Construction materials are emerging as a low cost carbon sink as chemists seek ways to tackle climate change.
The Intergovernmental Panel on Climate Change says that mankind will have to start removing 12bn.t of carbon dioxide (CO2) from the Earth’s atmosphere every year by 2050 if it wants to halt global warming.
Many experts believe that treating the greenhouse gas as a raw material that could be used to manufacture marketable products offers a viable way forward.
Its potential uses vary – from fuels to carbonated drinks. But among the plethora of applications, the built environment stands out as a key beneficiary.
Carbon-enriched rock, insulating foams, cement and carbon fibre structures are all being developed in the hope that they can lock away CO2 for a long period of time while aiding construction of our infrastructure and buildings.
While this may sound idealistic, proponents of these technologies say they are not cost prohibitive and are already quite close to market.
In March 2018, Econic Technologies, a spin-out from Imperial College London, opened a demonstration plant in Alderley Park, near Manchester, where it manufacturers precursors for the production of insulating foams from waste CO2 captured from industrial plants.
The company can replace up to 50% of the main conventional raw material, known as feedstock, for making polyurethane with CO2 . According to Econic head of sales and licensing Leigh Taylor the approach offers many benefits. In addition to sequestering CO2 the resulting polyurethane, also known as proplylene oxide, is cheaper than the conventional alternative and performs better in many aspects of its functionality.
In rigid foams, we have seen that not only do we get really good thermal properties. We also get good fire performance
“Propylene oxide is roughly $2,000 (£1,500) per tonne of raw material as feedstock, whereas carbon dioxide can be as low as £23 to £38 a tonne as feedstock,” Taylor tells New Civil Engineer. “Even the most pessimistic views of the cost of carbon dioxide following capture are still substantially lower than the cost of the conventional propylene oxide raw material.
Econic is designing its system to be easily incorporated into existing polymer manufacturing facilities, hoping to remove barriers to adoption.
“We believe that our technology and the commercial and technical proposition that we have stands on its own two feet regardless of any kind of subsidies or legislation that would facilitate adoption,” says Taylor.
“It’s not only benefiting the environment but it makes sense from the commercial point of view as well.”
When tested, the CO2-enriched foams perform better than standard alternatives in other areas, according to Taylor.
“In rigid foams, we have seen that not only do we get really good thermal properties, we also get a good fire performance,” he said.
The carbon-eating polymers can also be used in adhesives and coatings. Taylor believes that if 30% of the industry adopted Econic technology, the green polymers would sequester or prevent about 3.5M.tonnes of CO2 emissions per year, which equates to taking about 2M cars off the road.
“The insulation is going to be there for the life of the house,” says Taylor.
“We are talking about multiple decades. These products can really have an environmental benefit first and foremost because they reduce the energy demand of those buildings, and second by sequestering CO2 within their chemical structure.”
California-based start-up Blue Planet has even bolder plans. The company’s chief executive, serial Silicon Valley entrepreneur Brent Constantz, believes that a significant portion of the 55 gigatonnes of rock that is mined and used globally every year could be replaced by artificial rock made of CO2 emissions.
Blue Planet operates a pilot plant in California next to a large gas-fired power station. The firm takes the raw flue gas from the power station and dissolves it in water. The carbon from the solution is then deposited onto small pieces of rock waste, creating a thick layer of carbonate coating.
“In 1.t of limestone that we make, we have 440kg of CO2 that is permanently converted into carbonate and mineralised,” says Constantz.
Constantz believes that the company can offer rock aggregate to the construction industry for equivalent or even lower prices than those of mined rock.
The price of rock, Constantz says, depends largely on the distance from source.
If we take 20% of all the waste manufactured in Europe, we could capture 1M.t of CO2 per year
Blue Planet’s facilities would always be based next to large industrial plants, which are usually close to where most of the construction work takes place.
British firm Carbon8 Systems has been pioneering a similar approach since 2006. Its subsidiary Carbon8 Aggregates currently operates three plants in the UK, which each manufacture 70,000t of construction aggregate by carbonating industrial waste and contaminated soils using purified CO2 from flue gas from industrial facilities.
“In 1t of waste we can sequester 100kg of CO2,” says Paula Carey, Carbon8 Systems’ managing director. “If we take 20% of all the waste manufactured in Europe, we could capture 1M.t of CO2 per year.”
The carbon-enriched aggregate is used to manufacturing blocks, which could be used for various construction projects.
Carey says that although the price of Carbon8’s blocks is slightly lower than that of those made from natural stone, the company finds it difficult to persuade construction companies to take a risk with such a novel product.
“They think all aggregate needs to be like granite,” says Carey. “Our aggregate may not be as strong as aggregate that has formed in millions of years, but it still has a use in many applications, and has several other advantages, such as its light weight and good thermal properties.”
Blue Planet hopes that legislation might eventually help green materials break into the construction market. In California, the 2017 Buy Clean Act obliges state authorities to only award state infrastructure contracts to firms using low carbon materials
Although the Act does not so far cover rock and cement, Blue Planet hopes it eventually will.
The question is now whether investors will finance the development of green construction materials, helping entrepreneurs to scale up production to take advantage of the carbon-sequestering potential of the built environment.
Novacem, a spinout from Imperial College London, sets a sad precedent. The company’s carbon-eating cement was once hailed as a breakthrough. But the company failed to attract investors and folded in 2012. With the debate about climate change intensifying, one might hope green innovators of today stand a better chance.