Projects that use concrete will need the material to be tested for ultimate strength – or maximum load-bearing capacity. The steps taken to test these specimens, starting in the field and ending in the lab, can tell designers and engineers much about critical safety performance of concrete in the structures that we use everyday; there are two main ways that QA/QC firms evaluate concrete strength: compressive strength and flexural strength.
While the former is most often used for vertical loads, such as a drilled pier foundation or a column in a high rise, flexural testing is used in situations where the load is assumed to be applied at some distance from the supports, such as cars on a reinforced freeway or landing strips at airports. The tests have similarities but are distinct in the ways that samples are broken to determine compressive and flexural failure limits.
At G3 Quality, we commonly test concrete samples either in our materials laboratory or with our mobile testing labs, which are convenient for remote jobs or urgent testing needs. A large volume of our projects over the past decade have involved inspecting, sampling, and testing concrete before, during, and after construction, ensuring that materials can handle forecasted loads so that projects meet safety standards.
Find out how we measure concrete strength at G3 Quality, and fill out a contact form on our website if your project has urgent materials testing needs.
The Science Behind Concrete
Before diving into how engineers and testers evaluate concrete for strength, it’s important to have a baseline understanding of the science behind the material.
Concrete is formed through a chemical reaction that occurs when water is added to cement and its adherence to aggregates. It’s initially in a semi-liquid “workable” state but gradually hardens over time due to that chemical reaction called hydration, during which cement compounds form chemical bonds with water molecules. The process calls for a specific amount of cement, water, and time for the concrete to cure. Once cured, testing for strength at a prescribed age can begin.
Ways to Measure Concrete Strength
There are typically two ways to evaluate concrete for strength, with similarities shared between both basic methods. Generally, any concrete strength testing involves bringing a prepared and cured concrete specimen to the lab and then applying force until failure. Testers will make the sample shatter, pop, and break until it can’t hold anymore load, and then use the results to determine the ultimate strength of the sample.
Still, there are differences in how structural concrete for residential and multi-story buildings are tests versus other construction such as roads and bridges. Here are the two core forms of concrete strength testing:
Compressive Strength Testing
Concrete excels at withstanding compression, as it’s capable of handling substantial loads – however, in tension it’s strength is reduced by about a factor of 10 . The primary method for testing concrete’s compressive strength is to apply a vertical force to a cylindrical sample until it crushes. With these results, engineers and testers can determine the maximum load the concrete can bear, dividing by the surface area, leaves us with compressive “strength” , typically measured as pounds per square inch (PSI).
For axially loaded projects, engineers employ compressive strength measurement as a basis for specifications. Once they’ve determined the necessary load being transmitted, they multiply by a factor of safety, and then specify the strength of concrete needed for construction, taking a conservative approach to safety. It’s a risk-conscious way to ensure that the structure can withstand its intended load.
Flexural Strength Testing (Modulus of Rupture)
When dealing with pavements or structures where loads may roll along the surface or create a bending force within the structure, such as taxiways, landing strips at airports and roads, designing with and measuring flexural strength becomes the priority. Unlike compressive strength, Modulus of Rupture is measured by subjecting concrete specimens to a flexural loading. It subjects the concrete to both compression and tension loading zones, and since concrete is weaker in tension – primarily assesses the material’s ability to resist being pulled apart, which provides valuable data for evaluation.
By measuring the load and determining the Modulus of Rupture, material testers such as the team at G3 Quality can deliver critical safety and load-bearing requirements to engineers on relevant projects such as roads and airports.
Measure Concrete Strength with G3’s On-Site & Mobile Labs
If your highway, road, or bridge project requires precise concrete strength testing before construction can continue, don’t hesitate to consult the experts at G3 Quality. We’ve carried out loads of significant projects around California, including our concrete testing of the I-710 for a pavement rehabilitation and bridge widening project, owned by Caltrans District 7.
Fill out a form on our Contact page to keep your materials in line with project and safety requirements.