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How to Evaluate Concrete: 7 Methods Contractors Use

How to Evaluate Concrete: 7 Methods Contractors Use

A contractor who knows how to evaluate concrete beginning a test.

Concrete experts have various methods and tools to help determine the strength of your concrete slab.

Key Takeaways:

  • The integrity of a concrete slab must be considered before working on it
  • Contractors have multiple evaluation procedures and tools available for concrete
  • Your contractor will select the method that works best for your situation
  • Expert technique and tools result in a smoother project with fewer complications

Determining the surface’s strength is one of the first steps when your concrete slab needs work. Your contractor needs this information to develop a repair plan because brittle concrete could require additional repairs to meet the customer’s vision.

When you hire a contractor to inspect your concrete floors, you might be shocked at how much information can be gathered on the age and use of the surface. This information is vital to your project, so your concrete expert will run tests to learn as much about the slab as possible.

There are various methods a contractor can use throughout this process. Here’s a look at seven techniques that can be used to evaluate concrete when starting a construction project.

1. Penetration resistance tests

A penetration resistance test involves driving a pin or probe into the concrete to see how far it will penetrate and how much power it takes to push the pin through. When the pin doesn’t go deep into the concrete or if significant force is required to penetrate, it signals a strong surface.

The main benefit of using this method is that it’s quick and easy. Your contractor can complete the test without sending samples away, minimizing the time required to complete the job.

However, the data the probe collects can be influenced by surface conditions. So, if a damaged section of the concrete is tested, it will throw the results off for the rest of the slab. 

2. Schmidt and rebound hammers

Using a specialized hammer is another common way to test concrete strength. This method uses a spring release mechanism to send the hammer toward a plunger penetrating the concrete floor. The distance the hammer rebounds after striking the plunger is assigned a number between 10 and 100. This scale represents the slab’s strength.

Contractors often use this method when estimating concrete because they can perform it on-site without sending data to a lab. However, much like with a penetration resistance test, inconsistencies in the surface could skew the results and lead to an inaccurate reading. 

3. Ultrasonic pulse velocity

Using vibrational energy to determine a slab’s strength through an ultrasonic pulse velocity reading is also possible. This technique sends vibrations into the slab and measures the resistance as it passes through the concrete. Ultrasonic pulse velocity also measures the slab’s density, resistance to deformation, and elasticity. 

The best thing about this method is that it doesn’t disrupt the concrete – you don’t have to poke a hole in the slab to get a reading when using this method. Ultrasonic pulse velocity can also identify cracks in the slab, providing an even greater value. 

However, this technology can be influenced by reinforcements like metal rebar in concrete. Vibrational energy will have more resistance if it does encounter metal. Moisture can also affect the reading because it could slow the vibrations.

4. Wireless maturity sensors

One more high-tech concrete evaluation method involves wireless maturity sensors. This technique involves inserting sensors into the concrete to measure its hydration temperature history. The information is then uploaded using a wireless internet connection. The technician then reviews the data, providing detailed information about the concrete’s strength.

Wireless maturity sensors provide an accurate reading in real-time, making them the most accurate and reliable concrete evaluation tool on the market. It’s important to note that the sensors must be placed when initially pouring the slab. This technology cannot be added if your concrete floor is already completed.

5. Pullout test

A pullout test involves placing a metal rod in a concrete slab and pulling on it. The force necessary to remove the rod is a surrogate for its compressive strength. This helps the contractor determine the slab’s condition. The rod might be cast in place, which requires installing it when pouring the floor. It can also be inserted into the slab at a later time if you choose.

The main benefit of the pullout test is its ease of use, as it doesn’t require any special equipment. This versatile technique is practical for both old and new construction. 

The main drawback is that you’ll have to damage the concrete to complete the test. A pullout test also requires various samples throughout the slab for the most accurate results. 

6. Drilled core

The drilled core technique uses a drill to extract concrete from inside the slab. The sample is then put into a machine and compressed to measure its strength. 

The best thing about the drilled core technique is that it provides a more accurate reading of the concrete’s state than any on-site methods your contractor might use. The process also considers the concrete’s thermal history and curing conditions.

The main downfall with drilled core testing is that the contractor must send the sample to a lab for diagnostics. This technique also damages the slab, which will require repairs before using it again. 

7. Cast-in-place cylinders

Like the method used with wireless maturity sensors, you’ll install cast-in-place cylinders when pouring the concrete. A contractor will pour the concrete into these molds as part of the slab and remove them after the curing process to test their strength

Cast-in-place cylinders accurately represent a slab’s strength because the sample shares the same curing conditioners as the rest of the floor. The issue with this method is that you can’t install them after the fact, so they’re only helpful on fresh pours. You’ll also have to damage the concrete to remove the cylinder, which will require some repair.

Get the most from your concrete floors

Determining the strength of your concrete surface is necessary before grinding or polishing to ensure the floor is in good enough condition to proceed with the job. It can also identify spots where repairs are required.

Concreate can assist with all the concrete repairs and maintenance you need – we do everything with concrete but pour it! We can take care of your concrete grinding, polishing, and sealing, ensuring your surface matches your vision. Visit thisisconcrete.com for more information on how to evaluate concrete.