Elastic and structural properties of alkaline-calcium silica hydrogels
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Sergey N. Tkachev and Murli H. Manghnani Hawaii Institute of Geophysics and Planetology, School of Ocean and Earth Sciences and Technology, University of Hawaii at Manoa, Honolulu, Hawaii 96822
Richard A. Livingston Office of Infrastructure R&D, Federal Highway Administration, McLean, Virginia 22101 (Received 29 March 2004; accepted 28 September 2004)
Brillouin scattering has been used to study the elastic properties of alkaline-calcium silica hydrogels synthesized from the precipitation of sodium silicate solution with calcium hydroxide. To the best of our knowledge, this is the first determination of the bulk elastic moduli for this type of alkaline-calcium silica hydrogel, also referred to as the alkali-silica reaction (ASR) gel. The measured bulk moduli for the alkaline-calcium silica hydrogels were found to be between 4 and 8 GPa for the gel containing 0.08 M Ca(OH)2 and between 10 and 25 GPa for the gel containing 0.8 M Ca(OH)2, increasing with increasing pressure. Fourier transform infrared measurements were made to correlate the moduli to the silica speciation and network formation within the gels as a function of Ca(OH)2 content. Significantly, for the concentrations considered, both the interconnection of the silica species and the bulk modulus increased with increasing Ca(OH)2 content. On this basis, Brillouin scattering was confirmed to be a useful method for distinguishing between the bulk moduli of alkaline-calcium silica hydrogels in terms of chemical composition. The potential for further characterization of ASR gels as a function of composition and water content by this technique is highly promising.
I. INTRODUCTION
One of the most destructive expansive reactions in concrete is the alkali-silica reaction (ASR) since it causes cracking and degradation that limit the durability and performance of concrete.1,2 While it is accepted that ASR results in the formation of gels that cause damage through swelling, the physicochemical nature of these gels and their precise expansive mechanism remain poorly understood.3 In particular, limited effort has been made to characterize the elastic properties of ASR gels, chemically referred to as alkaline-calcium silica hydrogels, in relation to their molecular composition and nanostructure. Even less effort has been made to characterize the elastic properties of ASR gels as a function of the conditions (e.g., hydrostatic pressures) ordinarily experienced during the service life of concrete. Such information would greatly enhance our overall understanding of the mechanism of ASR damage. a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0061 344
http://journals.cambridge.org
J. Mater. Res., Vol. 20, No. 2, Feb 2005 Downloaded: 23 Mar 2015
The elastic modulus of alkaline-calcium silica hydrogels is a fundamental parameter of intrinsic importance to their characterization. This is because it is central to any micro- or chemo-mechanical models of expansion or swelling, which are growing in popularity as predictive and p
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