Abstract

The effect of using some kinds of natural admixtures on the setting time of one type of Iraqi gypsum has been studied by using lime stone, calcium carbonate, hydrated lime, white kaolinite and metakaolin.
Results showed that the setting time of gypsuın can be increased from 5 min. to 10min., 12min., 27min., 9min., and 12min. by using 15% lime stone, 10% CaCO), 15% hydrated lime, 5% kaolinite and 5% metakaolin respectively. Results also showed that by using a specific weight percent of adding lime stone, CaCO, and hydrated lime the compressive strength of gypsum
increasing by 5%, 9.78%, 34.1% respectively, and decreasing for some weight
percent of adding by 13.64% and 19% for kaolinite and metakaolin
respectively. An obvious decrease in the modulus of rupture of gypsum can be observed when using the above admixtures.