Nanotechnology Now

Our NanoNews Digest Sponsors



Heifer International

Wikipedia Affiliate Button


android tablet pc

Home > Press > Cement's basic molecular structure finally decoded

Abstract:
Robustness comes from messiness, not a clean geometric arrangement

Cement's basic molecular structure finally decoded

Cambridge, MA | Posted on September 11th, 2009

In the 2,000 or so years since the Roman Empire employed a naturally occurring form of cement to build a vast system of concrete aqueducts and other large edifices, researchers have analyzed the molecular structure of natural materials and created entirely new building materials such as steel, which has a well-documented crystalline structure at the atomic scale.

Oddly enough, the three-dimensional crystalline structure of cement hydrate - the paste that forms and quickly hardens when cement powder is mixed with water - has eluded scientific attempts at decoding, despite the fact that concrete is the most prevalent man-made material on earth and the focus of a multibillion-dollar industry that is under pressure to clean up its act. The manufacture of cement is responsible for about 5 percent of all carbon dioxide emissions worldwide, and new emission standards proposed by the U.S. Environmental Protection Agency could push the cement industry to the developing world.

"Cement is so widely used as a building material that nobody is going to replace it anytime soon. But it has a carbon dioxide problem, so a basic understanding of this material could be very timely," said MIT Professor Sidney Yip, co-author of a paper published online in the Proceedings of the National Academy of Sciences (PNAS) during the week of Sept. 7 that announces the decoding of the three-dimensional structure of the basic unit of cement hydrate by a group of MIT researchers who have adopted the team name of Liquid Stone.

"We believe this work is a first step toward a consistent model of the molecular structure of cement hydrate, and we hope the scientific community will work with it," said Yip, who is in MIT's Department of Nuclear Science and Engineering (NSE). "In every field there are breakthroughs that help the research frontier moving forward. One example is Watson and Crick's discovery of the basic structure of DNA. That structural model put biology on very sound footing."

Scientists have long believed that at the atomic level, cement hydrate (or calcium-silica-hydrate) closely resembles the rare mineral tobermorite, which has an ordered geometry consisting of layers of infinitely long chains of three-armed silica molecules (called silica tetrahedra) interspersed with neat layers of calcium oxide.

But the MIT team found that the calcium-silica-hydrate in cement isn't really a crystal. It's a hybrid that shares some characteristics with crystalline structures and some with the amorphous structure of frozen liquids, such as glass or ice.

At the atomic scale, tobermorite and other minerals resemble the regular, layered geometric patterns of kilim rugs, with horizontal layers of triangles interspersed with layers of colored stripes. But a two-dimensional look at a unit of cement hydrate would show layers of triangles (the silica tetrahedra) with every third, sixth or ninth triangle turned up or down along the horizontal axis, reaching into the layer of calcium oxide above or below.

And it is in these messy areas - where breaks in the silica tetrahedra create small voids in the corresponding layers of calcium oxide - that water molecules attach, giving cement its robust quality. Those erstwhile "flaws" in the otherwise regular geometric structure provide some give to the building material at the atomic scale that transfers up to the macro scale. When under stress, the cement hydrate has the flexibility to stretch or compress just a little, rather than snapping.

"We've known for several years that at the nano scale, cement hydrates pack together tightly like oranges in a grocer's pyramid. Now, we've finally been able to look inside the orange to find its fundamental signature. I call it the DNA of concrete," said Franz-Josef Ulm, the Macomber Professor in the Department of Civil and Environmental Engineering (CEE), a co-author of the paper. "Whereas water weakens a material like tobermorite or jennite, it strengthens the cement hydrate. The 'disorder' or complexity of its chemistry creates a heterogenic, robust structure.

"Now that we have a validated molecular model, we can manipulate the chemical structure to design concrete for strength and environmental qualities, such as the ability to withstand higher pressure or temperature," said Ulm.

CEE Visiting Professor Roland Pellenq, director of research at the Interdisciplinary Center of Nanosciences at Marseille, which is part of the French National Center of Scientific Research and Marseille University, pinned down the exact chemical shape and structure of C-S-H using atomistic modeling on 260 co-processors and a statistical method called the grand canonical Monte Carlo simulation.

Like its name, the simulation requires a bit of gambling to find the answer. Pellenq first removed all water molecules from the basic unit of tobermorite, watched the geometry collapse, then returned the water molecules singly, then doubly and so on, removing them each time to allow the geometry to reshape as it would naturally. After he added the 104th water molecule, the correct atomic weight of C-S-H was reached, and Pellenq knew he had an accurate model for the geometric structure of the basic unit of cement hydrate.

The team then used that atomistic model to perform six tests that validated its accuracy. "This gives us a starting point for experiments to improve the mechanical properties and durability of concrete. For instance, we can now start replacing silica in our model with other materials," said Pellenq.

Other team members are graduate student Rouzbeh Shahsavari of CEE and Markus Buehler, MIT's Esther and Harold E. Edgerton Career Development Associate Professor of Civil and Environmental Engineering; Krystyn Van Vliet, MIT's Thomas Lord Associate Professor of Materials Science and Engineering; and NSE postdoctoral associate Akihiro Kushima.

This research was funded by the Portuguese cement manufacturer, Cimpor Corp., enabled through the MIT-Portugal Program.


####

About Massachusetts Institute of Technology, Department of Civil and Environmental Engineering
The MIT Department of Civil and Environmental Engineering (CEE) is dedicated to balancing the built environment with the natural world. In our research, we seek to understand natural systems, to foster the intelligent use of resources and to design sustainable infrastructure systems.

We provide leadership in the field by focusing on technological innovations, seeking advances in basic knowledge and taking a systems perspective. We concentrate our efforts on quantitative and analytical approaches, novel experiment-based modeling, and the development and/or use of appropriate tools and technology.

CEE is an innovative and vibrant place of learning, where undergraduates, graduate students and postdoctoral researchers pursue their educational and research interests in order to lead the next generation in transforming the disciplines of civil and environmental engineering.

Our research and graduate education programs coalesce around three fields of inquiry: environmental science and engineering; mechanics, materials and structures; and transportation. We offer ABET-accredited undergraduate degree programs in civil engineering and environmental engineering science.

For more information, please click here

Contacts:
Denise Brehm

617-253-8069

Copyright © Massachusetts Institute of Technology

If you have a comment, please Contact us.

Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.

Bookmark:
Delicious Digg Newsvine Google Yahoo Reddit Magnoliacom Furl Facebook

Related News Press

News and information

A new, tunable device for spintronics: An international team of scientists including physicist Jairo Sinova from the University of Mainz realises a tunable spin-charge converter made of GaAs August 29th, 2014

Nanoscale assembly line August 29th, 2014

New analytical technology reveals 'nanomechanical' surface traits August 29th, 2014

New Vice President Takes Helm at CNSE CMOST: Catherine Gilbert To Lead CNSE Children’s Museum of Science and Technology Through Expansion And Relocation August 29th, 2014

Chemistry

Production of Toxic Ion Nanosorbents with High Sorption Capacity in Iran August 17th, 2014

Scientists fold RNA origami from a single strand: RNA origami is a new method for organizing molecules on the nanoscale. Using just a single strand of RNA, this technique can produce many complicated shapes. August 14th, 2014

Could hemp nanosheets topple graphene for making the ideal supercapacitor? August 12th, 2014

Iranians Find Novel Method for Processing Highly Pure Ceramic Nanoparticles August 12th, 2014

Possible Futures

Air Force’s 30-year plan seeks 'strategic agility' August 1st, 2014

IBM Announces $3 Billion Research Initiative to Tackle Chip Grand Challenges for Cloud and Big Data Systems: Scientists and engineers to push limits of silicon technology to 7 nanometers and below and create post-silicon future July 10th, 2014

Virus structure inspires novel understanding of onion-like carbon nanoparticles April 10th, 2014

Local girl does good March 22nd, 2014

Discoveries

A new, tunable device for spintronics: An international team of scientists including physicist Jairo Sinova from the University of Mainz realises a tunable spin-charge converter made of GaAs August 29th, 2014

Nanoscale assembly line August 29th, 2014

Copper shines as flexible conductor August 29th, 2014

Novel 'butterfly' molecule could build new sensors, photoenergy conversion devices August 28th, 2014

Materials/Metamaterials

Fonon Announces 3D Metal Sintering Technology: Emerging Additive Nano Powder Manufacturing Technology August 28th, 2014

SouthWest NanoTechnologies CEO Dave Arthur to Discuss “Carbon Nanotubes and Automotive Applications” at The Automotive Composites Conference and Expo 2014 (ACCE2014) August 28th, 2014

Nanodiamonds Are Forever: A UCSB professor’s research examines 13,000-year-old nanodiamonds from multiple locations across three continents August 27th, 2014

Competition for Graphene: Berkeley Lab Researchers Demonstrate Ultrafast Charge Transfer in New Family of 2D Semiconductors August 26th, 2014

Announcements

A new, tunable device for spintronics: An international team of scientists including physicist Jairo Sinova from the University of Mainz realises a tunable spin-charge converter made of GaAs August 29th, 2014

Nanoscale assembly line August 29th, 2014

New analytical technology reveals 'nanomechanical' surface traits August 29th, 2014

New Vice President Takes Helm at CNSE CMOST: Catherine Gilbert To Lead CNSE Children’s Museum of Science and Technology Through Expansion And Relocation August 29th, 2014

Environment

New Nanosorbent Helps Elimination of Colorants from Textile Wastewater August 25th, 2014

Production of Toxic Ion Nanosorbents with High Sorption Capacity in Iran August 17th, 2014

PerkinElmer to Display Innovative Detection and Informatics Offerings at ACS National Meeting & Exposition Detection, Data Visualization and Analytics for Chemistry Professionals August 8th, 2014

Nature inspires a greener way to make colorful plastics July 30th, 2014

Industrial

Nanoscale assembly line August 29th, 2014

Iranians Find Novel Method for Processing Highly Pure Ceramic Nanoparticles August 12th, 2014

PerkinElmer to Display Innovative Detection and Informatics Offerings at ACS National Meeting & Exposition Detection, Data Visualization and Analytics for Chemistry Professionals August 8th, 2014

Nanostructured metal-oxide catalyst efficiently converts CO2 to methanol: Highly reactive sites at interface of 2 nanoscale components could help overcome hurdle of using CO2 as a starting point in producing useful products July 31st, 2014

NanoNews-Digest
The latest news from around the world, FREE



  Premium Products
NanoNews-Custom
Only the news you want to read!
 Learn More
NanoTech-Transfer
University Technology Transfer & Patents
 Learn More
NanoStrategies
Full-service, expert consulting
 Learn More














ASP
Nanotechnology Now Featured Books




NNN

The Hunger Project







© Copyright 1999-2014 7th Wave, Inc. All Rights Reserved PRIVACY POLICY :: CONTACT US :: STATS :: SITE MAP :: ADVERTISE