When evaluating the environmental aspects of building materials, concrete's sheer pervasiveness makes it easy to overlook. It's with us everywhere — from homes to buildings to highways. But using concrete as a construction material actually helps protect our natural resources and offers consumers benefits that aren't available with other building products. In an era of increased attention to the environmental impact of construction and sustainable development, concrete has much to offer.

Resource efficient

Using concrete minimizes the depletion of our natural resources. Its ingredients come directly from readily available materials: water, aggregate (sand and gravel or crushed stone), and cement. Cement is composed of 75% limestone — the most common mineral on earth. Although extracting any raw material from the earth takes a toll on the environment, extracting the raw materials for concrete has a lower impact than that of other construction materials. Because the ingredients for concrete are so plentiful, supplies are virtually inexhaustible.

Quarries, the primary source of raw materials, are readily reclaimed for recreational, residential or commercial development. Or, they can simply be restored to their natural state.

Recycled and recyclable

A nearly inert material, concrete is suitable as a medium for recycling waste or industrial byproducts. Many materials that would otherwise be deposited in landfills are used in making concrete. Aggregate, for example, can contain blast furnace slag, a byproduct of steel-making. Other aggregates used to create a lightweight concrete consist of recycled polystyrene. Almost all concrete contains fly ash, a byproduct of coal-burning electric plants. Of the almost 20 million tons of fly ash produced each year, 7 million tons are used in concrete.

The process of making cement also uses waste materials. Scrap tires have high energy content and supplement coal as fuel. And, industrial byproducts such as ash from coal combustion, fly ash from power stations, and mill scale and foundry sand from steel casting provide the silica, calcium, alumina and iron needed for making cement. Even kiln dust, a solid waste generated by cement manufacturing, is often recycled back into the kiln as a raw material.

Old concrete that has reached the end of its service life can be recycled and reused as aggregate for new concrete mixtures. Concrete yields 45% to 80% usable coarse aggregate and can be crushed and reused in new concrete or as a base material.

Reinforcing steel used in concrete is made from recycled steel. And, like concrete itself, old rebar is recycled into new.

Energy efficient

Concrete requires small percentages of only one product of any energy-intensive consequence — portland cement. Cement content in typical concrete ranges from 10% to 15%. The other ingredients for concrete — aggregate and water — have very low energy requirements.

Energy for transportation is low because concrete is produced locally. Materials used for making concrete are in great supply and exist almost everywhere. This means that concrete products and ready-mixed concrete can be made out of local resources and can be manufactured near the job site. Because it is shipped locally, fuel requirements for handling and transportation are minimized. At least 60% of all concrete is made within 100 miles of the job site.

Once in place, concrete offers significant energy savings over the lifetime of the building or pavement. Studies have shown that concrete's rigid pavement design means that heavy over-the-road trucks consume less fuel than when driving on asphalt pavement. Concrete pavement is also light-reflective and requires less energy than other materials to illuminate.

In homes and buildings, concrete's thermal mass plays a role in its energy efficiency. Insulation must be added to all building materials to obtain high R-factors, but thermal mass also is a factor. Concrete's high thermal mass provides significant benefits when used to construct buildings. By storing and releasing the energy needed for heating or cooling, concrete's thermal mass delivers year-round energy benefits by reducing temperature swings in homes and buildings. While insulation attempts to reduce energy losses through the building envelope, concrete's thermal mass uses walls themselves to store and release energy. Modern concrete wall systems use both insulation and thermal mass to deliver an energy-efficient building.

Waste minimization

Using concrete minimizes construction waste: whether cast-in-place or precast, concrete is used on an as-needed basis. Whatever amount is left over can be reused in total or reclaimed and used as aggregate in new concrete.

Long life

Concrete is a durable material that actually gains strength over time and conserves resources by reducing maintenance and the need for reconstruction. This makes concrete an affordable, long-term building product.

Concrete is a versatile product that has existed in various forms for centuries. But only recently is it becoming known that concrete plays a significant and valuable role in protecting and enhancing our environment.

Cement Manufacturers Pledge to Cut Greenhouse Gas Emissions

Members of the Portland Cement Association have adopted the goal of reducing carbon dioxide emissions per ton of product by 10% (from 1990 levels) by the year 2020. The goal is consistent with the Bush Administration's climate change initiative, termed “Climate VISION,” to reduce greenhouse gases through voluntary industry programs. Cement industry representatives announced the target recently as administration officials unveiled similar voluntary commitments by other industries. President Bush called on industries to set voluntary goals as part of his program to reduce greenhouse gas emissions by 18% over the next 10 years.

Continuous Improvement

The industry is now implementing a three-part program to achieve this goal and to foster reductions by cement users. The three parts address the cement manufacturing process, product formulation, and product application:

• Reduce emissions through increased efficiency, decreased fuel use, greater use of alternative fuels and raw materials.

• Formulate cements using a lower portion of calcinated material, thereby reducing carbon dioxide emissions per unit of product.

• Promote the use of energy-efficient concrete buildings, homes, and highways as a solution to climate change.

The carbon dioxide reduction goal is part of the U.S. cement industry's continuous improvement program that sets voluntary emission and waste-reduction goals, conducts an environmental awards program, and furthers the objective of achieving continuous improvement in environmental performance. In 2000, the cement industry received the Environmental Protection Agency's Climate Protection Award for its partnership with EPA's Climate Wise program.

Cement vs. Concrete

Although the two words concrete and cement are used interchangeably, cement is actually one of the ingredients in concrete. It's the fine gray powder that, in combination with water, binds sand and gravel or crushed stone into the rocklike mass known as concrete. Therefore, even though cement constitutes only 10% to 15% by weight of concrete's total mass, cement is the essential binding agent in concrete.