Human bone inspires tougher cement

The bio-inspired design allows the material to resist cracking and avoid sudden failure, unlike conventional, brittle cement-based counterparts.

In an article in Advanced Materials, the research team led by Reza Moini, an assistant professor of civil and environmental engineering, and Shashank Gupta, a third-year PhD candidate, demonstrate that cement paste deployed with a tube-like architecture can significantly increase resistance to crack propagation and improve the ability to deform without sudden failure.

“One of the challenges in engineering brittle construction materials is that they fail in an abrupt, catastrophic fashion,” Gupta said in a statement.

In brittle construction materials used in building and civil infrastructure, strength ensures ability to sustain loads, while toughness supports resistance to cracking and spread of damage in the structure. The proposed technique tackles those problems by creating a material that is tougher than conventional counterparts while maintaining strength.

Moini said the key to the improvement lies in the purposeful design of internal architecture, by balancing the stresses at the crack front with the overall mechanical response.

“We use theoretical principles of fracture mechanics and statistical mechanics to improve materials’ fundamental properties ‘by design’,” he said.

The team was inspired by human cortical bone, the dense outer shell of human femurs that provides strength and resists fracture. Cortical bone consists of elliptical tubular components (osteons), embedded weakly in an organic matrix. This architecture deflects cracks around osteons and prevents abrupt failure while increasing overall resistance to crack propagation.

The team’s bio-inspired design incorporates cylindrical and elliptical tubes within the cement paste that interacts with propagating cracks.

“One expects the material to become less resistant to cracking when hollow tubes are incorporated,” said Moini. “We learned that by taking advantage of the tube geometry, size, shape, and orientation, we can promote crack-tube interaction to enhance one property without sacrificing another.”

The team discovered that such enhanced crack-tube interaction initiates a stepwise toughening mechanism, where the crack is first trapped by the tube and then delayed from propagation, leading to additional energy dissipation at each interaction and step.

“What makes this stepwise mechanism unique is that each crack extension is controlled, preventing sudden, catastrophic failure,” said Gupta. “Instead of breaking all at once, the material withstands progressive damage, making it much tougher.”

Unlike traditional methods that strengthen cement-based materials by adding fibres or plastics, the Princeton team’s approach relies on geometric design. By manipulating the structure of the material itself, they achieved improvements in toughness without the need for additional material.

In addition to improving fracture toughness, the researchers introduced a new method to quantify the degree of disorder. Based on statistical mechanics, the team introduced parameters to quantify the degree of disorder in architected materials. This allowed them to create a numerical framework reflecting the degree of disorder of the architecture.

The researchers said the new framework provides a more accurate representation of the material’s arrangements, moving towards a spectrum from ordered to random, beyond the simple binary classifications of periodic and non-periodic. Moini said that the study makes a distinction with approaches that confuse irregularity and perturbation with statistical disorder such as Voronoi tessellation and perturbation methods.

“This approach gives us a powerful tool to describe and design materials with a tailored degree of disorder,” said Moini. “Using advanced fabrication methods such as additive manufacturing can further promote the design of more disordered and mechanically favourable structures and allow for scaling up of these tubular designs for civil infrastructure components with concrete.”