How will graphene change construction?
Created By RISC | 1 week ago
We saw in the last post how graphene has extraordinary strength, thinness, and conductivity for heat and electricity.
But how will graphene be used, especially in building?
Concrete is the main material in construction, used in every building, house, bridge, tunnel, and road. It’s the planet’s top man-made resource. Concrete has 3 components: coarse aggregate, fine aggregate, and water. Cement is also a big factor in global pollution, accounting for 8% of global CO2 emissions. If cement manufacturing were a country, it would be the world’s 3rd largest carbon emitter, trailing only China and the United States.
Concrete’s properties usually depend on the type and quantity of cement, coarse masses, fine masses of sand, and gravel. But adding graphene could boost efficiency and reduce the use of cement.
So how does graphene enhance concrete?
First, it speeds up hydration (nucleation effect), helping the reaction between cement and water. Calcium silicate hydrate (Ca-S-H) is a new compound that improves the strength of concrete against compressive forces. When dispersed in cement paste, its small size with high specific area can help stimulate the hydration reaction, resulting in an increased amount of Ca-S-H.
Second, it can reduce porosity in composite concrete structures (nano-filling effect). As graphene is so small, it can help to fill gaps inside the cement paste. This allows for a reduction in the number and size of pores in the structure. Conventional cement pastes have a highly porous structure and crack after 28 days of curing, whereas cement pastes containing 0.05% graphene have less porosity and don’t crack. The cement paste's compactness and consistency will aid in compressive strength.
Third, chemical bonding between graphene, cement particles, and compounds produced by hydration reactions increase strength and adhesion (bonding effect). The 2 bonds are an ionic bond between the hydrated compound (Ca-S-H) and the oxygen functional group on graphene oxide, and a hydrogen bond between water molecules in cement, Ca-S-H, and hydroxyl groups on graphene oxide. These chemical bonds will strengthen the concrete.
Finally, graphene prevents the formation and spread of small cracks (toughening effect). When concrete is subjected to compressive stress, the force is transmitted to graphene, which is a very strong material capable of absorbing the force and distributing it to different parts of the concrete. This helps prevent cracking and crack propagation. Adding 0.02-1% graphene to concrete can significantly improve its mechanical properties such as bending, compression strength, and stretching. Furthermore, graphene reduces water absorption by up to 80% and increases durability for longer use.
Graphene can improve the quality of building materials. But it remains more expensive than other chemicals. So graphene is still rarely used in composite concrete. But we’ll certainly see more of it in the future.
Story by: Supunnapang Raksawong, Materials Researcher, RISC
Youli Lin and Hongjian Du. Graphene reinforced cement composites: A review, Construction and Building Materials. 265 (2020) 120312.