Concrete is placed as a liquid and develops its strength as it cures over days or weeks. Curing is the process where the proper conditions for cement particles to hydrate are created and maintained, through which concrete gains its strength. The ability to place concrete as a liquid has many advantages including easier shipment, pumping concrete in ways similar to water, and the ability to place concrete into nearly any form on the project site. Concrete contractors in Portland, such as The Conco Companies, provide expert concrete services for complex projects throughout the Western U.S. Part of all concrete placement services is to test the strength of concrete as it cures to determine if it meets its designed performance specifications.
Concrete Testing Standards
Concrete strength testing is a well characterized and defined process. The American Concrete Institute (ACI) developed standards to ensure that concrete strength is consistent in every commercial project. ACI 318-14 defines that concrete compressive strength will be based on 28-day test results, with the average of three tests being the final value as long as no strength is below 500 psi or 10% below the specified strength. This means that while three day or seven day tests may be done to determine if the concrete is strengthening as designed, under most conditions, the 28-day test is the final determination of the concrete’s long term strength.
Concrete Testing Methods
Testing concrete in place, and not in the lab, offers the ability to determine when concrete formwork can be removed on new concrete and to determine the strength of existing concrete, for example, when a building use is changing and the structure strength needs to be re-evaluated accordingly. Testing methods can be destructive or non-destructive. While non-destructive methods are preferred, they do not measure the compressive strength directly, and if there is any question of the concrete’s strength, destructive measures will be used. Methods for in-place testing include rebound number, penetration resistance, pullout test, breakoff number, ultrasonic pulse velocity, maturity method, and cast in-place cylinders. Cast in-place cylinders are test cylinders that are poured when placing concrete and are tested after different periods of time to determine the progress of the compressive strength over time.
Conco’s mission is to be the best supplier of concrete services in the Western United States and to bring expertise, experience, and quality of each project. We continue to upgrade and expand facilities to better serve the growing market for commercial, educational, public works, and parking structure projects as well as other construction development. Please call or email for more information on how Conco can assist your next project with Confoam™, our cost-saving cellular concrete.