No matter if it is a giant complex, a high-rise, or an underground project, modern architecture cannot get along without concrete. The component in concrete that holds the other components together is cement.
In order to control the properties of concrete, it is important to know what occurs as it hardens. German scientists have now successfully watched the first few seconds in the “life” of cement by means of X-ray diffraction. In the journal Angewandte Chemie, they explain the role of the superplasticizers added to concrete.
Concrete is made from sand, gravel, additives, water, and cement. Portland cement is a complex mixture of finely ground limestone, clay, sand, and iron ore—mainly calcium silicate with fractions of aluminum and iron compounds and sulfates. Once mixed with water, chemical reactions occur between the components of cement, and it solidifies and hardens. When the process is finished, it remains solid and stable, even under water.
The enormous stability of concrete comes from crystalline needles that form during this process and are firmly interlocked with each other. Various additives are used to optimize the properties of concrete, including a class of superplasticizers based on polycarboxylate (PCE). These improve the flow of the concrete, making it easier to pour. The water content can be reduced to improve the concrete’s compressive strength.
“Detailed insight into the different stages of the hydration process is essential for a more complete understanding of how these processes can be effectively influenced,” explains Franziska Emmerling of the BAM Federal Institute of Materials Research and Testing in Berlin (Germany). “In particular, the phase development at the beginning of hydration is not yet well understood.” The very rapidly initiated reaction of the cement clinker component C3A (Ca3Al2O6) with sulfate (SO42-) to form ettringite (Ca6Al2(SO4)3(OH)12•26H2O) seems to be critical. By means of high-resolution X-ray diffraction experiments, Emmerling’s team has now been able to follow this reaction on the millisecond timescale. The deflections experienced by X-rays as they pass through a material provide information about its crystal structure. In order to prevent interference from any supporting material, the sample is held in suspension by acoustic waves.
This has also made it possible to clarify the function of PCE superplasticizers. Says Emmerling: “Immediately after water contacts the cement, the PCE adsorbs onto the surface of the clinker C3A; the particles remain in suspension because they then repel each other. The PCE is then gradually replaced by sulfate ions, which retards the incipient ettringite crystallization. This leaves more free water in the system, dissolving more crystalline components—the resulting concrete can thus flow for a longer period and becomes more dense.”
Angewandte Chemie International Edition, Permalink to the article: http://dx.doi.org/10.1002/anie.201200993
Franziska Emmerling | Angewandte Chemie
Argon is not the 'dope' for metallic hydrogen
24.03.2017 | Carnegie Institution for Science
Researchers make flexible glass for tiny medical devices
24.03.2017 | Brigham Young University
Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.
The results will be published on March 22 in the journal „Astronomy & Astrophysics“.
Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...
Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...
In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...
20.03.2017 | Event News
14.03.2017 | Event News
07.03.2017 | Event News
24.03.2017 | Materials Sciences
24.03.2017 | Physics and Astronomy
24.03.2017 | Physics and Astronomy