Minimum Shotcrete Strengths Pools Watershapes

Shotcrete Strengths for Swimming Pools

The minimum compressive strength for shotcrete (wet mix or dry mix method) shall be 4000 PSI.  The minimum compressive strength of the concrete is fc’=4,000 psi with a maximum water-cementitious material ratio (w/cm) of 0.50.
  
American Concrete Institute
 

The American Concrete Institute’s ACI 318-08 Building Code Requirements for Structural Concrete includes Chapter 4 Durability Requirements. Also contained therein are two applicable tables:

Table 4.2.2 specifies the Requirements for Special Exposure Conditions. 

Table 4.3.1 Requirements for Concrete by Exposure Class defines a Category P1 exposure as concrete “in contact with water where low permeability is required.”   

American Shotcrete Association

The  American Shotcrete Association has also stated that their approved minimum compressive strength shall be 4,000 psi (as stated in the their Position Statement #1).

International Building Code

The IBC also specifies 4000 PSI shotcrete, by making direct reference to the ACI 318 standard.

The IBC (2012) 1910.6 Rebound Removal, also states that all rebound and trimmings shall be removed from the structure.

 

Therefore, all rebound, trimmings and loose debris shall be removed from the structure and shall not be used in any manner within the structure.

Paolo Benedetti, SWD Aquatic Artist, Watershape Consultant, Expert Witness, International Construction Management 
Contact the author at: info@aquatictechnology.com or 408-776-8220
"Creating water as art."™ 
Aquatic Technology Pool and Spa© 
©www.aquatictechnology.com All rights reserved.

Limiting Suction Outlet Plumbing Velocities

Standards Mandate the MAXIMUM SPEED LIMIT
 
Standards dictate that the MAXIMUM velocity limit in the plumbing at the suction outlets is 6 feet-per-second (ANSI/APSP-7).  I recommend that the maximum designed velocity on the suction side of the pump be limited to 4 feet-per-second.

Why lower that the maximum?  In suction lines speed is not a good thing.  In fact, excessive speed causes equipment wear, friction, lost energy and pump noise.

Since pump selection is the last task performed when designing a suction system, oftentimes there is not a pump curve that EXACTLY fits the system requirements.  By designing below the maximum allowed velocity, the designer has the ability to select the closest pump curve, even if it slightly exceeds the 4 FPS design - safely remaining below the maximum.

Isolation Valves 

When isolation valves are placed in suction lines between a pump and the suction outlets, any singular suction line supplying water to the pump MUST be capable of providing 100% of the systems’ designed flow rate at a maximum line velocity of 4.5 FPS.  

This is required, because if valves are closed and lines are improperly isolated, and if the pipes are not of sufficient diameter, the line velocity would quickly exceed the 6 FPS standard.

Energy Efficiency

Energy efficiency is greatly enhanced by lowering the line velocity.  Cavitation, operating noises & suction entrapment hazards are also reduced by lowering the line velocity.

Line velocities cannot be reduced much lower than 4 FPS, otherwise pipe scour would not occur.  Debris and sediment could eventually collect in the pipes.

Paolo Benedetti, SWD Aquatic Artist, Watershape Consultant, Expert Witness, International Construction Management 
Contact the author at: info@aquatictechnology.com or 408-776-8220 
"Creating water as art."™ 
Aquatic Technology Pool and Spa© 
©www.aquatictechnology.com All rights reserved.

Salt Water Pools Galvanic Corrosion

The current rave is have a "salt water" pool.  Many owners are under the false impression that these pools are "chlorine free."  Though, this is hardly the case.

Electrolytic Solution

Salt is placed into the pool to create a solution much weaker than that found in the ocean.  In fact there should only be about 3,000 ppm of salt present in a salt water pool.  A special device at the equipment pad, then splits the sodium chloride (salt) into CHLORINE!  These owners are merely using the salt to generate chlorine in their pipes!

But placing salt into the pool also turns the pool water into a electrolytic solution.  Add some stray current and the pool becomes in effect a giant electroplating tank.

A salt water pool is really a very weak, but giant battery!

Galvanic Corrosion

These stray currents will cause staining of the plaster surfaces, galvanic corrosion of less noble metals.  Copper heat exchangers will actually dissolve from the inside and decay on the outside, as their molecular structure is attacked.  Metals suspended in the pool water will bond to more noble metals, plating them in unusual colors.

Sacrificial Anode

Many in the pool industry have drawn on "a solution" that boat owners have used for years - SACRIFICIAL ANODES.  HOWEVER, a SACRIFICIAL ANODE is not the placebo everyone is seeking. 

On a boat, a sailor does not care if the anode erodes, or if the anode's metals dissolve into the water (ocean).  The anode on a boat is a lot cheaper than the wiring, an expensive bronze prop or brass components.  It prevents the corrosion of the boat's precious components, by SACRIFICING itself instead. 

Placing a sacrificial anode in a swimming pool is doing the same thing as on a boat.  One is merely offering a SACRIFICIAL metal for the galvanic corrosion to attack, instead of the precious components.  It does nothing to address the actual cause - GALVANIC CORROSION.

So instead of plating surfaces with copper, you will be plating them with zinc or magnesium from the sacrificial anode.  The sacrificial anode will save the copper, but it will not stop the staining or plating of the stainless steel components.  That will now occur with the metal from the anode.  

This is exactly why anodes need to be periodically replaced - they are sacrificed.  And where those sacrificed metals go is out of your control!

The Source of Stray Current

The equipotential bonding grid does not prevent galvanic corrosion.  In fact, if there is stray voltage finding it's way to the pool through the property's CONTINUOUS GROUNDING SYSTEM, the equipotential bonding grid may actually be feeding voltage to the pool's metallic components. 

The bonding grid can actually function as either the electrode or cathode, depending if there is stray voltage present or if it is providing a path to ground (where the equipotential bonding grid and the grounding grids are cross connected - pumps, heater's, panel boards, etc).

For these very reasons, many pool builders that I know and I, have ceased installing salt systems.  We now promote "off-line" on-site generation of liquid chlorine from salt or tanks of liquid chlorine and then the controlled dispensing via a ORP/pH Controller.


Paolo Benedetti, SWD Aquatic Artist, Watershape Consultant, Expert Witness, International Construction Management 
Contact the author at: info@aquatictechnology.com or 408-776-8220 
"Creating water as art."™ 
Aquatic Technology Pool and Spa© 
©www.aquatictechnology.com 
All rights reserved.