A British start-up company developing a cement that absorbs carbon dioxide has raised 1 million pounds ($1.7 million) to fund its work, underscoring the growing interest in eco-friendly construction ventures.

Novacem, a spin-out from Imperial College London, is one of a number of young companies tapping new technologies to reduce the cement industry's notoriously large carbon footprint.

With an annual production of more than 2.5 billion tons, conventional Portland cement is responsible for an estimated 5 percent of global CO2 emissions, more than the airline industry.

Novacem believes its "carbon-negative" cement answers the problem because it absorbs more carbon dioxide over its life cycle than it emits.

The trick is to make cement from magnesium silicates rather than calcium carbonate, or limestone, since this material does not emit CO2 in manufacture and absorbs the greenhouse gas as it ages.

Other companies working on rival low- or zero-carbon systems using a range of new materials and recycled industrial by-products include Calera of California, Australia's Calix, Carbon Sense Solutions of Canada and British-based Cenin.

Novacem Chairman Stuart Evans said the cash injection from Imperial Innovations, the Royal Society Enterprise Fund and the London Technology Fund would help fund a pilot plant that should be up and running in northern England in 2011.

The company is working with Rio Tinto on the supply of raw materials and is in discussions with a number of cement makers on future commercial production, which could be around five years away. "We are definitely knocking at an open door here," Evans told Reuters.

"The building and construction industry knows it has got to do radical things to reduce its carbon footprint and cement companies understand there is not a lot they can do without a technology breakthrough."

Novacem estimates that for every ton of Portland cement replaced by its product, around three-quarters of a ton of CO2 is saved, turning the cement industry into a big emitter to a big absorber of carbon.

Major cement makers are working hard to reduce CO2 emissions by investing in modern kilns and using as little carbon-heavy fuel as possible, but it reductions to date have been limited.

The world's top cement producers include France's Lafarge, Swiss-based Holcim and Cemex of Mexico.