mjd

A concern with very large volumes of concrete is temperature. Concrete curing is an exothermic process which produces a considerable amount of heat. Often the heat of hydration is a welcome byproduct, especially in cold weather, but with very large placements the heat produced can be excessive, which (for various reasons) results in poor quality concrete with low strength and low durability. The Hoover Dam would have been far too large a volume of concrete to place in one placement for this reason alone.Another reason it had to be placed in batches is purely logistic. Delivery of cement to the site was difficult and to place it in one pour would have required the cement to either be present all at once or reliably delivered on a rapid schedule. The dam was in the middle of nowhere back ...

A concern with very large volumes of concrete is temperature. Concrete curing is an exothermic process which produces a considerable amount of heat. Often the heat of hydration is a welcome byproduct, especially in cold weather, but with very large placements the heat produced can be excessive, which (for various reasons) results in poor quality concrete with low strength and low durability. The Hoover Dam would have been far too large a volume of concrete to place in one placement for this reason alone.Another reason it had to be placed in batches is purely logistic. Delivery of cement to the site was difficult and to place it in one pour would have required the cement to either be present all at once or reliably delivered on a rapid schedule. The dam was in the middle of nowhere back in the day.Finally, fresh concrete is essentially a liquid. The pressures on the formwork for the dam would have been pretty much impossible to resist had it been placed in one continuous placement. Bridge abutment walls, which are orders of magnitude smaller than the dam, have formwork failures all the time for this reason, when the forms are not built correctly.