26-07-2012, 01:28 PM
USE OF EPOXY COMPOUNDS WITH CONCRETE
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INTRODUCTION
1.1 -- Background
1.1.1 -- There are many characteristics of epoxies and
their uses which make them a desirable adhesive for use
with concrete. Some of these advantages are:
1.1.1.1 Adhesion -- Epoxy resins have excellent adhesive
qualities and will bond to nearly all construction
materials. A few of the nonpolar thermoplastics such as
polyethylene, present adhesion problems and are exceptions.
1.1.1.2 Versatility -- The wide range of available
physical and chemical properties of epoxy resin systems
makes their consideration requisite in any situation involving
repair, overlay, coating, or adverse environment,
of concrete. The variety of curing agents, extenders, diluents,
fillers and other modifiers available to the formulator
permit the attainment of special characteristics for
any particular application.
HISTORY OF EPOXIES
-- Origin of epoxies
2.1.1 General -- The word “epoxy” is of Greek derivation.
The Greek word “epi,” which means “on the outside
of,” was combined with the word “oxygen” which describes
the presence of the oxygen atom in the molecular
structure. In short, the word is a Greek description of the
chemical symbol for the family of epoxies (see Fig. 2.1).
2.1.2 Discovery of epoxy applications -- The first practical
application of epoxy resin took place in Germany
and Switzerland in the 1930s with concurrent experiments
being conducted in the United States, although the basic
chemistry had been known for several decades. The first
known patent on epoxy was issued to Dr. Pierre Castan
in Switzerland in 1936. Three years later, Dr. S.O.
Greenlee of the United States explored and developed
several basic epoxy systems, many of which we use today
as adhesives and coatings.
CHEMICAL AND PHYSICAL CHARACTERISTICS OF EPOXY RESINS
3.1 -- General
Epoxy compounds are generally formulated in two or
more parts. Part A is most often the portion containing
the epoxy resin and Part B is its hardener system. Almost
without exception, epoxy systems must be formulated to
make them suitable for specific end uses.
3.2 -- Adhesion properties
3.2.1 General -- Epoxies bond well (Fig. 3.1) to almost
every material providing that an appropriate surface
preparation has been given (see Chapter 5). Because the
quality and surface condition of concrete is rarely completely
known, tests for adhesion are advised (see Appendix
A). There are many reasons why epoxies make good
adhesives including, but not limited to, the following:
Thermal expansion
3.8.1 -- A major difference between epoxy compounds
and concrete lies in their coefficients of thermal
expansion (see Fig. 3.6).
3.8.2 -- Steel and concrete usually have similar thermal
expansions. Combined as reinforced concrete, the difference
in their coefficients of thermal expansion does not
usually become a problem either in design or use. On the
other hand the considerable difference in coefficient of
thermal expansion between epoxies and portland cement
concrete does require careful consideration.