The SMH has an article on a “green concrete" producer in Queensland - Queensland concrete goes green.

A Toowoomba-based company's carbon emissions-free concrete could be the latest weapon in the fight against carbon emissions. Wagners CFT's Queensland-made "green concrete" has already been used in Brisbane and Toowoomba footpaths and has been recognised by the state government's ClimateSmart program.

In the company's home city, the "earth-friendly concrete" has been trialled in some building slabs and it is estimated the concrete could save 9.2 tonnes of carbon emissions in every 300 square metre slab. If it was used in every house slab that went down in Queensland, it could save about 270,000 tonnes of greenhouse gas emissions a year.

Wagners general manager Michael Kemp said the carbon-free concrete used two very common waste products with very little carbon; fly ash and slag from blast furnaces On Friday, his product development crew took out the biggest environmental award at the Premier's Climatesmart Sustainability Awards.

The more commonly used Portland cement is limestone and the carbon has to be "driven-off"' the fine, grey cement so it can be mixed with the concrete.

"That process of making the cement creates the massive carbon dioxide emissions associated with concrete," Mr Kemp said. "In a typical house in Queensland for example, using our concrete at market as opposed to traditional concrete, in one housing slab you will save 9500 kilograms of carbon dioxide. "There are something like 30,000 homes built a year in southeast Queensland, so when you do the maths, the potential savings for carbon dioxide is massive."

Transamterial has a post on a cardle-to-cradle compliant waterproofing treatment for concrete - Element.

Hycrete’s Element is an environmentally friendly admixture that integrally waterproofs concrete used in commercial construction. Certified Cradle-to-Cradle by McDonough Braungart Design Chemistry, LLC (MBDC), Element eliminates the need for external membranes typically used to waterproof concrete, thereby making the concrete more-easily recyclable following demolition. This approach can eliminate thousands of pounds of Volatile Organic Compounds (VOCs), CO2 and non-renewable content. Additionally, the admixture enhances structure durability by protecting against corrosion of steel rebar.

The New York Times has an article on efforts to produce concrete without emitting large volumes of CO2 - Concrete Is Remixed With Environment in Mind.

Concrete may seem an unlikely material for scientific advances. At its most basic, a block of concrete is something like a fruitcake, but even more leaden and often just as unloved. The fruit in the mix is coarse aggregate, usually crushed rock. Fine aggregate, usually sand, is a major component as well. Add water and something to help bind it all together — eggs in a fruitcake, Portland cement in concrete — mix well, pour into a form and let sit for decades.

Let a lot of it sit. Every year, about a cubic yard of concrete is produced for each of the six-billion-plus people on the planet.

Think of it this way. The stretch of sidewalk in front of your house? That is you and your spouse’s share. That concrete truck rumbling down the street? It holds a yard for each member of the New York Yankees’ starting lineup. Add the Mets and the Red Sox, and you have enough for the typical house foundation and basement floor.

But those are small projects. The St. Anthony Falls Bridge used about 50,000 yards of concrete. Hoover Dam used more than three million. And the Three Gorges project in China contains more than a yard for every man, woman and child in Canada, population 33 million.

All that concrete may seem the same. And the basic product did remain relatively unchanged since the invention of Portland cement in the early 1800s. (The ancient Romans made concrete, too, but from volcanic ash.) Producers have always tinkered with the mix to find the right proportions of concrete’s basic ingredients, but the recipe never varied much.

Now the experimentation is more elaborate, designed to tailor the concrete to the need. Increasingly, that need includes the environment. Aesthetic considerations aside, concrete is environmentally ugly. The manufacturing of Portland cement is responsible for about 5 percent of human-caused emissions of the greenhouse gas carbon dioxide.

“The new twist over the last 10 years has been to try to avoid materials that generate CO2,” said Kevin A. MacDonald, vice president for engineering services of the Cemstone Products Company, the concrete supplier for the I-35W bridge.

In his mixes, Dr. MacDonald replaced much of the Portland cement with two industrial waste products — fly ash, left over from burning coal in power plants, and blast-furnace slag. Both are what are called pozzolans, reactive materials that help make the concrete stronger. Because the CO2 emissions associated with them are accounted for in electricity generation and steel making, they also help reduce the concrete’s carbon footprint. Some engineers and scientists are going further, with the goal of developing concrete that can capture and permanently sequester CO2 from power plants or other sources, so it cannot contribute to the warming of the planet. ...

Some researchers want to eventually eliminate Portland cement entirely and replace it with other cements to produce zero-carbon, or even carbon-negative, concrete.

Portland cement is at the heart of concrete’s environmental problems. About a ton of CO2 is emitted for every ton of cement produced. The basic manufacturing process involves burning limestone and other minerals at about 2,700 degrees Fahrenheit to create an intermediate product called clinker.

“Essentially, we’re trying to make the same minerals that they did in 1825,” said Mr. Stehly, who is head of a committee addressing sustainability issues at the American Concrete Institute.

The cement industry, particularly in the United States and Europe, has reduced CO2 emissions through the use of more efficient kilns and processes, and is now allowed to add some ground unburned limestone to the clinker, reducing the actual cement in the mix. But about half of the CO2 from cement cannot be eliminated — it is produced in the reaction, called calcination, that occurs as the limestone (which consists of calcium carbonate) is being burned.

So to reduce concrete’s carbon footprint to near zero or less, different approaches are needed. Novacem, a British startup, is developing a cement that does not use carbonates and can make concrete that absorbs carbon dioxide. Carbon Sense Solutions, in Halifax, Nova Scotia, wants to bubble CO2 through wet cement, sequestering the gas through carbonation (a process that occurs naturally, though very slowly, under normal conditions).

At a site adjacent to a gas-fired electricity generation plant in Moss Landing, Calif., the Calera Corporation is developing a process to bubble power plant flue gases through seawater or other brackish water, using the CO2 in the gases to precipitate carbonate minerals for use as cement or aggregates in concrete. The process mimics, to some extent, what corals and other calcifying marine organisms do.

Calera calculates that producing a ton of these minerals consumes half a ton of CO2, so the resulting concrete could potentially be carbon negative — sequestering carbon dioxide permanently.

Brent R. Constantz, the company’s founder, has a background in cements, having made specialty products for use in orthopedic surgery. But he does not describe Calera as a cement company. “We’re primarily driven by the need to capture large amounts of CO2 and sequester it,” he said.

The company probably will begin by making aggregate, because the barriers to making a commercially acceptable product are lower than with cement. Even with aggregate, any new product must meet standards and must be accepted by the concrete industry, which can be conservative. “Any time you introduce anything new,” Dr. Constantz said, “it’s a challenge.”

Tyler Hamilton has an article at Technology Review on a company that claims to have a new process that stores carbon dioxide in precast concrete - A Concrete Fix to Global Warming.

A Canadian company says that it has developed a way for makers of precast concrete products to take all the carbon-dioxide emissions from their factories, as well as neighboring industrial facilities, and store them in the products that they produce by exposing concrete slurry to carbon-dioxide-rich flue gases during the curing process. Industry experts say that the technology is unproven but holds great potential if it works.

Concrete accounts for more than 5 percent of human-caused carbon-dioxide emissions annually, mostly because cement, the active ingredient in concrete, is made by baking limestone and clay powders under intense heat that is generally produced by the burning of fossil fuels. Making finished concrete products--by mixing cement with water, sand, and gravel--creates additional emissions because heat and steam are often used to accelerate the curing process.

But Robert Niven, founder of Halifax-based Carbon Sense Solutions, says that his company's process would actually allow precast concrete to store carbon dioxide. The company takes advantage of a natural process; carbon dioxide is already reabsorbed in concrete products over hundreds of years from natural chemical reactions. Freshly mixed concrete is exposed to a stream of carbon-dioxide-rich flue gas, rapidly speeding up the reactions between the gas and the calcium-containing minerals in cement (which represents about 10 to 15 percent of the concrete's volume). The technology also virtually eliminates the need for heat or steam, saving energy and emissions.

Work is expected to begin on a pilot plant in the province of Nova Scotia this summer, with preliminary results expected by the end of the year. If it works and is widely adopted, it has the potential to sequester or avoid 20 percent of all cement-industry carbon-dioxide emissions, says Niven. "If the technology is commercialized as planned, it will revolutionize concrete manufacturing and mitigate hundreds of megatons of carbon dioxide each year, while providing manufacturers with a cheaper, greener, and superior product." He adds that 60 tons of carbon dioxide could be stored as solid limestone--or calcium carbonate--within every 1,000 tons of concrete produced. Further, he claims that the end product is more durable, more resistant to shrinking and cracking, and less permeable to water.

Keith Johnson at the WSJ's Environmental Capital blog has a look at proposals to reduce the price (and time taken to construct) of offshore wind farms by using concrete instead of steel in the supporting structures.

Sometimes the race toward clean energy is tripped up by politics. Other times, by nuts and bolts. Or steel.

Offshore wind power is supposed to be the great white hope of renewable energy. Out of sight, offshore wind farms could theoretically supply as much electricity as the U.S. currently produces with coal, gas, and nuclear plants. Britain fancies itself the “Saudi Arabia” of wind power, given its abundant offshore wind resources. So far, though, that’s translated into just under one-half of a regular coal-fired plant. (And things aren’t getting any better this week.)

What’s the holdup? Lots of things. Offshore wind costs more than regular, onshore wind—which already costs more than traditional power sources. Getting transmission lines from offshore platforms to the electricity grid has scuppered loads of offshore wind projects. There’s another holdup—building offshore wind platforms means bidding for the same construction materials that are needed for a lot of other things, raising costs and delaying projects.

But what if offshore wind developers were to end-run the obstacles? Britain’s New Civil Engineer reports this month that wind-power development companies, including Germany’s E.On and Denmark’s Dong Energy, might have a solution: concrete instead of steel. At a swoop, that would eliminate the need for pricey steel and all the supporting cast needed to plant it in the seabed. Says New Civil Engineer:

The project has the dual purpose of reducing industry reliance on steel monopiles for foundations and eliminating the need for the heavy lift ships and jack-up barges typically used during turbine foundation installation. In addition the large hydraulic hammers usually needed for piling are no longer required, further reducing equipment and support vessel hire costs.

Granted, developers have been trying to get around regular offshore bottlenecks for years. Floating offshore wind platforms, borrowing from oil-rig technology, are the current flavor of the day.