four phases according to ISO 14001; Goal and Scope Defi- nition, Life Cycle Inventory Analysis (LCI), Life Cycle Impact Assessment (LCIA) and Interpretation (Fig. 2).

Asphalt is mainly used for paving all kinds of roads as well as for other applications such as airports, playing and sporting areas, agricultural and industrial constructions [6,7]. Asphalt can be defined as a cement-like material that contains a mixture of aggregates, binder and filler. Crushed rocks, sand and gravel are used as aggregates. A binder, most commonly bitumen, is used to bind these materials into asphalt mixture. There are hot, warm and cold types asphalt production due to different requirements of sectors. Pollutant gases and global warming problems arise from hot and warm asphalt production due to higher energy requirements. Therefore the energy use is the key for calculating emissions of asphalt production [6,7].

There are several researches dealing with environmental effects of asphalt pavement production, recycling and in use [8-10]. These studies usually identify the environmental effects of asphalt pavement

Department of Environmental Engineering Gebze Technical University

Kocaeli 41400, Turkey

Polat and Bektaş, Sustain. Environ. Res., 25(5), 275-281 (2015)

use of additives could be used to decrease energy use. Huang et al. reviewed relevant LCA models available worldwide for construction and maintenance of asphalt pavements using up-to date findings [12]. LCI studies for asphalts made from three different recycled asphalt

in use. However energy use and emissions during the production process are also important. Butt et al. studied LCA of asphalt pavements for entire life time [11]. Their results showed that the asphalt production was a highly energy-consuming process. Therefore, the

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RawMaterials Energy

Acquistion andPreparation

PRODUCTION

Transportion

Use

Recycle

Disposal

Air EmissionsWater EmissionsSoil EmissionsSolid WasteOther Emissions

GA

TE T

O G

ATE

GRA

DLE

TO

GA

TE

GRA

DLE

TO

GRA

VE

Fig. 1. Schematic diagram of life cycle stages of a product and LCA boundaries [1,3].

Fig. 2. LCA phases [1-4].

Goal and Scope Definitions

InterpretationInventory Analysis

ImpactAssesment

LCI Data ImpactAnaysis

APPLICATIONS


within the framework of LCA.

1.1. System description and boundariesIn the plant, asphalt was produced by mixing

suitable size aggregates and stone powder with bitumen using well known formulas. Aggregates used in the process transferred from mining areas to the plant. Then these aggregates were crushed into different sizes and removed dust and moisturise by heating and drying processes. Afterward different size aggregates were carried to vessels with conveyor bents. Bitumen was delivered to the plant and kept warm at certain temperature in tanks using natural gas as an energy sources. Then all necessary ingredients according to receipts were mixed to produce asphalt in the mixing vessels then transferred to application areas. Gate to gate LCA can be explained as a comprehensive evaluation of the environmental effects through the production stage. It includes the analysis from the reception of the raw materials to the end of production without considering further actions. The boundary of this LCA study was also chosen to limit to the production stage of the asphalt and the schematic asphalt production process within these boundaries is given in Fig. 3. Therefore the boundaries of this study were determined as follows:

• Aggregate crushing to suitable size, dust-free (electricity use for crushing equipment)

• Aggregate transport with conveyor belt, mixing and heating processes for asphalt production (electricity use for equipments)

• Heating bitumen tanks (natural gas usage)Electricity and natural gas consumptions were pro-

vided by the company as their monthly consumptions.

materials and traditional warm mix asphalt were compared by Chiu et al. [13]. The results showed that LCA is a useful tool regarding the choice of recycled materials on rehabilitating pavements. Vidal et al. carried out a comprehensive LCA study on a variety of asphalt products including hot mix asphalt, warm mix asphalt with zeolites, and asphalt mixes with reclaimed asphalt pavement [14]. After the comparison made among four different asphalt pavements, it was shown that the impacts of asphalt mixes were significantly reduced when reclaimed asphalt pavement was added.

The aim of this study is to perform and compare life cycle analyses of three different asphalts produced at the same plant. Therefore, environmental impacts and their sources can be better understood for these different asphalt products.

MATERIALS AND METHODS

LCAs (gate to gate) of three different asphalts produced for different purposes in an asphalt plant with different contents were performed in this study. The guidelines from ISO 14040:2006 was used throughout the analyses. The commercial LCA software SimaPro® was used for inventory and impact assessment phases of different asphalt productions. The software usually comes along with inventory and impact assessment database. Impact2002+ was used in this study. If there is no necessary data were available in database, data were collected from either the company or scientific literature [15]. Inflows (raw materials and energy inputs) and outflows (emissions, wastewater and solid waste sources) for relevant process were collected, listed and loaded to the software. Then the data were processed into a number of environmental impacts (climate change, resource depletion, etc.) and gate to gate LCAs for different asphalt types were calculated using the commercial software.

METHODOLOGY

The four stages of LCA, describes in the ISO 14001 standard, applied the subject study and given below:

1. Goal and Scope Definition

The aim of the present study is to calculate the environmental impacts of different types of asphalt using LCA as a tool. The results for the different asphalt production were compared with each other to determine the best alternative in environmental terms. The field data from asphalt plant and proceeded with the software and compute the environmental impacts

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Fig. 3. Processes flow diagram for asphalt production.

CrushingHeatingDrying

Aggregate Production Bitumen Production

Aggregate Stock Area

BitumenStock Area

Handling andWeighing

Mixing Reactor

Hot Stroge Tank

Loading to Vehicles

GATE

TO

GAT

E LC

A


the plant. These materials used in the production of different type asphalts are shown in Table 1.

2.2. Energy consumptions Electricity and natural gas were used as energy

resources in the plant (Istanbul, Turkey). Electric crusher was used to crush aggregate to obtain different sizes of aggregate. Bitumen tank was kept hot using natural gas during production. Also electric mixers were used in the production of asphalt. Energy needs in the plant are summarized in Table 2. These numbers were obtained from the company. No further assumption was made in this study.

3. LCIA and Interpretation

In the LCIA stage, inputs and outputs of process were evaluated from an environmental point of view and environmental impacts within impact categories were produced using the software. The findings from inventory and impact analysis steps were used in the interpretation phase of LCA. In this final stage, the study was evaluated according to LCA guidelines and general recommendations and improvement possibilities were given.

RESULTS AND DISCUSSION

In this study, three different asphalts were evaluated using LCA as a tool. The environmental indicators selected from the database of program were used to determine the level of environmental impacts. The impact categories for an LCA can be chosen on individual choice; however, the most common in the literature include global worming potential, acidification potential, eutrophication, ozone layer depletion and resource consumption.

These results of LCIA based on the internationally accepted Impact2002+ were identified as given in Table 3.

The selected environmental impacts of three different asphalt types were compared shown in Fig. 4. The highest environmental impact for each category is set to equal to 100% with other type of production shown at a relative percentage. Based on comparison results, Type 5 seems to be much detrimental to the

1.2. Functional unitThe functional unit of this present study is one

ton asphalt production. Materials and energy inputs, in-house transport and all emissions are calculated according to this functional unit.

2. LCI Analysis

In this stage, the necessary data for LCA study was collected to quantify the inputs and outputs of the processes. Then the data can be transformed into number of environmental impacts (climate change, resource depletion, acidification, respiratory effect, carcinogenesis, ecotoxicity and ozone layer depletion). The LCA software program calculated the inputs and outputs of asphalt process using process simulation. Information for raw material and energy inputs used in the asphalt production was collected from the plant itself. The energy-related data and some data could not get from plant were taken from the program database or literature.

2.1. Asphalt productionA drum type asphalt production facility with 90

t h-1 asphalt production capacity was studied in this work. The most widely used type asphalts (Type 1, Type 5 and Binder) were produced in this plant. Gate to gate LCA created here was limited to only production stage of asphalt. Therefore, it was necessary to identify all raw materials and energy input in these production steps. Raw materials used in used were collected from

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Table 1. Materials used in different types of asphalt

Material Quantity, kg t-1 asphalt

Type-1 Stone powder (0-5 mm) 320 Aggregate (5-12 mm) 480 Aggregate (12-19 mm) 110 Filler 50 Bitumen 50/70 45

Type-5 Stone powder (0-5 mm) 900 Filler 50 Bitumen 50/70 60

Binder Stone powder (0-5 mm) 320 Aggregate (5-12 mm) 200 Aggregate (12-19 mm) 110 Aggregate (22-32 mm) 250 Filler 60 Bitumen 50/70 42

Table 2. Energy required for operation and maintenance in the plantProcess Energy Consumptions

Bitumen tank Natural gas (90 m3 t-1; 3362 MJ t-1)Mixer Electricity (2 kWh t-1)Aggregate crusher Stone powder (0-5 mm) 0.5 kWh t-1

Aggregate (5-12 mm) 0.2 kWh t-1



Filler 1.1 kWh t-1


sources in the plant investigated.

CONCLUSIONS

Gate to gate LCAs for the different type asphalts productions in a mix plant were analyzed regarding the defined goal and scope of the study. The LCA guidelines given in ISO14040:2006 were applied accordingly. The SimaPro LCA software was used to develop the study more efficiently. Field data for the study were provided by the local asphalt company (Istanbul, Turkey). The comparison among three different types of asphalt products was made and environmental effects of each production were also analyzed to determine environmental impacts of production. One ton asphalt production was selected as the functional unit. According to the comparisons, asphalt Type 5 has the highest environmental effects due to high consumption of bitumen. From this case study, it was found that average 10% decrease of environmental effects can be achieved when the less bitumen was used in the asphalt production. At the same time carbon emission was also 5% higher in the binder type asphalt production where bitumen needs to be kept warm. Therefore heating plays an important role in terms of carbon emissions. These results can also be very useful for paving industry for choosing environmental friendly asphalt products. It can be also suggested to create a complete LCA (from cradle to

environment in terms of selected environmental effects, followed by asphalt Type 1 and Binder type asphalt.

Global warming or climate change can be referred to as a change in the Earth’s surface average temperature causing climate system change with either cooling or warming trends. Especially global warming was caused mostly by increasing concentrations of greenhouse gases (GHGs) in the atmosphere. Carbon dioxide equivalencies are used as a unit of a range of GHG emissions. Therefore Global Warming Potential (GWP) can be calculated mathematically and is expressed relative to that of CO2 [16,17] and the unit of GWP is given as carbon dioxide equivalent. The GHG Protocol was used to quantify and manage GHG emissions in this study [18]. Figure 5 and Table 4 show CO2 sources for three processes. Overall, each process contributed 300 kg equivalent CO2 through production stage of the asphalt process. Only a small amount CO2 was emitted from biogenic and land transformation sources. Biogenic carbon from living processes does not consider CO2 emissions since they balance each other. Therefore biogenic carbon, came from petroleum productions can be considered a negative CO2 footprint contribution.

Also the contribution to global warming impacts for each production stage was analyzed. The carbon emissions for different stages of asphalt product’s ingredients are given in Fig. 6. Bitumen production, natural gas use and transportations are the main CO2

Fig. 4. Comparison of the environmental impacts for different asphalt types.

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Table 3. The inventory results of each production type (per functional unit)Impact Category End points/Indicators Units, kgeq Binder Type-1 Type-5Abiotic depletion Resources Sb 3.3 3.38 3.71

Acidification Water pollution SO2 0.595 0.614 0.692Eutrophication Water pollution PO4 0.154 0.159 0.169

Global warming Air pollution/climate change CO2 306 308 313Ozone layer depletion Air pollution/climate change CFC11 5.48E-5 5.62E-5 6.27E-5

Human Toxicity Air pollution/climate change 1,4-DCB 72.5 74 78.9Fresh water aquatic ecotoxicity Water pollution 1,4-DCB 20.4 20.9 21.8

Marine aquatic ecotoxicity Water pollution 1,4-DCB 6.26E4 6.42E4 6.87E4Terrestrial ecotoxicity Soil contamination 1,4-DCB 0.356 0.365 0.388

Photochemical oxidation Air pollution/climate change C2H4 0.0459 0.047 0.0516


resources, transportation, distributions, in use, waste or converted into by-products.

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Fig. 5. CO2 sources in asphalt productions according to GHG protocol.

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Fig. 6. Contributions CO2 sources of different asphalt productions (a) Type 1 (b) Type 5 (c) Binder type.

Table 4. The amount of kg CO2 eq. emitted during production stage of asphalt

Impact categories Binder Type-1 Type-5Fossil CO2 308 310 316

Biogenic CO2 0.91 0.929 0.961CO2 from land transformation

0.00328 0.00335 0.00355

CO2 uptake 0.921 0.94 0.973


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Discussions of this paper may appear in the discus-sion section of a future issue. All discussions should be submitted to the Editor-in-Chief within six monthsof publication.

Manuscript Received: August 12, 2014Revision Received: February 2, 2015

and Accepted: April 22, 2015

life cycle assessment of asphalt pavement product -...

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