Concrete is a great building material.
However, it also has its weaknesses. For example, it has a low tensile strength compared to other building materials.
When concrete needs repair, how can you ensure that your repair will be sufficient?
This article will cover the various types of damage and techniques to repair them.
What Caused the Need for Structural Concrete Repair?
Before you can repair existing concrete, you must first assess the damage and determine what caused that damage.
When you find out what caused the damage, you may need to rectify what’s causing the concrete to crack or weaken before repairing it.
Otherwise, you may find yourself with damaged concrete once more.
Types of Concrete Defects
Concrete can show damage in a variety of ways. Depending on the type of defect present, your method of repair and repair material will differ..
Here are the different types of concrete defects that may occur:
The most common defect found in structural concrete is a crack.
A crack on the concrete surface could come from:
- Improper concrete construction
- Overloading the concrete slab
A crack can be very shallow and repaired easily. Or, a crack can be significant and deep. It may even require extensive repairs — or be unrepairable and need a completely new structure.
Delamination happens when the concrete sealing happens before the bleeding process finishes.
Bleeding occurs after pouring concrete when the heavier compounds settle. As a result, it allows air and water to rise to the top and eventually dissipate.
If the sealant application occurs before this process is complete, the air and water remain trapped inside.
The result: delamination.
Delamination shows in a few different ways. For instance, you may see some blistering or weak areas where layers of thin concrete are chipping off.
The flaking of the surface of the concrete is “scaling,” caused by a repeated freeze-thaw cycle of the concrete.
Using low water to cementitious ratio concrete can help to avoid this situation since there will be less water in the mix that can freeze.
The chipping or breaking of concrete at the edges, corners, or near reinforcements is “spalling.”
Spalling typically stems from blunt force from the impact of a large and heavy mass or the application of deicing salt, which contains sodium and chloride ions.
These ions penetrate the concrete until they reach the reinforcing steel or rebar and cause it to corrode.
The steel then becomes corroded iron, which takes up more space, pushing the concrete until it breaks from the inside out.
Structural Concrete Repair Techniques
As already discussed, there are various concrete repair products and techniques.
The ideal repair method will depend on the type of concrete defect and the severity of the deteriorated concrete.
Let’s discuss each type of repair, how they work, and when they come in handy.
Carbon Fiber Wraps
Carbon fiber wraps are high-performance fiber-reinforced fabric coated with epoxy wrapped around the repair area. These are a good choice for repairing seismic damage or replacing damaged reinforcements.
Carbon fiber wraps are often used as corrosion inhibitors. In layman’s terms, they strengthen underwater structures, waterproofing the concrete.
Routing and Sealing
One of the most popular methods to fill concrete cracks is routing and sealing.
With this method, a saw or chipping tool will enlarge the crack. This crack is then filled with a joint sealant, which will cure. The use of a bond breaker ensures the repair stays put.
The stitching method involves drilling holes on both sides of a crack. Then, you’ll install large staple-looking metal units into these holes to keep the crack from expanding.
These oversized staples must be anchored into the concrete with the polymer modified, rapid setting grout, or epoxy.
Epoxy injections can fill thin cracks to full depth with injection ports and an injection tube.
This method requires the cracks to be completely dry and clean, often possible with the help of compressed air.
But, of course, you must fix the cause of the crack first, or the crack will reappear after repair.
Hydraulic cement is liquid cement that expands as it dries in just a matter of minutes. That’s why hydraulic cement is a great choice if you find leaks in your concrete.
Hydraulic cement can repair cracks on:
- Elevator pits
Bonding agents are chemicals or additives mixed into mortars or concrete. These chemicals improve the adhesion and durability of concrete repairs.
Several bonding agents can also improve the stability of the repair in a freeze-thaw environment.
Prestressing steel could be cables or bars that add a compressive force to cracks to reinforce repairs further.
This method is usually added after injecting epoxy into the crack or applying a mortar.
Drilling and Plugging
Alternatively, you can use the drilling and plugging method to fix small vertical cracks.
To use this method, drill a hole down into the crack and then fill that hole with grout. This grout-filled hole acts as a plug to keep the crack from expanding further.
Dry packing is another popular option for repairing concrete due to its workability and ease of use. You create dry pack mortar with one part cement and two and a half parts sand mixed with water.
Dry packing is also very useful in filling holes from bolts or ties. However, it’s unsuitable for small or fully extended cracks from one side of a slab to the other.
Before applying the dry pack mortar, the crack or hole must be free of any debris.
There are also several methods for applying a dry pack to form a strong bond.
Pile encapsulation repairs and prevents corrosion of sub-structure concrete.
This method uses epoxy and fiber-reinforced polymer jackets to cover concrete pilings.
This method is popular for:
- Offshore facilities
There are also various applications for repair mortars in completing concrete repairs.
Repair mortar is useful for large volume structural repairs. That includes overhead, horizontal, or vertical repairs.
Self-consolidating mortar provides a repair with less resulting honeycombing. This occurs without the need for vibration.
Sprayable repair mortars are similar to Shotcrete that can be broadcast across the surface of concrete for a coverall type repair.
This mortar is often fiber-reinforced with silica fume, and a corrosion inhibitor is added.
3. Traffic Bearing
For high-traffic bearing areas requiring repair, it’s best to use traffic bearing repair mortar.
This mortar is an early high-strength and fast-curing mortar. It also allows you to make repairs faster to continue your construction project with less delay.
4. Vertical Overhead Repair
Vertical and overhead repair mortar will stay put, even upside down. Simply use a trowel to apply a generous amount of mortar to the concrete defect.
Surface treatments repair minor surface defects on concrete slabs before they become a real issue.
Urethane, epoxy, acrylic, or polyester coats the surface of the concrete as a barrier to more damage and as a binder to the concrete below.
To finish, aggregate is mixed with the coating or broadcast over the surface. This step adds traction to the surface of the concrete to prevent slipping.
An overlay is a thin slab of mortar or concrete laid over the surface of the current slab.
This method can help cover dormant cracks, mostly for visual appeal. The use of conventional portland cement concrete is the material of choice.
Testing Structural Concrete Repairs
The concrete repair is now complete. Now, the structural integrity of the concrete should undergo testing to ensure that the bonding strength is sufficient.
You can test your concrete repairs through several different methods, including these:
1. Rebound Hammer or Schmidt Hammer
With this method, a spring-powered hammer releases an impact into the surface of the concrete. It’ll measure how far it rebounds from the concrete and determine the strength of the concrete.
This method is quite convenient since it’s doable on-site and is an easy tool to use.
However, the results are not always exact and can differ due to debris or internal rebar. Also, accurate readings depend on accurate and correct pre-calibration.
2. Penetration Resistance Test
Another relatively easy test is the penetration resistance test. This test works by driving a small pin into the surface of the concrete with a specific force.
The measurement of the resulting hole depth gives the results for concrete strength.
This is another convenient test that can occur on-site with a simple handheld device.
Similar to the Shmidt hammer, this device requires pre-calibration. The measurements can be altered depending on the concrete type and the surface concrete condition.
3. Ultrasonic Pulse Velocity
The above two testing methods may be easy, but they require you to damage the concrete to test the resistance to this damage.
Ultrasonic pulse velocity testing does not require any damage done to the concrete.
To test this method, a device sends ultrasonic energy through the concrete. The ease of travel of this energy determines the strength of the concrete.
Yet, this test shows more than just the strength of the concrete. It also reveals its elasticity, its resistance to stress, and if there are any cracks or honeycombing inside the concrete.
Similar to the testing methods already discussed, a few factors can manipulate ultrasonic pulse velocity testing results. For example, steel reinforcements present, moisture, and specific aggregates in the concrete slab.
4. Pullout Test
The pullout test is a very damaging test for concrete strength that involves pulling on a steel rod cast in place in the concrete.
The amount of force needed to pull that rod out is the measurement of how strong the concrete is.
It may seem counterintuitive, but it’s still an option for some since it’s usable on both old and new construction.
5. Drilled Core
With this method, a drill will core out a sample of the concrete. It’s then placed inside a device that uses compressive force to measure the strength of the concrete.
This is another destructive testing method that will require some repair of the hole drilled afterward.
That said, it’s one of the most reliable concrete strength tests.
6. Cast-In-Place Cylinders
For this testing method, a cylinder must be placed inside the formwork before pouring the concrete.
These cylinders contain the same concrete as the poured slab and are removed once fully hardened.
The concrete in the cylinders is measured with the same device as the drilled core technique using compressive force.
This is a less messy version of the drilled core technique but still requires repair where the cylinders were removed.
7. Wireless Maturity Sensors
A newer and more complex technique uses sensors placed inside the formwork before pouring the concrete.
These measure the temperature of the concrete in intervals. The idea here is that this correlates with the compressive strength of the concrete.
An app will monitor the temperature and measure the strength. The contractors can easily read this without having to do any math.
Even the best structural engineers will encounter the need to complete a structural concrete repair.
Building projects with concrete is a popular and viable option for many commercial buildings.
But concrete can be easily affected by natural and human forces. So repairs will be necessary from time to time.
Of course, this process should be handled carefully with the correct corresponding procedure.
When completed, it should also undergo testing to ensure that the repair has bonded successfully. It’ll also verify that the structure’s service life has been extended.
This process shouldn’t be handled by anyone but an experienced professional.
Need one? We’re happy to help.