[Image above] Credit: Mason Bryant; Flickr CC BY-SA 2.0
Concrete: The material’s been around since ancient Rome and is still one of the most widely used construction materials to date. It can be found in some of the world’s longest-standing structures, like the Pantheon and Colosseum, so it’s clearly able to stand the test of time.
Current concrete manufacturing practices are carbon-intensive, however. In fact, today’s standard Portland cement production accounts for nearly 5% of the world’s total carbon emissions.
That’s a hefty environmental price to pay for a material we need to use to bolster so many of our man-made structures.
So some researchers are focusing on cleaner, greener ways to manufacture concrete and reduce this material’s carbon footprint.
Earlier this year, researchers at Rice University in Houston, Texas, took an atomic-level look at how concrete is produced. They published the results of computer modeling studies that reveal how dislocations—or screw-like defects—in raw crystals used for concrete affect manufacturing efficiency, according to a Rice news release.
The team found that tricalcium silicates (C3S) that consist of pure rhombohedral crystals are better than others for producing “clinkers”—round lumps of C3S that, when ground into a powder, mix with water to make cement, the glue that holds gravelly concrete together. When a clinker is easy to grind, manufacturers don’t need to work as hard, the release explains. And that means the process requires less energy.
While the team at Rice is looking to make concrete production greener, other researchers are looking to redesign concrete altogether—and they’re using nature for inspiration.
Researchers at Massachusetts Institute of Technology are comparing cement paste—concrete’s binding ingredient—with the structure and properties of natural materials, such as bones, shells, and deep-sea sponges. They found that these biological materials are exceptionally strong and durable, partly due to their precise assembly of structures at multiple length scales, from the molecular to the macro level, explains an MIT News article.
The team, led by Oral Buyukozturk, professor in MIT’s Department of Civil and Environmental Engineering, has come up with a bio-inspired, “bottom-up” approach for designing cement paste.
“These materials are assembled in a fascinating fashion, with simple constituents arranging in complex geometric configurations that are beautiful to observe,” Buyukozturk says in the article. “We want to see what kinds of micromechanisms exist within them that provide such superior properties, and how we can adopt a similar building-block-based approach for concrete.”
The researchers aim to identify materials in nature that may be used as sustainable, longer-lasting alternatives to our current energy-intensive standby, Portland cement.
“If we can replace cement, partially or totally, with some other materials that may be readily and amply available in nature, we can meet our objectives for sustainability,” Buyukozturk says.
The team examined how a material’s structure affects its mechanical properties. Through observation, they found that a deep sea sponge’s onion-like structure of silica layers provides a mechanism for preventing cracks, the article explains. Nacre (mother-of-pearl), on the other hand, has more of a “brick-and-mortar” arrangement of minerals that creates a strong bond between layers, which makes for an extraordinarily tough material.
“In this context, there is a wide range of multiscale characterization and computational modeling techniques that are well established for studying the complexities of biological and biomimetic materials, which can be easily translated into the cement community,” says Admir Masic, CEE assistant professor and one of the co-authors of the research.
The team’s ultimate goal is that this new framework will help engineers identify components within biomaterials that have the potential to be adapted for use in concrete production that will improve the material’s longevity and sustainability.
For example, “to see whether volcanic ash would improve cement paste’s properties, engineers, following the group’s framework, would first use existing experimental techniques, such as nuclear magnetic resonance, scanning electron microscopy, and X-ray diffraction to characterize volcanic ash’s solid and pore configurations over time,” according to the release.
Comparing those measurements with simulation models of concrete’s evolution over time, the idea is that researchers could determine how a particular additive would contribute to specific properties of the resulting concrete.
“Hopefully this will lead us to some sort of recipe for more sustainable concrete,” Buyukozturk says. “Typically, buildings and bridges are given a certain design life. Can we extend that design life maybe twice or three times? That’s what we aim for. Our framework puts it all on paper, in a very concrete way, for engineers to use.”
The research, published in Construction and Building Materials, is “Roadmap across the mesoscale for durable and sustainable cement paste–A bioinspired approach” (DOI: 10.1016/j.conbuildmat.2016.04.020).