ISSN:
1662-9752
Source:
Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
A number of failures of large concrete structures during construction have been reported in the lastdecades [1]. The overestimation of concrete strength at early ages was one of the reasons for thefailures. Consequently, reliable information about early age properties of the material is essential toguarantee life-time performance of structures. Portland cement is a complex heterogeneousparticulate material and a full knowledge of kinetics of the hydration reactions, for example, is stillmissing. Gel constitutes the major phase in the hardening cement paste and the correspondingstructure and dynamics represent an important contribution to determine the concrete performance.X-ray diffraction, which is widely used for the study of crystalline cement components, does notgive information about the gel, amorphous, phase. Conversely, 1H stray-field magnetic resonanceimaging (STRAFI-MRI) technique has proved to be a powerful tool to follow the early hydrationand hardening periods of Portland cement (type I) [2-4]. The setting of cement pastes depends onparameters like the initial water/cement ratio, R, or particle size of the powder (G) and thecompressive strength can be used to characterize the behaviour of hardening concrete. Wateravailability at the particle surfaces, which is controlled by R and G, limits cement hydration. At lowR, G effects are less important. In general, it is accepted that for R〈0.42, unreacted solid remain, asall the free volume is filled with hydration products [5]. For example, hydration of Portland cementpastes as a function of R (0.24-0.48) was studied using by STRAFI-MRI and hydrogen maps, fromdifferent types of water (capillary, gel or chemically bound water), enabled a spatially-resolvedkinetics to be obtained [4]. Using STRAFI-MRI was now evaluated the influence of G (〈70 μm to〈 90 μm) on the early stages of hydration and hardening of Portland cement.Portland cement uses extend well beyond construction. For example, a mineral trioxide aggregate isnow being applied as a root-end filling material, which was shown to have a similar chemicalconstitution to that of Portland cement except for the addition of bismuth compounds, seemingly tomake the materials radiopaque for dental use [6]
Type of Medium:
Electronic Resource
URL:
http://www.tib-hannover.de/fulltexts/2011/0528/02/12/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.514-516.1633.pdf
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