Concrete Epoxy Injection
Dr. Adel El Kordi
Civil and Environmental
Faculty of Engineering
Epoxy Injection Resin is a system for welding cracks back together. This
welding restores the original strength and loading originally designed
into the concrete. Epoxy injection restores the structural qualities, the
concrete design intended. It creates an impervious seal to air, water,
chemicals, and other contamination.
• A crack, obviously, is a sign of
failure caused by:
2. Inadequate design
3. Improper curing
• One of the dangers of a
structural crack is the effect
that it has on the reinforcing
bar. The reinforcing represents
one of the main structural
values of the concrete.
The conventional basis for cathodic protection (CP) relies on shifting the
potential of the steel to more negative values. CP of steel reinforced concrete
structures can be achieved by polarizing the steel reinforcement with an
external direct current(DC).
Cathodic Protection Using Active Corrosion Control
In the passive cathodic protection, the steel in
the structure is made the “cathode” and a
more easily “sacrificial” metal is connected to
it, acting as the “anode”. The chemical reaction
between the two metals generates an
electrical current. The sacrificial metal then
corrodes, protecting the original structure.
Eventually that metal part has to be replaced.
For both environmental and operating cost
reasons, the traditional passive protection is
being replaced by active corrosion control. In
the ‘active’ method, a sophisticated electronic
current control system is used to inject a
reverse current to that generated from
corrosion to protect the structure. This is also
known as impressed current cathodic
1. As with all repair and rehabilitation of concrete, the initial
job analysis is by far the most important step. Epoxy
Injection Resin will weld concrete cracks but, of course,
will not repair the cause of the cracking.
2. Analyze each potential injection application to determine
the exact causes of the cracking. Correcting the cracking
problem can be fairly simple, or may be difficult involving
3. Consult a structural engineer when design changes are
necessary. Do this before starting the injection. Repairing
cracks by Injection is effective after these design changes.
Prevent future cracks by fixing the original cause of the
cracking, when ever possible.
Epoxy injection resin has two
1. It effectively seals the crack
to prevent the damaging
2. It welds the structure
together. Most people
assume that this welding of
the structure is the most
important result of the repair.
Actually what is most
important is the sealing.
Epoxy injection purposes
The sealing properties of the
injection prevents premature
deterioration of the
reinforcing. This can be of
equal, or in some cases
greater importance than the
structural welding. It would
theoretically always be
desirable to get this welding
Parking garages are an example of cracking problem that
require a structural engineering analysis.
• Proper job preparation is essential to insure maximum
results. Preparation before injection is even more important.
Once the resin is in the crack, there is no turning back. The
two most effective systems for setting injection ports:
Drilling for Ports
• It is extremely important that the drilling of all ports be done
with vacuum attached drill chuck and hollow drill bits.
Concrete dust can be detrimental to the injection processes
in several ways.
• For example, any dust remaining in the drill hole near a crack
can combine with the very low viscosity injection resin,
forming a semi-paste. This paste can slow or even block the
resin flow. Drilling very tight crack with a solid drill forces
dust into the crack. This seals the crack from resin flow.
Determining the spacing of
ports is done by a highly
experience applicator. This
spacing is a factor of the
tightness of the crack and
the depth of the concrete
substrate. Spacing is
normally between four (4)
and eight (8) inches.
spacing of ports
Port Setting and Sealing
Align ports directly over cracks Sealing the exterior of cracks
Epoxy crack injection can restore the original strength and
loading of concrete. Epoxy injection creates an impervious
seal to air, water, chemicals, ...
This system ensures that the crack will be thoroughly filled
with epoxy, making the crack not only structurally sound but
preventing water intrusion
Testing The System
• Test cracks that are ill defined, or if dust or debris is in the
crack. This testing may be done by injecting water into the
• Water left in the cracks will not effect the injection
process or the curing of the Epoxy. Heavier injection resin
forces the water out the cracks. Water injection helps
clean the cracked areas. More important, is that it helps
avoid the unexpected. This process of flushing the cracks
is commonly skipped by more experience contractors,
who can tell if there will be a flow of resin, by just looking
at them. However, when in doubt, water testing is a must.
Testing The System
If the cracks contain algae, chlorinated
water containing copper sulfate is
injected. After pumping , this mixture
is left over night. The next morning the
crack is flushed by pumping fresh
water, into it. This flushes it out before
resin injection begins.
• Efflorescence builds up on the bottom of a
crack in a horizontal slab. Water in the crack
extracting soluble calcium hydroxide is the
cause. The water evaporates at the surface
leaving the lime, which later reacts with the
carbon dioxide in the air to form limestone.
The inside of the crack, is frequently free of
limestone and making it suitable for
On vertical cracks, injection is start at the lowest point, and continue
upward on the crack area. While injecting the lowest port, resin will flow
to and out of the next higher port.
• Epoxy Injection Resin Systems should be of very low viscosity for most
applications. That way it will flow in the smallest hair line cracks. Resin
can travel several feet from the point of injection. It may take some time
before reaching the next port or penetrating through pin holes in the
surface. Coring samples have shown that epoxy injection effectively fills
cracks including small voids and hairline cracks.
Injection During hot Weather
• A hot substrate results in premature jelling of the
resin with sequential loss of penetration. During
extremely hot weather an open bridge deck may
exceed temperatures as high as 140 Degrees F.
Special precautions are necessary before
injection work can be done in such weather.
• The precaution may be shading the bridge, and
water cooling. Always check substrate
temperature. The injection machine and its hoses
require isolation from extremes of temperature.
Injection During cold Weather
• A cold substrate will cause an increase in the viscosity
of the injection resin. This slows down the rate of
injection. Epoxy injection undertaken during cold
weather also requires special precautions.
• When doing injection work in freezing conditions,
determining if there is ice present in the crack is
critical. Determining if a cracks inner surfaces are ice
coated, is equally important. When injecting under
these conditions, the resin will not bond to the
substrate and no structural rebonding will result. It is
usually safer to preheat the portion of the structure
you are injecting.
Injection Against A Head of Water
• It requires a slightly different
procedure than normal injection.
If water is running from a crack,
applying a hydraulic cement (fast
setting) seals the cracks and sets
the ports. Epoxy pastes will not
set up under this type of wet
condition. The hydraulic cement
seals the cracks and diverts all
water flow through the injection
Injection Against A Head of Water
• Hydraulic cement is fast
setting, but it does not have
the strength needed for an
Injection Sealer. Epoxy
Concrete Bonder can have the
strength to prevent leaks while
injecting. After the hydraulic
cement cures applying Epoxy
Concrete Bonder. That solves
Injection Against A Head of Water
• The injection process follows the procedures
described before. The Injection resin forces
the water out of the crack and through the
adjacent ports. The resin has an amber color
and does not look like water. Pure resin flows
from the higher port before capping and
moving on. The head of water will require
increasing the injection pressure used.
Epoxy Resin Properties
• Epoxy Injection Resin should be ASTM C881 Type 1 Grade 1. For
maximum filling of cracks a low viscosity injection resin must be
used. ASTM C881 allows a viscosity of up to 2000 CPS. However,
the viscosity should be in the 300 -600 CPS range for most
injection applications. Any thicker you get poor fill (or you have to
pump at excessive pressure), any thinner and you get excessive
• Tensile and Bond Strengths are very important, to prevent re-
checking if the structural member injected is put into tension. In
general the Tensile Strength (ASTM D-638) should never be less
than 45 MPa. Injection Resin should have a bond strength of 50
MPa or greater. Compressive strength with most epoxies will be
close to or in excess 70 MPa. The resins that we have It is the
Epoxy Bonders used to seal the ports should be:
1. Epoxy Injection Systems is very effective at repairing concrete cracks
when used according to manufacturers recommendations.
2. Job analysis and proper preparation are very important to insuring the
maximum performance from the Epoxy Products, or any other concrete
3. The right equipment is critical. Proper setup continuous mixing epoxy
injection machines must always be used with no exception.
4. Injection staff and management must have the training and experience
to do the work right the first time.
5. Epoxy injection has to be done right the first time. There is no second
chance. So it is critical that your injection work be done by well trained
and equipped, experienced personnel.