ESTIMATING GYPSUM HEMIHYDRATE CONTENT USING DENSITY OF GYPSUM RECYCLED FROM WASTE GYPSUM BOARD

: Studies on recycled gypsum as a geotechnical improvement material have been extensively conducted, as the increase in gypsum board waste has become an urgent issue. In this paper, to investigate a method to measure gypsum hemihydrate content in a shorter period, the test results of the density method obtained in previous studies are reviewed to confirm whether sufficient accuracy could be secured even in a shortened measurement period. The results obtained showed that the way of the density test for cement is effective in measuring the density of gypsum, gypsum hemihydrate content could be estimated from the density with some accuracy, even with an elapsed period of 1 d, and a difference of only approximately 5% was observed. In addition, the density method was validated through a full-scale experiment using a rotary kiln furnace. The gypsum hemihydrate content obtained from the density method was consistent with that obtained from the X-ray diffraction analysis.