Estimating net changes in life-cycle emissions from adoption of emerging civil infrastructure technologies.

ABSTRACT

There is a net emissions change when adopting new materials for use in civil infrastructure design. To evaluate the total net emissions change, one must consider changes in manufacture and associated life-cycle emissions, as well as changes in the quantity of material required. In addition, in principle one should also consider any differences in costs of the two designs because cost savings can be applied to other economic activities with associated environmental impacts. In this paper, a method is presented that combines these considerations to permit an evaluation of the net change in emissions when considering the adoption of emerging technologies/materials for civil infrastructure. The method factors in data on differences between a standard and new material for civil infrastructure, material requirements as specified in designs using both materials, and price information. The life-cycle assessment approach known as economic input-output life-cycle assessment (EIO-LCA) is utilized. A brief background on EIO-LCA is provided because its use is central to the method. The methodology is demonstrated with analysis of a switch from carbon steel to high-performance steel in military bridge design. The results are compared with a simplistic analysis that accounts for the weight reduction afforded by use of the high-performance steel but assuming no differences in manufacture.

INTRODUCTION

Civil construction is one of the largest users of energy, material resources, and water, as well as a formidable polluter. Approximately 5% of the total global industrial energy consumption, 5% of the total anthropogenic carbon dioxide (C[O.sub.2]) emissions, and significant emissions of sulfur dioxide (S[O.sub.2]) and oxides of nitrogen (N[O.sub.x]) are attributed to the production of approximately 1.45 billion Mg of global cement. (1) Environmental impact assessment is increasingly considered in decisions related to civil infrastructure. (1,2) This paper presents a method for the environmental assessment of new technologies for civil infrastructure.

The method that is presented is based on economic input-output life-cycle assessment (EIO-LCA). Life-cycle assessment (LCA) is a common framework for environmental assessment as direct and indirect impacts are evaluated; standards exist for its implementation, e.g., the ISO 14001 system. (3) EIO-LCA is one of two distinct approaches that have emerged; the other is SETAC-LCA (Society of Environmental Toxicology and Chemistry Life-Cycle Assessment). (4) EIO-LCA is built around economic input-output (EIO) modeling that allows analysis of the direct and indirect impacts of public decisions, for example, to assess changes in unemployment from shifts in government spending. (5,6) The application of the EIO-LCA method has been facilitated with development of the web-based "EIOLCA model." (7)

Previous applications of the EIO-LCA method to civil infrastructure were limited to standard infrastructure. In these applications, the civil infrastructure was "built" using the outputs of existing economic sectors included in the EIO national tables. For example, in an LCA of steel versus steel-reinforced concrete bridges, the bridges were built using the outputs of the economic sectors of iron and steel mill (Standard Industrial Classification [SIC] code 331111) and ready-mix concrete manufacturing (SIC code 327320). (8) In another LCA study that compared asphalt and steel-reinforced concrete pavements, the pavements were built from the outputs of the iron and steel mill, ready-mix concrete manufacturing, and asphalt paving mixture and block manufacturing (SIC code 324121) sectors. (9) The method that is developed in this paper focuses on the LCA of new materials (high-performance steels [HPS], high performance concrete, pervious concrete) that are not represented by the existing sectors.

There are several reasons why users of the EIO-LCA model may find it problematic to "build" new materials from existing sectors. First, the model user would need to identify all of the main sectors that contribute a significant burden of any type and then assign appropriate values. Because there are typically many sectors that contribute a significant amount of at least one type of environmental burden, this imposes a large information requirement. For example, an EIO-LCA model run of the steel sector reveals that if only the top six input sectors (on the basis of dollars) are included, 45% of volatile organic compounds would be missed. Second, it would be difficult to meet this information requirement in a way that ensures consistency with the information embodied in the input-output tables that underlies the EIO method. For example, in building HPS steel, it would be important to ensure consistency with the iron and steel sector. Third, without specific understanding of the input-output tables and knowledge and access to tools for linear algebra, errors such as double counting can be easily introduced. The developed method details how a user can incorporate external data to effectively modify the standard sector to reflect that of the new material. In doing so, the method lessens data requirements, enforces a measure of consistency, and prevents errors.

The method that is developed is applicable to the assessment of civil infrastructure (e.g., bridges, buildings, or pavements) and other examples of final demand (i.e., goods or sales to final consumers, which includes households and the government). To evaluate the impact of the use of new materials that are to be intermediate inputs to other producing sectors, a more involved approach is required, such as that of Joshi. (10) Such an approach does require practitioner knowledge of linear algebra and associated computer implementations.

This paper explores an issue not investigated in the previous EIO-LCA studies. There typically will be differences in costs between alternative technologies for civil infrastructure that have the same function, for example, two bridges designed to the same standards with one built from a standard steel and the other from HPS. For proper comparison, such cost differences should be accounted for in an environmental assessment, because any savings from choosing the less costly alternative would be applied to other economic activities, with additional environmental burdens. The method that is presented addresses this issue.

The purpose of this paper is to develop a method for use by practitioners that can be used to evaluate the change in life-cycle burdens when switching from a standard material, which is well represented by an EIO sector, to a nonstandard, or emerging material that is not represented by an existing EIO sector. The evaluation of such a switch has not previously been explored. In the next section, a background on EIO and EIO-LCA is provided. We include this background to present a clear mathematical introduction for practitioners (that is not included in other EIO-LCA papers) and because the equations are used later in the development of the method. Following the development of the method is a demonstration involving a LCA of a switch from a carbon steel bridge (standard) to a high-performance (nonstandard) steel bridge. The results are compared with a simpler method that accounts for differences in material quantities for the carbon and HPS steels but ignores differences in their manufacturing inputs. The results are then discussed and conclusions are offered.

BACKGROUND ON EIO AND EIO-LCA

Economic Input-Output Modeling (EIO)

The EIO modeling approach was developed by Wassily Leontief, for which he received a Nobel Prize in Economics in 1973. Others have further explored the approach. (11) EIO modeling can be used to assess the approximate effect on the column vector of sector output, x, from changes in final demand, represented by a column vector, f. EIO modeling is an approximation in that it assumes an economy at general equilibrium. (5)

An EIO table, or direct requirements matrix, D, describes the flow of goods and services between all of the individual sectors of an economy. (5) It has traditionally been represented and expressed in monetary terms in a base year. The U.S. Department of Commerce Bureau of Economic Analysis regularly generates EIO tables for the national economy; the 1997 table consisted of 491 X 491 sectors. (12) A simplified three-sector version is shown in Figure 1.

Production of a steel bridge is used as an example in the illustration (Figure 1). The manufacture of steel requires as inputs many direct and indirect materials represented by several economic sectors, including for example iron ore mining (SIC code 212210), lime manufacturing (SIC code 327410), coal mining (SIC code 212100), ferroalloy and related product manufacturing (SIC code 331112), wholesale trade (SIC code 420000), and truck transportation (SIC code 484000). For the purposes of this illustration, only two direct inputs are considered: iron ore mining, designated sector 1, whose total output and final demand are [x.sub.1] and [f.sub.1], respectively, and power generation and supply (SIC code 221100), sector 2, with total output and final demand of [x.sub.2] and [f.sub.2]; the total output and final demand of the iron and steel mill are [x.sub.3] and [f.sub.3]. The sectoral interactions are represented by the direct requirements matrix D, which is shown in Table 1 for the illustrative example. Values for the illustration are actual values taken from the 1997 Bureau of Economic Analysis EIO data.

The total sector output x can be broken down into that meeting final demand (f) and that which serves as an input to other sectors, represented as Dx. That is,