Why Not Use Only Break Tests?
1. Limited Visibility => Potential Risk of Delays
Compression tests are a widely used method, but these are often the reason for unwanted delays and increased costs. Moreover, this type of test only shows a single or few strength data points.
As shown above, the break test will only give you a data point occasionally, when a specimen is tested. The use of concrete sensors gives you continuous information during the concrete’s curing process.
2. Cubes/Cylinders Risk to Show Wrong Results Due to Curing Conditions
A challenge that can occur both on job sites and in precast facilities is incoherence between the in-place strength and the one from the specimen cured on-site, next to the concrete structure. The reason for this incoherence normally is due to the different curing temperatures.
A small concrete cube/cylinder has smaller mass than the structure so the heat development will be lower in it. Moreover, the often much larger concrete structure is exposed to a significantly higher internal heat development caused by the hydration process. The higher internal heat will in turn make the curing process faster. This mean that when comparing a specimen to the actual structure this has: lower mass, lower internal heat and therefore, lower strength development.
In the graphs shown above, you can see the graphs showing the temperature, maturity and strength development of two structures. The green ones show the development under cold conditions while the orange one shows it under hot conditions. If you observe the graphs, you can see that when the temperature rises, the maturity is gained faster, see red line. Moreover, if the temperature is comparatively higher, the strength development will also be gained faster.
If you are only using the compressive strength of your cube/cylinder, then you may not know for sure if you have achieved the desired strength. What you are in fact validating is that the concrete used on the job site is able to gain a certain strength after a certain amount of days. In other words, the 28-day water bath cured compressive strength just validates the concrete used is able to gain that strength.
3. Cheaper and Faster Results With Sensors
Concrete sensors are obviously available in different price classes, but in most cases are significantly cheaper and faster to provide a return on investment. A break test often requires extensive labor work, transport to concrete lab, waiting time to get results – all while the concrete is still curing. With Maturix, you only need to embed a thermocouple into the concrete with averaging costs on the embedded to around 1-10€. It is rare that you can do a compression test for those costs – and also get the added benefit of seeing the results in real time!
4. Avoid Low Break Test Delays.
Low compression test results can require a contractor to simply wait for the next planned specimen testing (for example wait for a 14-day cube testing) in order to be able to move on with the project.
The reason why a break test suddenly is significantly lower than expected or even required might be many, but some of the most common issues are:
- Improper cylinder handling, curing or testing
- Improper production of concrete – Reduced strength due to mistakes in concrete mix design (not as specified). This can be too much water, high air content or similar.
Using sensors reduces risk of an unexpected low break test. Sensors provide continuous vital information about concrete temperature and strength. So if there is something wrong with the concrete you will be able to see it early on and correct it right away.
So for all these reasons, it is a good idea to use the maturity method in conjunction to break tests. This way you can comply with the standards and requirements while also getting continuous information that can be used to make better decisions.