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Engineers look to nature for better concrete

Concrete

Bones and shells could provide the blueprint for stronger and more durable concrete, according to new research from the Massachusetts Institute of Technology (MIT).

A team led by Oral Buyukozturk, a professor in MIT’s department of civil and environmental engineering, has been comparing cement paste with the structure of natural materials such as bones, shells and deep-sea sponges.

From the research, a new framework for designing cement paste has been proposed. The ultimate aim of the research is to find a new sustainable alternative to cement.

“These materials are assembled in a fascinating fashion, with simple constituents arranging in complex geometric configurations that are beautiful to observe,” said Buyukozturk. “We want to see what kinds of micromechanisms exist within them that provide such superior properties, and how we can adopt a similar building-block-based approach for concrete.

“If we can replace cement, partially or totally, with some other materials that may be readily and amply available in nature, we can meet our objectives for sustainability.”

There are currently no techniques available to precisely control concrete’s internal structure and overall properties, but the research is aiming to change this so that its strength is controllable on a ‘mesoscale’ – what researchers describe as the connection between microscale structures and macroscale properties.

“We’re dealing with molecules on the one hand, and building a structure that’s on the order of kilometers in length on the other,” added Buyukozturk. “How do we connect the information we develop at the very small scale, to the information at the large scale? This is the riddle.”

The researchers examined the current findings into structures such as bone and compared the structures and behaviour with that of cement paste. For example, the researchers found that a deep sea sponge’s onion-like structure of silica layers provides a mechanism for preventing cracks.

They took this knowledge, as well as knowledge on current cement paste design, and developed a set of guidelines for engineers to design better cement, inspired by nature. The guidelines aim to help engineers determine how certain additives or ingredients will impact cement’s strength and durability.

An example of how this would work is given in the research into volcanic ash as a cement additive. Using the new framework, engineers would start off by using existing experimental techniques, such as nuclear magnetic resonance, scanning electron microscopy, and x-ray diffraction, to examine volcanic ash’s solid and pore configurations over time.

They could then input these measurements into models that simulate concrete’s long-term evolution, to identify mesoscale relationships between, for example, the properties of volcanic ash and the material’s contribution to the strength and durability of an ash-containing concrete bridge. The findings can then be validated with conventional compression and nanoindentation experiments to test actual samples of volcanic ash-based concrete.

The university’s civil engineering department head Markus Buehler said: “The merger of theory, computation, new synthesis, and characterisation methods have enabled a paradigm shift that will likely change the way we produce this ubiquitous material, forever.

“It could lead to more durable roads, bridges, structures, reduce the carbon and energy footprint, and even enable us to sequester carbon dioxide as the material is made. Implementing nanotechnology in concrete is one powerful example of how to scale up the power of nanoscience to solve grand engineering challenges.”

Co-authors on the paper include lead author and graduate student Steven Palkovic, graduate student Dieter Brommer, research scientist Kunal Kupwade-Patil, departmental assistant professor Admir Masic, and department head Markus Buehler.

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