Page 86 - Machinery Component Maintenance

Machinery Foundations and Grouting 71

rate for concrete or steel. When reviewing properties of a grout,
compressive strengths should be considered along with the modulus
of elasticity (the slope of the stress-strain curve). Generally, the more
rigid the material, the steeper the slope and the higher the modulus of
elasticity. Rubber, for example, is elastic according to the lay defini-
tion, but relatively nonelastic according to the technical definition.
Strength-There are several methods of measuring strength of a
grout. It can be measured under compression, tension, impact, and
under flexure. Bond strength, shear strength and cleavage are mea-
surements of adhesion rather than strength. Usually when strength of
a grout is mentioned, it is the ultimate compressivc strength that is
implied. The term yield strength should be reserved for tensile tests
of metals which work-harden before reaching the ultimate strength.
Grouting materials do not work-harden, and there is but one peak in
the stress-strain curve. More important than the ultimate strength.
however, is the proportional limit, because beyond that level of
stress, the material is permanently distorted and will not return to its
original dimension after the load is removed. Data from compression
tests can be used for design calculations because static loads are usu-
ally known and dynamic loads can be reasonably estimated. Grout is
seldom placed under tension, except at rail ends, etc., during start-
up. The tensile strength of the grout is important, because if it is
known at the operating temperature, the maximum distance between
expansion joints can be calculated. In addition to the tensile strength,
tensile modulus of elasticity, operating temperature range, and linear
coefficient of thermal expansion must be known.

This should illustrate that epoxy grouts are sophisticated products.
There are literally thousands of possible residcuring agent combina-
tions. It is not realistic to believe that a good epoxy grout can be devel-
oped from scratch on a small budget utilizing independent testing lab-
oratories for screening and obtaining data. The process is simply too
expensive. Even if all necessary equipment, including that shown in Fig-
ure 3-1, should be available in one’s laboratory, the efforts of a develop-
ment chemist must be directed by someone knowledgeable in concrete,
loading requirements of machinery, and the degree of precision neces-
sary to maintain machinery alignment. Developing, manufacturing, and
marketing of epoxy grouts is not the business for small timc formulators
with bath tub and boat paddle type equipment. Prospective epoxy grout
suppliers should be screened on the basis of their technology and capa-
bilities. If the reader retains nothing more than this one fact, he will have
learned within a short period what others have learned through great an-
guish over a long period and at considerable expense.