Seashell inspired cement is super flexible, crack resistant, unbreakable

Inspired by materials found in oyster and mussel shells, Princeton University researchers have created a new, highly versatile cement composite.

This design mimics the structure of a brick and mortar shell and increases durability by supporting inelastic deformation and hierarchical strengthening.

The newly developed material is 19 times more flexible, can stretch without breaking and is 17 times more resistant to cracking than conventional cement.

According to the team, the results may ultimately improve crack resistance in a variety of brittle ceramic materials such as porcelain and concrete.

Structural strength inspired by nature

Unlike materials such as glass, wood and steel, cement without fibers and reinforcement is brittle and not very flexible. These shortcomings limit its use in structural applications.

Several methods have been tried to improve the low fracture toughness and ductility of cementitious materials by adding polymer, glass, or metal reinforcements to cementitious composites. According to the researchers, these approaches lead to only a small increase (about a one-fold increase) in energy absorption and fracture resistance, mostly at the cost of directly changing the microstructure of the materials.

The Princeton team found that alternating thin layers of polymer and patterned cement paste can significantly improve ductility — the ability to bend without breaking.

The group drew inspiration for their work in creating materials from biology. In this case, the group created a composite modeled after nacre, a naturally occurring substance found inside concrete shells.

According to the researchers, nacre consists of hexagonal tablets of the hard mineral aragonite held together at the microscopic level by a soft biopolymer. Its 3D brick and mortar structure allows the tablets to slide and the biopolymer to deform, absorb energy and increase toughness.

These mechanisms, along with nano-asperities and interlocking tablets, make mother-of-pearl durable despite its fragile components.

“This synergy between hard and soft components is fundamental to the remarkable mechanical properties of nacre,” said Shashank Gupta, a graduate student in Princeton University’s Department of Civil and Environmental Engineering.

New cement composites

The Princeton researchers used common construction materials such as Portland cement paste and a small amount of polymer to create new nacre-inspired composites.

Layers of cement paste boards were alternated with polyvinylsiloxane, a highly flexible polymer. By alternating thin layers of polymer with sheets of cement paste, the researchers were able to create multilayered tiny beams.

Then, to assess crack resistance (also known as fracture toughness), each of these beams underwent a three-point notch bending test.

The researchers created three types of beams: the first with alternating layers of cement paste and thin polymer plates; the second with hexagonal grooves laser-engraved into cement boards stacked with polymer layers; and a third with completely separate hexagonal cement tablets bonded with a polymer that imitates mother-of-pearl. These were compared to a solid cast cement paste reference.

The results showed that these composites mimic the sliding and energy absorption mechanisms of nacre tablets. The nacre-mimicking composites had 17 times higher fracture toughness and increased ductility by 1791 percent compared to solid cement.

Strengthening mechanisms include interlayer deformation, tortuous crack propagation, and tablet sliding. By using laser processing and elastomeric interlayers, this approach significantly improves the mechanical properties of the cement while reducing the risk of failure.

According to the researchers, future work may explore different soft materials for resilient infrastructure, refine groove shapes for better integration of defects, and streamline manufacturing methods using integrated lamination-laser or additive manufacturing processes for broader infrastructure applications.

Details of the team’s research were published in the journal Advanced functional materials.