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San Francisco 49ers Buy Low-CO2 Concrete for New Stadium

Central Concrete, a US Concrete company, will supply about 80,000 cubic yards of its low-CO2 concrete for the new San Francisco 49ers stadium, the company said.

The mixes selected, which will be used for the auger cast piles and overall stadium structure, use less materials than traditional concrete and will reduce the stadium’s overall carbon footprint by 23 million pounds of CO2, Central Concrete said. The company has supplied low-CO2 concrete for the San Francisco Public Utilities Headquarters, NASA Ames Building, San Francisco Academy of Sciences, San Jose Arena, Stanford Stadium and Santa Clara University Stephen Schott Baseball Stadium.

Typically, creating 1 ton of traditional cement releases 1 ton of CO2 into the atmosphere, Central said. To combat this problem, the company uses what it calls “EF Technologies,” including alternative or supplementary cementitious materials such as fly ash and slag. EF stands for “environmentally friendly.”

Fly ash (also known as a coal combustion product or CCP) is the mineral residue resulting from the combustion of powdered coal in power generating plants. It consists mostly of silicon dioxide, aluminum oxide and iron oxide. It is pozzolanic in nature, meaning it reacts with calcium hydroxide and alkali to form cementitious compounds.

Most power plants are required by law to reduce their fly ash emissions to less than one percent, Central Concrete says. The remaining 99 percent is collected using electrostatic precipitators or filter bags. Initially, power plants disposed of this collected ash in ash ponds or landfills. Once the ash’s pozzolanic properties were discovered, however, some companies began using it as a replacement for Portland cement in concrete.

Portland cement is the glue that binds concrete together. According to Central Concrete, the production of Portland cement accounts for about five percent of human-generated CO2 worldwide, and fly ash can replace up to 50 percent of the Portland cement required to manufacture concrete.

Central Concrete has also been using slag, the by-product of smelting ore to purify metals. Processing blast furnace slag into slag cement or slag aggregate reduces the air emissions at the blast furnace and the material in landfills. Slag also decreases Portland cement usage by as much as 50 percent.

According to Central Concrete, using a 50 percent slag cement substitution saves between 165 and 374 pounds of CO2 per cubic yard of concrete—a 42 to 46 percent reduction in greenhouse gas emissions (see chart). Slag cement requires nearly 90 percent less energy to produce than an equivalent amount of Portland cement, the company says.

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4 thoughts on “San Francisco 49ers Buy Low-CO2 Concrete for New Stadium

  1. Mineral admixtures like FA, BFS, SF, MK and others are used in cement and concrete for quite sometime. However focus should be on maximising their utilisation, not compromising strength and durability characteristics of concrete.

  2. They are ignoring the fact that there is no flyash or slag produced in California. The slag comes from high-emission blast furnaces in China. It has to be shipped here, and they are also ignoring the 0.3 tons of GHG per ton of slag emitted during the trans-pacific voyage. It’s illegal to buy electrical power from a coal-burning plant, but we brag about using their waste product?!

  3. This is all fine and dandy, but I want my concrete strong. If this is as good as the portland cement mixture and is cost effective, then let the whale saving trre huggers feel good. If it is not, than anyone who uses it doesn’t give a hoot about anything but politics, and politics makes crappy buildings.

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