One group of engineers at MIT decided to focus its work on the nanostructure of concrete, the world's most widely used material. The production of cement, the primary component of concrete, accounts for 5 to 10 percent of the world's total carbon dioxide emissions; the process is an important contributor to global warming.
In the January issue of the Journal of the Mechanics and Physics of Solids, the team reports that the source of concrete's strength and durability lies in the organization of its nanoparticles. The discovery could one day lead to a major reduction in carbon dioxide emissions during manufacturing.
"If everything depends on the organizational structure of the nanoparticles that make up concrete, rather than on the material itself, we can conceivably replace it with a material that has concrete's other characteristics-strength, durability, mass availability and low cost-but does not release so much CO2 into the atmosphere during manufacture," said Franz-Josef Ulm, the Esther and Harold E. Edgerton Professor of Civil and Environmental Engineering.
The work also shows that the study of very common materials at the nano scale has great potential for improving materials in ways we might not have conceived. Ulm refers to this work as the "identification of the geogenomic code of materials, the blueprint of a material's nanomechanical behavior."
Cement is manufactured at the rate of 2.35 billion tons per year, enough to produce 1 cubic meter of concrete for every person in the world. If engineers can reduce carbon dioxide emissions in the world's cement manufacturing by even 10 percent, that would accomplish one-fifth of the Kyoto Protocol goal of a 5.2 percent reduction in total carbon dioxide emissions.
Ulm considers this a very real possibility.
He and Georgios Constantinides, a postdoctoral researcher in materials science and engineering, studied the behavior of the nanostructure of cement. They found that at the nano level, cement particles organize naturally into the most densely packed structure possible for spherical objects, which is similar to a pyramid-shaped pile of oranges.
Cement, the oldest engineered construction material, dating back to the Roman Empire, starts out as limestone and clay that are crushed to a powder and heated to a very high temperature (1500 degrees Celsius) in a kiln. At this high temperature, the mineral undergoes a transformation, storing energy in the powder. When the powder is mixed with water, the energy is released into chemical bonds to form the elementary building block of cement, calcium-silicate-hydrate (C-S-H). At the micro level, C-S-H acts as a glue to bind sand and gravel together to create concrete. Most of the carbon dioxide emissions in this manufacturing process result from heating the kiln to a temperature high enough to transfer energy into the powder.
Ulm and Constantinides gathered a wide range of cement pastes from around the world, and, using a novel nano-indentation technique, poked and prodded the hardened cement paste with a nano-sized needle. An atomic force microscope allowed them to see the nanostructure and judge the strength of each paste by measuring indentations created by the needle, a technique that had been used before on homogenous materials, but not on a heterogeneous material like cement.
To their surprise, they discovered that the C-S-H behavior in all of the different cement pastes consistently displays a unique nanosignature, which they call the material's genomic code. This indicates that the strength of cement paste, and thus of concrete, does not lie in the specific mineral, but in the organization of that mineral as packed nanoparticles.
The C-S-H particles (each about five nanometers, or billionths of a meter, in diameter) have only two packing densities, one for particles placed randomly, say in a box, and another for those stacked symmetrically in a pyramid shape (like a grocer's pile of fruit). These correspond exactly to the mathematically proved highest packing densities allowed by nature for spherical objects: 63 and 74 percent, respectively. In other words, the MIT research shows that materials pack similarly even at the nano scale.
"The construction industry relies heavily on empirical data, but the physics and structure of cement were not well understood," said Constantinides. "Now that the nano-indentation equipment is becoming more widely available-in the late 1990s, there were only four or five machines in the world and now there are five at MIT alone-we can go from studying the mechanics of structures to the mechanics of material at this very small scale."
If the researchers can find-or nanoengineer-a different mineral to use in cement paste, one that has the same packing density but does not require the high temperatures during production, they could conceivably cut world carbon dioxide emissions by up to 10 percent.
This aspect of the work is just beginning. Ulm estimates that it will take about five years, and says he's presently looking at magnesium as a possible replacement for the calcium in cement powder. "Magnesium is an earth metal, like calcium, but it is a waste material that people must pay to dispose of," he said.
He recently formed a research team with colleagues in physics, materials science and nuclear engineering to perform atomistic simulations, taking the work a step deeper into the structure of this ubiquitous material.
The research was funded in part by the Lafarge Group.
Elizabeth A. Thomson | MIT News Office
Foxes in the city: citizen science helps researchers to study urban wildlife
14.12.2018 | Veterinärmedizinische Universität Wien
Machine learning helps predict worldwide plant-conservation priorities
04.12.2018 | Ohio State University
Researchers from the University of Basel have reported a new method that allows the physical state of just a few atoms or molecules within a network to be controlled. It is based on the spontaneous self-organization of molecules into extensive networks with pores about one nanometer in size. In the journal ‘small’, the physicists reported on their investigations, which could be of particular importance for the development of new storage devices.
Around the world, researchers are attempting to shrink data storage devices to achieve as large a storage capacity in as small a space as possible. In almost...
The more objects we make "smart," from watches to entire buildings, the greater the need for these devices to store and retrieve massive amounts of data quickly without consuming too much power.
Millions of new memory cells could be part of a computer chip and provide that speed and energy savings, thanks to the discovery of a previously unobserved...
What if, instead of turning up the thermostat, you could warm up with high-tech, flexible patches sewn into your clothes - while significantly reducing your...
A widely used diabetes medication combined with an antihypertensive drug specifically inhibits tumor growth – this was discovered by researchers from the University of Basel’s Biozentrum two years ago. In a follow-up study, recently published in “Cell Reports”, the scientists report that this drug cocktail induces cancer cell death by switching off their energy supply.
The widely used anti-diabetes drug metformin not only reduces blood sugar but also has an anti-cancer effect. However, the metformin dose commonly used in the...
A research team from the University of Zurich has developed a new drone that can retract its propeller arms in flight and make itself small to fit through narrow gaps and holes. This is particularly useful when searching for victims of natural disasters.
Inspecting a damaged building after an earthquake or during a fire is exactly the kind of job that human rescuers would like drones to do for them. A flying...
12.12.2018 | Event News
10.12.2018 | Event News
06.12.2018 | Event News
18.12.2018 | Materials Sciences
18.12.2018 | Physics and Astronomy
18.12.2018 | Physics and Astronomy