Page 107 - Machinery Component Maintenance

90 Machinery Component Maintenance and Repair

ping away the surface, sandblasting or grinding in this order of prefer-
ence. At one time acid washing was widely respected as a means of
surface preparation, but this practice has not proved reliable. When con-
taminants, such as oil or grease, are present, special consideration should
be given to surface preparation and epoxy thickness.
Although concrete can absorb oil, the process is, fortunately, relatively
slow. Once oil has been absorbed a gradual degradation in both tensile
and compressive strengths will follow and given enough time the com-
pressive strength of the concrete may be reduced to the point where it can
be crumbled between the fingers. Preventive measures, such as sealing
the concrete with an epoxy sealer to provide a barrier, can avoid this
problem. This is usually done at the time of original construction. Reme-
dial measures can also be used once the problem has occurred. Most of
these remedial techniques involve surface preparation, patching, or
transfer of loading.
The importance of epoxy grout thickness is better understood when it
is recognized that in solid materials, forces resulting from compressive
loading are dispersed throughout the solid in a cone-shaped pattern with
the apex at the point of loading. In tensile point loading the force pattern
is such that, on failure, a hemispherically shaped crater remains. Conse-
quently, the weaker the concrete, the thicker the epoxy covering should
be in order that loading can be sufficiently distributed before force is
transferred to the concrete. For example, a severely oil degraded founda-
tion may be capped with a thick layer of epoxy grout in much the same
manner as a dentist caps a weak tooth. If you can contain a weak mate-
rial, you can maintain its strength.
There have been many repair jobs with epoxy grout on foundations of
reciprocating machinery where oil degradation was so severe that it was
impossible to remove all oil-soaked concrete before regrouting. In such
cases, regrouting can sometimes be done with the equipment in place.
Such repairs are accomplished by chipping away the oil grout from the
foundation shoulder and as far as one-half of the load bearing area under
the equipment. It is important that enough grout remain to support the
equipment while repairs are being conducted. The advantage of remov-
ing some of the old grout under the equipment is to provide a structurally
sound area after repairs, equivalent to that supporting area which would
be available had the equipment originally been installed on rails or sole
plates. Once this is done, the equipment can be pressure-grouted as dis-
cussed later in this chapter. Enough concrete is removed to round off the
shoulders to a cross-sectional radius of 1V2 to 2 ft. Then vertical holes
can be drilled into the exposed concrete with a pneumatic rock drill. Usu-
ally these holes are placed two ft (about 60 cm) apart and are drilled to a
depth to provide penetration through the remaining oil-soaked concrete