Appeal No. 2006-2413 Page 2
Application No. 10/250,412
Because they behave like fluids in their working state, “cementitious mixtures
tend to sag, run or slump during and immediately after application” to ceilings or sloping
or vertical surfaces. Id. Also, spraying cementitious mixtures onto surfaces can be
inefficient because the mixtures tend to spatter or bounce off the surfaces being coated.
Id., page 2.
“Typically, the method of increasing viscosity is to add less water to the
cementitious mixture.” Id. However, lowering the water content “significantly decreases
the working time of the cement. Decreased water premix concrete, for example, could
harden before delivery.” Id. Decreasing the water content of cementitious mixtures also
makes pumping the mixture more difficult, and can adversely affect the mechanical
properties of the final product. Id.
The specification discloses that the viscosity of a cementitious mixture can be
controlled “without negatively affecting the working ability or final mechanical properties
of the set and/or hardened cementitious mixture” by adding a polyelectrolyte comprising
a positively charged repeat unit and a polyelectrolyte comprising a negatively charged
repeat unit. Id.
Suitable polyelectrolytes comprising a positively charged repeat unit include
polymers containing a quaternary ammonium group in the repeat unit, such as
poly(diallyldimethylammonium chloride)(PDAD), as well as polymers containing a
pyridinium group in the repeating unit, such as poly(N-methylvinylpyridine)(PMVP).
Page 6. Suitable polyelectrolytes comprising a negatively charged repeat unit include
polymers containing a sulfonate group in the repeat unit, such as poly(styrenesulfonic
acid) (PSS), as well as sulfate-containing polymers, such as carragenin. Pages 5-6.
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