About the Cool Climate Concrete Program

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C3 is a monitored and verified offset program based on the use of blended cement concrete in construction and civil works projects. The goal of the program is to offset 250,000 metric tons of CO2 by May of 2007 by using less ASTM C150 Portland cement. Through the C3 program, participants create offsets through the decreased use of Portland cement. Additional program details and sample calculations.

Participants can be any company that blends cements, including cement companies, concrete companies and concrete product companies (also known as pre-cast concrete companies). Suppliers of pozzolans can also become participants by aggregating concrete companies or other blenders.

The C3 program is funded through the Climate Trust, a non-profit organization in Oregon that implements offsets for CO2 emissions in excess of Oregon’s carbon dioxide standard. Horst, Inc. is a sustainable materials firm contracted with the Climate Trust to run the C3 Program. More on program management and background.

Why Blended Cement?

Cement is the binder in concrete. Depending on the strength of the concrete, cement usually accounts for 12%–15% of a concrete mix. As a material, our society uses concrete second only to water. Concrete is a relatively benign material; the major CO2 burdens of concrete come from Portland cement production. Even though the amount of cement in concrete is small, the total greenhouse gas impacts are large.

The production of Portland cement (ASTM C150) is a CO2 intensive process. Depending on the efficiency of the cement kiln and the fuels used, approximately half of the emissions associated with Portland cement come from energy used to heat limestone, minerals and other materials in the kiln to create clinker. The other half comes from process emissions of calcination, a chemical reaction that occurs in the creation of Portland cement clinker, which makes up 95% of Portland cement. For every metric ton of Portland cement clinker produced, approximately one metric ton of CO2 is produced (USGS).

With sound technical advice, and based on individual location and projects, supplementary cementitious materials allow for the reduction of standard Portland cement (ASTM C150) and its associated environmental burdens. Examples of these materials include Ground Granulated Blast Furnace Slag (GGBFS), a by-product of steel production in blast furnaces, and flyash, a by-product of coal burning in power plants. When these by-product materials are used to decrease the amount of Portland cement in a concrete mix, the associated CO2 emissions are equivalently lowered.

Blended cements are cements that contain Portland cement blended with supplementary cementitious materials. Blended cement as a technical term often refers to cement products blended by cement companies. In the C3 program, the term is used to describe cement blended by any type of company.