Sunday, November 24, 2013

ACI 318-11 thicker stronger shotcrete pools

ACI 318-11 requires that the shotcrete walls on salt water pool be increased in strength and thickness.  Shotcrete is defined as either the wet or dry process of pneumatically placing concrete.

ACI - The American Concrete Institute

ACI is the definitive expert on concrete.  So much so, that they publish a myriad of standards that relate to concrete and it's use.

ACI Standard 318-11, "Building Code Requirements for Structural Concrete" has been directly incorporated into the International Building Code (adopted by 48 States, except Minnesota) and by the California Building Code.  This effectively makes it the law of the land. 

ACI 318-11 changes the requirements

ACI 318-11 redefined the parameters of the required coverage of concrete required over the reinforcing steel.  Prior versions of ACI 318 were ambiguous as to what was actually defined as sulfate or corrosive conditions.

ACI 318-11 establishes the additional shotcrete protection required when exposed to defined levels of sulfates, water containing chlorides (salts) and permeability.

ACI 318-11, Table 4.2.1 indicates that shotcrete swimming pools are required to meet the criteria for Permeability - P1 (condition defined as: "in contact with water where low permeability is required") AND Corrosion Resistance - C2 ( a condition defined as: "concrete exposed to moisture and an external source of chlorides from
deicing chemicals, salt, brackish water, seawater, or spray from these sources").

The resulting P1 and C2 classifications require specific mix design ratios (ACI 318-11, Table 4.3.1).

ACI 318-11, Table 4.3.1, P1 classification sets a maximum water to cement ratio (w/cm2) of 0.50 and a MINIMUM 28 day compressive strength (f'c) of 4,000 PSI.  While the C2 classification establishes a maximum water to cement ratio (w/cm2) of 0.40 and a MINIMUM 28 day compressive strength (f'c) of 5,000 PSI.

Therefore, any swimming pool that is going to be treated with sodium compounds is REQUIRED to have a maximum water to cement ratio (w/cm2) of 0.40 and a designed compressive strength (f'c) of 5,000 PSI.  Sodium compounds utilized in swimming pool sanitization include sodium chloride (chlorine), sodium bromide (bromine) or sodium (salt-electrolysis chlorination).

The C2 classification (Table 4.3.1) further specifies that the requirements of ACI 318-11, 7.7.6 "Corrosive Environments" be met.  Section 7.7.6 states that the coverage over reinforcing steel shall not be less than 2 inches for walls and slabs subject to such corrosive environments.

Structural Engineers & Building Departments

Many structural engineers and building departments do not abide by the requirements of ACI 318-11.  They either attempt to justify design criteria less than the standards, are not versed on the most up to date requirements or simply fail to comply with the codes.

When there is an issue of structural integrity on your pool, the most recently adopted version of the IBC, CBC or ACI standards will apply in court, whether or not they were enforced by the engineer or building inspector.

Do you want to be left hanging with a structural engineer who will have to defend his decision to design a structure that was below the requirements of the building codes?  
Do you want to take the risk that he will be able to convince a jury of lay people that a weaker structure is acceptable?

I thought not!

Contact the author, Paolo Benedetti of Aquatic Technology Pool and Spa at: or 408-776-8220. 
Visit his website at: 
All Contents © Aquatic Technology Pool & Spa, 2013. 
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To contact the author, Paolo Benedetti of Aquatic Technology pool and Spa, email him at: or call 408-776-8220.
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