Engineers Have Discovered the Stunning Secret to Making Cement 17x Stronger

Concrete is both a necessity and vulnerability. Its rugged properties cause it to crack and thus greatly reduce the life expectancy of buildings, bridges, and roads. In an idea to armor against cracking, reinforced concrete was created that thereby inferred only further durability, complexity, cost and an environmental toll to a product that already has a massive GHG footprint. 

In production, cement is in fact one of the single largest global greenhouse gas emissions offenders.It makes cement from heating limestone to products at temperatures above 1,400 °C. The CO₂ originates from not only breaking down limestone, but from the fuel used to heat the product, and from the chemical changes of limestone itself. On average for every ton of a concrete product produced there is a ton of CO₂ produced, making it one of the planet’s most carbon-laden products.

Thus, there are two challenges for engineers:

• Improve mechanical properties – The durability, flexibility, and cracking margin for cement-based products must be improved.
• Reduce environmental impact – Emissions and waste generation when producing and maintaining cement-based products must be reduced.

For the team at Princeton what these two challenges meant was not a challenge of synthetic chemistry – it was about biological architecture.  

A Lesson from the Ocean: The Armor of the Oysters

Oysters may look delicate but they endure in harsh and changing marine environments in part due to their amazing natural masterpiece hidden inside, nacre or “mother of pearl”. 

While the beauty of nacre has long been associated as an aesthetic for jewelry, it is in fact the inner structure that has captured the attention of scientists. Nacre at the micro-scale has a structure consisting of a series of hexagonal aragonite tablets – a crystal form of calcium carbonate – that are layered and reinforced with frivolous, flexible organic layers that serve as mortar. This recognized brick and mortar architecture provides nacre with its impressive strength and toughness. 

When a loading condition is applied to nacre it simply does not fail like a normal non-bio plastics and minerals do, or more typically just shatter. In contrast, with nacre’s several layers, cracks are redirected, held off, and absorbed, making nacre extremely tough despite its lightweight design. It is estimated that nacre is 3000 times tougher than aragonite. 

Through millions of years of evolution, Mother Nature has engineered nacre to be lightweight, tough, and energy-efficient…everything we as humans are striving toward in highly advanced structural materials. Researchers at Princeton University viewed nacre as a template of a new base. 

The research team started by characterizing the micro-architecture of nacre through high-resolution imaging. They found that the strength of nacre was not due to its chemistry, rather the architecture of nacre — the ordered structure of these layers is a means to distribute stress and compliance and preemptively stop cracks from propagating. 

From this understanding, the team produced a nacre-style architecture in cement. They adapted advanced processing techniques and produced micro-laminated layers, like that of an oyster shell, separating the hard and soft layers. 

What happened next was astounding. The nacre inspired cement, while loaded, had calculated toughness of 17 times tougher than normal cement, thus it could take more forces without cracking. This research represents a paradigm shift in material science: As an engineering community are now moving into designs of understanding smart designs at the micro-architecture rather than just mixed materials of higher strength. 

The Discoveries: 17x Tougher, Durability, Resilience 

The data told an incredible story that appropriately represented its architectural toughness.As a component of the mechanical assessment, the nacre-like cement absorbed nearly 17 times more energy to failure than traditional samples. The design of the cement microstructure rerouted crack propagation, and the galleries (layered arches) formed between the layers systemically added to toughness and ductility. 

What do these findings mean as it relates to a practical outcome?

Increased life span via a longer lifespan of the infrastructure resulting in explosive performance (stress, earthquakes, and environmental weathering). 

• Reduced maintenance costs via cracks taking longer to develop resulting in less wear and need for replacements — for example, it took 13 months before another maintenance intervention was needed on nacre-like cements. 
• Increased material efficiency by using less material to achieve similar performance along with a resistance to crack propagation. 
• Reduced carbon footprint via a reduced cement footprint and thus emissions that would occur during cement production. 

This finding could have incredible ramifications for the future sustainable urban development providing opportunity for cities to grow without continuing the further deterioration of the environment — a life of cities built by nature!