Monitoring of concrete maturity to ultimately deliver strong and durable concrete – and to minimise any cracking as a result of restrained early-age thermal effects - is of vital importance from an economic point of view and more importantly, it’s a health and safety issue.
For companies involved in concrete production - from Readymix to Precast - the required European Standard that applies is ‘I.S. EN 206-1: 2002, Concrete - Part 1: Specification, performance, production and conformity'. Certification in this standard is designed to ensure a quality product is being used in the building industry and a core requirement of EN 206 is that good practice is used when placing, compacting and curing concrete. The COMMAND Centre (www.pjbonner.com/systems/commandcentre) offers an innovative, practical system that helps engineers and project managers to comply with best practice in maturity monitoring.
Outline of concrete maturity
Concrete maturity shows the level of progression of the curing process. It represents the way in which three elements are working together – the temperature of the concrete, the time and the level of strength secured. These factors are combined into a measurement, or index, that can be identified in real time, onsite.
Maturity evaluation
In the construction business, time on a site really is money and commercial pressures are always pushing to move projects forward quickly. Yet with concrete, safety and strength concerns need to be given due respect. In the past projects could be delayed while samples of the concrete were sent off-site to be tested in a lab. However handheld and temperature probes can now be used onsite. Maturity is assessed over a period of time, through the tracking of changes in temperature in fresh concrete. Once the level of maturity is established, we can accurately assess the strength of the concrete.
There are three stages in this process:
- Monitor temperatures while curing.
- Apply these measurements to assess maturity (develop a maturity curve).
- Establish strength by using the strength-maturity relationship.
There are many good reasons why engineers are careful when specifying maturity on construction sites. We’ve mentioned time already – by being accurate in this process and implementing it onsite, time can be saved as exact measurements are known instantly. This is an opportunity to deliver cost savings and profit increases for clients. This pro-active approach also means that project managers can give their customers a better service, building loyalty which may help secure future work and it distinguishes your service from others.
One of the biggest benefits is health and safety concerns, and these are also addressed through this process as effective maturity monitoring ultimately delivers the right strength level at the appropriate time, giving confidence to all involved that any risks in this respect are eliminated.
Use maturity meters to measure the maturity curve
It’s a simple process to assess concrete strength when you use the type of technology currently available. Here’s how it works, for example,
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Create a maturity curve:
This is a graph which shows the relationship between concrete strength and maturity. To create the base information, maturity sensors are put into concrete items, such as poured floors etc, made with a concrete mix that represents the one to be applied during the construction project. The data is then gathered using a suitable device, for example, a computer and it’s mapped into a curve.
Obviously the accuracy of this process is hugely dependent on the concrete tested being as near as possible to the concrete used during construction. Any movement away from this undermines the measurements so elements such as the mix, the batch size and the supplier should be exactly as is planned for the project in reality.
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Establish concrete strength:
At this stage the hard work is done; various methods are used to test the concrete on-site or in the laboratory, such as slump and cube testing. Just batch the exact same concrete that was applied in the curve calculation and run some standard QC/QA tests to be confident that the concrete is of the exact same quality and that it meets the minimum specifications required.
Once the construction project is under way, the actual measurements of the poured concrete can be achieved by inserting the sensors into the concrete onsite – be sure to double check that high-quality delivery, consolidation and curing practices have been implemented as these are fundamental to the assumptions made when measuring maturity.
Now it’s easy to use the measured maturity value in conjunction with the maturity curve documented earlier to establish the in-place strength measurement.
Verification process:
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The maturity curve and strength-maturity measurements should be verified on a regular basis. Over the course of any construction project, elements can vary over time, for example, the concrete mix may change, construction conditions and environmental change and so on. Verification should be implemented before any critical operations are undertaken, to ensure the associated risks are minimised.
Verification typically takes one of two forms. Either other methods like pull-out tests can assess the in-place strength and this can be compared with the expected level or the maturity of strength of concrete used in the actual construction can be monitored and mapped against the maturity curve.
PJ Bonner & Co is the sole distributor in Ireland of the Command Centre Concrete Maturity System from Transtec Group. Irish Concrete Federation