Characteristics of Building Gypsum

Building Gypsum

Gypsum  is an air-hardening  materials  mainly  consisting of calcium  sulfate. And   its  products   have   many   excellent  characters,   commonly   used   in construction.  There  are various  kinds  of gypsum  binding materials,  such as building     gypsum,     high-strength     gypsum,     anliydrite     cement,     and high-temperature-calcined gypsum.

Characteristics of Building Gypsum

Compared  with  other binding materials, building gypsum has the  following characteristics:

  1. Fast Setting and Hardening

The setting time of building gypsum changes with the calcination temperature, grinding  rate  and  impurity  content.  Generally,  mixed  with  water,  its  initial setting needs just a few minutes at room temperature, and its final setting is also within  30min. Under the natural  dry indoor conditions, total hardening needs  about  one  week.  The  setting  time  can  be  adjusted  according  to requirements.  If the  time  needs  to be  postponed,  delayed  coagulant  can  be added to reduce the solubility and the solution rate of building gypsum, such as sulfite alcohol wastewater, bone glue activated by borax or lime, hide glue, and protein glue; if it needs to be accelerated, accelerator can be added, such as sodium chloride, silicon sodium fluoride, sodium sulfate, and magnesium sulfate.

  1. Micro-expansion

In the hardening process, the volume of building gypsum just expands a little, and  there  won’t  be  any  cracks.  Thus,  it  can  be  used  alone  without  any extenders, and can also be casted into construction members and decorative patterns with accurate size and smooth and compact surface.

  1. Big Porosity

After hardening, the porosity of building gypsum can reach 50%-60%,  so its products are light, insulating,  and sound-absorbing. But these products have low strength and large water absorption due to big porosity.

  1. Poor Water Resistance

Building gypsum has low softening coefficient (about 0.2-0.3)  and poor water resistance. Absorbing water, it.wil1 break up with the freeze of water. Thus, its water resistance and frost resistance are poor, not used outdoors.

  1. Good Fire Resistance

The main  component  of building  gypsum  after  hardcning  is CaS04*2H20.When it contacts with  fire, the evaporation of crystal water will absorb heat and  generate  anhydrous  gypsum  which  has  good  thermal  insulation.  The thicker its products are, the better their fire resistance will be.

  1. Large Plastic Deformation

Gypsum and its products have an obvious performance of plastic deformation.Creep becomes  more serious especially  under  bending  load.  Thus,  it  is not used  for  load-bearing  structures  normally.  If  it  is  used,  some  necessary measures need to be taken.

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