Page 85 - Machinery Component Maintenance

70 Machinery Component Maintenance and Repair

preference over ease of placement characteristics. These properties are
of key importance:

Nonfoaming-Without a doubt, the single most important character-
istic of a grout from a performance standpoint is its ability to stabi-
lize and disperse any air introduced with the aggregate or entrained
during normal, nonviolent mixing. Otherwise, a weak, foamy sur-
face would develop soon after pouring, and be unable to maintain
alignment. Surface foam can always be eliminated by selecting the
proper aggregate and maintaining viscosity of the mixed grout with
proper aggregate ratio. This ratio cannot be fixed for all temperature
conditions because the viscosities of the liquid ingredients change
with temperature as do other hydrocarbons. The aggregate ratio will
increase as the temperature of the ingredients becomes higher. Incor-
porating air release agents and surface defoamers in the grout formu-
lations does improve the uppeurunce of the exposed foundation
shoulders, but does not prevent entrapment of air bubbles under the
equipment base. Even with a time lapse between grout mixing and
grout placement, air cannot be properly released because of the dif-
ference in rise rates of various size air bubbles, particularly in
“soupy” mixes.
Dimensional Stability -Three causes of dimensional change in
grouts are shrinkage while curing, thermal expansion or contraction
from temperature changes, and stress deformation or creep. Shrink-
age in epoxy grout systems can occur if the formulation contains
nonreactive volatile solvents that can, with time, gradually evaporate
from the grout. This material loss usually results in shrinkage or
cracking. Shrinkage is also theoretically possible in cases where im-
proper ratio of resin to curing agent exists as a result of dispensing
error or as a result of poor or incomplete mixing. Shrinkage is virtu-
ally nonexistent in properly formulated and properly mixed epoxy
grout.
Grout expansion-Thermal expansion coefficients of grouts should
be compared with the rate of thermal expansion of concrete and steel
since it will be sandwiched between the two materials. Concrete and
steel have about the same linear coefficient of thermal expansion.
Unfilled epoxy resin systems expand or contract at about ten times
the rate of concrete and steel. The high rate of expansion of unfilled
epoxy does not cause problems when the epoxy is of a nonbrittle for-
mulation and is present only in thin films, as in pressure grouting.
When aggregate is added to the liquid epoxy/curing agent mixture to
form a mortar, the linear coefficient of thermal expansion can be re-
duced to the range of 1.2-1.4 x in./in.’F, or about twice the