Improving properties of high-volume fly ash cement paste blended with β-hemihydrate from flue gas desulfurization gypsum

摘要

The present study investigated the effects of utilizing the treated flue gas desulfurization (FGD) gypsum on the improvement of properties of high volume fly ash (FA) cement pastes. The FGD gypsum was subjected to heat treatment at 150 degrees C in a kiln to change its compositions and convert into beta-hemihydrate gypsum. The ordinary Portland cement (OPC) was partially used in the FA-cement paste at two different levels: 50 wt% for Set I mixture and 30 wt% for Set II mixture. The beta-hemihydrate was added to partially replace the FA with 3,5, and 10 wt%, respectively, for both Sets. Experimental works, including workability, setting time, compressive strength, dynamic moduli, and microstructural analysis by scanning electron microscopy (SEM) and X-ray diffraction (XRD) tests were conducted. The workability of fresh blended pastes was found to be decreased with the increase of beta-hemihydrate amount, while the compressive strength, dynamic moduli and thermal conductivity were improved. Lower amount of beta-hemihydrate was found to be more effective in improving the early-age strength, while higher amount of beta-hemihydrate had more effect on enhancing the later-age strength. Based on the microstructural analysis, the addition of beta-hemihydrate increased the sulfate compound in the binder and in turn increased the formation of ettringite. (C) 2020 Elsevier Ltd. All rights reserved.