Footings Early Strength 3000 psi vs 4000/5000
Footings Early Strength 3000 psi vs 4000/5000
(OP)
Hello -
I have a footing design requirement for a mezzanine (very long spans), that is calling for 3000 psi with 7 days cure before dead load and 28 days before live load. The engineer is on vacation now. I can't afford to wait the 28 days, so was trying to find out how long it would take 4000 psi or 5000 psi concrete to get to a 3000 psi strength, especially if we used high early strength.
I do not have the loads for the footings, but the dead load is 10 lbs/sq ft and live load of 75 lbs/sq ft.
So the question is:
With 4000 psi HES, how long would I need to wait for dead load and live load. What about 5000 psi HES?
I have uploaded the footing locations and engineer's notes.
Thanks
I have a footing design requirement for a mezzanine (very long spans), that is calling for 3000 psi with 7 days cure before dead load and 28 days before live load. The engineer is on vacation now. I can't afford to wait the 28 days, so was trying to find out how long it would take 4000 psi or 5000 psi concrete to get to a 3000 psi strength, especially if we used high early strength.
I do not have the loads for the footings, but the dead load is 10 lbs/sq ft and live load of 75 lbs/sq ft.
So the question is:
With 4000 psi HES, how long would I need to wait for dead load and live load. What about 5000 psi HES?
I have uploaded the footing locations and engineer's notes.
Thanks





RE: Footings Early Strength 3000 psi vs 4000/5000
RE: Footings Early Strength 3000 psi vs 4000/5000
Side comment... by not involving your engineer in this decision, you are assuming all the liability of any outcome here... good or bad. I strongly suggest you at least involve the local jurisdiction that approved the planset..
Mike McCann, PE, SE (WA)
RE: Footings Early Strength 3000 psi vs 4000/5000
Mike, you need to watch those little keys. Or predictive text...or something.
RE: Footings Early Strength 3000 psi vs 4000/5000
RE: Footings Early Strength 3000 psi vs 4000/5000
Mike McCann, PE, SE (WA)
RE: Footings Early Strength 3000 psi vs 4000/5000
RE: Footings Early Strength 3000 psi vs 4000/5000
5.11 — Curing
5.11.1 — Concrete (other than high-early-strength)shall be maintained above 50°F and in a moist condition for at least the first 7 days after placement,
except when cured in accordance with 5.11.3.
5.11.2 — High-early-strength concrete shall be maintained above 50°F and in a moist condition for at least the first 3 days, except when cured in accordance with 5.11.3.
RE: Footings Early Strength 3000 psi vs 4000/5000
RE: Footings Early Strength 3000 psi vs 4000/5000
I have no idea if this engineer is logical or not. But according to ACI, it might be logical to assume that the concrete may reach approximately 70% of its 28 day strength after 7 days of moist curing (assuming Type I cement). More or less if different types of cement are used or if temperatures are high or low.
RE: Footings Early Strength 3000 psi vs 4000/5000
Curing - normally 7 days and for fly ash mixes 10 to 14 days - and I've used up to 50% fly ash in mixes. I would have read the requirement as "concrete being cured and required strength to be 3000 psi at 7 days". And this is why words count; and clear precise and concise requirements need to be carefully spelled out.
RE: Footings Early Strength 3000 psi vs 4000/5000
Note #6 is perfectly clear to me - 7 days of cure before you can apply any dead load.
Does this make logical sense? Probably not.
But I have had EoR's take a very simple stand - "That's what my notes (or specs) require and that is what I expect. Period, end of conversation."
Would the mezzanine be 100% complete at 28 days after the footings have been cast? What kind of live load would be applied so early on in the structures life?
Ralph
Structures Consulting
Northeast USA
RE: Footings Early Strength 3000 psi vs 4000/5000
RE: Footings Early Strength 3000 psi vs 4000/5000
The EoR was concerned about strength at 28 days in initial conversations. So it would seem to me that an HES which reaches 3000 psi at 7 or 10 days would suffice. The mezzanine only will take about 10-12 days to put up, so that is what I am most concerned with. After that, conveyors will be installed, but would be several weeks to reach the full live load of the system. At 3-4 days, all I want to do is start erecting columns...we have a lot of them to do, but only footings on about a 3rd.
This is an indoor pour in GA, so no issue with temp or moisture.
Thanks again.