When it comes to any construction project that requires the use of concrete, whether it’s a hospital, residential building, road, bridge, or dam, concrete strength testing is an essential step in ensuring the integrity and durability of a structure. Furthermore, whether or not a project will move forward is dependent on those test results, impacting a project’s timeline and budget, as well as a company’s reputation. The ability to gather the most accurate data is of utmost importance to contractors, managers and engineers alike.
The Concrete Cylinder Test
The concrete cylinder test involves casting concrete cylinders on-site before sending them off to a third-party lab for compression testing. This method involves two types of concrete cylinder specimens:
According to ASTM C31: Standard Practice for Making and Curing Concrete Test Specimens in the Field, field-cured concrete samples have the same temperature and humidity that the completed structure will be subjected to. In order to achieve this, the samples are stored alongside the concrete structure. Field-cured specimens are predominantly used to determine whether a structure is ready for formwork removal, opening roads and shoring.
Standard curing, on the other hand, involves testing concrete specimens in a third-party testing lab where they are subjected to standard conditions, defined in ASTM C31 as 23.0 ± 2°C and relative humidity that’s greater than 95% as outlined in the project’s specifications. Standard-cured specimens are typically used for quality control and standard acceptance.
When the specimen is ready, the technician must examine, measure, and weight the concrete cylinders before placing the sample in a hydraulic compression testing machine. The results from this test are used to determine if it is safe to move on to the next step in the project. Typically, cylinders are tested 3, 7, and 28 days after installation.
Concrete cylinder break tests have been around for over 180 years. As the most widely used and established compressive strength testing method, it generally provides accurate results. That being said, it’s not completely foolproof due to the time it takes to complete and high costs over the long-term.
The Maturity Method
The maturity method is a non-destructive approach that estimates the strength of in-place concrete. The method, which can be measured in real-time, uses the hydration temperature history of the concrete during the curing phases to estimate strength development.
There are several ways to calculate concrete maturity:
- Temperature-Time Factor (TTF)
- Datum Temperature Calculation
- Rate Constant (K-Value)
- Equivalent Age
- Weighted Maturity
ASTM C1074: Standard Practice for Estimating Concrete Strength by the Maturity Method provides two maturity functions, the Nurse Saul Function (also known as the Temperature-Time Factor) and the Arrhenius Function. In North America, the Nurse-Saul maturity function is the most commonly used approach as it’s simpler to implement than other methods. This approach takes into consideration that the maturity value is linearly dependent on temperature and can simply be represented by the area below the temperature curve.
The maturity method requires a calibration to create a unique relationship between the Maturity Index (obtained using the temperature profile) and concrete strength. This process only needs to be completed once, as long as you do not make any adjustments to the mix design.
When it is time to begin pouring your optimized concrete mix, the maturity method will accurately estimate the in-situ compressive strength of your concrete, allowing you to optimize your time and work efficiently.
Which Method Should You Choose?
If you’re looking for a quick, highly accurate and non-destructive method to measure the strength of your concrete elements, the maturity method is the superior option. Why?
The concrete cylinder break test is widely known by the construction industry to be a time-consuming process. After the concrete has been poured, a technician has to make the cylinders and place them in the proper curing environment. Standard-cured concrete specimens must sit for 8-24 hours before they can be collected and transported to the third-party testing lab for a break test to be completed.
Once the specimens arrive at the lab, field personnel and project managers will need to wait until the break tests are complete before moving onto the next steps of the project. How long it takes will depend on how many specimens need to be tested.
One of the reasons why concrete cylinder tests are commonly used on construction projects is that individual tests are inexpensive. However, these costs undoubtedly add up over time, especially on larger construction projects. There is a lot of room for human error during the handling, transportation and storage of the specimens as they can cause micro-fractures in the concrete, resulting in a low break. Finally, it is very easy for third party laboratories to falsify numbers if errors occurred, and there is no way to verify the results. All of these factors leave a lot of room for inaccurate results, delays, and can overall create an ineffective process.
The concrete maturity principle is an often overlooked and underused alternative to measure concrete strength, yet this shouldn’t be the case as it provides precise measurements without all the delays that come with concrete cylinder tests.
An advanced wireless maturity sensor like SmartRock® makes it easy to carry out real-time temperature and strength monitoring. The temperature data is collected with SmartRock sensors that are installed within the concrete formwork. This data is subsequently uploaded to a smart device where the concrete’s psi/MPa is displayed in real-time and updated every 15 minutes. The data from embedded sensors is often considered to be more accurate than cylinder break tests, because you are monitoring the temperature of the actual concrete slab you are working with. On the other hand, field cylinders are based on the concept that a cylinder kept beside the slab will represent the temperature and strength of the entire slab. This is rarely the case, as the exothermic nature of cement hydration in large concrete element typically leads to a heat rise much more significant than a small cylinder. To put it simply, a concrete cylinder and a large slab will seldom gain strength at the same rate.
By using the maturity method and wireless sensors, you can reduce your reliance on break tests and third-party labs, taking back control over your project. This will prevent unnecessary and expensive project delays.
Beyond providing accurate, real-time calculations, Giatec’s suite of solutions can empower field personnel and project managers in a way that other methods, like the concrete cylinder break test, are unable to:
- Giatec 360™ is the world’s most advanced web-based dashboard for controlling and predicting the quality of concrete pours. With it, you will benefit from next-level user management capabilities, reporting, and data analytics for your SmartRock wireless sensors.
- Roxi™ is an AI program that uses machine learning algorithms to detect possible errors in concrete maturity calibrations and mix proportions. Roxi has access to millions of data points thanks to the SmartRock sensors currently being used in 6,000+ construction projects around the world.
- SmartHub™ is a 24/7 remote monitoring system that automatically collects data recorded by your wireless SmartRock sensors and uploads it to the Giatec 360 cloud. The data synced to your team’s mobile devices, allowing everyone to be aware of the temperature and strength of the concrete and receive alerts without having to physically be on a job site.
There’s no better time than now to save thousands of dollars or more long-term, optimize your concrete elements’ strength and durability and shorten project timelines with high-tech maturity sensors.