The engineering properties of a South African class F fly ash were studied as a
potential base liner for a dry coal ash dump. In order to increase the unconfined
compression strength, lime and gypsum were added to the fly ash while also aiding
in reducing the hydraulic conductivity. Lime was added in the range of 1 to 10%
while the gypsum amounts were varied at 1% and 3% per specimen. The constant
head method was used to determine the hydraulic conductivity of compacted
specimens in the laboratory. Gypsum was observed to have more influence in
reducing the hydraulic conductivity as specimens with 3% gypsum had a more
reduced hydraulic conductivity that those with 1%. The variations in lime
percentages did not appear to reduce the hydraulic conductivity but rather displayed
higher values than fly ash specimens without additives when higher percentages of
lime were used. A fly ash admixture of 3% lime and 3% gypsum was found to have
the lowest hydraulic conductivity of 2.27 x10-9 m/s after 60 days of percolating with
brine water.
The unconfined compression strength also appeared to be more influenced by
gypsum than lime percentages as specimens with 3% gypsum obtained higher
strength values than those with 1% gypsum added. Unreacted lime was observed in
specimens with higher percentages of lime added and these specimens also
presented lower strength values. The addition of lime and gypsum was observed to
have limited the release of some trace elements from fly ash. The secondary mineral
ettringite was detected and could have possibly precipitated and captured out these
toxic elements. An attempt was also made to increase the plasticity index of fly ash
using lignosulphonate and values recommended by the South African legislative
guidelines for liner materials were obtained. The plasticity was however not retained
with subsequent leaching.
Two multi-layer liner systems were loaded under different compaction rates in
permeameter cells with fitted inflow and outflow points. The primary liners of both
systems were able to contain over 95% of leachate that percolated through a waste
layer. Compaction rate was found to affect the liners performance as primary liners with a higher compaction rate had less seepage than primary liner compacted at a
lower rate. An addition of lime and gypsum improved the overall engineering
properties of fly ash to levels accepted by the South African legislative guidelines for
a liner material that is able to line hazardous waste. Even though concentrations of
some trace elements in fly ash were reduced by addition of lime and gypsum the
level of some of these trace elements remain above the threshold set by South
African legislative guidelines and therefore remains a health and environmental
concern.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-05132014-104626 |
| Date | 13 May 2014 |
| Creators | Mokhahlane, Lehlohonolo |
| Contributors | Prof G Steyl |
| Publisher | University of the Free State |
| Source Sets | South African National ETD Portal |
| Language | en-uk |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.uovs.ac.za//theses/available/etd-05132014-104626/restricted/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University Free State or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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