Green Concrete is a technological response to the estimates that the manufacturing and use of traditional Ordinary Portland Cement (OPC) accounts for 5% of global emissions of carbon dioxide. Traditional concrete is manufactured through heating pulverized limestone clay with sand to 2,600°F (1,450°C) and generates carbon dioxide from the heating and the carbon-heavy limestone. A metric ton of cement releases 650 to 920 kilograms of CO2 .
The form Green Concrete takes depends on the philosophy a manufacturing company follows. This includes the inclusion of new materials, including graphene, to increase the strength and durability of concrete and reduce the amount needed in construction; and it can mean changing the manufacturing process of concrete to reduce the carbon emissions and materials necessary for the process. Concrete can also be recycled into sub-base material for construction or into decorative recycled elements for floors, counter-tops, and desks.
Reduced Carbon-emissions concrete is a process to reduce and even sequester carbon-emissions in the concrete manufacturing process.
For the reduction of emissions, this includes LafargeHolcim's ECOPact concrete which is manufactured using a less carbon emissions and their Susteno concrete which recycles granulate from demolished buildings. Other traditional concrete manufacturers work to reduce carbon footprint of their manufacturing plants to reduce the overall carbon footprint of their product. This includes the use of biofuels for firing their plants or delivery trucks.
Other technologies include carbon sequestration in the process of concrete manufacturing. CarbonCure Technologies leads one approach to this where they capture carbon dioxide from industrial processes (including the kilning of limestone in the manufacturing of traditional concrete) and inject the capture carbon dioxide into water used in the construction of the concrete. This method can improve the concrete's strength by 10 to 20 percent, but is estimated to reduce the carbon emissions of the concrete by only 5 percent.
Solidia Technologies uses a similar carbon sequestration as CarbonCure Technologies, where they mix cement powder with sand and fill open spaces with water and sequestered carbon dioxide. The process reacts to make calcium carbonate and silica and hardens into concrete estimated to be 10 to 25 percent stronger and more resistant to cracking in freezing and thawing environments.
Concrete waste material and unused concrete can be recycled into different uses. Companies like U.S. Concrete recycle unused concrete returned to their plants for fresh concrete or they will pour unused concretes into blocks to be sold in block form. Others will recycle old and broken concrete for sub-base material in new construction sites. Or companies can use recycled materials such as glass and porcelain for decorative concretes or concrete sub-base material.
Insulated concrete and pervious concrete are other types of concrete often considered green concretes. The construction or manufacturing process of these concretes do not make the resulting material "green" or "clean", rather their characteristics help construct green buildings.
Insulated concretes are used to control the temperatures in buildings to allow for less heating or cooling and overall energy use reduction. These usually are insulating concrete forms, insulated cast-in-place concrete, or insulated tilt-up and precast concrete structures.
Pervious concrete is a type of porous concrete used to allow water from precipitation or other sources to pass directly through, reducing run-off and allowing groundwater recharge. This type of concrete is traditionally used in parking areas, residential streets, pedestrian walkways, and greenhouses. By allowing water to pass through them, pervious concretes reduce wash-out from water build-up and reduce the possibility of flooding. They are considered a sustainable building material and are used by builders to protect water quality and help buildings receive LEEDs certification.
Mixing concrete with non-traditional materials is a method of innovation to reduce the amount of concrete necessary. This approach includes using graphene, fly ash, and ground granulated blast furnace slag in the construction of concrete. Concretes using fly ash or blast slag are also known as supplementary cemetitious material concretes.
The use of graphene has been done in laboratory conditions and resulted in concrete expected to be more durable — with claims ranging from greater protection against water and helping protect against cracks forming — and with the ability to trap and store greenhouse carbon dioxide or break down pollutants.
Other companies are manufacturing concrete alternatives intended to be used in place of concrete. Suggested materials include mass timber and bamboo, both of which have lower carbon footprints than traditional concrete.
Nexii is a manufacturer of their proprietary product Nexiite – a heavy-concrete or concrete-like product – which has a lower carbon emission than traditional concrete, and Nexii says is faster to manufacture and deploy than traditional concrete and is less expensive to manufacture. Nexii says their materials are suitable for commercial, institutional, industrial, mixed-use, multi-family residential and single-family residential buildings and for retro-fitting existing buildings.
Marin Country, California has introduced The Marin County, California Low Carbon Concrete Code, addressing the negative environmental externalities of concrete and mandating low carbon concrete specification to the Marin County Building Code.
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Materials and Technologies for Low-Carbon Concrete
- Clean technologyA process, product, or service which reduces negative impacts on the environment while offering competitive returns for investors and customers. Clean technologies provide solutions which reduce energy usage, use sustainable resources, or protect the environment.
- ConcreteComposite construction material
- Carbon sequestrationCarbon sequestration is the capture or removal of atmospheric carbon dioxide to mitigate or reverse climate change.
- CarbonCure TechnologiesCarbon capture and storage company founded in 2007 and based in Dartmouth, Nova Scotia, Canada. CarbonCure Technologies Inc. provides carbon dioxide sequestering technology to concrete plants in a system for recycling carbon dioxide waste from industrial emitters and incorporating it into concrete products.
- Solidia TechnologiesSolidia Technologies is a Piscataway, New Jersey-based technology company offering solutions for using CO2 for manufacturing construction and industrial products.
- LafargeHolcimLafargeHolcim is a Jona-based manufacturer of building materials founded by Lafarge.
- GrapheneGraphene is a Bi-dimensional crystalline structure of carbon
- U.S. Concrete, IncU.S. Concrete is an American company that operates and sells concrete and related construction materials within the United States.
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