Keywords : Technical Plaster


Physical Properties and Compressive Strength of the Technical Plaster and Local Juss

Auday M. Al-Rawas; Zeki A. Aljubouri

Iraqi National Journal of Earth Sciences, 2009, Volume 9, Issue 2, Pages 49-58

Five physical properties (water/powder ratio, setting time, fineness, porosity and dendsity) and compressive strength were determined and compared for technical plaster and local juss.Data were monitored using a standard dental stone. The relationships between these properties were also studied. It was revealed that local juss has inferior properties compared with technical plaster. It has lower compressive strength; higher water/powder ratio; shorter setting time; larger grain size and higher porosity. There is an inverse relationship between compressive strength and the two properties water/powder ratio and porosity. There is a direct relationship between compressive strength and the two properties particle size and density. There is also a direct relationship between setting time and the two properties particle size and water/powder ratio.

The Petrography and Mineralogy of Technical Plaster and Local Juss

Zeki A. Aljubouri and Auday M.Alrawas

Iraqi National Journal of Earth Sciences, 2006, Volume 6, Issue 1, Pages 1-11

The petrography and mineralogy of two types of technical plaster, an English dental stone and two types of local juss were studied.
Thee petrography of the studied thin sections, revealed that technical plasters consist of dispersed prismatic, monoclinic crystals, with ill – defined edges ( bassanite of the β –hemihydrate). Dental stone consists of more packed, prismatic monoclinic crystals with well defined and sharp edges (bassanite of the α – hemihydrate ). Some crystals are pseudo- hexagonal. Bassanite of local juss in thin sections is identical to that of technical plasters.
x-ray diffraction studies proved that technical plaster consist of about (95%) bassanite and (5%) gypsum, compared with (99%) bassanite and (1%) gypsum for the English dental stone. Local juss consists of anhydrite (63-70%), bassanite (20%) and gypsum (10-17%).
The three mineral phases, in the final product, the juss, exist as a mechanical mixture, rather than transformation phases. The occurrence of a phase is a function of the distance of raw material, the gypsum from fire source.