Lets say we have a very large and deep circular footing for a tall tower such as an industrial chimney or a wind turbine, and for convenience we want to pour it not at once but in sections. Can this be done, provided that we have sufficient dowels between the pour sections? Or it must be a single pour?
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$\begingroup$ Could you elaborate why you want to pour it in sections? Do you want to use different materials at each section? Also do you want the pouring to happen simultaneously or (pour, wait to solidify, repeat)? $\endgroup$– NMech ♦Aug 30, 2021 at 8:09
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$\begingroup$ Dams have been made with 32000m^3 of concrete - that was not poured at once. Removed my answer as the downvoter did not understand :) $\endgroup$– Solar MikeAug 30, 2021 at 8:38
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$\begingroup$ NMech: I undertsand you are not in construction as you are asking using different materials or not. It is the same concrete. You do not pour one section in concrete and another in wood) We pour in sections because sometimes long pours cannot logistically continue or to liminate hydration heat of cement harming concrete if the poured masses are so large. $\endgroup$– upstreamAug 30, 2021 at 10:57
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2 Answers
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-Yes, it is possible and is routinely done.
A couple of concerns,
Massive concrete creates a huge amount of heat and thermal expansion, thus the elaborate systems of cooling the pour.
Also the curing under different climates is not good so careful planning is needed.
The cold joint should be placed far from a critical change in stress.
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$\begingroup$ As far as the shapes of the sections, what do you think about it? The first thing that comes to mind is like pizza slices. Or pouring a smaller middle circle, and then pouring the gap between two circles in a few sections that divides the 360 degree to a few pieces is better? I think the second one, which allows simpler geometry and avoids stress concentration in the middle if pizza slices were used... Is there a code or manual etc... that would show which pattern is better for such pour of a circular footing? $\endgroup$– upstreamAug 30, 2021 at 11:09
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$\begingroup$ One tries to leave any rebar change of grouping or overlap out of the cold joint. No dead-locked zone pour. They plan these pours so that they don't fight the gravity and geometry constraints. One way seems to pour radially, maybe in quadrants. $\endgroup$– kamranAug 30, 2021 at 15:11
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Since the footing is "large and deep", both the vertical and horizontal construction or expansion joints can be utilized to partition the concrete pour.
Note, other than the capability/capacity of the concrete plant and crew to produce and handle the concrete placement, the amount of heat generated during hydration needs to be evaluated, as it is usually the most important factor in determining the size and thickness of an individual pour, with the consideration of the available temperature control method employed.
Another factor affecting the thickness of the pour is the potential of aggregate separation when poured from the height. It can be difficult to vibrate the concrete uniformly and adequately, that usually the main cause for having honeycombs in the concrete.
