Smart and stronger 3D printed concrete may be closer to reality after engineers created stronger concrete that is easier to print by adding graphene oxide to cement mixture.

Conducted by RMIT University and the University of Melbourne, the latest research examined the effects of graphene oxide on the printability and compressive properties of 3D printed concrete.

It found that the addition of graphene oxide gave the concrete electrical conductivity and increased the strength of  the concrete by up to 10 percent.

Graphene oxide is a very small ‘nanomaterial’ which is commonly used in batteries and electronic gadgets.

Research Supervisor and RMIT Associate Professor Jonathan Tran stressed that the research was preliminary in nature.

Nevertheless, he said that the breakthrough could help to revolutionise concrete use in two ways.

First, the electrical connectivity referred to above means that the addition of graphene could help to deliver a form of ‘smart’ concrete which is able to detect and monitor small cracks.

As things stand, current detection methods include ultrasonic or acoustic sensors. These are non-destructive and are widely used in construction to detect large cracks in concrete structures.

However, early detection of smaller cracks remains a challenge.

The equipment for these methods is often bulky, making it difficult to regularly use for monitoring very large structures such as bridges or tall buildings.

“But the addition of graphene oxide creates the possibility of an electrical circuit in concrete structures, which could help detect structural issues, changes in temperature and other environmental factors,” Tran said.

Beyond this, Tran said that the addition of graphene could pave the way to make 3D printed concrete more viable.

This could have beneficial impacts in terms of the cost and sustainability of construction.

As things stand, Tran says that current concrete structures are created using formwork – a process that involves creation of a mold into which fresh concrete mixture is poured.

This is labour intensive, time consuming and costly. It also generates large volumes of waste.

By contrast, 3D concrete printing saves time, money and labour. It also enables creation of more complex structures and reuse of some construction waste in cement-based materials.

Thus far, a limitation of 3D printed concrete involves concerns about its strength. Such concerns arise as the layer-by-layer printing which is associated with 3D printing can potentially lead to weaker bonds between each layer.

However, the research found that the addition of graphene oxide in concrete makes it easier to extrude. This creates better inter-layer bonding, which can help to maximise strength.

“Graphene oxide has functional groups on its surface, which are like sticky spots on the surface of a material that can grab onto other things,” Tran said.

“These ‘sticky spots’ are mainly made of various functional groups containing oxygen, which play a crucial role in facilitating its stronger bonds with other materials like cement. This strong bonding can improve the overall strength of the concrete.”

“However, more research is needed to test if concrete with graphene oxide can match or surpass the strength of traditionally cast concrete.”

Not Too Much

To maximise the strength of the concrete, the research indicates that it will be important to get the optimal mix in order to improve the bond between the graphene oxide and the concrete.

On this score, the results indicate that too much graphene may be counter-productive.

Indeed, the research tested two dosages of graphene oxide in cement. It found the lower dosage (0.015 percent of the weight of cement) was stronger than the higher one (0.03 percent of the weight of cement).

According to Tran, the addition of too much graphene oxide could impact the strength and workability of the concrete mix. This can lead to potential issues with printability, strength and durability.

“Concrete is a carefully balanced mixture,” he said.

“Adding too much graphene oxide can disrupt this balance, particularly the hydration process, which is crucial for concrete strength.

“Too much graphene oxide can impact the flow of concrete, making it harder to extrude and therefore creating a structure with more gaps between layers of concrete.

“Graphene oxide can also clump together instead of spreading out evenly, which can create weak spots in the concrete and reduce its overall strength.”

The study was published in Additive Manufacturing Letters. (DOI: 10.1016/j.addlet.2023.100157).

The research was led by RMIT PhD candidate Junli Liu. Phuong Tran, Thusitha Ginigaddara and Priyan Mendis are co-authors.

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