How is Concrete Tested

How Is Concrete Tested?

If concrete is not mixed correctly or laid properly, there are plenty of things that could go wrong. The concrete could be weaker than it should be. It may begin to develop cracks very early on. Concrete testing is pertinent for ensuring the strength of the finished product. 

Of course, there are many tests and each of them can determine something different. How exactly is concrete tested? You’ll find out in this in-depth guide below.

 

The Current State Of The Concrete

First and foremost, you should know that there are numerous ways to test concrete. When attempting to find the right method for your individualistic needs, you will need to look at the current state of the concrete. 

There are specific tests that can be used to determine the strength of hardened concrete. The others are effective for testing fresh concrete, before it is allowed to set. 

It should also be known that some testing methods are moderately destructive, while some are not. Therefore, you will need to work with a professional to determine what is right for you.

 

Concrete Slump Test

The concrete slump test is performed before the concrete has time to set. This test helps to determine the overall workability of the concrete and how much it’ll be able to flow. The test is primarily designed to help indicate a batch of concrete that has been mixed incorrectly. 

This type of test is incredibly popular, because it is very simple. For concrete that is too fluid to be measured using the conventional concrete slump test, you may need to use the slump-flow test.

 

How The Concrete Slump Test Works

The concrete slump test utilizes a metal mould, which is referred to as a slump cone or an Abrams cone. The cone will be opened at both ends and it’ll have handles on both sides for easier handling. The cone should be placed on a hard surface, which is non-absorbent. 

Then, it will need to be filled with fresh concrete in three separate stages. Each layer of concrete should be tamped twenty-five times with a 2-foot metal rod. After the third layer of concrete has been added and tamped, it should be cut off flush with the very top of the cone.

The cone should be removed carefully to avoid disturbing the concrete underneath. This will eventually lead to the concrete slumping or subsiding. Then, precise measurements are taken from the peak of the slumped concrete to the peak of the cone.

 

Understanding The Results

There are a number of things that can happen when the slump test is performed. First and foremost, the concrete may collapse. There is also a possibility that a side of the concrete will shear off and slide downward. 

If the concrete collapses, you’re most likely dealing with a mix that is simply too wet. If you’re unable to achieve a true slump, you’ve got problems on your hands. A true slump means that the concrete has managed to hold its shape.

 

Concrete Shrinkage Test

It is also possible to test the concrete to determine how much it will shrink due to moisture changes. The test will utilize an apparatus with a dial gauge. It is capable of measuring the length precisely down to the 0.005 mm. 

You’ll also need an appropriate drying oven. In order to perform this test, you’ll need to first obtain a suitable sample. It should measure in at 15 to 30 cm in length and it should be 7.5 cm in depth and width.

A small depression should be drilled in each end of the sample to ensure the 6.5 mm diameter steel ball will sit. The balls should be fixed into the concrete by cementing the balls. After the balls have been fixed, you should remove any excess cement and apply lubrication to prevent corrosion. 

Then, the samples should be placed in a moist area for at least twenty-four hours. This will allow the cement to harden. After twenty-four hours have passed, the samples should be placed in water at 24 to 30 degrees Celsius for at least 28 days.

 

Testing Process

After finally removing the samples from the water, you should go ahead and remove the grease from the balls. Measure the length of the new samples. This measurement is known as the original wet measurement. 

The samples should then be dried in an oven for a minimum of 44 hours. Remove the samples and allow them to cool. Once again, measure the length of the samples and write down the number. This process should be repeated multiple times, until you’ve able to achieve a consistent length. 

The difference between two measurements should be less than .01 mm. These measures are referred to as the dry measurements. You’ll also want to take a measurement of the sample near to the balls. This is known as the dry length.

 

Analysing The Results

Finally, you should get the results. In order to do that, you should determine the difference between your original wet number and your dry measurement. Then, find the percentage of that number compared to the dry length. 

This will help you determine the concrete’s initial drying shrinkage. Since the test is so tedious and complex, it is something that is best left to a professional.

 

Microscopic Examination

The microscopic exam is utilized to assess concrete, looking for aggregate and other additives, such as ground granulated blast furnace slag and fuel ash. This type of examination may be utilized in forensic, bomb and fire testing. 

Manufacturers may also utilize the microscopic exam to determine how well their concrete will stand up to unusual activities, such as natural disasters, extra-heavy weight and increased traffic.

During the assessment, the examiner will look for compaction, micro-cracking, cracking and carbonation depth. The examination is more likely to be utilized during the invention phase, as compared to any other time.

 

The Compressive Strength Test

Concrete is designed for strength and durability, so it only makes sense that the strength of the concrete is properly tested before leaving the factory. How is this accomplished? Well, the concrete samples are formed into either three blocks or three cylinders. 

Once formed, they are left to harden for 28 days, which is when they reach their maximum strength. After the 28 days the two blocks or cylinders will be placed in a compression machine. The purpose of this machine is to exert force on the blocks or cylinder of the concrete and see if they holdup. 

Now, you might be wondering why only two of the samples of concrete are being tested when three samples were made.

The third sample is simply for backup. In the event that one or both samples of concrete fail the third sample would then be tested.

 

Water Permeability Test

Another common test that concrete has to undergo is the water permeability test. This test was actually designed to determine the resistance of concrete against water pressure. This entire testing period last for 3 days and it is crucial when it comes to determining the durability and lifespan of a concrete sample. 

3 samples of concrete will be taken and cured for 28 days before the testing process begins. After the 28-day curing period, the three samples will be placed is a specially designed machine where they are subjected to hydrostatic water pressure for three days.

After the three days are up, the concrete samples are removed, and cracked open vertically. This will allow the tester to determine how deeply the water penetrated the concrete.

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