Concrete is the world’s #1 building material. While it is incredibly useful, it also has well-known limitations. This article will briefly review the background of concrete, as well as its drawbacks. This article will then briefly discuss graphene and what distinguishes large, thin and nearly defect free graphene flakes from other materials marketed as graphene. It will then discuss problems encountered with using sub-optimal quality graphene as an additive to improve concrete. This article concludes that large (>30 µm diameter), thin (1-5 atomic layers) and almost defect free (LTDF) graphene flakes can create a more robust concrete for high performance applications.
Background of Concrete
The oldest concrete discovered was the slab of a hut in present-day Israel from 7000 BC. The first concrete structures were made by Nabataea traders in 6500 BC in present day Syria and Jordan. The Nabataea used concrete for floors, housing structures and underground cisterns. The Romans were the first to make widespread use of concrete, using a mixture of volcanic ash, lime and seawater to form the mix. By 200 BC, the Romans used concrete in the majority of their construction. The quality of their concrete was such that, after more than 2,000 years, some Roman structures still stand.
Modern concrete is manufactured by mixing sand, gravel and cement with water and pouring the mixture into molds before it solidifies. Cement is made by roasting limestone, a rock composed of calcium carbonate, to drive off CO2 and leave behind calcium oxide. Cement is heated to 1400°C in a kiln, resulting in “clinker”. Clinker is the key bonding agent in cement that provides concrete’s structural integrity.
Concrete’s Limitations and Cause for Concern
While we all know concrete’s many contributions, concrete suffers from important physical drawbacks. Concrete has high compression strength but it is relatively weak because it has poor tensile and flexural strength. This means that it’s easy for concrete to chip and crack — damage which can easily grow and spread over time, as we can see everyday in our nation’s infrastructures. Concrete is also subject to scaling/flaking, buckling and spalling. Additionally, the manufacture of concrete has increasingly caused environmental concerns. The chemical reaction taking place during clinker formation – the conversion of limestone (or calcium carbonate, CaCO3) into calcium silicate (Ca2SiO4) – releases approximately 600 kg of CO2 for every tonne (1000 kg) of cement produced. “If the cement industry were a country, it would be the third largest carbon dioxide emitter in the world with up to 2.8bn tonnes, surpassed only by China and the US,” writes The Guardian.
Graphene Flakes: A Remarkable Additive Material
Most of us have heard of graphene and its superlative properties.
- Tensile strength (150,000,000 psi) – 200x stronger than steel
- Flexibility – bendable
- Thin – 1 million times thinner than a sheet of paper
- Light – 1 gram sheet would cover a soccer field
- Electronic properties – electrons move through graphene at close to the speed of light
- Heat conductivity – best material for conducting heat
- Electrical conductivity – nearly perfect conductor
- Invisibility – transmits 97% of light (glass window transmits 80%-90%)
- Impermeability – graphene is hydrophobic, enabling water filtration and purification
“What most people in the concrete industry are unaware of is that only LTDF graphene flakes possess all of these properties,” says Phil Van Wormer, Chief Commercial Officer of graphene technology company Avadain. “Research studies agree that graphene’s fantastic tensile strength begins at >30 µm in lateral flake size. While graphene is defined as 10 or fewer atomic layers, research has also found that to possess graphene’s optimal electrical and thermal conductivity, graphene flakes need to be 1-5 atomic layers with few (or no) defects.” In this article, we refer to LTDF graphene flakes as “high quality” because only this material possesses the full combination and range of graphene’s superlative properties. We refer to all other materials which are graphene but lack one or more of these essential qualities as “sub-optimal” graphene. Sub-optimal graphene materials include:
- Nanoplatelets (sometimes marketed as graphene nanoplatelets)
- Graphene Nanoparticles
- Graphene Oxide
- Reduce Graphene Oxide
Sadly, many companies are marketing graphitic materials and even graphite powder as graphene, leading The Graphene Council to warn of “fake graphene”.
How Graphene Can Enhance Concrete
“By integrating graphene into concrete, engineers and architects can create structures that require less material, while still achieving the same structural performance as traditional concrete,” reports The Graphene Flagship. “Graphene-enhanced concrete is 2.5 times stronger and 4 times less water permeable than standard concrete. It uses much less cement to deliver the desired strength. As a result, it is expected to reduce CO2 emissions by 30%.” The dramatic cut in CO2 emissions is particularly important for architects and others who have committed to cutting CO2 emissions but are having a tough time delivering on these commitments.
Britain’s Nationwide Engineering (NE), in conjunction with the University of Manchester, developed a method to mix graphene oxide into cement to achieve mechanical support and an active surface for the chemical reactions that occur during the cement hydration and hardening. According to NE, this mixture “used in real construction projects was up to 30-50% stronger than standard concrete. Subsequent lab tests have shown strength gains that surpass 100%.” As a result, the volume of cement required can be significantly reduced without impairing performance. It should be noted that the price of concrete is increasing while supply has decreased. Adding a tiny amount of graphene can not only improve concrete’s performance but also stretch the existing supply of concrete.
A range of sub-optimal graphene (predominantly graphene oxide) has been used to improve concrete, with varying results.
Tensile Strength
A recent survey of scientific literature reported surprisingly mixed results of using sub-optimal graphene to enhance concrete. For example, one study reported that the concrete exhibited an increase of up to 146% in compressive strength and up to 79.5% in flexural strength, as well as a 78% reduction in the maximum displacement due to compressive loading. Another study reported that graphite nanoplatelets (GNPs) were found to increase the tensile and flexural strengths of ultra-high-performance concrete (UHPC) by 40%-45% and 39-59%, depending on the type and quality of GNPs. Other studies have reported lesser and more problematic results. One finding was that higher doses of graphene materials led to a decrease in compressive strength, most likely because agglomeration of the graphene material caused by Van der Waals forces created weak zones in the concrete. Another reported result found no effect of graphene on flexural strength, most likely caused by the small size and aspect ratio of the sub-optimal graphene material that was used.
In contrast, LTDF graphene should outperform sub-optimal graphene materials because the large flake size reduces the amount of graphene required, as well as agglomeration risk, while conferring fantastic tensile and flexural strength.
Workability
It is important to place fresh concrete in forms as quickly as possible. Thus, “workability” is an important consideration. Studies have reported that sub-optimal graphene materials (especially graphene oxide) decrease the workability of concrete. One reason was the graphene utilized was hydrophilic and tended to agglomerate. This agglomeration not only hinders workability but can also cause weak zones in the concrete.
Since Avadain’s LTDF graphene is hydrophobic, we expect workability to remain similar or improved.
Durability
Graphene should be able to increase the durability of concrete structures. For example, it was reported that concrete containing sub-optimal graphene had better performance after 200 freezing and thawing cycles, evidenced by lower mass/compressive strength loss, as well as lower damage on the surface. The resistance of concrete to chloride ingress was improved by using a 1.5% dosage of sub-optimal graphene, which reportedly reduced water permeability, chloride diffusion coefficient and chloride migration coefficient by 80%, 80% and 40%, respectively. Another study reported that concrete’s loss of mechanical strength after exposure to 800 °C can be reduced from 70% to 35% with the addition of graphene. Because of the large surface area and hydrophobicity of Avadain’s LTDF graphene flakes, we expect to see better results with a lower additive amount of LTDF graphene flakes.
Conclusion
Graphene is widely recognized as a game-changer for the construction industry. Graphene-enhanced concrete can significantly improve this incredibly useful material by adding tensile and flexural strength, durability and resistance to scaling/flaking, buckling and spalling. At the same time, graphene-enhanced concrete can reduce the amount of concrete needed by an estimated 25%-35% — a huge step in decreasing CO2 emissions and stretching the supply of concrete without sacrificing performance. However, only LTDF graphene flakes can deliver the optimal properties.
There are many reports of disappointing results using materials marketed as “graphene” to enhance concrete. This is largely due to the use of sub-optimal graphene or graphitic powder. Such materials lack LTDF graphene flakes’ incredible tensile strength and hydrophobicity. Sub-optimal graphene materials, such as graphene oxide, are hydrophilic, creating agglomeration which poses a significant impediment to workability and can create dangerous weak zones.
LTDF graphene flakes can revolutionize the construction industry, making possible new structures that use less concrete, perform better, last longer and are significantly more eco-friendly. e behind calcium oxide. Cement is heated to 1400°C in a kiln, resulting in “clinker”. Clinker is the key bonding agent in cement that provides concrete’s structural integrity.
