Chemical state analysis of alkali silica gel by using soft X-ray XAFS

Author(s): M. Mizuta, K. Ohda, K. Nakanishi, T. Ohta and T. Kojima
Paper category: conference
Book title: Microstructural-related Durability of Cementitious Composites
Editor(s): Guang Ye, K. van Breugel, Wei Sun and Changwen Miao
Print ISBN: 978-2-35158-129-2
e-ISBN: 978-2-35158-123-0
Publisher: RILEM Publications SARL
Publication year: 2012
Pages: 253 - 258
Total Pages: 6
Language: English

Abstract: The Alkali-Silica Reaction (ASR) is known as a reaction which occurs in concrete between alkali ions from cement and silicate from aggregates. Although the ASR has been studied intensively with a number of experimental approaches, its mechanism has not been completely clarified yet. The aim of this study is to investigate the chemical structure of ASR gel using the X-ray Absorption Fine Structure (XAFS) spectroscopy. The XAFS spectroscopy is a unique technique to reveal the local structure around an X-ray absorbing atom and can be applied to amorphous materials as in this case.
Samples were prepared in three different ways. Those in the first group were directly taken from a reinforced concrete specimen deteriorated by ASR. The specimen was cut out and some powder samples were collected from some portions of the cross section. Those in the second group were prepared in an ideal well-defined ASR process. Fine powdered reactive aggregates were dipped in 1 mol/L NaOH aqueous solution and filtrates were used as the samples. Those of the third group were prepared by an artificial ASR process. First, a block of a hardened cement paste was dipped in distilled water. Then, fine powdered reactive aggregates were immersed in the solution and the supernatant liquid was skimmed off. Both of two types of the sample were prepared in liquid and dried states.
The following is a summary of this study:
(1) Any spectral difference was not observed between the reactive aggregate before and after use and between the surface and bulk regions of the reactive aggregate.
(2) Only difference observed is the Ca content of the non-reactive aggregate, which is more than the reactive aggregate, and Ca exists not as CaO, but CaCo₃.
(3) The ASR was confirmed in the artificial condition, and the ASR product was found to be close to water glass.
(4) Since this is the result of an ideal situation, more realistic experiments with more sophisticated methods will be necessary to clarify the mechanism of the ASR.
Keywords: Alkali-Silica Reaction, XAFS, ASR gel, chemical structure

Online publication: 2012-05-16
Publication Type: full_text
Public price (Euros): 0.00