Researchers at MIT are seeking to redesign concrete — the most widely used human-made material in the world — by following nature’s blueprints.
In a paper published online in the journal Construction and Building Materials, the team contrasts cement paste — concrete’s binding ingredient — with the structure and properties of natural materials such as bones, shells, and deep-sea sponges.
As the researchers observed, these biological materials are exceptionally strong and durable, due to their precise assembly of structures at multiple length scales, from the molecular to the macro, or visible, level.
From their observations, the team proposed a new bioinspired, “bottom-up” approach for designing cement paste.
Ultimately, the team hopes to identify materials in nature that may be used as sustainable and longer-lasting alternatives to Portland cement, which requires a huge amount of energy to manufacture.
Implementing #nanotechnology in concrete is one powerful example to scale up the power of nanoscience to solve grand engineering challenges
It could lead to more durable roads, bridges, structures, reduce the carbon and energy footprint.
Today’s concrete is a random assemblage of crushed rocks and stones, bound together by a cement paste. Concrete’s strength and durability depends partly on its internal structure and configuration of pores. For example, 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.
The researchers want to change the culture and start controlling the material at the mesoscale.
The “mesoscale” represents the connection between microscale structures and macroscale properties. For instance, how does cement’s microscopic arrangement affect the overall strength and durability of a tall building or a long bridge? Understanding this connection would help engineers identify features at various length scales that would improve concrete’s overall performance.
According to the researchers, “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, “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 this connection, the MIT team looked to biological materials such as bone, deep sea sponges, and nacre 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 macroscales, with that of cement paste.
They looked for connections between a material’s structure and its mechanical properties. For instance, the researchers found that a deep sea sponge’s onion-like structure of silica layers provides a mechanism for preventing cracks. Nacre has a “brick-and-mortar” arrangement of minerals that generates a strong bond between the mineral layers, making the material extremely tough.
Applying the information they learned from investigating biological materials, as well as knowledge they gathered on existing cement paste design tools, the team developed a general, bioinspired framework, or methodology, for engineers to design cement, “from the bottom up.”
The framework 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, the researchers are 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, such as nuclear magnetic resonance, scanning electron microscopy, and X-ray diffraction to characterize volcanic ash’s solid and pore configurations over time.
