Life Cycle Modeling of Infrastructure Systems

The focus of macroscale life cycle modeling is highlighted in figure below. The infrastructure life cycle system consists of material production, construction, use, repair and end-of-life management processes, which are defined by the specific material inputs and infrastructure application. The ECC material composition also determines the material and mechanical properties that ultimately influence system performance and service life.

Macro-scale life cycle modeling

Material Flow Analysis

The key attributes of sustainable infrastructure systems are – extended service life, enhanced performance, optimal life cycle costs, and minimal environmental life cycle impacts including the use of virgin raw materials. The rate of addition of new stock and the repair of existing stock are key determinants of infrastructure sustainability. The condition and performance of, especially, concrete infrastructure, in the United States has shown an alarming decline and it is anticipated that billions of dollars of investment will be required over the next decade to replace and/or rehabilitate existing structures. Cement is an essential component of concrete, usually in the range of 10-15% by volume. The production and use of cement are both energy- and material- resource intensive. The objective of this study is to characterize the stocks and flows of cement mobilized and utilized during the twentieth century in United States using the generic cement life cycle. The motivation for estimating historical inventories of cement stocks and flows is to provide accurate informed estimates of contemporary cement in-use stocks in U.S. infrastructure and future discards to relevant stakeholders such as federal highway administration, department of transportation, public/private utilities, and the construction and cement industries.

Generic life cycle of cement

A dynamic substance flow model is being developed using time-series data on apparent cement consumption and lifetime distributions for each cement end-use infrastructure application. There is buildup of stock when the inflows exceed the outflows of the use reservoir. The lifetime distribution determines the residence time of the in-use stock in the use reservoir. The Weibull distribution is the most commonly used and preferred distribution in lifetime modeling of productsThe consumption of cement has increased six-fold over the last fifty years. During the last century, the consumption of cement in the United States was approximately 4.5 billion metric tons. Apparent cement consumption was partitioned into various end-use markets such as roads, bridges, highways, buildings (residential, public, commercial), water and wastewater utilities, based on historical and contemporary data available from the Portland Cement Association and United States Geological Survey. For the time periods where cement end-use market share data were not available, missing values were interpolated based on existing trends. The use of cement for road infrastructure accounts for about one-third of this market.

Spatial Analysis

Spatial analysis research will examine trade-offs between local production from numerous small mines versus production from a few large mines. A trend in the aggregate industry has shifted production from local quarries to a few large “megaquarries” for production of aggregate that ship their product long distances. Examples of such megaquarries can be found in the UK, which serve the European market, as well as Caribbean quarries serving the U.S. market.

To start, our study is confined to the Great Lakes region area around Chicago. Using a GIS approach, surface and bedrock geologic maps are employed to determine the location of all lithologic or alluvial units most likely to contain cement and aggregate deposits. The location of existing cement and aggregate operations, as well as infrastructure and cultural features will then be determined. This information will be used in two ways: First, areas of preferable limestone resources for cement production will be delineated. Second, this information will be coupled with a multimodal transportation network that will evaluate the transportation burdens associated with moving cement materials to their markets. The analysis results will provide understanding of the tradeoffs between the distributed versus centralized cement production scenarios from environmental, economic, and social perspectives..

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       University of Michigan

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