Concrete is the second most-consumed resource on Earth after water, with a global production that exceeds 16 billion metric tons per year. One way to decrease the material's carbon footprint: Make sure it doesn't break.
By introducing nanoparticles into ordinary cement, a Northwestern University lab, led by civil and environmental engineering professor Ange-Therese Akono, has formed a more durable, multi-functional building material.
The Northwestern team's research was published this month in the journal Philosophical Transactions of the Royal Society A .
Akono, the lead author of the study, examined the particles' impact on fracture behavior.
With an innovative analysis method called "scratch testing," Akono investigated two types of nanoparticles, and their impact on cement strength. Graphene nanoplatelets – both open flakes and rolled-up tubes – demonstrated high fracture toughness, due to their larger surface area and thickness.
“The role of nanoparticles in this application has not been understood before now, so this is a major breakthrough,” Akono said in a recent news release . “As a fracture mechanics expert by training, I wanted to understand how to change cement production to enhance the fracture response.”
Akono’s lab efficiently formed predictions on the material’s properties in a fraction of the time. The scratch test measures fracture response by applying a conical probe with increasing vertical force against the surface of microscopic bits of cement. Fracture toughness is then computed using a nonlinear fracture mechanics model.
Akono, who developed the novel method during her Ph.D. work, said the process requires less material and accelerates the discovery of new ones.
“I was able to look at many different materials at the same time,” Akono said . “My method is applied directly at the micrometer and nanometer scales, which saves a considerable amount of time. And then based on this, we can understand how materials behave, how they crack and ultimately predict their resistance to fracture.”
Graphene nanoplatelets were shown to improve the resistance to fracture of ordinary cement. Incorporating a small amount of the nanomaterial improved water transport properties, including pore structure and water penetration resistance, with reported relative decreases of 76% and 78%, respectively.
Through scratch testing, the nanomaterials bridged nanoscale air voids, leading to pore refinement, and a decrease in the material's porosity and the water absorption. The study noted a positive correlation between the fracture toughness and the mass fraction of nanofiller for graphene-reinforced cement.
Learn more about graphene-reinforced cement. Read the report .
In a short Q&A with Tech Briefs below, Prof. Akono explains what makes this kind of cement so important as the population expands.
Tech Briefs: What makes the cement “smart?” so to speak?
Prof. Ange-Therese Akono: The cement is smart due to its broad multifunctionality. Some potential applications include structural health monitoring, electromagnetic interference, and portable batteries. These applications are possible thanks to a wide array of unique properties such as electrical conductivity, magnetic conductivity, piezoelectric properties, high water penetration resistance, high mechanical performance, and low carbon footprint.
Tech Briefs: Can you provide a few specific details about what the “nanoparticles” are? What is special about these nanoparticles, and what inspired you to add them and go with this approach?
Prof. Ange-Therese Akono: The nanoparticles are carbon-based nanomaterials such as graphene nanoplatelets or carbon nanofibers. What is unique about these nanoparticles is their high strength and their nanoscale structure.
Basically, the idea is to learn from nature. Natural materials such as bone are intrinsically multifunctional, strong, and tough, thanks to a sophisticated architecture that integrates several levels of structural hierarchy along with a hybrid composition, organic-inorganic. In this case, we choose our nanoparticles to replicate that multiscale structure and organic-inorganic composition to yield advanced cement.
Tech Briefs: The alternative approach, says the news release , has been to increase the amount of carbon. Can you tell me more about this process, how it works, and why your method is a better alternative?
Prof. Ange-Therese Akono: The conventional approach to achieve higher performance is to increase the volume of cement, for instance, to sustain higher loads. This approach, in turn, leads to bulky structures with thick sections and a high carbon footprint. The other issue is the high susceptibility of current cement to cracking and its high porosity and low water penetration resistance, limitations that drive up the maintenance costs over the lifetime of the structure.
In contrast, we leverage nanoscience and nanotechnology to yield a new structural design for cement at the nanoscale, that is denser, with a higher water penetration resistance and increased mechanical properties. The key point is to change the distribution of the basic building block of cement using nanoparticles and advanced processing. Thus, we reinforce the cement directly at the fundamental scale, nanoscale and below, to drastically enhance the performance at the structural level.
Tech Briefs: What needs to happen before this material can start getting used in cities?
Prof. Ange-Therese Akono: We are currently investigating the long-term performance and the durability of our novel nano-cement. We will then proceed to further testing at the structural level, where the focus will be on scaling up our novel manufacturing process and leveraging the multifunctionality of our material.
Tech Briefs: Why is this kind of material so valuable?
Prof. Ange-Therese Akono: Our material is valuable as it provides an advanced construction material solution to promote urban expansion while mitigating climate change. The world population is growing exponentially and being concentrated mainly in cities. This rapid urbanization calls for advanced construction materials to meet the needs of this expanding population without straining existing urban resources in terms of infrastructures and buildings.
Another challenge is to mitigate climate change by reducing the carbon footprint. Currently, the cement industry accounts for 8% of man-made greenhouse gas emissions. We meet both challenges through a novel material with enhanced performance, a low carbon footprint, and a high multifunctionality, to promote advanced sensing and connectivity.
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