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article imageEssential Science: New cement paste gets stronger when it cracks

By Tim Sandle     Oct 8, 2018 in Science
Scientists have used 3D printing technology to develop a super-strong form of cement. This is based on the addition of an ingredient that becomes stronger the more pressure that is applied to it.
The strengthening effect as pressure is applied is analogous to the toughening that shells of lobsters and beetles experience. It is hoped that this 3D printed, arthropod-inspired innovation will lead to stronger structure that are more resilient in the face of earthquakes.
A weakness with conventional cement rests with the pore regions located at the "interfaces" between the printed layers. These pores can promote cracking. Furthermore, the chemical reaction, which causes concrete to go from the liquid or plastic state to a solid state, requires water but often too much water is added to the mix.
File photo of a concrete slab on an overpass.
File photo of a concrete slab on an overpass.
Photo by Achim Hering (CC BY 3.0)
The Purdue University study began with looking at arthropod shells, trying to figure out how the shells can control the way damage spreads when a pressure is applied. This concept led to a series of 3D printed designs, each one focused on how the overall structure could be strengthened.
It was found that they may material is arranged in spiral formation was the most important factor. The researchers drew a comparison between trying to break one uncooked spaghetti noodle and a bunch of noodles compacted together.
On Wednesday in the early afternoon  an earthquake struck Southern Ontario  parts of Quebec and New ...
On Wednesday in the early afternoon, an earthquake struck Southern Ontario, parts of Quebec and New York state. The earthquake's epicenter was about 61 km (38 miles) north of Ottawa near the Quebec-Ontario border.
Photo courtesy U.S. Geological Survey, National Earthquake Information Center
Commenting on this, lead researcher Professor Jan Olek states why the natural world became the source of inspiration: “Nature has to deal with weaknesses to survive, so we are using the 'built-in' weaknesses of cement-based materials to increase their toughness.”.
He adds further that the exoskeletons of arthropods have an in-built crack propagation system, together with toughening mechanisms. What the researchers at the civil engineering department thought to do was to reproduce these natural mechanisms with the 3D-printed cement paste.
Of particular interest to the researchers was the mantis shrimp (stomatopods). A mantis shrimp's carapace (the bony, thick shell that covers crustaceans and some other species) is incredibly strong. The shell covers only the rear part of the head and the first four segments of the thorax
It didn’t take too long for the researchers to achieve this on the laboratory bench scale. However, seeking to scale this up proved more challenging in terms of replicating the performance.
New York City skyscraper
New York City skyscraper
Harry Vale (CC BY 2.0)
The scale-up issue was achieved by developing the appropriate mold for different design configurations. These were developed by running computerized tomography scans at the micro-level. This led to the optimal 3D printed designs being selected: "honeycomb," "compliant" and "Bouligand" designs.
The process is illustrated in the following video:
The new insight should help with the development of flaw-tolerant structural elements like beams or columns. Such structures could then be more resistant to natural disasters, such as earthquakes.
The new process has been presented to the 1st RILEM International Conference on Concrete and Digital Fabrication. The research has also been published in the science journal Advanced Materials. The research paper is titled “Additive Manufacturing and Performance of Architectured Cement-Based Materials.”
Essential Science
Artist s reconstruction of the new horned dinosaur Regaliceratops peterhewsi in the palaeoenvironmen...
Artist's reconstruction of the new horned dinosaur Regaliceratops peterhewsi in the palaeoenvironment of the Late Cretaceous of Alberta, Canada.
Artwork by Julius T. Csotonyi / Courtesy of Royal Tyrrell Museum, Drumheller, Alberta
This article is part of Digital Journal's regular Essential Science columns. Each week Tim Sandle explores a topical and important scientific issue. Last week we reviewed how researcher have begun to use new technologies to help quantify the vast and curious fossil finds that are stored, and in some cases remained untouched for decades, on museum shelves.
The week before we considered new research which determined there are four personality types. The new study could alter the fundamentals of psychology, overturning established paradigms.
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