Maturity meters for Precast

[diazmeyer]

Hello,

I would like to know which concrete maturity meters are most popular in Precast applications.
Where can I find more about them?.

Best wishes

 

[civilperson]

Better to use extra cylinders and break at 8 hours, 10 hours, 12 hours, etc. The maturity meter is not for steam heated product above 140 degrees in the first 8 hours after initial set. It is mainly for form stripping or traffic application on highway and bridge construction with variable form shapes and variable site conditions. Precast factories have enormous experience, (thousands of placements), with boiler generated steam heat cure at controlled temperature conditions which make concrete strength predictions almost a sure thing.

 

[conceng]

It is my understanding that most precast companies are using a match-cure system. In a match-cure system, thermocouples are embedded it the precast panel and are fed to a control system. Cylinders are placed in a temperature controlled container. The control system heats the cylinder to the same temperature as the concrete in the precast bed. The cylinders are then broken as needed, just prior to form removal or releasing tendons to verify sufficient strength.

This eliminates the need for developing maturity indexes and the uncertainty due to batch variations from the calibrated mix.

Gregory A. Johnson, P.E.

http://www.midwesttestinglabs.com

 

[diazmeyer]

Thanks for the replies,

By keeping the test cylinders covered up in the mould we get results which vary considerably, delaying stripping or strand cutting unnecessarily in occasions.
We find that the reliability of our test results are affected by the shape of the element being manufactured, the air temperature, the curing system , etc.

I studied the maturity method a couple of years ago curing the samples in a box at different curing temperatures and found surprisingly good predictions, even using the data with different temperature-time curves. Was impressed by the fact that data with different curing conditions would fit rather well one maturity index-strength curve.

I suppose that If we had reproducible curing conditions we could relatively easily obtain reliable results using test cylinders alone, as civilperson suggests.
Match curing is presently a good alternative (I can imagine that it might be more expensive than the maturity system alone due to the necessary temperature control system for the test cylinders)

 

[concretemasonry]

Traditional concrete cylinder testing was developed to check the properties of the mix and has no real relationship to the actual strength of the concrete in place or the properties of the product made.

The bottom line is the conditions the concrete was exposed to and how the accelerating energy was distributed within the concrete, considering the heat transfer and the mass.

In a repetitive situation for commonly produced products (flat slabs, tees, columns, etc.), there is noting better than the PCI certification of the plant that goes far beyond the quick testing "snap shot" of the strength at a given time. The professionalism of the PCI requirements and enforcement is far beyond what you find in field produced construction.

If you are out of the realm of the PCI certification or doing on site work, cylinders are good indication, but matched curing provides a means to fine tune the results. Accelerated curing is affected by the mass/volume/shape/heat transfer of the products created. Established plants have found that the controls and records required for certification are necessary from a reliability, quality and cost standpoint.

Dick

 

[diazmeyer]

Thanks for all the information.