Concrete—the world’s most widely used building material

Roads are continually being built in this area, throughout the U.S. and the world. Debates about roads arise and die. The proposed roundabout at North Main and Auburn has been challenged by some who prefer not to have established local businesses destroyed. The roundabout proposed for downtown Oregon has also been challenged by those who are opposed to the demolition of historic buildings. Considered necessary by some and accepted as a normal part of life by others, road building deserves a closer look.

Roads are built of concrete. It is a mix of 60 to 75 percent sand, gravel, or crushed stone, 15 to 20 percent water, 10 to 15 percent cement and other ingredients. Cement is limestone, clay, and other ingredients which have been “roasted.” Cement is the glue that holds concrete together.

Producing a ton of cement releases about a ton of CO2 to the atmosphere. Cement manufacture accounts for about 8 percent of the CO2 produced globally. A modern road is 14 to 25 inches deep. Producing materials for one mile of one lane road emits between 100 and 150 tons of CO2 to the atmosphere.

Although a significant amount of CO2 is emitted during the production of cement, once pavement is laid, it can last 50 years with little energy expended on upkeep. When a road needs replacement, it can be ground up and reused, not demolished and discarded. Reusing and recycling can save much of the original energy used and prevent environmental impacts imposed by producing new materials.

The more roads are built, the more they are used, expanding urban sprawl and lessening opportunities for mass transit. The traffic that flows on them produces more pollutants in terms of CO2, NOX, and CO than building the roads themselves. High lighting levels along roadways can be a big energy drain, using about one-fourth the energy used in building the road itself.

Concrete is used for many purposes in addition to roadways. New forms of concrete are being developed that will enhance its use for many purposes in addition to roadways. Substituting steel or polymer fibers for steel bars should double the life expectancy of a concrete structure. Superplasticizers help concrete flow into forms, leaving a smooth finish. Glass optical fibers properly aligned in concrete allow light to penetrate a wall, providing low energy use daylighting.

A Kyoto related goal is to halve the amount of CO2 released in manufacturing concrete. Since 90 percent of the energy used in making concrete is used in making cement, other binders are being looked for. When they are tested, properties including compression strength, durability and time needed to harden and cure are assessed. Materials or procedures that reduce the spaces between bits of sand and gravel assuring that these aggregates are more tightly packed also reduce the amount of cement needed.

Concrete is the world’s most widely used building material. Reducing the energy used in making it is a significant environmental achievement.

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