Construction of Asphalt Pavement in China - Essay Sample

Abstract

In China, the construction of asphalt pavement has a significant impact on the environment, and energy use and greenhouse gas (GHG) emissions from asphalt pavement construction have been receiving increasing attention in recent years. At present, there is no universal criterion for the evaluation of GHG emissions in asphalt pavement construction. This paper proposes to define the system boundaries for GHG emissions from asphalt pavement by using a process-based life cycle assessment method. A method for evaluating GHG emissions from asphalt pavement construction is suggested. The paper reports a case study of GHG emissions from a typical asphalt pavement construction project in China. The results show that the greenhouse gas emissions from the mixture mixing phase are the highest, and account for about 54% of the total amount. The second highest GHG emission phase is the production of raw materials. For GHG emissions of cement stabilized base/subbase, the production of raw materials emits the most, about 98%. The GHG emission for cement production alone is about 92%. The results indicate that any measures to reduce GHG emissions from asphalt pavement construction should be focused on the raw materials manufacturing stage. If the raw materials production phase is excluded, the measures to reduce GHG emissions should be aimed at the mixture mixing phase.

Is your time best spent reading someone else’s essay? Get a 100% original essay FROM A CERTIFIED WRITER!

Save 25%

Introduction

As the Chinese highway system continues to grow in mileage and traffic volume, it is important to construct highways sustainably and with low environmental impact. In China, the highway network is 4.5 million km in length, wherein the length of expressways is 111,900 km. For expressways, asphalt pavement is predominantly used, accounting for over 90%, compared to cement concrete pavement. The asphalt pavement is composed of aggregate, cement, and asphalt binders. The manufacture of the raw materials and construction of asphalt pavements consumes a lot of energy and emits large quantities of greenhouse gases (GHGs).

Since the first expressway was built in China in the 1990s, the total expressway length has increased quickly up to the current 111,900 km by the end of 2014. Some 7500 km of expressway were built in 2014. Due to the increasing use of asphalt highways in China, the rapid growth of energy consumption and GHG emissions from its construction has caused public concern, making it necessary to assess the related environment impacts. However, there is a lack of suitable evaluation criteria and benchmark figures in China for GHG emissions generated from asphalt pavement construction.

Literature Review

Horvath et al. studied the environment impacts of pavements made of asphalt and steel-reinforced concrete by a life cycle inventory analysis based on publicly available data [1]. They found that asphalt pavement appears to have higher energy input, lower ore and fertilizer input requirements, and lower toxic emissions, but generates higher amount of hazardous waste in comparison with steel-reinforced concrete pavement.

Kim et al. conducted a series of studies on the GHG emissions from road construction projects. They established the framework method for the estimation of GHG emissions based on the data for a pavement project at the planning phase. The framework was applied to 23 typical highway construction projects in the Republic of Korea [2]. The project also studied the GHG emissions from onsite equipment usage during road construction, and summarized the eight major GHG-producing activities during the construction [3,4].

Hong et al. analyzed the GHG emissions during the construction of a building in China in an extended system boundary by using detailed onsite process data [5]. In the building process of infrastructure for urban highways, construction materials, building operations and transportation are found to be the main elements related to energy consumption and GHG emissions [6-10].

Santero and Horvath researched the global warming potential of pavement by dividing the construction into eight components: materials extraction and production, transportation, onsite equipment, traffic delays, carbonation, lighting, albedo, and rolling resistance. The ranges of potential impact for each component were calculated and compared. The results covered both the variability of pavements and uncertainty in the values. Two ranges were determined: a probable range of values based on the best estimates and an extreme range of value based on outlying data and less likely scenarios [11].

In 2010, greenhouse gas emissions in the United States totaled nearly 6.8 billon tons of CO2 equivalents. Of this total, the transportation sector was responsible for more than 1.8 billion tons of emissions, or 27.1% of total GHG. The transportation sector is the single greatest contributor of CO2 to the earth's atmosphere in the U.S. and accounts for about 31.1% of all CO2 emissions [12].

Huang developed a life cycle assessment model for construction and maintenance of asphalt pavement. Details are presented on both the methodology and data acquisition in the U.K. The model is applied to an asphalt pavement project comparing the environmental impact of virgin aggregate, waste glass, incinerator bottom ash and recycled asphalt pavements [13,14].

The energy consumption and environmental impacts of asphalt and reinforced concrete pavement (materials and construction) were researched by Zapata [15]. According to the study, the main consumption of energy from extraction to asphalt placement occurs during the mixing and drying of aggregate (48%) for the pavement. Moreover, the production of bitumen accounts for about 40% of the total energy consumption.

The GHG emissions related to highways and vehicles have attracted the interest of researchers for the last 20 years [16-22]. The highway construction industry plays an important role in economic development, but is also a main source of carbon emissions. The GHG emissions from aggregate heating, bitumen refinery, and mixture mixing phase have been evaluated [17]. The total emissions are estimated by adding those from different processes of construction by different project types, such as subgrade, pavement, bridge, and tunnels [22].

Globally, there are several tools like LEEDS and GreenRoad in the U.S. and CEEQUAL and asPECT in the U.K., available to measure the CO2 or sustainability. Other tools are available in Australia and Germany. In addition, many studies have evaluated the GHG emissions related to the highway infrastructure construction. The oversea evaluation methods and resources are mostly based on local data that are not representative of the Chinese circumstances. Moreover, some methods and software are commercial products, not available for academic research. At the present, the main challenge in the study of environmental impacts of asphalt pavement in China is a lack of project validated data and sector approved methods of life cycle carbon analysis. This study focuses on the GHG emissions

Int. J. Environ. Res. Public Health 2016, 13, 351 3 of 15

Int. J. Environ. Res. Public Health 2016, 13, 351

of asphalt pavement construction. The process is divided into the production of raw materials, the of raw materials, the mixture mixing, mixture transportation, paving, and rolling of the asphalt mixture mixing, mixture transportation, paving, and rolling of the asphalt mixture. Moreover, at high mixture. Moreover, at high temperature, the GHG emissions from asphalt mixture are included. temperature, the GHG emissions from asphalt mixture are included.

Materialsand Methods

Evaluation System Boundary

Figure 1. Evaluation system boundary of GHG emissions for asphalt pavement construction.

Figure 1. Evaluation system boundary of GHG emissions for asphalt pavement construction.

According to the Kyoto Protocol, there are six maim greenhouse gases, namely carbon dioxide According to the Kyoto Protocol, there are six maim greenhouse gases, namely carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PHCs) (CO2), methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PHCs) and and sulphur hexafluoride (SF6) [23]. Since HFCs, PFCs and SF6 are not commonly present in the asphalt sulphur hexafluoride (SF6) [23]. Since HFCs, PFCs and SF6 are not commonly present in the asphalt pavement construction process, this study only focuses on three types of GHG: CO2, CH4 and N2O. pavement construction process, this study only focuses on three types of GHG: CO2, CH4 and N2O.

Evaluation Method

The simplest expression of a GHG account (EGHG) is the product of activity data (AD) and The simplest expression of a GHG account (EGHG) is the product of activity data (AD) and emission factor (EF), shown as Equation (1) below.

E =ADEF (1)

EGHG AD EF (1)

While carbon dioxide is the GHG of greatest concern, there are several other GHGs. As the global warming potential (GWP) of these GHGs varies, a group of conversion coefficients are While carbon dioxide is the GHG of greatest concern, there are several other GHGs. As the global established to convert the emission of a specific GHG into carbon dioxide equivalents (CO e). In this warming potential (GWP) of these GHGs varies, a group of conversion coefficients are established2 to convert the emission integralofspecific GHG into carbon dioxide equivalents (CO2e). In this context, GWP text, GWPtheof the global warming effect ofGHG compared with that of CO2 in the same time interval, commonly using a time horizon of 100 years. The 100 year GWPs of CO , is the integral of the global warming effect of a GHG compared with that of CO2 in the same time2

CH4 and N2O are 1, 23 and 296 respectively [24]. , CH4 and N2O are 1, interval, commonly using a time horizon of 100 years.Therefore:100 year GWPs of CO2 23 and 296 respectively [24]. Therefore: e = AD EF GWP (2) The carbon account of asphalt pavementCO ADisthe sumEF ofGWallPrelevant emission sources, so the final(2)