Homogeneous single C-S-H gels have been prepared for the investigation of alkali binding potential and crystallisation. A distribution coefficient, R<sub>d</sub>, was introduced to express the partition of alkali between solid and aqueous phases at 25°C. R<sub>d</sub> is independent of alkali hydroxide concentration and depends only on Ca:Si ratio over wide ranges of alkali concentration. The trend of numerical values of R<sub>d</sub> indicates that alkali bonding into the solid improves as its Ca:Si ratio decreases. Reversibility is demonstrated, indicating a possibility of constant R<sub>d</sub> value of the material. Al has been introduced to form C-A-S-H gels and their alkali sorption properties also determined. Al substituted into C-S-H markedly increases R<sub>d</sub>, indicating enhancement of alkali binding. However, the dependence of R<sub>d</sub> on alkali concentration is non-ideal with composition. A two-site model for bonding is presented. Crystallisation both under saturated steam and 1 bar vapour pressure has been investigated. It has been shown that heat treatment by saturated steam causes crystallisation of gels. The principal minerals obtained were (i) C-S-H gel and Ca(OH)<sub>2</sub> at ~55°C, (ii) 1.1 nm tobermorite, jennite and afwillite at 85-130°C, and (iii) xonotlite, foshagite and hillebrandite at 150-180°C. Properties of crystalline C-S-H were also reported for reversible phase transformation, pH conditioning ability, seeding effect and solubility. At 1 bar pressure, crystallisation is slower than in saturated steam due to lower water activity. Tobermorite-like nanodomains develop during reaction at low Ca/Si ratios. In some Ca-rich compositions, Ca(OH)<sub>2</sub> is exsolved and occurs as nano-sized crystallites.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:310573 |
| Date | January 2000 |
| Creators | Hong, Sung-Yoon |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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