Here’s how researchers are considering fly ash, recycled phones and slag to lower global carbon emissions from cement

• The production of cement accounts for 8% of all carbon emissions in the world.
• The demand for cement has increased like never before and it is only going to rise.
• Researchers are working on developing low-carbon alternatives to traditional cement.

Concrete is one of the most used materials in the world, with 30 billion metric tons being used every year. It is being used to construct and repair bridges, roads, highways, high-rise buildings, sewage systems, homes and more.

The problem isn’t with the usage of concrete, but the emission of carbon that accounts for roughly 8% of the world’s carbon dioxide emissions. As per a report in c&en, we are using more concrete per capita than ever in human history thanks to the infrastructural development taking place in Asia and Africa, and upgrades to ageing structures in Europe and the Americas.

Most of the carbon emissions from concrete are caused during the process of making its binding component, cement. Researchers are exploring ways to bring down the carbon emission by using waste materials such as fly ash, slag and recycled phones. In this article, we take a look at how cement is made, the alternatives that are being researched to reduce carbon emissions and its overall impact on the environment.

The method of making cement needs reconsideration

Cement, which is the base material used in making concrete, is created by heating powdered limestone, which is found in abundance, along with clay at roughly 1,450 °C in a kiln. It is then ground and mixed with gypsum, which prevents the powder from clumping and controls its subsequent reaction with water.

This process is said to produce 800kg of carbon dioxide for every metric ton of cement. To make concrete, suppliers mix cement with sand and gravel, before adding water to trigger a chemical reaction that converts the paste into a rock-solid building material.

Cleaner alternatives are the way to go

To reduce the amount of carbon dioxide, manufacturers will need to use less limestone and replace it with a low-carbon alternative such as fly ash. Fly ash is the by-product of coal combustion done at power plants.

The fly ash can be found accumulated around the coal-fired power plants and is said to have enough supply to make cement for 130 years at its current usage. The fly ash not only helps in lowering carbon emissions but also adding durability to the concrete.

The problem with fly ash is that not all of it can be used for making cement due to the difference in chemical composition that can meet the standards of making cement. Another reason is the decline in coal-power plants as they are now being fueled by natural gas.

Slag
Another alternative that is being considered is slag. It is calcium aluminosilicate, the by-product of smelting iron ore during steelmaking. Slag is known to emit lower carbon during the process of making cement-like material, than traditional cement.

There are manufacturers across the globe like Mexico-based Cemex, that are offering concrete containing both slag and fly ash. As per Davidé Zampini, Cemex’s head of R&D, the company’s products help reduce carbon emission by up to 60% by using waste products.

But according to a researcher at Swiss Federal Laboratories for Materials Science and Technology (EMPA), there isn’t enough slag or fly ash to meet the industry’s requirement.

Recycled Phones
Researchers are now looking at using by-products of recycled cellular phones to use as a binding material for cement. The EMPA group has teamed up with a company that uses a metallurgical process to remove precious metals from phones leaving behind a residue that contains calcium, silicon, aluminium, and iron.

This residue can be used as a carbon dioxide-free cement binder. As per the report, the EMPA team is studying how to best use the residue material in cement formulations.

Impact on the environment

If the researchers find a definite low-carbon alternative to traditional cement with similar properties, it would reduce the environmental impact caused by high carbon emissions. Since the demand for cement is not going to fade away, it will be important that research carries on in this field until a certain alternative is found.

If slag and fly ash are not enough, the by-products of recycled cellular phones are only going to grow in the near future.

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