May 09, 2019
Breaking Down Concrete Testing in Our CMT Lab
By: Trang Vu
Concrete Testing, also known as “breaking cylinders.” is a process that tests the strength of a sample of concrete used for bridge supports, floors of multi-story buildings, foundations, walls, parking lots, sign posts, or any number of other uses. At Timmons Group, we test it all! Our lab is AASHTO and USACE certified and we perform these tests daily for numerous projects in Virginia.
7 Easy Steps to Concrete Testing
Step 1: The compression process starts with concrete collected from construction sites by our construction field technicians and cast into multiple 4” x 8” cylinders. It’s then brought to our lab in Chesterfield, VA. Step 2: The concrete is stored in curing tanks of water (shown below) to enjoy a 28 day soak. We also commonly perform 3 and 7 day compression tests on some cylinders from the sample batches so that we can warn the contractor that the concrete may not reach the desired compressive strength even at 28 days. Fun CMT Fact: The 7 day curing results will generally show that the concrete has reached 64-70% of its 28-day strength.
Step 3: After the soak is complete, the cylinders are carefully measured and weighed (width, height, and density) by one of our certified Construction Materials Tester, to prepare for “breaking.”
Step 4: Our Testers prepare the cylinder by sawing off any rough edges to ensure that their planeness meets the required standards.
In our Chesterfield lab, we have a 250,000 lb compression machine used daily to determine the strength of concrete to make sure that all sites and structures constructed are up to standards. These cylinders can typically withstand at least 3000-4000psi (pounds per square inch) after 28 days of curing. Step 5: The cylinder is placed in the compression machine wrapped in a sleeve with pad caps at the ends to distribute the test load uniformly. Weight is applied at a continuous rate until the specimen fails and a pop noise occurs.
Step 6: The strength of the concrete is measured by the compression test under carefully controlled conditions (see the concentration in the image below) matching the standards prescribed for the required angles, planeness, and speed to determine its ability to resist loads which would compress it at the anticipated job site.
Step 7: The maximum load and fracture type are recorded. The break report includes details such as the date of testing, age at testing, the maximum load applied, compressive strength, type of fracture, and the calculated compressive strength. The contractors can adjust the mixes of future pours with this knowledge and take measures to improve the quality control at the site to avoid a recurrence of the low strength concrete.
And there you have it! The test is complete and the finalized report will be sent to the construction manager to validate that the concrete can (or cannot) withstand the pressures on the site. Our CMT team regularly tests concrete, soils, mortar, grout, asphalt, structural fill, and aggregate materials to make sure that they’re up to standards for construction, so don’t worry, we’ve got all of your materials testing covered for your project!