For every ton of cement manufactured there is a ton of CO2 emitted into the atmosphere.

To reduce greenhouse emission, global warming and to save virgin materials to the next generation , we must add or mix Natural Pozzolana, Fly Ash or Slag to the cement clinker in the cement factory or at ready mix concrete plant. Please refer to ENV, ACI OR ASTM for the min. and max. Percentage of  the blended cement.

 

Introduction

Portland cement concrete is the most widely used construction material in the world.

Each year, the concrete industry produces approximate 12 billion tons of concrete and uses about 1.6 billion tons of Portland cement worldwide. In addition to consuming considerable amounts of nature materials (limestone and sand) and energy, producing each ton of Portland cement releases one ton of carbon dioxide(CO2) into the environment. Concerns for the sustainable development in the cement and concrete industries are increasingly addressed.

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One of the immerging concrete technologies for sustainable development is to use“Green” materials for construction. The “green” materials are considered as materials that use less natural resource and energy and generate less CO2. They are durable and recyclable and require less maintenance. Some researcher had developed non-clinker “green” cement using two industry wastes: cement kiln dust and fly ash.

www.cptechcenter.org/publications/sustainable/shahkiln.pdf

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Green Cement: The key to building a sustainable future.

Global climate change has become the hot topic in sectors spanning from development, policy, planning and foreign relations to security, energy, transportation and, surprisingly, cement.

Cement, the binding ingredient used to create concrete, is not usually the first thing that comes to mind when discussing climate change. However, the manufacture of cement results in 5-7% of yearly global anthropogenic greenhouse gases. The post-Kyoto international consensus is that action must be taken on climate change. If global CO2 equivalent is to be stabilized at double pre-industrial levels (550 ppm), then the cement industry will need to find a way to reduce their emissions.

There are two major sources of CO2 resulting from the production of cement. The first source of emissions results from the extremely high (1450 °C) kiln temperatures needed to modify the raw materials. Fossil fuels are commonly used for this process due to their high energy content, abundance and low costs. The second source of CO2 results from the calcination of limestone (mainly CaCO3) to form the main binding ingredient of cement (CaO). The chemical conversion results in CO2 as shown below.
CaO3 + heat --> CO2 + CaO

Thus for every ton of cement manufactured there is a ton of CO2 emitted into the atmosphere. Current focus on reducing emissions includes the use of renewable fuels in the kiln, improved kiln efficiency and the addition of admixtures (e.g. fly ash, slag). Although these solutions are beneficial, they do not offer long-term solutions; the supply of alternative fuels is insufficient, kiln efficiency is nearing its limit and the amount of admixtures is determined by building codes. The true sustainability of the cement industry must come from a new and innovative alternative binder.

Project mission:

Utilize the state of the art research facilities at UC Berkeley to research, test and advance the state of knowledge of alternative cementitious binders.

Potential impact:

As cement consumption will continue to rise, particularly in developing countries, low CO2 cement is essential in addressing global climate change. The university research environment offers numerous benefits that are needed to provide the scientific assurances required of such a new technology.

Fundamental research into green cement will provide the foundation for the long-term sustainability of the built environment.

 Additional info:

The research environment and the expert faculty at UC Berkeley offer one of the best locations for researching low CO2 cements. In collaboration with the faculty of the Civil Engineering department, the research will focus on finding a real application that can play a crucial role in combating global climate change. http://bigideas.berkeley.edu/node/135

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 Greening Concrete

Concrete has a major green attribute: it's strong and durable. But it also has some strikes against it from a green standpoint: cement production uses a lot of energy, which generates greenhouse gases. In addition, concrete requires aggregate, and that doesn't have to come from a quarry, it can be recycled from some other waste stream and save space in a landfill.

Enter cement substitutes and concrete aggregates. They make concrete a very green product. That's why they're on the 2007 PATH Top 10 list.

Recycled Cement Substitutes

Cement substitutes like coal fly ash, blast furnace slag, natural pozzolana) and other mineral admixtures can replace up to 75% of the cement in concrete, while improving the quality of concrete and reducing costs. Cement substitutes also use a byproduct that might otherwise end up in a landfill.

• Produced by coal-fired power plants, fly ash provides a durable alternative to regular cement. How durable is it? Think of the Pantheon. Built 2,000 years ago using fly ash, it still stands today. That kind of durability makes fly ash a very green alternative to cement.
• Slag, a byproduct of steel production, is another cement substitute that lowers concrete's CO2 footprint. Slag is more lightweight than cement, which increases its strength-to-weight ratio. It is often easier to find than fly ash.

Cement substitutes are widely available from most concrete suppliers. Just ask specifically for them.

You can also get one point on the LEED for Homes rating system, the U.S. Green Building Council's Leadership in Energy and Environmental Design program that rates "green" homes, for replacing at least 30% of your foundation's cement with a recycled cement substitute. (Credit MR 2.2)

 Concrete Aggregate Substitutes

Various solid wastes like fiberglass, discarded glass, and granulated plastics can substitute for sand, gravel and stones in concrete. This keeps the wastes out of the landfill, eliminates the need for producing virgin materials, and can produce an attractive and unique concrete.

The use of these recycled aggregates is becoming especially popular for interior uses, such as concrete floors and countertops.

Again, you can get a point on the LEED for Homes rating system for replacing at least 25% of your foundation's concrete aggregates with a post-consumer recycled material. (Credit MR 2.2)

http://www.pathnet.org/sp.asp?id=22603

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 Green Cement

The ABC's Catalyst show this week had a segment on green cement from a company called Zoobond - trying to reduce the huge carbon emissions that cement making currently entails.

An Australian company has started to make concrete which promises to dramatically cut the carbon dioxide ordinarily emitted during production. Concrete is the second most widely used material on earth, after water. Figures vary, but it’s estimated that the manufacture of cement, the reactive ingredient in concrete, is responsible for over 5% of the world’s CO2 emissions.

Using a technique to make geo-polymers similar to those found in some natural volcanic rocks, a concrete alternative called E-Crete is now being manufactured in Melbourne, which claims to have reduced the amount of CO2 ordinarily emitted in the manufacture process by an estimated 80-90%.

Narration: What’s the fast growing source of greenhouse gas?

You might be surprised but it’s cement. Cement’s already the 3rd largest man-made source of carbon dioxide - more than two billion tonnes of it a year. That’s after fossil fuels and defrorestation. And because of all the construction going on around the world, cement’s carbon footprint is growing rapidly.

 http://peakenergy.blogspot.com/2008/05/green-cement.html

 

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Green cement may set CO2 fate in concrete

Carrie Sturrock, Chronicle Staff Writer

Tuesday, September 2, 2008

Back when Stanford Professor Brent Constantz was 27 he created a high-tech cement that revolutionized bone fracture repair in hospitals worldwide. People who might have died from the complications of breaking their hips lived. Fractured wrists became good as new.

Now, 22 years later, he wants to repair the world.

Constantz says he has invented a green cement that could eliminate the huge amounts of carbon dioxide spewed into the atmosphere by the manufacturers of the everyday cement used in concrete for buildings, roadways and bridges.

His vision of eliminating a large source of the world's greenhouse CO{-2} has gained traction with both investors and environmentalists.

Already, venture capitalist Vinod Khosla is backing Constantz's company, the Calera Corp., which has a pilot factory in Moss Landing (Monterey County) churning out cement in small batches.

And Carl Pope, executive director of the Sierra Club, says it could be "a game changer" if Constantz can do it quickly, on a big scale and at a decent price.

"It changes the nature of the fight against global warming," said Pope, who has talked with Constantz about his work.

That might sound like hyperbole, but the reality is that for every ton of ordinary cement, known as Portland cement, a ton of air-polluting carbon dioxide is released during production. Worldwide, 2.5 billion tons of cement are manufactured each year, creating about 5 percent of the Earth's CO{-2} emissions.

When Constantz learned about the high CO{-2} levels, he thought he could do better. After all, the majority of his 60 patents have to do with medical cement.

He claims his new approach not only generates zero CO{-2} , but has an added benefit of reducing the amount of CO{-2} power plants emit by sequestering it inside the cement.

To make traditional cement, limestone is heated to more than 1,000 degrees Celsius, which turns it into lime - the principal ingredient in Portland cement - and CO{-2}, which is released into the air.

Constantz uses a different approach, the details of which remains secret pending publication of his patent.

At his pilot factory, a former magnesium hydroxide facility that made metal for World War II bombs, magnesium crunches underfoot as Constantz, wearing a pressed, blue button-down shirt with rumpled shorts and sandals, outlines how the process works.

He pointed to two enormous smokestacks billowing flue gases full of carbon dioxide next door at Dynegy, one of the West's biggest and cleanest power plants.

Constantz takes that exhaust gas and bubbles it through seawater pumped from across the highway. The chemical process creates the key ingredient for his green cement and allows him to sequester a half ton of carbon dioxide from the smokestacks in every ton of cement he makes.

Constantz believes his cement would tackle global warming on two fronts. It would eliminate the need to heat limestone, which releases CO{-2}. And harmful emissions can be siphoned away from power plants and locked into the cement.

The same process can also be used to make an alternative to aggregate - the sand and gravel - that makes up concrete and asphalt, which would sequester even more carbon dioxide from power plants.

"The beauty here is we're taking this old industrial polluting infrastructure and turning it into something that will save the environment," Constantz said.

On a per-person basis, the United States is the world's worst CO{-2} polluter from all sources. But according to the Netherlands Environmental Assessment Agency, China just surpassed the U.S. for total carbon dioxide emissions.

China is expected to produce 47 percent of the world's 2.5 billion tons of cement this year, Constantz said.

To power its new buildings and sustain its building boom, China constructs at least one coal-fired power plant a week. Each one belches out enough CO{-2} to cancel the benefits of every hybrid on U.S. roadways, said Constantz.

A CO{-2} molecule can travel from Beijing to San Francisco in less than a day through atmospheric circulation, he said. So even with California mandating that CO{-2} emissions fall to 1990 levels by 2020, a crisis remains.

"Carbon dioxide is a global problem, not a regional problem," he said.

As far as cost, Constantz estimates his cement would retail for $100 a ton versus roughly $110 for Portland.

The reason no one invented it before now, he said, is that people didn't truly understand the dangers of CO{-2} until less than a decade ago.

Skeptics question product

He has skeptics.

Portland cement has a track record of more than 100 years, and any new material would have to get incorporated into building codes, noted Rick Bohan, director of construction and manufacturing technology for the Portland Cement Association in Skokie, Ill.

And Tom Pyle, a Caltrans engineer who serves on the cement subgroup of Gov. Arnold Schwarzenegger's Climate Action Team, acknowledged that the technology is possible, but he still wants to examine Constantz's cement.

"We hope they have a carbon-reducing viable construction material," he said. "They need to show up with a bag of this so we can test it."

Constantz is confident he will prove himself. Initially, he proposes mixing his new invention with Portland cement to ease a conservative industry into a new product. Concrete bigwigs have invited him to speak about Calera cement at their annual World of Concrete in Las Vegas next February.

Power plant partnerships

Constantz envisions building cement factories next to power plants the world over. A team is scouting out U.S. locations. While Dynegy has supplied Constantz with some flue gas, it hasn't entered into a formal agreement.

"As we're looking into the future, we're very interested in technology that would help capture CO{-2} from the flue gases and turn it into a product that offers a benefit," said Dynegy spokesman David Byford.

It could be good for business. California has mandated emissions reductions. And Congress is working on legislation that would allow high polluters to buy credits from those with low emissions. Power plants would have a huge incentive to sequester their CO{-2} in cement.

But even if Constantz succeeds, the world would still need to do much more to fight CO{-2} emissions, said Chris Field, director of the department of global ecology at the Carnegie Institution for Science at Stanford. "It's a big, long complicated game," he said. "As we develop each new segment of the solution we need to embrace it and deploy it and work hard to develop the next segment of the solution."

Coral basis of idea

Big ideas can form in haphazard ways. The one for bone cement began during a televised football game, when Constantz read an osteoporosis article in the New England Journal of Medicine. Three weeks later, as he studied a coral reef, it occurred to him he could maybe synthesize coral skeletons in human bones.

His new cement mimics how coral reefs form, too. Coral uses the magnesium and calcium present in seawater to create carbonates much as he's using CO{-2} and seawater to make carbonate.

This latest invention took 18 months to conceive and execute. He feels it's one of the most important things he's ever done.

"Climate change is the largest challenge of our generation," he said.

 

Who is Brent Constantz?

Profession: An associate consulting professor in Stanford's department of geological and environmental sciences and founder of the Calera Corp. Created and sold three other companies - Norian Corp., Corazon Technologies Inc. and Skeletal Kinetics.

Education: UC Santa Barbara, bachelor's of science (1981); UC Santa Cruz, doctorate (1986)

http://sfgate.com/cgi-bin/article.cgi?f=/c/a/2008/09/02/MNGD12936I.DTL