Piotr Krajewski
Area Sales Manager | CONTROLS

Automation in a concrete testing lab is a game changer as it will expand how testing labs are run and operated. This article presents an alternative to the manual testing of Modulus of Elasticity (MOE) by:
•    First giving you the low down on MOE
•    Then, showing you how to achieve total compliance with ASTM C469
•    Finally helping you increase your lab profitability with automation.

The Low down on MOE (Modulus of Elasticity)

Most concrete testing is performed to test the compressive strength of concrete. However in many cases, it is necessary to understand the ability of concrete to deform elastically to ensure that our structures can withstand huge compressive forces and loads.

This applies to any structural design using concrete such as bridges and sky-scrappers and this is when Modulus of Elasticity testing comes into the fore. MOE measures the stiffness of concrete and shows its ability to deform elastically: it is equal to the stress applied divided be the resulting elastic strain.

In short, the stiffer material, the higher the Modulus of Elasticity.

Burj Khalifa — the tallest building in the world
Concrete requirements:
Compressive strength – 11,600 psi
Modulus of Elasticity – 6.35 Mpsi

In real life, Modulus of Elasticity and Poisson’s Ratio values are used to:
•    size reinforced and non-reinforced structural members,
•    establish the quantity of reinforcement, and;
•    compute stress for observed strains.

ASTM C469 is the standard of reference for MOE testing in the USA

Standard Test Method for Static Modulus of Elasticity and Poisson’s Ratio of Concrete in Compression.

This is how a test procedure is run:
•    Use at least two companion specimens to determine the compressive strength in accordance to ASTM C39 test method
•    Set-up the ASTM C469 compressometer on the cylinder
•    Load the specimen at 35 psi/s to 40% of the estimated compressive strength then unload at 35 psi/s
•    Repeat this cycle 3 times – do not record any data during the first loading
•    Base your calculations on data taken from cycles 2 and 3
•    Round the average to the nearest 50,000 psi.

It is important to note that instead of loading your sample until the point of failure, as you would in traditional compression testing, you need to load your specimen to 40% of its estimated strength. Then MOE is measured over cycle 2 and 3 in order to derive the means value as final result.

ASTM C469 demands that not only loading but also unloading rate MUST be maintained at 35 psi/s.
In order to achieve total compliance with the ASTM standard, your testing machine must be ableto control the loading of the sample but also the unloading at precisely 35 psi/s. Today, this level of precision can only be obtained with automatic compression machines.

Manual / semi-automatic vs automatic testing
Today, most laboratories use manual or semi-automatic compression machines. Often equipped with dial gauges, these machines make it difficult to take the readings of the transducers at a certain load during the test. In fact, sometimes, the whole test needs to be recorded so that the reading of strain at the load of 40% can be read.

Then from these readings, the MOE must be manually calculated for each of the two cycles… in other words, performing the MOE test using a manual machine is time consuming.

You need to be an expert to know how to perform the MOE test and how to make all the correct calculations. In practice it often requires two operators to perform the test: one to operate the machine, the other (more experienced) to ensure the readings are correct and calculations done properly.

As the manual machine cannot control the unloading rate, it is also impossible to ensure compliance with the ASTMC469 standard. This lack of control means there is no repeatability either.

Where do go from there?

Now consider a new way: the automatic way!

With an automated system, all you need to know is the strength of concrete, input its value, just press the START…and then everything is calculated automatically. Magic! On average, a manual testing machine can perform 3 to 4 tests per day. And automatically? 30.

This is a real game changer.
The best bit is that only one operator with limited skills is required. There is no need of a second more experienced engineer to check loads, make calculations… so while the test is being run, you’re free to attend other duties…the machine no longer needs you!

Tests run from 10 to 20 minutes, depending on the concrete strength, and as these are done automatically, it frees up your time to even enjoy a cup of coffee.

The cherry on the cake is that since the unloading rate is completely under control (only very few suppliers in the world offer this so make sure to ask for proof of this and in the US, only CONTROLS machines), your results are totally repeatable. 

Find out how easy it is to run the Modulus of Elasticity Test with CONTROLS Automax Multitest and watch tutorial now

Are you ready to increase your lab profitability?

Using an automatic compression machines for all your standard and advanced testing will:

  • Reduce time required to perform tests
  • Increase your lab’s profit margins: higher productivity, means more revenue
  • Give you total peace of mind: total compliance with standards even when less experienced operators  run the test makes your lab reliable and trustworthy
  • Take you from headache to total peace of mind: no fiddly manual adjustments, difficult calculations and better use of your staff’s time.
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