Plaster materials from waste calcium sulfate containing chemicals, organic fibers and inorganic additives

Plaster materials made of waste gypsum or flue-gas-desulferized (FGD) gypsum with chemicals;organic and inorganic additives were studied. Glucose;citric acid and sodium bicarbonate were incorporated to retard the hydration of plaster. Saw dust (SD);coconut fibers (CCF) and tobacco waste fiber (TWF) were incorporated to improve the thermal property. Diatomaceous earth (DE);fly ash (FA) and bottom ash (BA) were incorporated to improve the mechanical and thermal properties. Citric acid;TWF;sodium bicarbonate and glucose could be used to retard the setting time of fresh FGD-plaster to approximately 25 min comparable to that of commercial plaster while the other additives did not retard the hydration. In presences of these retarding additives;needle shaped gypsum changed into lower aspect ratio particles. SD;CCF;DE;FA and BA modified gypsum crystal growth and reduced the crystal length. These changes in morphology consequently gave significant alterations of mechanical and thermal properties of the materials. The additions of organic and inorganic additives resulted in a reduction of bulk density and increases in water absorption;and similar strength compared to commercial gypsum. A good thermal insulating property was obtained from the samples with the incorporation of coconut fiber;BA and DE. In addition;these samples had a good performance in fire proof.

► Tobacco waste fibers contain carboxylic acid could retard the hydration of plaster.
► Tobacco waste fibers also improved the mechanical properties of set plaster.
► Pure carboxylic acid chemicals used retard the hydration only.
► Fly ash and bottom ash when are present in set plaster acted as fire protectors.
► Diatomite also acted as fire protector due to the open pores of the set plaster.