Category Materials and the Environment: Eco-Informed Material Choice

Summary and conclusion

Products, like organisms, have a life, during the course of which they inter­act with their environment. Their environment is also ours; if the interac­tion is a damaging one, it diminishes the quality of life of all who share it.

Life-cycle assessment is the study and analysis of this interaction, quantifying the resources consumed and the waste emitted. It is holistic, spanning the entire life from the creation of the materials through the manufacture of the product, its use, and its subsequent disposal. Although

standards now prescribe procedures for doing this, they remain vague, allowing a degree of subjectivity...

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The strategy for eco-selection of materials

The need, as we’ve already said, is for an assessment strategy that addresses current concerns and combines acceptable cost burden with sufficient pre­cision to guide decision making. The strategy should be flexible enough to accommodate future refinement and simple enough to allow rapid "What if?" exploration of alternatives. To achieve this goal, it is necessary to strip off much of the detail, multiple targeting, and complexity of method that makes standard LCA techniques so cumbersome. The approach developed here has three components.

Adopt simple metrics of environmental stress. The preceding discussion points to the use of energy or of a CO2 footprint as the logical choices. The two are related and are understood by the public at large...

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Streamlined LCA

Emerging legislation imposes ever-increasing demands on manufactur­ers for eco-accountability. The EU Directive 2005/32/EC on Energy Using Products (EuPs), for example, requires that manufacturers of EuPs must demonstrate "that they have considered the use of energy in their products as it relates to materials, manufacture, packaging, transport, use and end of life." This sounds horribly like a requirement that a full LCA be conducted on each one of a manufacturer’s products; because many manufacturers have thousands of products, the expense in terms of both money and time would be prohibitive.

The complexity of an LCA makes it, for many purposes, unworkable...

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Life-cycle assessment: details and difficulties

Formal methods for LCA first emerged in a series of meetings organized by the Society for Environmental Toxicology and Chemistry (SETAC), of which the most significant were held in 1991 and 1993. This led, from 1997 on, to a set of standards for conducting an LCA, issued by the International Standards Organization (ISO 14040 and its subsections 14041, 14042, and 14043). These prescribe procedures for "defining goal and scope of the assessment, compiling an inventory of relevant inputs and outputs of a product system; evaluating the potential impacts associated with those inputs and outputs; interpreting the results of the inventory analysis and impact assessment phases in relation to the objectives of the study...

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The material life cycle

The idea of a life cycle has its roots in the biological sciences. Living organ­isms are born; they develop, mature, grow old, and, ultimately, die. The progression is inherent in the organism—all follow the same path—but the way the organism develops on the way and its behavior and influence depend on its interaction with its environment—here, the natural environ­ment. Life-cycle studies explore and track the interaction of organisms with their environment.

The life-cycle idea has since been adapted and applied in other fields: in the social sciences (the interaction of individuals with their social envi­ronment), in the management of technology (the study of innovation in the business environment), and in product design (the interaction of prod­ucts with the natural, social, and ...

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The materials life cycle

The materials life cycle

Manufacture

The materials life cycle

Resources

Use

The materials life cycle

Disposal

3.1 Introduction and synopsis

The materials of engineering have a life cycle. They are created from ores and feedstock. These are manufactured into products that are distributed and used. Like us, products have a finite life, at the end of which they become scrap. The materials they contain, however, are still there; some (unlike us) can be resurrected and enter a second life as recycled content in a new product.

Life-cycle assessment (LCA) traces this progression, documenting the resources consumed and the emissions excreted during each phase of life. The output is a sort of biography, documenting where the materials have been, what they have done, and the consequences for their surroundings.

Подпись: Material Подпись: CONTENTS
The materials life cycle
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Summary and conclusion

Growing global population and prosperity increase the demand for energy and materials. The growth in demand is approximately exponential, meaning that consumption grows at a rate that is proportional to its current value; for most materials it is between 3% and 6% per year. Exponential growth has a number of consequences. One is that consumption doubles every 70/r years, where r is the growth rate in percent per year. It also means that the total amount consumed (the integral of the consumption over time) also doubles in the same time interval.

Most materials are drawn from the minerals of the Earth’s land masses and oceans. The resource base from which they are drawn is large, but it is not infinite. Its magnitude is not easy to estimate so that at any point

in time only a fraction of it...

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. Reserves, the resource base, and resource life

The materials on which industry depends are drawn, very largely, from the Earth’s reserves of minerals. A mineral reserve, R, is defined as that part of a known mineral deposit that can be extracted legally and economically at the time it is determined. It is natural to assume that reserves describe the total quantity of minerals present in the ground that is accessible and, once
used, is gone forever, but this is wrong. In reality, reserves are an economic construct, which grow and shrink under varying economic, technical, and legal conditions. Improved extraction technology can enlarge them, but environmental legislation or changing political climate may make them shrink. Demand stimulates prospecting, with the consequence that reserves tend to grow in line with consumption...

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Exponential growth and doubling times

A modern industrialized state is extremely complex, heavily dependent on a steady supply of raw materials. Most materials are being produced at a

Table 2.2 The water demands of energy

Energy source

Liters of water per MJ

Grid electricity

24

Industrial electricity

11

Energy direct from coal

0.35

Energy direct from oil

0.3

rate that is growing exponentially with time, at least approximately, driven by increasing global population and standards of living. So we should look first at exponential growth and its consequences.

Подпись: dp dt Exponential growth and doubling times Подпись: (2.1)

If the current rate of production of a material is P tonnes per year and this increases by a fixed fraction r % every year, then

Подпись: P Подпись: Po exp Подпись: r(t - t0) 100 Подпись: (2.2)

Integrating over time t gives

Exponential growth and doubling times Exponential growth and doubling times Exponential growth and doubling times

where P0 is the production rate at ...

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Resource consumption

Materials. Speaking globally, we consume roughly 10 billion (1010) tonnes of engineering materials per year, an average of 1.5 tonnes per person, though it is not distributed like that. Figure 2.1 gives a perspective: it is a bar chart showing consumption of the materials used in the greatest

Подпись: Annual world production (tonnes/year)
Подпись: Resource consumption 17

FIGURE 2.1

 

The annual world production of 23 materials on which industrialized society depends. The scale is logarithmic.

 

Resource consumption

Metals

(dominate by steel)

Resource consumption

A pie chart of materials usage (tonnes) by family. Ceramics dominate because of the enormous annual consumption of concrete.

 

FIGURE 2.2

quantities. The chart has some interesting messages...

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