engineers discover what causes concrete creep

[amor de cosmos]

MIT engineers find way to slow concrete creep to a crawl
Denise Brehm, Civil and Environmental Engineering
June 15, 2009

MIT civil engineers have for the first time identified what causes the most frequently used building material on earth -- concrete -- to gradually deform, decreasing its durability and shortening the lifespan of infrastructures such as bridges and nuclear waste containment vessels.

In a paper published in the Proceedings of the National Academy of Sciences (PNAS) online Early Edition the week of June 15, researchers say that concrete creep (the technical term for the time-dependent deformation that occurs in concrete when it is subjected to load) is caused by the rearrangement of particles at the nano-scale.

"Finally, we can explain how creep occurs," said Professor Franz-Josef Ulm, co-author of the PNAS paper. "We can't prevent creep from happening, but if we slow the rate at which it occurs, this will increase concrete's durability and prolong the life of the structures. Our research lays the foundation for rethinking concrete engineering from a nanoscopic perspective."



In their PNAS paper, the researchers show experimentally that the rate of creep is logarithmic, which means slowing creep increases durability exponentially. They demonstrate mathematically that creep can be slowed by a rate of 2.6. That would have a truly remarkable effect on durability: a containment vessel for nuclear waste built to last 100 years with today's concrete could last up to 16,000 years if made with an ultra-high-density (UHD) concrete.

http://web.mit.edu/newsoffice/2009/creep-0615.html