科研之友
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摘要
A chemical model is presented here for investigation of the alkali-silica reaction (ASR) of reactive aggregates. The ASR formation was studied with experiments involving aggregates (Yoro- and Seto-chert) and Ca(OH)(2) with alkalinity under accelerated conditions at 80 degrees C. The role of Ca on ASR formation was also investigated by varying the contents of Ca(OH)(2) in the reacting system. The investigation employed Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES), X-ray Diffraction (XRD), Scanning Electron Microscopy with Energy Dispersive X-ray Analysis (SEM/EDX), and Si-29 Nuclear Magnetic Resonance (Si-29-NMR) analysis. The experimetits demonstrated there are two types of ASR which are produced (i) tobermorite type C-S-H due to the reaction between dissolved Si and Ca ions and (ii) alkali calcium silicate hydrate (C-Na-S-H) from the reactions among dissolved Si, Ca and Na ions. It was found that by addition of small content of Ca(OH)(2), the XRD peaks of C-S-H located at 29.3 degrees 2 theta shift to 30.0 degrees 2 theta and the spectra of Si-29-NMR displayed the peaks at -79 ppm (Q(1) sites), -85 ppm (Q(2) sites) and -95 ppm (Q(3) sites). These results indicated the formation of ASR of C-Na-S-H. Correlating these experimental results with simulation by PHREEQC program leads to insight into the mechanism of ASR-affected structures. The sequence of ASR have confirmed, in particular the ASR formation in the presence of Ca(OH)(2). The C-S-H and C-Na/K-S-H presented here ensure that tobermorite type C-S-H is the first likely structures as analog ASR product when Ca ions are present. After Ca ions almost consumed, C-Na/K-S-H is readily formed due to the available source of alkali.
- 出版日期2015-10-1
