Temperature and Shrinkage Reinforcement for Shotcrete

[rowe]

A Pool Contractor in business for 30 years has used #3 bars at 12" o.c. in 6" thick pool slabs and walls (5' high) in all of his pools. No significant problems with cracking have occurred.

Question 1: does shotcrete and normal concrete have the same requirements regarding temp and shrinkage reinforcement?

Question 2: What is the range of extreme temperatures for concrete slabs addressed by ACI318 in the temperature reinforcement requirement.

Question 3: Why haven't these slabs developed serious cracking problems?

 

[JAE]

Shotcrete is a much denser product that concrete - it is also placed with very low water/cement ratios, thus less shrinkage.

 

[ATSE]

Shotcrete is concrete.
While shotcrete has distinct advantages, it should not be held to a lower standard for code requirements.

I'm not sure where your project is, but one reason most pools do well (minimal cracking) in the southern and western US is because they are filled with water most of the time, which both moderates temperature and eliminates shrinkage cracking seen in exposed structures because of saturation.
A good reference is ACI 224. See figure 3.3

Another reason for good performance is typical shotcrete has a very low w/cm ratio.

As for your question #3, I would repeat that too loudly. There is a lot of poor performance of concrete structures out there - just because this contractor has missed the bullet (or tells you he has) doesn't negate the volume of legitimate residential and commercial pool problems associated with cracking. Just ask a concrete repair contractor.

However, pools are design-build by nature and tend to push the limits more, and reinforcing tends to be a little light compared to ACI 318 code stds.