Production of Concrete as Compared to Wood


A life cycle inventory systematically examines measurable quantities of all inputs (all raw materials, air, water, energy) and outputs (products, co-products, emissions, effluents, and solid wastes) over a defined sequence of manufacturing steps. When life cycle methodology is used to evaluate a building, a series of inventories are conducted to collect information for each of the materials used in construction, including the data for transportation of the materials and the activities involved in the construction process.

Concrete construction is often promoted as environmentally advantageous to alternative forms of construction of homes. Claimed advantages of concrete include an ability to recycle and to incorporate recycled content, high durability, and superior energy efficiency of some concrete construction systems. What is the scientific fact behind these claims?

Dovetail Partners, Inc. released a study presented by Dr. Jim Bowyer and associates of Dovetail Partners, Inc. The study reveals that over the past several decades numerous life-cycle based studies of the environmental impacts of concrete construction have been conducted.

When comparing concrete, wood, and steel life cycle impacts in construction, differences are often substantial, and consistently point to impacts of concrete construction that are higher than for comparable wood-framed structures, but lower than for structures framed in steel.

These differences in impact primarily relate to the extraction and production of the construction materials. This means that the environmental implications of building material choices are immediate, and the initial advantage of one building material over another persists throughout the life of the structure (although the relative magnitude of difference tends to narrow with each year of building operation).

Concrete is formed when sand gravel and other aggregate materials are bound by cement. Cement comes from natural materials, such as limestone (calcium carbonate) but the environmental impact of cement production is relatively high due to:1) the quantity of energy needed to reduce the calcium carbonate to lime (or calcium oxide). This takes place in a cement kiln where temperatures above 2700 degrees Fahrenheit are maintained; and 2) the substantial release of Co2 that is inherent in the process.

So, in addition to the mining activity necessary to obtain the limestone, sand, and gravel (and sometimes clay and other ingredients), cement production includes significant environmental impacts from the combustion of coal or natural gas and associated emissions to air, as well as direct release of carbon dioxide in the production of lime. In general, the production of a ton of cement results, in the release of about a ton of carbon dioxide.

Cement comprises about 12 to 15 percent of the weight of dry concrete. The study by Dr. Bowyer and associates reveals that of the three primary structural materials used in construction, lumber requires by far the lowest energy input in the manufacturing phase, followed by 100 percent recycled steel, concrete, and virgin steel. As a result, there are large differences in net emissions of carbon associated with production of basic construction materials (Table Below).

Material

Net Carbon Emissions (kg C/ Metric ton)

Softwood Lumber

33

Recycled steel (100% from scrap)

220

Concrete

265

Concrete block3/

291

Steel (virgin)

694




1/ Values are based on life cycle assessment and include gathering and processing of raw materials, primary and secondary processing, and transportation.

2/ Source: USEPA (2006).

3/ Based on the EPA concrete value and information about energy requirements in block-making.

The information in this article is based upon the paper presented by Dr. Jim Bowyer and associates of Dovetail Partners, Inc.

We encourage you to view the paper in its entirety

HERE



RSS 2.0 feed. Reply to post, or trackback.

Leave a Reply