The issue of leaving gaps when pouring floor slabs
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There is a project in which the factory building has 14 axes horizontally; the distance between axes 7 and 8 is 1 meter, while the distance between each other axis and its adjacent axis is 6 meters. When pouring each floor slab, most of it is poured first, leaving a 1-meter gap along axes 7 and 8, which is then poured after one week. What’s the big deal about it?
This is likely a post-cast strip. To prevent cracks caused by the temperature of the concrete as well as those resulting from uneven settlement of the foundation, concrete is often poured in sections; a gap is left between these sections without pouring concrete there for now, with pouring taking place later. This concrete that is poured later is what is known as a post-cast strip. You can look up more information on post-cast strips by searching for that term
6 meters per axis is the axis modulus for factory buildings, but when the building exceeds a certain length (around 50 meters), expansion joints need to be provided. Under normal circumstances, the foundation is integral as a whole; when the building structure settles, it does so as a single unit. However, at the expansion joints, the foundations are separated from each other, mainly to prevent damage to the building’s foundation due to thermal expansion and contraction. As we know in equipment layout for our manufacturing processes, it is not possible to place equipment that spans expansion joints, as the settlement at those junctions may vary. This post was last edited by fanxh on 2009-4-16 13:27]
Those upstairs have already replied; I’m just adding here that this is likely a post-cast strip. The concrete in large areas of the factory building is poured separately because, during the curing process, the solid volume of the cement hydrates is smaller than the total volume of the materials before the reaction takes place, which leads to contraction of the concrete – also known as chemical shrinkage. This kind of shrinkage cannot be reversed. Although the amount of shrinkage is small and it does not cause damage to the concrete structure, the shrinkage of large areas of concrete cannot be ignored. Moreover, due to this shrinkage, fine cracks may form within the concrete, affecting its load-bearing capacity and durability.