A dissertation submitted to the Faculty of Science
University of the Witwatersrand, Johannesburg
for the degree of Master of Science / The object of this dissertation is to develop a cost effective plasticiser/water-reducer from
tannin extracts which does not retard initial strength development. Model compounds of
tannins indicated the suitability of substiuued phenols for this purpose, Catechol with
adjacent hydroxide groups gave a good combination of improved workability with
compressive strengths equivalent to the control. Combinations with ammonia and
torrnaldehyde resulted in some greatly improved performances, but also reduced stability
of the additives. Urea and metabisulphite did provide some improvements ai!1ddid not
adversely affect shelf life.
Some of the tannin extracts tested on their own gave considerate improvements in
workability and some strengths. To improve the stability of extract solutions, tannins
were modified with urea, metabisulphite, small amounts of potassium hydroxide and a
alcohol mixture used for pretreatment. Only the first two listed were consistently effective
without producing any disadvantages. They even further improved the concrete
performance of condensed tannins in particular. Small additions of TEA or its acetate salt
resulted to better one day strengths of the modified tannins.
Analytical techniques such as infrared and nuclear magnetic resonance were used to
monitor some; modifications of the tannins and their result. A test representing early
hydration conditions and X-ray diffraction provided clues to the additives mechanism in
its interaction with cement. The additives performance was evaluated by comparison with
a leading plasticiser/water-reducer, an independent concrete testing laboratory and
conduction calorimetry by a research and testing council. A tannin based plasticiser made
largely from local raw materials was quickly accepted during a recession by brick and
precast manufactures . / Andrew Chakane 2018
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/26124 |
| Date | January 1994 |
| Creators | Kaspar, Hanno Rolf Erich. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
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