Acid Leaching

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Acid Leaching Concrete Pretreatment

• Joe Choromanski
• Ripley Aquariums

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Acid Leaching Concrete Pretreatment

• LESSON 1
• NEVER conduct an informal survey of your fellow
  aquarium colleagues on anything!
• If you do, you will become the de-facto expert
  and be asked to present your scientific data at
  an international symposium

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Acid Leaching Concrete Pretreatment

• LESSON 2
• If you DO conduct such a survey (which will
  result in you being asked to present the
  results of), try to pick a topic which is mildly
  interesting
• something other than Acid Leaching Concrete
  Pretreatment
• or Activated Carbon

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Acid Leaching Concrete Pretreatment

• LESSON 3
• If you DO conduct such a survey (which will
  result in you being asked to present the
  results of), try to pick a topic which you might
  know something about
• In my case
• something other than Acid Leaching Concrete
  Pretreatment
• or Activated Carbon

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Acid Leaching Concrete Pretreatment

• THE ISSUE
• New concrete, especially uncoated surfaces such
  as newly poured tank walls or artificial
  rockwork, will typically leach alkalis.
• These alkalis can potentially adversely affect
  the pH of the final aquarium water.

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Acid Leaching Concrete Pretreatment
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Acid Leaching Concrete Pretreatment

• THE HISTORIC SOLUTIONS
• Some aquarists simply pre-fill the exhibit with
  freshwater for a period of time (5-10 days),
  drain it, refill with saltwater and then add
  small amounts of acid to bring pH into ranges
  normally expected for seawater (i.e. 8.0-8.5).

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Acid Leaching Concrete Pretreatment

• THE HISTORIC SOLUTIONS
• Other aquarists pre-fill the exhibit with
  freshwater and add large volumes of acid reducing
  the pH to 3.0 to 5.0 and continue to add acid
  until the pH stabilizes (usually a longer period
  e.g., 45 days), and then dump and refill with
  saltwater.

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Acid Leaching Concrete Pretreatment

• THE HISTORIC SOLUTIONS
• Still other aquarists choose to skip the
  freshwater pre-fill, adjusting pH after the final
  saltwater fill using small acid additions over a
  longer period, often during biofilter run-in
  and/or with animals in the water.

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Acid Leaching Concrete Pretreatment

• THE CHOICE
• Concrete type, tank and/or rockwork surface area,
  as well as system type (open, closed, etc.) may
  determine which of these methods should be used.
• Perhaps even more critical in freshwater systems.

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Acid Leaching Concrete Pretreatment

• INFORMAL SURVEY (1)
• E-mail request sent by Joe Choromanski November
  1998
• Sent to 67 people representing 37 institutions
  (not scientific)
• Mostly aquariums some consultants
• Mostly U.S. a few international
• 19 responses

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Acid Leaching Concrete Pretreatment

• INFORMAL SURVEY (2)
• E-mail request sent by Joe Yaiullo April 10, 2000
• Sent to AZA Listserve (aqua-ig)
• Wide distribution worldwide
• 2 responses to list (perhaps more to Joe Y.)

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Acid Leaching Concrete Pretreatment

• INFORMAL SURVEY (3)
• E-mail request sent December 2002 by Pete Mohan
• Sent to 5 people (2 responses)
• All U.S. aquariums
• Requested for water parameters chapter of
  Elasmobranch Husbandry Manual

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Acid Leaching Concrete Pretreatment

• SURVEY RESULTS
• Basically four different strategies
• Do nothing (only one response)
• Fill w/ freshwater and sit (or multiple fills
  dumps) no acid additions
• Adjust pH after filling w/ final water making
  minor adjustments w/ acid w/ animals in tank over
  a long term

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Acid Leaching Concrete Pretreatment

• SURVEY RESULTS
• Basically four different strategies
• Add acid (usually HCl) in freshwater to reach a
  pH of 4.0 (/- 1.0) for several days to several
  weeks until pH stabilizes and additional acid
  additions are unnecessary dump and refill with
  final aquarium water.

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Acid Leaching Concrete Pretreatment

• SURVEY RESULTS
• Majority (65) of responses were 4, the
  aggressive acid additions to a tank initially
  filled w/ freshwater, targeting a pH of 4.0 until
  stabilization.

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Acid Leaching Concrete Pretreatment

• SURVEY RESULTS
• No scientific literature on this subject from
  husbandry perspective.
• Mostly aquarist word-of-mouth, previous
  experiences, common sense, etc.
• Some data from coating companies acid etching
  for coating adherence.

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Acid Leaching Concrete Pretreatment

• SURVEY RESULTS
• Exhibit theming contractor recommends acid
  leaching for shotcrete which they partially help
  with by using acid stains via a plant sprayer
  during painting.
• Contact acid treatment can be used on smaller
  exhibit concrete walls.

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Acid Leaching Concrete Pretreatment

• SURVEY RESULTS
• There are some advantages to 2 4 as most new
  concrete tanks require an initial freshwater fill
  for contractual reasons (e.g. testing water
  tightness of tank, pipe penetrations, acrylic)

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Acid Leaching Concrete Pretreatment

• QUESTIONS
• Is there any risk to this more aggressive acid
  leaching procedure?
• Is it even necessary given the other three
  approaches?
• Variables?

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Acid Leaching Concrete Pretreatment

• QUESTIONS
• Is there any risk to this more aggressive acid
  leaching procedure?
• YES
• (but acceptable)

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Acid Leaching Concrete Pretreatment

• CONCRETE 101
• Concrete is the strongest construction material
  known to man, at least in COMPRESSION, however it
  has no TENSILE strength.
• Consequently, concrete must be internally
  reinforced with steel.

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Acid Leaching Concrete Pretreatment

• CONCRETE 101
• Steel is used because
• High tensile strength.
• Shares the same thermal expansion coefficient as
  concrete (expand and contract at similar rates).

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Acid Leaching Concrete Pretreatment

• CONCRETE 101
• Steel is also problematic because
• High ferrous content.
• Prone to corrosion by oxidation, carbonation, and
  chloride ions (such as in saltwater and
  Hydrochloric acid solutions!)

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Acid Leaching Concrete Pretreatment

• CONCRETE 101

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Acid Leaching Concrete Pretreatment

• CONCRETE 101

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Acid Leaching Concrete Pretreatment

• CONCRETE 101
• Resulting in spalling..
• spalling is BAD!

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Acid Leaching Concrete Pretreatment

• CONCRETE 101
• Steel is safe in concrete
• Due to concrete hydration reactions, pH of
  concrete is 12.5 (/- 1.0).
• In this alkaline environment a protective oxide
  layer is formed around the rebar creating a
  passivating environment for the rebar
• Rebar corrosion occurs at pH lt 11.0 (9.0?)

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Acid Leaching Concrete Pretreatment

• THE DILEMMA
• Structural Engineers want to keep the pH of the
  concrete very high (alkaline pH 12.0 minimum) to
  create and maintain the protective oxide coating
  or passivating layer which protects the
  required reinforcing steel (rebar)

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Acid Leaching Concrete Pretreatment

• THE DILEMMA
• Aquarists, on the other hand, want their exhibit
  water maintained at the appropriate pH (8.3 /-
  for SW 6.8 or lower for FW) and not have the
  concrete continually forcing this pH up creating
  problems (e.g. ammonia toxicity, acid base
  balance, etc.)

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Acid Leaching Concrete Pretreatment

• SOLUTIONS
• Possible Rebar Protection Solutions
• Epoxy Coated Rebar
• Stainless Steel Cladded Rebar
• Stainless Steel Rebar
• FRP Rebar
• Cathodic Protection (no way Jose)

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Acid Leaching Concrete Pretreatment

• Epoxy Coated Rebar

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Acid Leaching Concrete Pretreatment

• Epoxy Coated Rebar

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Acid Leaching Concrete Pretreatment

• Epoxy Coated Rebar
• PROBLEMS
• Powder coating / paint can crack and flake off
• If bent after coating
• During transport
• During handling at construction site
• Touch up painting assigned to laborers
• Tie wires usually not coated

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Acid Leaching Concrete Pretreatment

• Cladding of ferrous rebar w/ Stainless Steel

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Acid Leaching Concrete Pretreatment

• Stainless Steel Rebar
• Too expensive
• Not 100 ferrous free
• FRP Rebar
• Too expensive
• Not nearly as strong as steel

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Acid Leaching Concrete Pretreatment

• SOLUTIONS
• Possible Rebar Protection Solutions
• Waterproofings (e.g., Vandex)
• Post-cure tank liners or coatings
• Good Concrete Formula
• Good Concrete Coverage (rebar)
• Good Concrete Construction

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Acid Leaching Concrete Pretreatment

• CONCRETE WATERPROOFINGS

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Acid Leaching Concrete Pretreatment

• CONCRETE COATINGS

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Acid Leaching Concrete Pretreatment

• GOOD CONCRETE IS THE KEY
• Good Concrete Formula
• Dense Low water to cement ratio (will prevent
  shrinkage and cracks)
• Cementitious additives (fly ash, microsilicates)

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Acid Leaching Concrete Pretreatment

• GOOD CONCRETE IS THE KEY
• Good Concrete Coverage
• 3 minimum

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Acid Leaching Concrete Pretreatment

• GOOD CONCRETE IS THE KEY
• Good Concrete Coverage
• Sea World Florida Shark Encounter

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Acid Leaching Concrete Pretreatment

• GOOD CONCRETE IS THE KEY
• Good Concrete Coverage
• Sea World Florida Shark Encounter
• One stemwall section was only 5 thick (no room
  for 3 coverage)
• ½ diameter rebar was rusting concrete
  spalling next bar in was OK
• 25 year old structure (better than theory 10 15
  years to reach 2)

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Acid Leaching Concrete Pretreatment

• GOOD CONCRETE IS THE KEY
• Good Concrete Construction
• No bubbles or air voids (porosity)
• Clean form interiors (porosity)
• Uniform porosity from top to bottom (not
  feasible bottom will be denser)
• Good long and controlled cure time to achieve
  design density

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Acid Leaching Concrete Pretreatment

• GOOD CONCRETE IS THE KEY
• Good Concrete Construction

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Acid Leaching Concrete Pretreatment

• Structural Engineers
• Would prefer we did not add acid but recognize
  the need
• Recommend the stronger acidity (4.0) for a
  shorter duration
• SW will infiltrate eventually

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Acid Leaching Concrete Pretreatment

• Shotcrete Rockwork Theming vs. Structural
  Concrete Walls
• Usually no rebar to worry about
• Can acid spray
• Can add microsilicates to achieve a final pH of
  8.3 in the shotcrete

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Acid Leaching Concrete Pretreatment

• CONCLUSIONS
• Acid leaching can be performed safely for the
  concrete walls and rockwork
• Short duration low pH
• Can use microsilicates in rockwork shotcrete to
  eliminate acid leaching of this aspect

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Thank you!Obrigado!
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The End?????