A group of researchers at Rice University in Houston, Texas, have come up with a way to “program” microscopic particles in cement that could lead to more durable concrete.
The team, headed by Rouzbeh Shahsavari, a materials scientist, developed a process that turns disordered clumps of particles into regimented cubes, spheres and other forms.
He and his colleagues have succeeded in synthesizing calcium silicate hydrate (C-S-H), which is the main product of the hydration of Portland cement and is primarily responsible for the strength in cement-based materials.
The ordered shapes their process yields serve as "seeds" for the bottom-up manufacture of stronger, more durable concrete. That, in turn, could lead to stronger structures that require less concrete.
The paper reporting the team’s work appeared last month in the Journal of Materials Chemistry A, which is published by the Royal Society of Chemistry. Rice University released a summary of the paper earlier this month.
In it, Shahsavari is quoted calling the material "programmable cement."
"The great advance of this work is that it’s the first step in controlling the kinetics of cement to get desired shapes," he said.
He said the research shows how to control the structure and size of the basic building blocks of C-S-H. These building blocks, or seeds, self-assemble into a cement that yields a far denser concrete.
Self-assembly is "a hot area" that has attracted researchers, he said.
"But when it comes to cement and concrete it is extremely difficult to control their bottom-up assembly. Our work provides the first recipe for such advanced synthesis."
Previous efforts to create ordered crystals in C-S-H involved high temperatures or pressures, prolonged reaction times and the use of organic precursors. But the methods were neither efficient or environmentally benign, Shahsavari said.
His team created the well-formed shapes by adding small amounts of calcium silicate and surfactants to C-S-H, then exposing the mix to carbon dioxide and ultrasonic sound. The seeds took shape around clusters of surfactant molecules within 25 minutes.
Once those seeds have formed they trigger the molecules around them to self-assemble into cubes, spheres and other shapes that are much, much larger.
Added to a concrete mix, the shapes created by the process can pack more tightly together than the shapes found when using conventional cement.
Shahsavari said using this new cement means less concrete is needed because it is stronger and more durable. And less porous concrete "makes it harder for unwanted chemicals to find a path through the concrete."
That means rebar is protected against corrosion.
The cement/concrete industry is acutely aware of the amount of greenhouse gases it’s responsible for, so there is a lot of research underway to limit emissions.
What Shahsavari and his team have done is use nanotechnology to engineer the new cement.
The science, engineering and technology that together make up nanotechnology haven’t been around long.
Physicist Richard Feynman spoke about it publicly late in 1959 when he described how it might be possible to manipulate and control individual atoms and molecules. It was more than a decade later that Norio Taniguchi coined the term nanotechnology.
Modern nanotechnology didn’t begin its evolution until 1981. That’s when the development of the scanning tunnelling microscope made it possible to "see" individual atoms.
Since the science is fairly new, the concept of manipulating such small particles — a billionth of a meter in diameter — still seems exotic to many.
But Shahsavari and his group recognized the potential that nanotechnology holds.
"Other research groups have tested bulk cement and concrete," says Shahsavari, "but no group had ever probed the mechanics of single C-S-H particles and the effect of shape on the mechanics of individual particles."
The research team has "mapped" the shapes it has synthesized, producing a unified diagram for those who wish to engineer concrete from the bottom up.
Korky Koroluk is an Ottawa-based freelance writer. Send comments to firstname.lastname@example.org.