Troubleshooting Pervious Concrete

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Copyright 2011 NPCPA

Text of Troubleshooting Pervious Concrete

  • 1. Presented By: National Pervious Concrete Pavement Association

2. Presented By: National Pervious Concrete Pavement Association 3.

  • National Pervious Concrete Pavement Association Mission
  • Expand and improvethe use of PC.
  • Partner together those who utilize PC.
  • Authoritative voice of pervious concrete.
  • Promote and advocate common positions.
  • Represent before industry, government, and the public.

4. 5.

  • National Pervious Concrete Pavement Association
  • Educational Partner of :
    • W.O.C.
    • ASLA
  • ISBN Publisher
    • Design of Pervious Concrete Mixtures 2.0
  • Certification & Accreditation
    • Design for Pervious Concrete Certification (DPC)

6. 7. 8.

  • Upon completing this session, youshould be able to:
  • Recognizequality PC mixtures;
  • Control the quality of a PC mix throughout a project;
  • Identify the cause offailure of PC pavements; and
  • Provide options for the repair of PC pavement.

9.

  • Pervious Concrete Mixes
  • Interconnected voids are termed porosity
  • Design Void Content (DVC), typically around 20%
  • Quality controlled by the design unit weight for a corresponding DVC

10.

  • The primary considerations when determining a mixture design are:
  • Strength for loading
  • Freeze-thaw resistance
  • Porosity

11.

  • Workability of pervious concrete is primarily controlled by:
  • Aggregate angularity and gradation
  • Mortar volume
  • Sand or fiber content
  • w/cm
  • Admixtures
  • Environmental factors

12.

  • Aggregate
  • Crushed (angular)
  • Gravel (rounded)
  • S.G. > 2.5
  • Absorption < 2.5%
  • Well graded
  • Clean

13.

  • Sand
  • Porosity and permeability decrease
  • Unit weight, compressive and tensile strength increase
  • Improves freeze-thaw response

14.

  • Fibers
  • Permeability increases
  • Unit weight, compressive and tensile strength increase
  • Improves freeze-thaw response

15.

  • Cement
  • TypeI & II Portland
  • Fly Ash
  • Slag
  • Silica Fume

16.

  • Admixtures used in a pervious concrete mixture:
  • Air entraining
  • Viscosity modifying
  • Water reducing
  • Internal curing
  • Hydration stabilizing

17.

  • Generally problems with PC are related to:
  • Water content
  • Admixture dosing
  • Mixture proportions
    • Yield

? 18.

  • Proper Yield is Key to Troubleshooting PC
  • Cementitious Content
  • Paste Content
  • Void Content
  • w/cm Margins
  • Measured by Density Test
    • (actual vs. theoretical)

19. 20. Paste Increases to 23% Voids Decrease to 17% 20% Voids 20% Paste 21. Mix Comparisons with Yield Issues (5%) Design Actual Cement 600 632 p/a 0.22 0.23 Unit Weight 128.88 130.42 Voids 20% +- >17% Allowable w/cm 0.30 0.23 22. 23.

    • Mix Design
    • Total Weight in Mix Design
    • = Yield
    • Unit Weight (UW)
    • QC in Field
    • Total Weight Batched
    • / UW = Yield
  • CY Batched

24.

  • Water Content
  • Extremely low w/cm
  • 0.27 0.40 w/cm
  • Wetter is Better
  • >0.42 full cement hydration

25. http://youtu.be/lTas3hbsk58

  • Verifying and Adjusting Workability
  • Inverted slump flow test
  • Flow mimics discharge

26. Event Late Fall parking lot placement Main Issue Sticky mixture required re-tempering with water several time perload to maintain workability.Mixture Rounded-river gravel with sand and fibers, fly ash, 0.29 w/c, waterreducer, hydration stabilizer, and air entrainment.Observations: Placement occurred during the fall and temperature had droppedbetween the test pour and actual placement. Hindsight:Pervious was batched with hot water.Remediation:Do not use hot water; increase hydration stabilizer dosage; ordose water reducer at the site. 27. Event Spring parking lot placement. Main Issue Change in mixture workability as placement progressed.Mixture Rounded-river gravel with sand and fibers, fly ash, 0.29 w/c, waterreducer, hydration stabilizer, and air entrainment.Observations: At the start of placement workability was correct. As the placementprogressed water was added when truck first arrived and halfwaythrough each load.Hindsight:Aggregate moisture was checked once at the beginning of theplacement, but changed throughout the day.Remediation:When workability began to change aggregate moisture should havebeen rechecked. 28. Event Early spring parking lot placement. Main Issue Discharge rate was slow and the sticky mixture required re- tempering several times per load.Mixture Rounded river gravel with water reducer, air entrainment, andhydration stabilizer.Observations: Contractor had been told pervious was supposed to be stiff andaccepted the concrete.Hindsight:The first truck should have been verified before batching additionalconcrete. Contractor should have rejected the third truck.Remediation:Do not use hot water; increase hydration stabilizer dosage; or addadditional water reducer at the site. 29. Event Fall parking lot placementMain Issue Mixture was very dry and had severe next day raveling.Mixture River gravel mixture with slag and hydration stabilizer.Observations: Mixture was dry on arrival and required significant water addition.During the secondplacement raveling occurred and it appeared theprevious days pour had not reached sufficient strength.Hindsight:Combination of slag and hydration stabilizer delayed set time.Remediation:Check aggregate moisture as the concrete is batched. Reduce theamount of slag and or hydration stabilizer or postpone adjacentplacement. 30. Sticky MixturePotential Cause(s)Actions to ConsiderChanges in water contentInform driver that no wash water should remain in thetruck before batching pervious concrete.Mixture proportionsCheck that batched materials followed the prescribedproportions.Admixture dosagesCheck ticket for correct admixtures and dosages.Increase water reducer dosage at plant. Add water reducer at the job site. 31. Sticky MixturePotential Cause(s)Actions to ConsiderAdmixture effectivenessUse a water reducer with a longer working timeAdd additional water reducer at the job site.Haul TimeIncrease w/c to higher end of allowable limit.Increase hydration stabilizer dosage at the plant.Add water reducer at the job site. Ambient temperatureCheck that batch plant is not using warm/hot water. 32. Workability is Different fromTest PlacementPotential Cause(s)Actions to ConsiderChanges in water contentCheck aggregate moisture contents and absorption.Make sure batch plant water is adjusted for actualaggregate moisture content.Make sure excessive free moisture is not lostform the aggregate stockpile and batching location. 33. Workability is Different fromTest PlacementPotential Cause(s)Actions to ConsiderMixture proportionsCheck that batched materials followed the prescribedproportions.Admixture dosages Check batch plant/delivery ticket for correct admixturesand dosages.Change in admixturesCheck that the correct admixtures were batched. 34. Workability is Different fromTest PlacementPotential Cause(s)Actions to ConsiderHaul TimeIncrease w/c to higher end of allowable limit.Increase hydration stabilizer dosage at the plant.Ambient temperatureCheck that batch plant is not using warm/hot water. 35. Changes in WorkabilityWithin a LoadPotential Cause(s)Actions to ConsiderInsufficient mixingCheck that the truck has at least 100 revolutions.Changes in water contentMake mix is adjusted for aggregate moisture content.Admixture dosageCheck ticket for correct admixtures and dosages.Increase hydration stabilizer dosage at the plant.Admixture effectivenessUse a water reducer with a longer working time.Use a moisture retaining admixture. 36. Changes in WorkabilityBetween Loads Potential Cause(s)Actions to ConsiderChanges in water contentRemove wash water in truck before batching.Mixture proportionsCheck that aggregate gradation has not changed (check unit weight).Ambient temp increaseIncrease w/c to higher end of allowable limit.Increase hydration stabilizer dosage at the plant. Ambient temp decreaseCheck that batch plant is not using warm/hot water. 37. Adding Water Does Not Improve WorkabilityPotential Cause(s)Actions to ConsiderAdmixture dosagesCheck ticket for correct admixtures and dosages.Increase hydr