PoolQ Can you please provide me a technical recommendation on whether or not expansion joints should be used in a large shotcrete pool that is approximately 230 ft x 135 ft (70 m x 41 m)? In my design I am calling for two expansion joints which would break the pool into three approximately 76 ft-8 in. (23 m) sections. The contractor is telling me that he typically does not use expansion joints in the pool and that they are unnecessary. I do not typically work with shotcrete and have limited pool design but given the size of the structure I would think it would be best to include expansion joints. Can you please recommend whether or not the expansion joints should be used? Any help would be greatly appreciated.
Shotcrete is a placement method for concrete. All normal concrete experiences drying shrinkage that creates a volume change in the hardened concrete. Pools will also experience volume change in the concrete due to thermal changes, especially summer to winter seasonal swings. Contraction and expansion joints are common in all kinds of concrete liquid-containing structures especially with walls of this length. Though we can’t provide a firm design recommendation you should consider these factors:
- What are the weather conditions when the pool is anticipated to be built? If during hot summer months, could there be enough seasonal temperature swing to require expansion joints?
- If expansion joints wouldn’t be needed would contraction joints be needed to handle anticipated temperature swings, and drying shrinkage?
- Will the pool be empty for extended times (this could lead to more shrinkage or direct exposure to solar gain or cold conditions?
- Is the pool to be kept full or empty during the winter months? (if the pool is in a geographic region where extending freezing conditions are prevalent)
Overall, the design for a shotcrete pool should be the same as one for a cast concrete pool.
