Cement is the most widely consumed material globally and the cement industry accounts for 8% of human-caused greenhouse gas emissions. Scientists worldwide are working tirelessly to find viable and greener solutions.

North-western University’s McCormick School of Engineering has recently created a more durable “smart cement” which is created by introducing nanoparticles into ordinary cement. While the researchers have believed for some time that their nano-infused cement could help to reduce the carbon footprint of cement composites, they had little knowledge about its impact on fracture behaviour.

Assistant Professor of Civil and Environmental Engineering, Dr Ange-Therese Akono’s laboratory investigates fracture events in complex materials using fundamentals of nanotechnology, materials science and theoretical and applied mechanics.

A research breakthrough

“The role of nanoparticles in this application has not been understood before now, so this is a major breakthrough,” said Dr Akono. “As a fracture mechanics expert by training, I wanted to understand how to change cement production to enhance the fracture response.”

Traditional fracture testing, in which a series of light beams is cast onto a large block of material, involves a lot of time and materials and seldom leads to the discovery of new materials. By using an innovative method called scratch testing, the researchers were able to form predictions on the material’s properties in a fraction of the time.

The method tests fracture response by applying a conical probe with increasing vertical force against the surface of microscopic bits of cement. Akono said this approach requires less material and accelerates the discovery of new materials.

“I was able to look at many different materials at the same time,” she said. “My method is applied directly at the micrometre and nanometre scales, which saves a considerable amount of time. Based on this, we can understand how materials behave; how they crack, and ultimately predict their resistance to fracture.”

Fracture resistance

Predictions formed through scratch tests also allow engineers to make changes to materials that enhance their performance at the larger scale.

Graphene nanoplatelets were used to improve the fracture resistance of ordinary cement. Graphene is rapidly gaining in popularity as a key component in forming smart materials. Incorporating a small amount of the nanomaterial was also shown to improve water transport properties including pore structure and water penetration resistance.

The researchers now want to gain a better understanding of the long-term performance of the material. “For instance, if you have a building made of carbon-based nanomaterials, how can you predict the resistance in 10, 20 even 40 years?” Akono asks.

Other studies
• Graphene, the wonder material discovered at the University of Manchester by Andre Geim and Konstantin Novoselov, has been shown to strengthen cementitious materials including concrete at molecular level.
• Graphene-reinforced concrete has greater compressive strength and water resistance (due to the low permeability of graphene). Scientists at Rice University recently demonstrated a process to convert waste from old rubber tyres into graphene which can, in turn, be used to strengthen concrete.
• Meanwhile, a joint venture between graphene specialists at the University of Manchester and alumni-led construction firm, Nationwide Engineering, has developed a product that could revolutionise the concrete industry and its impact on the environment.
• In a similar vein, researchers from the University of Tokyo have developed a new method of producing concrete without cement. Their technique offers a way for the construction industry to reduce its carbon emissions, as well as offering potential for building on the moon and Mars.
• A five-year University of British Columbia study has concluded that recycled concrete can perform as well as – and in some cases better than – conventional concrete.
• Another alternative mix proposed by researchers for making concrete is to swap out the commonly used sand for a clay material that can easily be obtained as waste from excavation works, resulting in a greener form of concrete.

By 2050, the United Nations has predicted that two-thirds of the world’s population will be concentrated in cities. Given this upward trend toward greater urbanisation, cement production is expected to skyrocket and with it, the associated carbon emissions.

We are anxiously keeping an eye on each of these initiatives. Finding a green concrete that employs lighter, higher-performing cement will reduce its overall carbon footprint by extending maintenance schedules and reducing waste. This is vital to ensuring the health of our planet and its inhabitants.

We acknowledge Engineering and Technology for some of the information contained in this article. Visit them for more information at https://eandt.theiet.org

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