Curing / Hardening Time for Concrete Foundations

Was the mix done on site or did it come from a batch plant?

If they only did 1m3 and nothing else, then it is likely that they did it themselves on site. It is also likely that they did not do cubes (150mm cube or cylinder) for testing later.

Is the foundation reinforced?

Did they cover the foundation for frost protection? In case the local temperature went below zero.

Concrete should be kept at a minimum temperature of 4.4 Celsius (40 degrees F) for at least two days to allow proper curing. After that time, the concrete will have cured sufficiently to prevent cracking or adversely effecting the curing process.

Your local temps are too cold for placing concrete without heating blankets or some type of insulation to keep the concrete from freezing. Without heating or protection, concrete strength will be compromised.

Admixtures can help with the low temps, but they must be added at the batch plant. Admixtures are specifically formulated for specific mixes and must be properly measured when added to the dry mix. Don't let them add anything to a site mix that they claim allows a placement in cold temps.

Most batch plant mixes, if place and cured properly, will reach most of their design strength in seven days. Typically you would wait seven days to backfill a concrete foundation wall to avoid damage and the potential for moving the wall. But you should be able to backfill a block that size pretty much the day you strip the forms. A cubic meter of concrete isn't going to get damaged by backfilling.

I'll leave it to the engineers to calculate whether a 2.6 US ton block can resist the forces imparted to a 10M mast (with flag?).

Hi Ian

I always let my foundations cure for 28 days. Always covered with a plastic sheet to prevent fast evaporation/rainfall/wind chill. Important not to let the concrete freeze as the moisture on the surface expands and causes minute crackes and compromises the surface strength. Use water as sparingly in the mix too as this can weaken the strenght of the mix. For a 10 m mast(dont know about wind loading) I would suggest a 35Mpa mix(2 stone 2 sand 2 cement)

Small pointers, hope it helps

Craig

I think your greater concern should be the manner in which this foundation was installed and poured. Was the concrete poured 'neat', i.e. without forms and against the sides of the excavation? In my experience, I have seen many poles overturn on account of having foundations that were poured into a form and then having inadequate compaction of the backfill material.

Typically, pole foundations like yours should be drilled with an earth auger anywhere from 18" to 30" in diameter, 5' to 8' deep, and the concrete should fill the hole so that it is fully coupled with undisturbed soil. If necessary, a short piece of Sonotube or a square collar form could be used at the surface to make a neat finish of the edges. I suggest that a 1m-deep foundation is not sufficient for your use unless you are in an area that never experiences gusty or sustained winds of any magnitude.

Ian: Concrete needs, let's say, 25 to 30 days to be cure enough, meaning, to reach the 85% strength of his desing.

Before that time, if you apply a heavy force to the foundation, concrete could be not ready (fresh yet) to recieved it, and could be fail.

Rain is good...concrete need to something cover it to avoid the water inside evaporated because of the "curing activity"

You better wait... let's say.... 20 days at leat

Good lok