Concrete Strength Development 1

[bandraoi]

We need to strike some formworks early and lift the concrete beams into place.
The concrete is standard 40N/mm2 concrete but it only needs to achieve 15N/mm2 for the lift.

Does anyone know what the equation is for the strength development curve, or have a reference for one?

Thanks

 

[crossframe]

My old concrete text book indicates that concrete reaches about 40% of it's 28-day strength in 2-3 days, however this is VERY dependent on the mix design, cement type, admixtures, etc. Use care.

Posting this in "Structural engineering other topics" and "Bridge engineering" will generate more responses.

 

[StephenA]

It is also very dependant on ambient temperature. I usually take additional cubes and keep them in the same conditions as the cast and then test them at the time that you want to strike the formwork. This way you can demonstrate the required cube strength to the Inspectors / Resident Engineer.

Beware of the size effect. The cube is a small volume of concrete and does not get the same heat of hydration that a large cast may get. Hence keep the cubes in their moulds with the top sealed with the cast concrete and insulated to achieve the same temperature.

StephenA