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Crack-resistant concrete inspired by shells

Researchers at the University of Princeton in the US developed a new cement composite that is 17 times more crack-resistant, which was inspired by shells.

Under the influence of weather and temperature, common concrete is prone to cracking. While earlier research has looked at making the concrete heal itself after cracking, the Princeton engineered try to prevent cracking from happening by looking at the structure of oyster and abalone shells.

The cement composite was inspired by nacre, or mother of pearl, which is the shimmering colourful inside of some shells. On a microscopic level, nacre consists of hexagonal tablets of the hard mineral aragonite glued together by a soft biopolymer. The tablets contribute to the strength, by sliding under stress, dissipating energy. The biopolymer adds flexibility and crack-resistance.

To mimic this in the new material, the researcher created alternating layers if tabulated Portland cement paste and a highly stretchable polymer, polyvinyl siloxane. The beams they created were then subjected to a notched three-point bending test, where each beam was tested under flexure to evaluate crack resistance (or fracture toughness).

They created three types of beams, once consisting of alternating layers of cement and polymer, one in which they used a laser to engrave hexagonal grooves into the cement sheets, which were then stacked with polymer layers, and thirdly, one where thy used the laser to cut through the cement completely creating separated hexagonal tablets connected by the polymer layer.

The most significant results were observed in the beams with completely separated hexagonal tablets, which are similar to nacre. These beams exhibited 19 times the ductility and 17 times the fracture toughness while retaining nearly the same strength as the solid cement paste beam.

Photo: Sameer A. Khan / Fotobuddy / Princeton / Dagmara Dombrovska