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Author(s): Surendra P. Shah
Paper category: Proceedings
Book title: Proceedings of CONSEC13 Seventh International Conference on Concrete under Severe Conditions - Environment and Loading Volume I
Editor(s): Z.J. Li, W. Sun, C.W. Miao, K.Sakai, O.E. Gjørv, N.Banthia
ISBN: 978-2-35158-124-7
e-ISBN: 978-2-35158-134-6
Publisher: RILEM Publications SARL
Publication year: 2013
Pages: 36-37
Total Pages: 961
Language : English

Abstract: In recent years, many studies in cement and concrete research have demonstrated the potential of incorporating nanoparticles in cementitious materials to exhibit enhanced or novel properties. Through nanomodification, it is possible to improve rheology, hydration kinetics, mechanical properties, durability, shrinkage, and even modify the structure of calcium silicate hydrate (C-S-H) itself. This presentation highlights recent work performed at Northwestern University pertaining to the use of nanoparticles (nanoclay, nanosilica, nano-calcium carbonate and carbonnanotubes) and various test methods in understanding the controlling effects of nanomaterials on concrete.
Replacing cement with fly ash is a strategy to reduce cement consumption and subsequently the carbon footprint of concrete. However, the shortcoming of the approach is that fly ash has negative effects on the early-age properties. Studies have demonstrated the potential of nanomodification in improving these properties in fly ash-cement systems. An in-depth study on the mechanisms underlying the effect of colloidal nanosilica(CNS) on the compressive strength development of high-volume fly ash (HVFA) cement mixtures is discussed. It was found CNS increased early age strength of HVFA, but the high pozzolanic activity of CNS increasedcalcium hydroxide (CH) consumption, impacting the long term reactions of fly ash. A separate study on calcium carbonate nanoparticles (nanoCaCO3) focused on dispersion to enhance the beneficial effect of the nanoparticles on the early-age properties of fly ash-cement pastes. It was apparent that the dispersion with ultrasonication of nanoparticles leads to a greater acceleration in rate of hydration. The shortened induction period indicates that this is tied to a seeding effect.Ultrasonicated nanoCaCO3 exhibited a substantial improvement in compressive strength compared to the plain 30% fly ash (30FA) paste. Dispersed nanoparticles were found to improve the rate of hydration and early-age compressive strength of fly ash-cement pastes while aggregated particles had a detrimental effect.
It has been demonstrated that a small addition of nanoclays (< 1% by mass of binder) can significantly increase the green strength of self-consolidating (SCC) mixtures. It was also found that such properties can effectively reduce SCC formwork pressure. This behavior has been tied to flocculation behavior, where studies have shown that clays increase flocculation strength and floc size.
The effect of multiwall carbon nanotubes (MWCNTs) on the macro and nanoscale mechanical properties of cement paste was investigated. An effective method of dispersing carbon nanotubes in cement paste matrix, by applying ultrasonic energy and using a surfactant, was developed. A detailed study on the effects of CNTs concentration and aspect ratio was conducted. The nano-mechanical properties of CNTs nanocomposites were compared to cement paste with silica fume. Samples reinforced with CNTs exhibit much higher Young’s modulus than plain cement paste. It can be observed that the optimum amount of CNTs depends on the aspect ratio. These results also indicate that the incorporation of CNTs increased the amount of high stiffness C-S-H gel resulting in a stronger material.

Online publication : 2013
Publication type : full_text
Public price (Euros) : 0.00

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