Their refinements to our understanding of how cement and concrete actually work, reported this week in Nature Materials,* ultimately may make possible improvements in the formulation and use of cement that could save hundreds of millions of dollars in annual maintenance and repair costs for concrete structures and the country’s infrastructure.
Cement may be the world’s most widely used manufactured material—more than 11 billion metric tons are consumed each year—but it also is one of the more complex. And while it was known to the Romans, who used it to good effect in the Colosseum and Pantheon, questions still remain as to just how it works, in particular how it is structured at the nano- and microscale, and how this structure affects its performance.
Cement is something of a paradox. It requires just the right amount of water to form properly—technically it’s held together by a gel, a complex network of nanoparticles called calcium silicate hydrate (C-S-H) that binds a significant amount of water within its structure. But once the cement has set, the C-S-H structure retains a tough, unchanging integrity for centuries, even in contact with water. To date, attempts to pinpoint the amounts and different roles of water within the C-S-H in cement paste have required taking the water out, either by drying or chemical methods. The NIST/Northwestern researchers instead combined structural data from small-angle neutron scattering experiments at the NIST Center for Neutron Research and from an ultrasmall-angle X-ray scattering instrument built by NIST at the Advanced Photon Source at Argonne National Laboratory. Their experiments are the first to classify water by its location in the cured cement.
As a result, the researchers were able to distinguish—and measure—the difference between water physically bound within the internal structure of the solid C-S-H nanoparticles and adsorbed or liquid water between the nanoparticles. They also measured a nanoscale calcium hydroxide structure that co-exists with the C-S-H gel. The new data, which imply significantly different values for the formula and density of the C-S-H gel than previously supposed, have implications for defining the chemically active surface area within cement, and for predicting concrete properties. They also may lead to a better understanding of the contribution of the nanoscale structure of cement to its durability, and how to improve it.
Michael Baum | EurekAlert!
Manchester scientists tie the tightest knot ever achieved
13.01.2017 | University of Manchester
CWRU directly measures how perovskite solar films efficiently convert light to power
12.01.2017 | Case Western Reserve University
Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.
As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...
At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).
Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...
Many pathogens use certain sugar compounds from their host to help conceal themselves against the immune system. Scientists at the University of Bonn have now, in cooperation with researchers at the University of York in the United Kingdom, analyzed the dynamics of a bacterial molecule that is involved in this process. They demonstrate that the protein grabs onto the sugar molecule with a Pac Man-like chewing motion and holds it until it can be used. Their results could help design therapeutics that could make the protein poorer at grabbing and holding and hence compromise the pathogen in the host. The study has now been published in “Biophysical Journal”.
The cells of the mouth, nose and intestinal mucosa produce large quantities of a chemical called sialic acid. Many bacteria possess a special transport system...
UMD, NOAA collaboration demonstrates suitability of in-orbit datasets for weather satellite calibration
"Traffic and weather, together on the hour!" blasts your local radio station, while your smartphone knows the weather halfway across the world. A network of...
Fiber-reinforced plastics (FRP) are frequently used in the aeronautic and automobile industry. However, the repair of workpieces made of these composite materials is often less profitable than exchanging the part. In order to increase the lifetime of FRP parts and to make them more eco-efficient, the Laser Zentrum Hannover e.V. (LZH) and the Apodius GmbH want to combine a new measuring device for fiber layer orientation with an innovative laser-based repair process.
Defects in FRP pieces may be production or operation-related. Whether or not repair is cost-effective depends on the geometry of the defective area, the tools...
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16.01.2017 | Power and Electrical Engineering