Engineers at Princeton University have developed a new cement-based material inspired by the architecture of human cortical bone, which demonstrates a significant increase in damage resistance. The novel material is 5.6 times more damage-resistant than conventional cement-based materials, addressing the common issue of brittle construction materials failing abruptly. This advancement was recently detailed in the journal Advanced Materials by a team led by Reza Moini, an assistant professor of civil and environmental engineering, and Shashank Gupta, a third-year Ph.D. candidate.
Cement-based materials used in civil infrastructure often prioritize strength, ensuring the ability to sustain loads. However, toughness, which supports resistance to cracking and damage propagation, has been a more elusive property in these materials. The innovative design from Princeton tackles these challenges by improving toughness without sacrificing strength, a key advancement in construction material science.
The researchers drew inspiration from the structure of cortical bone, particularly the outer layer of human femurs, which is known for its resistance to fractures. Cortical bone is composed of elliptical tubular structures called osteons, embedded in a weaker organic matrix. This arrangement deflects cracks, preventing sudden, catastrophic failures. Applying this concept to cement, the research team incorporated cylindrical and elliptical tubes within the cement paste, interacting with propagating cracks in a controlled manner.
Shashank Gupta highlighted the critical difference between brittle construction materials and the new material: "One of the challenges in engineering brittle construction materials is that they fail in an abrupt, catastrophic fashion," he said. The new bio-inspired cement material, however, avoids such sudden failures, progressively dissipating energy as cracks form and propagate.
The core of this advancement lies in the geometry and architecture of the material. "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," said Moini. By controlling the interaction between cracks and tubes, the material undergoes a stepwise toughening mechanism. Each crack is first trapped by a tube, then delayed from propagating further, resulting in additional energy dissipation at every interaction. This mechanism prevents abrupt failure and makes the material more resistant to damage.
Unlike traditional methods that rely on adding fibers or plastics to strengthen cement, the Princeton team’s approach relies entirely on geometric design, manipulating the internal structure of the cement paste. This method significantly improves toughness while maintaining structural strength, without the need for extra materials.
In addition to the mechanical improvements, the researchers introduced a new method for quantifying the degree of disorder in the material’s internal architecture. This framework, grounded in statistical mechanics, enables a more precise classification of materials based on their arrangement, moving beyond simple binary distinctions between ordered and non-ordered structures. Moini noted that previous methods, such as Voronoi tessellation and perturbation, often confused irregularity with statistical disorder. The new approach allows for the design of materials with a tailored degree of disorder, improving their overall mechanical performance.
Moini emphasized the importance of this innovation: "Using advanced fabrication methods such as additive manufacturing can further promote the design of more disordered and mechanically favorable structures and allow for scaling up of these tubular designs for civil infrastructure components with concrete."
The team has already begun experimenting with advanced techniques, including robotics and additive manufacturing, to fabricate these designs with high precision. By applying these methods to other brittle materials, the researchers hope to develop a broader range of damage-resistant structures. Gupta expressed excitement about the future potential, stating, "We've only begun to explore the possibilities. There are many variables to investigate, such as applying the degree of disorder to the size, shape, and orientation of the tubes in the material."
This breakthrough offers promising opportunities for the construction industry, with potential applications extending to various brittle materials, improving the resilience and durability of civil infrastructure in the future.
