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