We use a lot of concrete. 4.4 billion tons per year to be exact. Since concrete is such a popular building material, it matters that concrete also has a bad environmental impact. In this article, we will be going over why concrete has such a high carbon footprint and some of the methods to make low carbon concrete.
Concrete Is a Top Producer of CO2 Emissions
Concrete has a large impact on the environment. The significant increase in the “urban heat island” effect and the creation of excess runoff are some of the issues, but they aren’t the biggest one.
The biggest issue is the carbon dioxide emissions. Worldwide, concrete production is responsible for up to 10 percent of annual global carbon dioxide emissions. That is almost equal to the amount carbon dioxide emissions from residential heating and electricity production for every person on the Earth (11.3 percent of annual global carbon dioxide emissions).
Low Carbon Concrete
We have been using concrete since ancient Roman times. It’s unlikely that we will come up with a completely new substitute for concrete. What we can expect to see is new technology to reduce the carbon footprint of concrete production – making low carbon concrete.
Currently, concrete is made by mixing Portland cement, water, and aggregate. It’s the Portland cement that is responsible for the fact that every ton of cement equals 900 kg of carbon dioxide emissions.
To make Portland cement, clinker is first made by heading limestone and clay to 1,450 °C. This not only produces carbon dioxide through the burning of fossil fuels, but carbon dioxide is also one of the byproducts of the chemical reaction.
So far, since Portland cement is the key ingredient to making concrete, it has been hard to reduce the carbon footprint of this industry.
Where Is Research Leading?
The methods to lower the carbon dioxide emissions of the concrete industry range from changes in the process to alternative fuels.
The very first step to low carbon concrete actually happened three decades ago. Over the years, there has been consistent improvement in the manufacturing. Most impactful was moving the production of concrete from wet manufacturing to dry.
Another promising area of research is reducing the amount of Portland cement needed by using an additive, known as secondary cementitious materials. Fly ash, ground granulated blast-furnace slag, calcine clays, volcanic ash, and glass fibers are secondary cementitious materials that show promise as a binder.
Yet another avenue that researchers are heading down is reducing the amount of cement needing in concrete. Traditionally, concrete designs have been over designed, and margins of safety were added in at every step.
New guidelines are reducing this tendency to overdesign, while not increasing the risk. Additionally, designers have started to view cement as a material to be used lightly. New calculators give engineers and architects the ability to determine if more carbon savings are possible in their design.
This is a worldwide effort. In the U.K. the precast concrete producer Laing O’Rourke is being given a grant from the government to research how to make precast concrete less carbon intensive. Part of this research will include the use of low carbon concrete for precast concrete production.