Sulphate Expansion of Lime-Stabilized Kaolinite: I. Physical Characteristics

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Abstract
The effect of gypsum additions on the physical performance of lime-stabilized kaolinite has been determined. Kaolinite containing different amounts of lime (i.e. 6 and 14 wt%) and gypsum (i.e. 2,4,6 and 8 wt%) was compacted into cylinders and moist cured at 30°C and 100% r.h. for periods from 2 days up to 20 weeks. Unconfined compressive strength, expansion during curing and subsequent soaking, and water absorption and swelling pressure were determined. The addition of lime and subsequent moist curing was found to reduce substantially the water absorption, linear expansion and swelling pressure of the kaolinite. Although small amounts of gypsum further reduced these parameters, higher gypsum levels (up to 8 wt%) produced substantial water absorption, extreme expansion and high swelling pressures. This excessive volume instability when in contact with water was found, for a particular lime content, to be very sensitive to both the initial moist curing time and the gypsum content. The results indicate that the overriding expansion mechanism operating is imbibition of water or transfer of water by osmosis. The question of what drives this process is the subject of Part II of this paper.