Preliminary studies of methylene blue adsorption as a method of evaluating degradable smectite--bearing concrete aggregate sands
✍ Scribed by Nelson B. Higgs
- Publisher
- Elsevier Science
- Year
- 1986
- Tongue
- English
- Weight
- 567 KB
- Volume
- 16
- Category
- Article
- ISSN
- 0008-8846
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✦ Synopsis
Smectite-bearing degradable concrete aggregate sands have given difficulties during construction of three dams and because of this feature similar type sands were rejected at two other dams.
The features that make these type sands objectionable is loss of slump, excessive water demands and potential drying shrinkage volume changes in the concrete. Methylene blue dye is adsorbed more by smectite than the other clay minerals.
For example, about three times as much chlorite is required to give the same MBA value as for smectite.
Accordingly, the MBA method was performed in separate sieve sizes of four sands: Mabels Pit, Libby, Elk Creek natural and Elk Creek West branch rod-mill. Mabels Pit is one of the source sands that caused construction difficulties.
The West Branch rod-mill sand contains mixtures of chlorite and minor smectite, the Libby sand mixtures of chlorite and illite and the Elk Creek natural and Mabels Pit only smectite.
The Libby and West Branch sands gave low MBA values, the smectite in the Mabels Pit sand was concentrated primarily in the fine sand sizes and for these fractions gave high MBA values.
The Elk Creek natural contains only minor amounts of smectite but gave high MBA results for all sieve fractions. This anomaly is judged to be from marked weathering of this sand. A degradation activity index (DAI) is derived to better pinpoint the degradation versus MBA values for these sands.
The DAI is 78.3 for Mabels Pit, 27.8 for Elk Creek natural but less than 6 for West Branch and Libby sands. ',./o I 16 No. ~' N.B. Higgs