Pretty interesting your info. By the way, I
that there is an ACI code or recommendation about
issue, ACI 515.1 R. Are your data meeting these
Raul Labbé S.E.
----- Original Message -----
Sent: Monday, May 03, 2004 1:28 PM
Subject: Chemical Resistant Concrete
A while back, someone asked about coating
concrete for chemical resistance. Here is some basic information.
In general, when you are looking for these coatings, you will be
looking at speciality products. Your friendly Sika or Masterbuilders rep
is probably not going to be much help.
Concrete Coatings for Chemical Resistance
aggressive chemicals can cause rapid deterioration of concrete floors.
If left unprotected, damaged floors can interfere with facility
operation and create safety hazards for workers; chemicals that leach through
the concrete can contaminate the surrounding soils.
A variety of
different types of coatings are used on floors that require chemical
resistance. These include epoxies, epoxy novolacs, urethanes, polyureas,
methyl methacrylates, polyesters, and vinyl esters. Within each category,
different formulations have been developed for enhanced resistance to specific
chemicals or application under specific conditions. The coatings
are typically thermosetting polymer resins that bond to the concrete surface.
Most of them can be applied as a thin film or as an aggregate-filled overlays
up to 3/8 in. thick. Overlays can also be reinforced with fiberglass mesh to
help them bridge small cracks.
Epoxies are the
most commonly used coating when chemical resistance is required. They adhere
well to concrete and have extremely low shrinkage, which prevents the buildup
of stresses that can cause delamination. They are generally two-component
systems consisting of a resin and a curing agent. Although there are a limited
number of suitable resins, there are hundreds of curing agents. Epoxies can
thus be formulated with a wide range of physical properties and a wide range
of chemical resistance. Epoxies typically have excellent abrasion resistance
and good resistance to alkalis, bleach, moderate organic acids, and some
solvents. They are less expensive than most other coatings and many are
moisture tolerant. They can form high-build films and have excellent
mechanical properties (tensile, compressive, and flexural strengths.) They can
also be formulated as 100% solids, which makes them very useful in application
where VOC emissions are a problem.
Epoxies are not resistant to
ultraviolet light (sunlight), however, and they have a limited service
temperature range; many cured epoxies soften at temperatures above about 150°
F. Their cure rate is affected by temperature; most products should not
be applied at temperatures below 40° F.
Epoxies used for general-purpose floor coatings are based on
Bisphenol A resin, epoxies used for more severe chemical exposure or higher
temperatures are based on Bisphenol F (Novolac) resin. Epoxy novolacs are
similar to conventional epoxies but the polymer chains are more highly
cross-linked. This makes them more rigid and chemical resistant, and
allows them to withstand higher service temperatures. Epoxy novolacs
have excellent resistance to alkalis, acids, bleach, and many solvents.
Because of the higher cross-linking, however, they are typically more viscous
than conventional epoxies, which can make them more difficult to apply.
Urethanes and Polyureas
Urethanes are available in a
wide range of formulations, ranging from thin film to high build coatings.
They have excellent abrasion resistance, relatively fast cure times and
they can be used over a wide range of service temperatures. They are
resistant to alkalies, moderate strength acids, some solvents, and bleach.
There are two general types of urethanes: two-component (chemical
cure) and one-component (moisture cure.) Two-component urethanes cure by
chemical reaction with a curing agent or catalyst. One-component urethanes
cure by reacting with moisture in the air. The two-component systems generally
provide better performance, but one-component urethanes are widely used
because of their convenience. Both the one- and two-component coatings perform
best when placed on dry concrete. Moisture in the concrete inhibits the cure
of two-component coatings and can cause blistering of one-component coatings.
Urethanes typically cost more than other types of coatings and most
urethanes contain solvents; some may not be VOC compliant. Urethanes are often
used as a topcoat over an epoxy system; this reduces application and VOC
problems, as well as costs. Epoxy-urethane hybrids have also been
developed. Urethanes are classified as either aliphatic or aromatic,
depending on the chemistry of the basic urethane raw material. Aliphatic
urethanes are UV resistant; aromatics are not.
Polyureas are similar
to polyurethanes but are based on slightly different resins. The resins used
for polyureas are extremely reactive and do not require a catalyst. They cure
rapidly and cure well even at cold temperatures; they are also somewhat more
tolerant of moist substrates than polyurethanes. The curing time may be
too fast for certain applications, however, and the abrasion resistance is
typically not as good as a polyurethane. Many products marketed as
polyurethanes are actually a polyurethane/polyurea blend.
Methyl methacrylates (MMAs) are fast curing overlays
that have moderate resistance to solvents abd are resistant to weak acids and
alkalis. They are two-component systems in which the methacrylate resin is
mixed with a solid powder initiator. Because the curing is inhibited by
oxygen, a paraffin wax is included in the resin. The paraffin rises to the
surface of the coating, forming a protective barrier. An aggregate
filler should be used to avoid entrapping air within the overlay.
room temperature, a typical MMA has a working life of 10 to 15 minutes and
reaches full cure in 1 to 2 hours. The cure rate can be maintained at low
temperatures by adding more catalyst; MMAs have been placed at
temperatures as low as -20° F. MMAs must be applied to dry concrete
because moisture interferes with bonding. MMAs have excellent intercoat
adhesion, however, and can be applied in several coats without delaminating.
MMAs are resistant to ultraviolet light, so can be used for exterior
applications; their maximum service temperature is 140° F.
Polyesters and vinyl esters
Polyesters and vinyl esters
are resistant to a variety of chemicals, including acids, alkalis, and
solvents; they also resist impact well and can withstand high temperatures.
Vinyl esters are resistant to all but the strongest acids and alkalis.
Polyesters are two-component systems in which a prepolymer resin dissolved in
styrene is mixed with a peroxide catalyst. Vinyl ester resins are a type of
polyester resin, where the prepolymers are formed by reaction of epoxy resin
with acrylic or methacrylic acid.
Polyesters and vinyl esters are
typically only used when strong chemical resistance is required, as they have
more critical application requirements than other coatings. They have a high
rate of shrinkage and a high coefficient of expansion, which can lead to
cracking or debonding. To offset these properties, they are often mixed
with sand or other mineral fillers and reinforced with fiberglass mesh. They
typically cannot be applied unless temperatures are above 50F and the concrete
is dry. The surface of the concrete must also be treated to neutralize
its alkalinity. Curing times depend on the temperature and the amount of
catalyst, but the slab can usually be opened to foot traffic in a few hours;
full cure can take up to seven days.