Posted on February 01, 2024
Ordinary Portland cement (OPC) requires high-temperature calcination of limestone. It is possible to use various emissions-reducing pozzolans in concrete. Fly ash comes from coal-fired power plants. Ground granulated blast furnace slag (GGBFS) comes from steel mills. Another SCM is metakaolin derived from kaolin. Brazil and Malaysia are major sources for the naturally occurring clay.
Production of highly reactive metakaolin also requires calcination, but at much lower temperatures. The difference is stark: about 750º C rather than about 1400º C. Recent research explores the addition of graphene to the metakaolin for enhanced concrete performance.
Geopolymer Concrete Overview
Graphene-infused metakaolin is an option in the production of geopolymer concrete. Geopolymer formulations rely on chemical reactions rather than heat. An alumina silicate matrix that is alkali-activated.
This type of concrete offers important advantages like reduced emissions and improved performance. It also saves water, preserves virgin resources, and reduces landfill use.
Other advantages include:
Extreme heat resistance (starts liquid phase at 1,800°F)
High resistance to chlorides
Holds up during freeze/thaw cycles
Resistance to cracking
As a result, this specialized material is used in a variety of demanding applications. It isolates nuclear and toxic waste, and it serves as a fireproofing spray. It is also a robust construction solution in both salty and frigid environments. Finally, it performs well in seismic zones.
An Expanding Market
Spurred by the quest for sustainability, the use of geopolymer concrete is expanding. Mordor Intelligence estimates the global geopolymer concrete market at $11.4B in 2023. By 2028, the research firm projects a $41.3B market, representing an impressive CAGR of 29.3%.
Brisbane West Wellcamp Airport (BWWA), Toowoomba, Queensland, BWWA opened in 2014. At the time, it represented the world’s largest deployment of geopolymer concrete. Heavy-duty geopolymer concrete 17 inches thick is capable of supporting 747 cargo jets. The project consumed more than 100,000 tons of the material. Designers specified geopolymer concrete because of it high tensile strength, low shrinkage and excellent workability.
What are Metakaolin and Graphene?
In brief, Metakaolin is an increasingly popular pozzolan, while graphene is proven to strengthen concrete.
Metakaolin
Metakaolin is the anhydrous calcined form of kaolinite (clay). In concrete, it serves as a supplementary cementitious material (SCM). It is produced from kaolin clay via calcination. Lower temperature production drives interest in using it to reduce emissions. In fact, it takes tens times the energy to produce an equivalent amount of OPC. White metakaolin yields a lighter colored product. Metakaolin particles are smaller than cement ones.
One analyst sees the global metakaolin market achieving annual revenues of $1.1 billion by 2028. That represents an average growth rate of about 5% per year.
Graphene
Graphene is a two-dimensional form of crystalline carbon appearing in a hexagonal lattice. In 2004, researchers first isolated graphene at the University of Manchester. Subsequently, Andre Geim and Konstantin Novoselov received the 2010 Nobel Prize in Physics “for groundbreaking experiments regarding the two-dimensional material graphene.”
Graphene possesses remarkable qualities. By weight, it is stronger than steel. It conducts both heat and electricity with great efficiency. Columbia University researchers cite it as the world’s strongest material. This is largely the result of robust covalent carbon-carbon bonds and defect-free graphene monolayers.
Graphene oxide (GO) comes from the chemical exfoliation of graphite. GO improves the mechanical properties and microstructure of concrete. It is effective in limiting nanoscale cracking. A 0.05% concentration improves the flexural strength of ordinary Portland cement (OPC) by 41 to 59%. It also improves compressive strength by 25–33%. In a self-compacting concrete formulation, researchers found that GO increased compressive strength by 17%, tensile strength by 40%, and flexural strength by 28%.
Grandview Research sees the global graphene market expanding at a CAGR of 46.6% through 2030. Revenue should increase from $250.7M in 2023 to $3.75B in 2030.
Why Infuse Metakaolin With Graphene?
Metakaolin aluminosilicate formulations may lose mechanical strength after exposure to high temperatures. Graphene infusion helps to mitigate this challenge. Producers deploy graphene oxide as a “nano reinforcement in cementitious composites as a filling, crack-arresting agent, and nuclei for cement hydration.”
Infusing metakaolin formulations with GO speeds electron transfer. It also accelerates substance transformation in the alkali activation reaction. It promotes the growth of geopolymer gel, reducing porosity and improving bending strength.
Graphene-infused metakaolin takes the idea of geopolymer concrete to another level. For example, it improves splitting tensile and flexural strength. This reduces the volume of concrete required for a given project.
Other advantages include:
Water repellency
Efflorescence control
Use plasticizers to improve workability
Selectively accelerate or retard setting times
Future of Metakaolin Concrete
Current sustainability trends suggest a bright future for graphene-infused metakaolin concrete. The green revolution will limit future access to certain popular SCMs, driving interest in metakaolin blends. Fly ash from coal-fired power plants is a prime example. Coal use declines as such plants close. In the United States, coal use declined 62% from 2008 to 2023. In January 2019, coal’s share of U.S. power stood at 29.0%. Four years later, in January 2023, it was just 18.2%.
Given the proliferation of emissions initiatives, metakaolin concrete will garner attention for the foreseeable future. Researchers now explore the benefits of infusing it with graphene. Compounds like graphene oxide improve strength, thus reducing emissions by reducing the amounts required. Further research will examine how varied formulations impact performance.
About PACA
The Pennsylvania Aggregate and Concrete Association (PACA) reports on industry innovation through SpecifyConcrete.org. Posts are for two primary audiences: PACA members and the general public.
The team at PACA welcomes any questions you may have about your upcoming concrete projects. Please contact us at your convenience.
