Durable Concrete Tanks
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Durable Concrete Tanks Improving resistance to corrosive attack Presented at the WPCA meeting January 2010 By Sam Lines, Concrete Sealants, Inc.
Transcript of Durable Concrete Tanks
Durable Concrete TanksImproving resistance to corrosive
attack
Presented at the WPCA meeting January 2010By Sam Lines, Concrete Sealants, Inc.
The Problem
This used to be aDistribution Box
Corrosion
0.58 WCR
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
Concrete Deterioration
Other types of attack include:CarbonationChloride-ion AttackDry shrinkage cracking
Problem Concrete
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
Quality Concrete Products
Quality Concrete Products
Proportioning
Proportioning
Cement hydration producesfour parts C-S-H (glue) plus one part Ca(OH)2 (free lime)
“Glue”
“I’m Outta Here!”
Cement Hydration
WCR =Weight of Water to
Weight of Cementitious Materials
Type IType IType I
WaterProportioning
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
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.
WCR and Permeability
Concrete Curing Effects
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.
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
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.
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
