Structural restoration of concrete by epoxy
injection is very often the only alternative to complete replacement. It therefore results
in large cost savings. Injection protects the rebar and stops water leakage. Concrete Epoxy Injection
The following article is written with enough information about resin injection systems to help protect the Owner from the misuse or improper installation of an injection systems. For more information contact Norm Lambert.
-- The Authors--
One of the most versatile, problem solving products available in epoxy systems today is Epoxy Injection Resin.
Structural restoration of concrete by epoxy
injection is very often the only alternative to complete replacement. It therefore results
in large cost savings. Injection protects the rebar and stops water leakage.
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. In other words under most conditions it makes the concrete as good as new. It creates an impervious seal to air, water, chemicals, debris, and other contamination.
A crack, obviously, is a sign of failure caused by stresses, inadequate design, improper curing, etc. 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.
Cracks left unprepared allow moisture, road salts and other contaminants to penetrate
and attack the rebar. The rebar deteriorates, losing the structu
ral value. Loosing the
entire structure is often the result.
Epoxy injection resin has two purposes. First, it effectively seals the crack to prevent the damaging moisture entry. Secondly, it monolithically 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.
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 effect.
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.
Analyze each potential injection application to determine the exact cause or causes of the cracking. Correcting the cracking problem can be fairly simple, or may be difficult involving design changes.
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.
Parking garages are an example of cracking problem that require a structural
engineering analysis.
Often inadequate design for expansion/contraction is the cause for
parking garage structural cracking. Avoid weld injecting a crack if there are not enough
expansion joints. Sometimes flexible overlays such as Epoxy.com
System # 485 can be used to overcome this defect. This does not however encapsulate the rebar in a way
that will totally stop the premature deterioration of the steel. Often times additional
joints are needed, thus the analysis of cracking problems is critical.
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:
drilled &
surface ports.
It is extremely important that the drilling of all ports be done with vacuum attached swivel 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. Do not allow shortcuts in the drilling procedures!
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.
Align ports directly over cracks. That allows injection resin to flow into the crack. Seal surface cracks. Sealing the exterior of cracks is done with Epoxy Gel type Bonder.
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 crack area.
Water left in the cracks will not effect the injection process or the curing of the Epoxy.com Injection Resin. 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.
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 injection.
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 leaks.
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 6,500 p.s.i. Injection Resin should have a bond strength of 7,000
P.S.I or
greater. Compressive strength with most epoxies will be close to or in excess of 10,000
p.s.i. The resins that we have It is the Epoxy Bonders used to seal the ports should be: C881 Type 1:
Grade 1, 2, or 3 may be used on the top side of horizontal
surfaces.
Grade 2, or 3 may be used on walls.
Grade 3 may be used on overhead surfaces.
Epoxy resin injection with any industry standard 2:1 injection machine or Epoxy.com Injection Gun designed for Epoxy.com Injection resin is the only way of assuring quality installation. Single component caulking guns, pressure pots, or similar batching equipment are not suitable for injection.
As an alternative to an epoxy injection machine,
Epoxy.com offers
450 ml
binary injection system. This uses a binary caulking gun and static mix tubes to inject this
resin.
Limit pressures to 40 p.s.i for most applications. Excessive pressures can create
additional stressing of 
the crack. It can also cause hydraulic lifting, rupturing of the
cracked substrate, or further elongation of the crack. Low pressures allow gradual resin
flow into the crack for deeper penetration. 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.
When pure resin is flowing out the next port cap, plug the current injection port and move to the next port. Then injection continues in the port showing resin flow. This procedure continues until all ports are full.
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.
A cold substrate will cause an increase in the viscosity of the injection resin. This slows down the rate of injection. 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.
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.
When heating a structure do not overheat it. This closes the crack. When removing heat, the crack may rapidly open. This will rupture the resin before it has a chance to achieve final cure. In most cases, indirect heating is much more desirable than direct heating. Maintain heat for several hours before and after the injection application.
The color of the sealer material used in resin injection is concrete gray. They are difficult to remove. If aesthetics require complete cleaning, the sealing material can be removed by grinding. This is normally done at an additional charge to the OWNER.
Injection of Epoxy Injection Resin against a head of water 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 ports.
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 blowouts or leaks while injecting. After the hydraulic cement cures applying Epoxy Concrete Bonder. That solves this problem.
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.
Delamination of concrete structures is an area where injection can also offer selective repair. A prime example is bridge decks or other self supporting structures. The most common delamination is shearing of the concrete. This is commonly at the upper rebar mat.
Another common situation is hollow plane that develop when concrete bridge piers are resurfaced. Old piers are encased in new concrete. Hollow planes in this type of application are common, especially against smooth sections of the old pier. Cracking then occurs on the surface perpendicular to the hollow plane.
These delaminated area is subject to chemical penetration from the surface and moisture which may attack the reinforcing bar. If the delamination is not repaired, traffic will cause the area to pop-out by pounding on the delaminated upper concrete layer. Freeze-Thaw damage will also tear the concrete apart. The greater the number of freeze-thaws, the more water in the cracks during these free-thaws, the greater, and quicker the damage to the concrete.
Map delaminations by drag chain, hammer or sounding device. The damaged area requires no less than four (4) ports drilled for resin flow, depending on the size and shape of the delamination. This prevents the trapping of water that may be present.
The delamination is normally hollow planes that run along the reinforcing bar. When injecting the delamination, the resin will follow these hollow planed areas and can travel several feet in filling the voids.
Epoxy Injection Systems is very effective at repairing concrete cracks, delaminations, and hollow planes when used according to manufacturers recommendations. Job analysis and proper preparation are very important to insuring the maximum performance from the Epoxy Products, or any other concrete repair products. The right equipment is critical. Proper setup continuous mixing epoxy injection machines must always be used with no exception. Injection staff and management must have the training and experience to do the work right the first time. 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.