Industrial dispersing aids based on bark and wood extracts.

[摘要] The object of this dissertation is to develop a cost effective plasticiser/water-reducer fromtannin extracts which does not retard initial strength development. Model compounds oftannins indicated the suitability of substiuued phenols for this purpose, Catechol withadjacent hydroxide groups gave a good combination of improved workability withcompressive strengths equivalent to the control. Combinations with ammonia andtorrnaldehyde resulted in some greatly improved performances, but also reduced stabilityof the additives. Urea and metabisulphite did provide some improvements ai!1ddid notadversely affect shelf life.Some of the tannin extracts tested on their own gave considerate improvements inworkability and some strengths. To improve the stability of extract solutions, tanninswere modified with urea, metabisulphite, small amounts of potassium hydroxide and aalcohol mixture used for pretreatment. Only the first two listed were consistently effectivewithout producing any disadvantages. They even further improved the concreteperformance of condensed tannins in particular. Small additions of TEA or its acetate saltresulted to better one day strengths of the modified tannins.Analytical techniques such as infrared and nuclear magnetic resonance were used tomonitor some; modifications of the tannins and their result. A test representing earlyhydration conditions and X-ray diffraction provided clues to the additives mechanism inits interaction with cement. The additives performance was evaluated by comparison witha leading plasticiser/water-reducer, an independent concrete testing laboratory andconduction calorimetry by a research and testing council. A tannin based plasticiser madelargely from local raw materials was quickly accepted during a recession by brick andprecast manufactures .

[发布机构] University of the Witwatersrand