Mechanisms by which ground granulated blastfurnace slag prevents sulphate attack of lime-stabilised kaolinite

Abstract This paper describes the mechanisms by which ground granulated blastfurnace slag (ggbs) prevents sulphate attack of lime-stabilized kaolinite. Microstructural and mineral phase analyses of compacted cylinders of lime-stabilised kaolinite with different percentages of lime replacement by ggbs have been carried out using scanning electron microscopy (SEM) and x-ray diffractometry (XRD). The cylinders were immersed in 4.2% Na2SO4 solution and also in deionised water for various time periods. The exposure data showed that the effect of ggbs in preventing the formation of expansive ettringite in lime-stabilised kaolinite, which had been exposed to 4.2% Na2SO4 solution was dramatic. The results also revealed three different growth mechanisms of ettringite in the lime-ggbs-kaolinite systems that were exposed to 4.2% Na2SO4 solution. These are: well-formed randomly orientated rods of high aspect ratio growing in pores and cracks, short needles covering surfaces of existing particles, and ‘flower-like’ needles radiating from isolated points and scattered randomly through the sample.

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