Gypsum produced by flue-gas desulfurization (FGD
gypsum) from the Mae Moh power plant, Thailand, was
precleaned, characterized and used as the starting material
for the preparations of [3-hemihydrate (15-HH) and multiphase
piasters with compositions within the three-phase
composition diagram of calcined gypsum [1]. Based on
performance requirements of commercial products, the
plasters obtained were fabricated into gypsum board specimens
using various additives as set regulators. The effect
of the additives on the morphology and mechanical properties
of the set plasters was studied in comparison with
those from natural gypsum. With the exception of calcium
sulfate dihydrate, it was found that additives caused a
characteristic change in structure with a trend towards
reduction of the aspect ratio of the hydrate crystals, as well
as a decrease in strength. The set plasters obtained from
FGD gypsum had higher strengths due to the finer crystal
size of the hydrate.