Microstructural analysis of young cement pastes using impedance spectroscopy during pore solution exchange
✍ Scribed by G.M. Moss; B.J. Christensen; T.O. Mason; H.M. Jennings
- Publisher
- Elsevier Science
- Year
- 1996
- Tongue
- English
- Weight
- 615 KB
- Volume
- 4
- Category
- Article
- ISSN
- 1065-7355
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✦ Synopsis
Impedance spectra were collected in situ during the exchange of the aqueous phase with an organic solvent in young (1-28 days old) ordinary portland cement (OPC) pastes at two water-to-cement ratios (w/c = 0.35 and 0.70). The high initial values of dielectric constant (103-105) and the rapid decline upon exchange support a model of dielectric amplification where layers of calcium silicate hydrate (C-S-H) gel separate capillary pores. When the liquid in pastes of w/c = 0.35 was exchanged with isopropanol, the residual dielectric constants were typically between 102-105, indicating that C-S-H has a dielectrically amplified microstructure. After methanol exchange, however, the residual dielectric constant was much smaller, 10-100. This suggests there are two kinds of water within C-S-H gel in pastes of w/c = 0.35--that which is exchangeable by both solvents (capillary pores) and that which is exchangeable by methanol but not isopropanol (gel pores). For pastes of w/c = 0.70, differences due to solvent types were negligible. These observations suggest that the nature of C-S-H varies with w/c ratio. ADVANCED CEMENT BASED MATERIALS 1996, 4, 68-75 ml ~ any aspects of the fragile and complex micro- structure of young cement paste make it prohibitive to study by conventional means, particularly if drying is required. Recently, however, impedance spectroscopy (IS) has emerged as a nondestructive technique for in situ microstructural analysis . Data are collected over a range of frequencies, varying from hertz to megahertz, allowing for the separation of bulk and electrode polarization effects. This enables the study of both bulk conductivity, from which diffusivity and permeability can be inferred , and electrode (steel rebar) corrosion .