durable concrete tanks
TRANSCRIPT
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Durable Concrete TanksImproving resistance to corrosive
attack
Presented at the WPCA meeting January 2010By Sam Lines, Concrete Sealants, Inc.
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The Problem
This used to be aDistribution Box
Corrosion
0.58 WCR
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Concrete Deterioration
Possible causes of concrete deterioration:H2S Attack– Hydrogen sulfide oxidation = H2SO4 sulfuric acid– Reacts with Ca(OH)2 (free lime) to become gypsum– Gypsum reacts with aluminates to form ettringite
Microbial Induced Corrosion– Through a biological chain, H2S is converted into
H2SO4 by Thiobicillus bacteria– H2SO4 reacts with free lime in the concrete
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Concrete Deterioration
Other types of attack include:CarbonationChloride-ion AttackDry shrinkage cracking
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Problem Concrete
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Durability: Your Best Defense
Durable concrete is the result of:A properly proportioned mixA low water-to-cementitious materials ratioThe use of Admixtures and Secondary Cementitious Materials (SCM’s)Proper Curing TechniquesSealers / Densifiers / Coatings
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Quality Concrete Products
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Quality Concrete Products
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Proportioning
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Proportioning
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Cement hydration producesfour parts C-S-H (glue) plus one part Ca(OH)2 (free lime)
“Glue”
“I’m Outta Here!”
Cement Hydration
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WCR =Weight of Water to
Weight of Cementitious Materials
Type IType IType I
WaterProportioning
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Water/Cementitious Materials Ratio
Low water/cementitious materials ratios are critical for
increased concrete strengthwater tightnessincreased durability
High water/cementitious materials ratiosHigh water content will evaporate, leaving large capillary poresIncreased porosityDecreased strength
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Importance of a Low WCR
Low High
High
Porosity
Stre
ngth
High
Low
Low
High
A low water-to-cement ratio (below 0.45) will produce a denser concrete with a lower porosity than that of a high water-to-cement ratio.
Dense concrete is stronger and more durable than porous concrete.
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WCR and Permeability
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Concrete Curing Effects
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Curing Agents
Cylinders 1-4 and 9 have a Cure and Seal applied.
All cylinders were field cured after 24 hours.
Photo is at 28 days of age.
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Sealers and Densifiers
Penetrating sealers can be used with old and new concrete.The chemicals react with the free lime present in the concrete and form a pore blocking crystalline structure.Some densifiers are added to the concrete in the mixer.Most are either Silicates, Silanes, or Siloxanes
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Penetrating Sealers / Densifiers
Sealed Unsealed
Initial Water Placed on Sample
Effects of Water After 120 Minutes
Both samples of concrete are from the same mix, cured in the same manner.
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Conclusion
Remember: Not all concrete is the same!!!Durable concrete with low porosity provides better resistance to chemical attackGood production practices produce good concrete products:– Well designed / proportioned mixes– Low water-to-cement ratios– Proper early age curing
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