Graphene a key driver in race for green cement and concrete

Like almost every industry around the world, reducing carbon emissions is a key focus for the cement and concrete sector. Chasing a 25 per cent reduction target for concrete and 20 per cent for cement by 2030, the quest for solutions is gathering plenty of momentum – and graphene is proving its worth at multiple stages across the supply chain.??

The race for greener cement and concrete solutions is moving at full speed.

Industry is looking for more than just laboratory research and is crying out for commercially viable options to help reduce the carbon footprint synonymous with cement and concrete manufacturing and usage.

Over the past 30 years, concrete usage has increased exponentially, largely driven by China’s economic boom. In 2020, the world consumed 14 billion cubic metres – or 4.2 billion tonnes – of concrete, according to the Global Cement and Concrete Association.

That’s the same association that pledged to achieve a 25 per cent reduction in carbon emissions from concrete, and 20 per cent reduction in cement, by 2030, and total net zero by 2050. To do so requires emissions to be addressed at every stage in the cement and concrete supply chain, from mining and quarrying of raw materials, to production processes, to the ways in which structures are designed and built.

Concrete is the second most used commodity in the world behind water. It is an essential product of the built environment and as the population continues to increase, so does the volume of concrete used, and the amount of cement required to make that concrete.

And therein lies the challenge, because for every tonne of cement manufactured, between 650kg and 900kg of carbon dioxide (CO2) is produced. That is the key reason the cement and concrete sectors are responsible for some 8 per cent of all global CO2 emissions.

Part of the concrete industry’s strategy to hit its 25 per cent target relies on cement manufacturers to provide greener products.?

Calcination and emissions

One of the primary sources of emissions is the heating of calcium carbonate (sourced predominantly from limestone). ?

The heating process fuses the calcium carbonate into calcium silicates, or clinker, and CO2. Clinker is the key bonding agent in cement and is exceptionally good at providing the binding properties essential to make concrete structurally sound.

What is more, the process requires extremely high temperatures of up to 1,450C, and reaching such temperatures needs a significant amount of energy input which, under current manufacturing processes, typically means fossil-fuel generated energy.

All the CO2 from this process of heating and fusing is an unwanted by-product, and most is released into the atmosphere.

A key focus for emission reduction is to reduce the amount of clinker required in favour of replacement products, known as supplementary cementitious materials, or SCMs. But a longstanding problem is the majority of SCMs do not provide the same binding characteristics as clinker, meaning concrete made from lower clinker factor cement has reduced performance in many applications.

Graphene’s role

For some time, it has been relatively well understood that small additions of pristine graphene can improve the performance of low clinker factor cements. Essentially, graphene serves as a replacement binding agent, thus allowing more SCMs and less clinker to be used to deliver equivalent or improved performance outcomes.

First Graphene and its industry and research partners initially focused on options to incorporate PureGRAPH? into concrete products through admixtures, developing a range of formulations to facilitate consistent incorporation into the concrete mix.

Initially, the challenge was to find a way to evenly distribute graphene through the concrete mix. In addition to revising mechanical processes, it was discovered larger platelet sizes could be incorporated more readily than smaller ones. For that reason, First Graphene developed its unique PureGRAPH? 50 product, which is made from 50-micron graphene platelets and is the optimised solution for use in cement and concrete applications.

However, incorporating admixtures does require additional steps in the concrete production process and alterations to the current “recipe”.

More recently however, the focus has moved further upstream to enable PureGRAPH? 50 to be added to Ordinary Portland Cement. This serves a number of key purposes.

It enables cement manufacturers to pursue the GCCA’s 2030 target of a 20 per cent reduction in emissions from the cement sector, while providing greener products to concrete companies that offer the same or improved performance characteristics to their existing, higher clinker factor offerings. That in turn provides those companies with a pathway towards achieving the 25 per cent emission reduction target for the concrete sector.

The graphene enhanced cement also enables concrete suppliers to create mixes with the right structural integrity without needing to change existing production methods, as may be required when using admixtures.

The most efficient way to incorporate the PureGRAPH? 50 into cement is via grinding aids, used at the final milling stage of cement manufacturing to reduce particle size. Graphene-enhanced grinding aids have also shown initial promise in reducing clumping of cement over time.

Other advances in cement and concrete

There are multiple areas being simultaneously researched, trialled and commercialised as the industry seeks to rapidly achieve emission reductions.

A recent study by the University of Wollongong and an Australian domestic water, sewerage and drainage statutory authority has confirmed the benefits of using of PureGRAPH? to enhance durability of concrete and mortar exposed to corrosive water environments.

In the peer-reviewed paper, results indicated that based on the mix formulation for wastewater infrastructure, graphene-enhanced concrete and repair mortar led to between 10 and 20 per cent improvement in 28-day compressive strength.

The best addition rate was found to be 0.02 – 0.1 per cent of PureGRAPH? 50, the product variant most suitable for dispersing into cement and concrete applications.

Importantly for use in such harsh conditions, sulphate and chloride resistance was shown to be substantially improved, in addition to a reduction in water permeability with graphene-enhanced concrete and mortars.

New Zealand-based GtM Action announced the release of its HexMortarTM product, a PureGRAPH? enhanced dry mortar used in shotcrete and pumping applications.

HexMortarTM provides improved flexural and compressive strength of 20 and 27 per cent respectively, leads to less rebound - hence less waste - and is equally as workable as other products for the same applications. The opportunity for reduction in CO2 emissions comes from the combination of those factors.

A trial is also underway to investigate how PureGRAPH? can improve the performance characteristics of recycled concrete products. Traditionally, old concrete has been crushed and used in applications such as road base, but there is far more supply than demand. If graphene can improve performance characteristics, there is potential for recycled product to be reformulated for a wider range of concrete applications.

At the same time, First Graphene commercial partners continue to research, develop and release to market a range of grinding aid and admixture solutions, all focused on emission reductions and performance enhancement.

Emission reduction along the supply chain

By far, the most direct and significant reduction in CO2 emissions can be achieved by reducing the amount of clinker required – and therefore the amount of clinker produced, and energy required to produce it.

Commercial scale trials are continuing to confirm the amount of clinker reduction that can be achieved, which in turn will provide specific metrics on reduced carbon emissions.

However, given graphene delivers a range of benefits to the overall performance of concrete, including improvements to flexural and compressive strength, improved thermal properties that lead to reduced cracking, and greater resistance to chemical and environmental degradation, the functional life of concrete products can also be improved. That means an overall reduction in the amount of concrete being produced globally each year.

Additionally, the improved strength could lead to a reduction in thickness requirements for concrete panels and slabs, further reducing overall volumes.

If improvements in the performance of recycled concrete can be achieved, even more reduction in the amount of new concrete – and therefore new cement – could follow.

In other words, there are opportunities for emission reductions to be realised from the very beginning of the supply chain to the very end.

Hitting the target

While a 25 per cent reduction in concrete CO2 emissions within the next eight years may seem a lofty target, First Graphene’s PureGRAPH? enhanced grinding aids offer significantly more effective clinker usage for reduced CO2 cements.

The outcomes from longer-lasting, more durable concrete are less tangible and may only become specifically apparent with the passing of time.

However, with a further focus on reducing energy consumption and converting to renewable energy sources in the production and use of cement and concrete, there’s every opportunity to achieve, if not exceed, that 25 per cent and help the industry on its course to hit the ultimate net zero goal.