Rice University scientists show how voids, particles sap energy from cracks
What does one need to strengthen or toughen concrete? A lot of nothing. Or something.
The "nothing" is in the form of microscopic voids and the "something" consists of particular particles embedded in the most common construction material on Earth. Rice University materials scientist Rouzbeh Shahsavari and postdoctoral researcher Ning Zhang analyzed more than 600 computer models of concrete's inner matrix to determine that both voids and portlandite particles are significant players in giving the material its remarkable qualities.
The research appears this month in the Journal of the Mechanics and Physics of Solids.
Shahsavari and his team set out to provide new insights and to design guidelines and strategies to make the cement hydrate -- known as calcium-silicate-hydrate (C-S-H) -- at the heart of concrete more tunable from the molecules up. They found that while concrete may appear brittle at the macroscale, it incorporates ductile fracture mechanisms at the nanoscale that help to keep it from failing.
"C-S-H is the smallest building block in concrete, and we want to understand and control it to our advantage," Shahsavari said. "Modeling how its molecules interact helps us understand its nanoscale structure, defects and fracture toughness. But this is very difficult to study through experiments alone because of the scale of the features we're looking at."
This latest in a series of studies from the Rice lab looks at how the interaction of either random air voids or random portlandite particles in C-S-H influence the mechanical qualities of strength, stiffness and toughness, especially where voids meet propagating cracks.
"Besides C-S-H, portlandite is another product of cement hydration, but it forms in lower quantities compared with C-S-H and mainly exists as sort of inclusions or isolated islands surrounded by the C-S-H matrix," Shahsavari said. "Because portlandite has different crystalline features and mechanical properties than C-S-H, its presence and distribution can significantly impact the mechanics of C-S-H."
Using molecular dynamics simulations, the researchers found that cracks tended to follow the path of least resistance and turn in the direction of either the nanovoids or portlandite particles they encountered. By deflecting or changing the geometry of a crack, the voids and particles sapped the crack of energy. Shahsavari said this likely contributes to concrete's overall toughness.
"When it comes to cement hydrate's strength and toughness -- properties that are typically exclusive in man-made materials -- random voids and portlandite particles play a key role by regulating a series of competing deformation mechanisms, such as crack growth, crack deflection, voids coalescence, internal necking, accommodation and geometry alteration of voids and particles," Shahsavari said. "Our work decoded all such complex competing mechanisms."
For C-S-H that is more amorphous than crystalline (as in tobermorite concrete), they found the addition of portlandite particles induced strong chemical reactions that increased the strength as well as the toughness of the product. They also determined that for all the variations tested, the smaller the mean diameter of both voids and particles, the stronger the material.
Since more than 30 billion tons of concrete are used each year and its manufacture contributes up to 10 percent of carbon dioxide emissions worldwide, the payoff from any small tweak is worth the effort, Shahsavari said.
"Our results provide, for the first time, new evidence of ductile fracture mechanisms in cement hydrate that are reminiscent of crystalline alloys and ductile metals," Shahsavari said. "Given that crack growth and strength are an inherent property controlled by nanoscale deformation mechanisms, our findings can impact the mechanical properties of concrete at larger scales, opening up new opportunities and strategies to turn brittle cement hydrate into a ductile material. This would impact the modern engineering of durable concrete infrastructures and potentially other complex brittle materials."
The National Science Foundation, the National Institutes of Health and an IBM Shared University Research Award in partnership with CISCO, Qlogic and Adaptive Computing supported the research.
The researchers used the NSF-supported DAVinCI supercomputer administered by Rice's Center for Research Computing and procured in a partnership with Rice's Ken Kennedy Institute.
A copy of the paper is available at: http://dx.
More information about is available at:
Multiscale Materials Laboratory homepage: http://rouzbeh.
Related research from Rice:
This release can be found online at news.rice.edu.
Follow Rice News and Media Relations on Twitter @RiceUNews.
Located on a 300-acre forested campus in Houston, Rice University is consistently ranked among the nation's top 20 universities by U.S. News & World Report. Rice has highly respected schools of Architecture, Business, Continuing Studies, Engineering, Humanities, Music, Natural Sciences and Social Sciences and is home to the Baker Institute for Public Policy. With 3,910 undergraduates and 2,809 graduate students, Rice's undergraduate student-to-faculty ratio is 6-to-1. Its residential college system builds close-knit communities and lifelong friendships, just one reason why Rice is ranked No. 1 for best quality of life and for lots of race/class interaction by the Princeton Review. Rice is also rated as a best value among private universities by Kiplinger's Personal Finance. To read "What they're saying about Rice," go to http://tinyurl.
David Ruth | EurekAlert!
Spider silk key to new bone-fixing composite
20.04.2018 | University of Connecticut
Diamond-like carbon is formed differently to what was believed -- machine learning enables development of new model
19.04.2018 | Aalto University
University of Connecticut researchers have created a biodegradable composite made of silk fibers that can be used to repair broken load-bearing bones without the complications sometimes presented by other materials.
Repairing major load-bearing bones such as those in the leg can be a long and uncomfortable process.
Study published in the journal ACS Applied Materials & Interfaces is the outcome of an international effort that included teams from Dresden and Berlin in Germany, and the US.
Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) together with colleagues from the Helmholtz-Zentrum Berlin (HZB) and the University of Virginia...
Novel highly efficient and brilliant gamma-ray source: Based on model calculations, physicists of the Max PIanck Institute for Nuclear Physics in Heidelberg propose a novel method for an efficient high-brilliance gamma-ray source. A giant collimated gamma-ray pulse is generated from the interaction of a dense ultra-relativistic electron beam with a thin solid conductor. Energetic gamma-rays are copiously produced as the electron beam splits into filaments while propagating across the conductor. The resulting gamma-ray energy and flux enable novel experiments in nuclear and fundamental physics.
The typical wavelength of light interacting with an object of the microcosm scales with the size of this object. For atoms, this ranges from visible light to...
Stable joint cartilage can be produced from adult stem cells originating from bone marrow. This is made possible by inducing specific molecular processes occurring during embryonic cartilage formation, as researchers from the University and University Hospital of Basel report in the scientific journal PNAS.
Certain mesenchymal stem/stromal cells from the bone marrow of adults are considered extremely promising for skeletal tissue regeneration. These adult stem...
In the fight against cancer, scientists are developing new drugs to hit tumor cells at so far unused weak points. Such a “sore spot” is the protein complex...
13.04.2018 | Event News
12.04.2018 | Event News
09.04.2018 | Event News
20.04.2018 | Physics and Astronomy
20.04.2018 | Interdisciplinary Research
20.04.2018 | Physics and Astronomy