GYPSUM

MATERIALS OF CONSTRUCTION_T.Y.ERDOĞAN
SAYFA 151

1.INTRODUCTION
Pure Gypsum : CaSO4 2H20, include CaO(lime), SO3, H2O
Impurities : Silica, Alumina, Ironoxide, Calcium carbonate, Magnesium carbonate

2.MANUFACTURE
grinding, calcination (burning), cooling, pulverizing

Calcination in rotary kilns :
CaSO4 2H20 -> (100-1900C) CaSO4 1/2H2O + 3/2H2O (partial)
CaSO4 1/2H2O : plaster of paris (adi alçı)

CaSO4 2H20 -> (1900C) CaSO4 + 2H2O (complete)
CaSO4 : anhydrite

3.SETTING AND HARDENING
mixed with water, result is plaster. Setting means loss of initial plasticity or gaining rigidity. Hardening means gain in strength.

4.PLASTERS AND MORTARS
Plaster is used in plastic state, mortar can be troweled and becomes hard in place, to bond bricks. Plaster form hard covering.

1.Plaster of paris
2.Hardwall plaster : Pop + admixture
3.Flooring plaster : anhydrite
4.Hardfinish plaster

PROPERTIES
Properties and uses :
1.Plaster of Paris :
setting : 5-20min.
sculpturing, small repairs, ornamental works

2.Hardwall plaster : Pop : admixture
setting : 1hr.
comp. strength : 7 MPa
prefabricated fabric units, masonry brick and blocks

3.Flooring and hardfinish plaster :
setting : 1-16hr
comp. strength > 7 MPa
prefabricated units, masonry brick and blocks, flooring and pavement bricks and tiles

Properties :
• not water resistant
• good fireproofing and sound isolation
• disintegrates when exposed with water
• expands 2-3times upon hardening