Concrete has been one of mankind’s most important building materials for thousands of years. Previously, we discussed efforts to crack the code of ancient Rome’s high-performance concrete, a 60-year lifecycle assessment of concrete homes by MIT, efforts to lower the carbon dioxide output involved with concrete production, and bacterially-infused concrete that repairs itself.
Science Daily reports that that a somewhat new flavor of concrete, steel-fiber reinforced concrete (SFRC), might have applications in conventional construction, in addition to some of the more esoteric and high performance situations where it has currently been used:
Reinforcing concrete with steel bars is a very common practice in construction. The industrial engineer and researcher Aimar Orbe-Mateo (UPV/EHU-University of the Basque Country) has studied the possible use of a material that is normally used for other applications for these tasks: concrete reinforced with steel fibers. What the study shows is that this material has certain advantages over conventional reinforced concrete; among others, it is less prone to cracking, and it can be used for purposes like the manufacture of cylindrical holding tanks.
According to Aimar Orbe-Mateo, an engineer at the Faculty of Engineering in Bilbao, right from the start of the study it was clear that “it had to be something that had a practical application, not just any piece of research.” Sothe team produced a material for research purposes and which had the potential for being used in construction: steel fiber reinforced self-compacting concrete (SFRSCC)…
Alongside the laboratory tests, the team also tested the use to which the material could in fact be put.For this purpose, a wall three metres high and six metres long was built and divided into 380 samples on which various tests were carried out, destructive as well as non-destructive ones, “to determine the structural capabilities of the steel fibers and, in general, the toughness of the wall,” highlighted Orbe.
The conclusion that the researchers reached is that this self-compacting, steel-fiber reinforced concrete is more resistant to cracking and is also more sustainable. The researchers were also quick to point out that the biggest obstacle to widespread adoption is the slow pace at which builders adopt new practices.
Source: Science Daily
Maintaining the Quality of Steel-Fiber Reinforced Concrete
Due to certain properties of SFRC, researchers and contractors alike have struggled to produce consistent results using the material. Specifically, evaluating the matrix of the steel fibers (the distribution of the fibers throughout a given section of concrete) in a sample is problematic because the steel fibers are difficult to see using standard test methodologies. If the fibers are not evenly distributed and oriented properly, the resulting concrete’s strength is greatly reduced.
This factor has meant that adoption of SFRC is extremely low. The risk in using a product whose quality can’t be readily established is just too great.
Last Fall, researchers at Fraunhofer Institute for Industrial Mathematics ITWM in Kaiserslautern, Germany reported success in faster and more efficient ways of evaluating SFRC:
Help has now arrived in the form of a new analysis method developed by mathematicians at the Fraunhofer Institute for Industrial Mathematics ITWM in Kaiserslautern. It uses probability calculations to work out the distribution of all the fibers within concrete samples in a matter of seconds. Project leader Dr. Ronald Rösch and his team of experts use X-ray computed tomography in a way he describes as not dissimilar to how CT scans are used in medicine. “The only difference is that we use it to examine samples taken from finished concrete components, not people,” Dr. Rösch explains. Scientists take a core sample about ten centimeters in length from the concrete to be tested. The sample is then X-rayed using an industrial CT scanner at a resolution around a thousand times finer than that achieved by medical scanners. This system reveals even the finest micrometer-sized structures within the material, and generates a high-resolution 3D data set for the concrete sample that contains some eight billion pixels — a huge file. Rösch and his team then use their new software to analyze this image data. By assessing differences in contrast, the software is able to assign each pixel to a particular structure within the material, be it concrete, a small stone, a trapped air bubble or a steel fiber. As the software works its way through the data set, all the fibers gradually become visible in the image.
Sadly, this approach still is not “ready for prime time”:
It goes without saying that Rösch is aware of the system’s current limitations; a CT scanner the size of a small wall closet is simply too big for practical use on a building site. “But this is an obstacle we can overcome,” he says. “Our colleagues at the Fraunhofer Development Center for X-ray Technology EZRT in Erlangen have already developed a machine the size of a beer crate.” A prototype for practical application could be available in five years, Rösch estimates.
Source: Science Daily
Image courtesy Wikipedia