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MIT researchers: Marine species suggest blueprints for better concrete structures

In a project funded by outside parties and independent of the Concrete Sustainability Hub, Massachusetts Institute of Technology researchers are seeking to redesign concrete by following nature’s blueprints, contrasting cement paste with the structure and properties of bones, shells, and deep sea sponges. As they observe in the current Construction and Building Materials paper, “Roadmap across the mesoscale for durable and sustainable cement paste—A bioinspired approach,”such biological materials are exceptionally strong and durable, thanks in part to their precise assembly of structures at multiple length scales, from the molecular to the macro, or visible, level.

A team led by Department of Civil and Environmental Engineering (CEE) Professor Oral Buyukozturk proposes a new bio-inspired, “bottom-up” approach for designing cement paste. “These [natural] materials are assembled in a fascinating fashion, with simple constituents arranging in complex geometric configurations that are beautiful to observe,” he contends. “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.”

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

“The merger of theory, computation, new synthesis, and characterization methods have enabled a paradigm shift that will likely change the way we produce this ubiquitous material, forever,” adds Buehler. “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 example [of how] to scale up the power of nanoscience to solve grand engineering challenges.”

Concrete strength and durability depend partly on internal structure and pore configuration; the more porous the material, the more vulnerable it is to cracking. However, there are no techniques available to precisely control concrete’s internal structure and overall properties, notes Buyukozturk, adding, “It’s mostly guesswork. We want to change the culture and start controlling the material at the mesoscale.”

The mesoscale represents the connection between microscale structures and macroscale properties, he observes. For instance, how does cement’s microscopic arrangement affect the overall strength and durability of a tall building or a long bridge? Understanding that connection would help engineers identify features at various length scales to improve overall concrete performance.

“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,” Buyukozturk affirms. “How do we connect the information we develop at the very small scale, to the information at the large scale? This is the riddle.”

To start to understand the connection, Buyukozturk and his colleagues looked to bone, deep sea sponges, and nacre (an inner shell layer of mollusks), which have all been studied extensively for their mechanical and microscopic properties. They looked through the scientific literature for information on each biomaterial, and compared their structures and behavior, at the nano, micro and macro scales, with that of cement paste. They looked for connections between a material’s structure and its mechanical properties, observing how a deep sea sponge’s onion-like structure of silica layers provides a mechanism for preventing cracks, while nacre has a “brick-and-mortar” arrangement that generates a strong bond between mineral layers, making the material extremely tough.

“In this context, there is a wide range of multiscale characterization and computational modeling techniques that are well established for studying the complexities of biological and biomimetic materials, which can be easily translated into the cement community,” says Masic.

The research team developed a general, bioinspired framework for designing cement “from the bottom up.” This methodology is essentially a set of guidelines that engineers can follow in order to determine how certain additives or ingredients of interest will impact cement’s overall strength and durability. For instance, in a related line of research, Buyukozturk is looking into volcanic ash as a cement additive or substitute. To see whether volcanic ash would improve cement paste’s properties, engineers, following the group’s framework, would first use existing experimental techniques—nuclear magnetic resonance, scanning electron microscopy and X-ray diffraction—to characterize the material’s solid and pore configurations over time.

Researchers could then plug such measurements into models that simulate concrete’s long-term evolution, to identify mesoscale relationships between the properties of volcanic ash and the material’s contribution to the strength and durability of an ash-containing concrete bridge. These simulations can then be validated with conventional compression and nano indentation experiments, to test actual samples of volcanic ash-based concrete.

Ultimately, the researchers hope the framework will help engineers identify ingredients that are structured and evolve in a way, similar to biomaterials, that may improve concrete’s performance and longevity. “Hopefully this will lead us to some sort of recipe for more sustainable concrete,” Buyukozturk says. “Typically, buildings and bridges are given a certain design life. Can we extend that maybe twice or three times? That’s what we aim for. Our framework puts it all on paper, in a very concrete way, for engineers to use.”

The research was supported in part by the Kuwait Foundation for the Advancement of Sciences through the Kuwait-MIT Center for Natural Resources and the Environment, National Institute of Standards and Technology, and the Argonne National Laboratory.