Cracking and Leakage at Reinforced Concrete Pomona Reservoir 5C

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Cracking and Leakage at ReinforcedConcrete Pomona Reservoir 5C

Piotr D. Moncarz, Ph.D., P.E.Patxi Uriz, Ph.D., P.E.

Reservoir 5C

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Summary Walls Roof Floor Recommendations Conclusions

Introduction and Summary

Concerns about integrity and serviceabilityExponent inspections and analysisDesign and construction errors led to inadequateperformanceStructural safety of the tank not significantlyimpactedHeightened repairs and maintenance required

Reservoir 5C

Defects

Summary

Exponent Evaluation

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Summary Walls Roof Floor Recommendations Conclusions

WallsWall concrete quality is goodExcessive temperature and shrinkage crackingDesign-reinforcement inadequate to controlcrackingAdditional future cracking likelyDefective construction led to wall patching andbuild-upContinued additional maintenance required:

Inspection for new cracksRepair of cracks on interior face of exterior wallsRepair of wall patching

Walls

Reinforcement Design

Interior Wall Patches

Shrinkage Analysis

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Summary Walls Roof Floor Recommendations Conclusions

RoofRoof concrete quality is goodLarge cracks foundExcessive temperature and shrinkage crackingDesign-reinforcement inadequate to controlcrackingAdditional future cracking likelyHeightened inspection and maintenancerequired

Roof

Roof Exterior Cracking

Roof Interior Cracking

Reinforcement Design

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Summary Walls Roof Floor Recommendations Conclusions

Visual inspection only

HST-VIO

0.100% per dayHST-100

0.075% per dayHST-075

0.050% per dayHST-050

0.025% per dayHST-025

No measurable lossHST-NML

Maximum amount of water loss to meet designation

Designation

Visual inspection only

HST-VIO

0.100% per dayHST-100

0.075% per dayHST-075

0.050% per dayHST-050

0.025% per dayHST-025

No measurable lossHST-NML

Maximum amount of water loss to meet designation

Designation

FloorInitial repairs complete

Repairs require monitoringRepair of new cracks required

Seepage from underdrain ~520 gal/dayLoss rate is relatively lowMore accurate test, if desired

Floor

Slab on Ground

Seepage

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Summary Walls Roof Floor Recommendations Conclusions

RecommendationsRepair of roof and wall cracking:

Use Exponent outlined approach (February 2007 report):Estimated material cost for walls ~$312,000Estimated material cost for roof ~$720,000Prices DO NOT include design, planning, contracting, and supervision

Continue repairs with current methodDevelop inspection and repair protocolHeightened inspection and repair frequencyRepairs of concrete patch material

Repair of tank floor cracking:During periodic tank emptying perform tank floor inspection for crackrepair failures and for new cracksRepaired cracks with filler failure are to be re-patchedNew cracks to be routed and repaired

Recommendations

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Summary Walls Roof Floor Recommendations Conclusions

ConclusionsDefective design and construction:

Led to inadequate performanceDid not significantly impact structural safety

Heightened repairs and vigilant maintenance required tomaintain intended useful life of the tankFuture repairs methodology based on existing scheme or basedon Exponent’s outline

Conclusions

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Summary Walls Roof Floor Recommendations Conclusions

End

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Summary Walls Roof Floor Recommendations Conclusions

Tank DescriptionApproximately 10MGreinforced concretereservoirDesigned and constructedin 2002-2003305 ft long x 207 ft wideExterior walls 3 ft thick;interior walls 2 ft thickRoof slab 9 in thickBottom slab 7 in thick

Reservoir5C

305 ft

207

ft

Summary

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Summary Walls Roof Floor Recommendations Conclusions

Concrete Design SpecificationsWater-cement ratio: 0.45Minimum 3500 psi compressive strength at 28 daysMaximum slump 4 inch

BACK

Summary

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Summary Walls Roof Floor Recommendations Conclusions

DefectsWall leakage

Photos taken November 17, 2006

Summary

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Summary Walls Roof Floor Recommendations Conclusions

DefectsRoof cracking

Photos taken November 17, 2006

BACK

Summary

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Summary Walls Roof Floor Recommendations Conclusions

Exponent EvaluationWall and roof exterior inspection November 17, 2006

Coring of the exterior walls December 5, 2006

Laboratory and numerical studiesExponent report February, 2007

Interior and exterior roof inspection November 8, 9, 2007

Tank interior inspection December 5, 2007

Interior inspection and roof supplemental report January, 2008

BACK

Summary

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Summary Walls Roof Floor Recommendations Conclusions

Exterior Wall Concrete EvaluationPetrographic analysis

Properly consolidated and curedExcellent strengthLow water-cement ratioDepth of carbonation minor to moderateNo deleterious reactionsVery few small shrinkage cracks along the exterior surface

Walls

BACK

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Summary Walls Roof Floor Recommendations Conclusions

Shrinkage, Temperature Analysis

Mechanism of stress development in the wall subject to temperature and shrinkage shortening

Crack width, crack length above the wall base, andsteel stress upon wall shrinkage equivalent to 27°F temperature drop

Walls

The as-designed wall was bound to develop excessively widecracks to the height of several feet from the ground

Stress [MPa]

Crack W

idth [mm

]

crack width [mm]

steel stress[N/mm²]

Steel yieldsdanger of yielding!

height above foundation [m]

“free“ unrestraint shortening offresh wall due to cooling,

shrinking...

bond between wall &foundation

resulting deformation and stresses

older stiff foundation

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Summary Walls Roof Floor Recommendations Conclusions

Consequences of Excessive CrackingOngoing leakageCorrosion of reinforcementLong-term integrity and serviceability affectedElevated inspection and maintenance needed

Walls

BACKPhotos taken December 5, 2007

Repaired cracks

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Summary Walls Roof Floor Recommendations Conclusions

Exterior WallReinforcement

Walls

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Summary Walls Roof Floor Recommendations Conclusions

Exterior Wall Reinforcement RequirementsCrack spacing and width control is accomplished throughreinforcement ratio and control joints

Wall control joints spaced at about 37 feet

Wall horizontal reinforcement ratio of 0.28%

Minimum horizontal reinforcement ratio of 0.4% per ACI 350R.01Table 7.12.2.1

Where crack tightness is critical ACI 224R-01 recommendsreinforcement ratio of minimum 0.6%

Restraint requires additional reinforcement (ACI 350-06)

Walls

BACK

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Summary Walls Roof Floor Recommendations Conclusions

Failed repair patch

Interior Wall RepairsWalls repaired in the interior through patch-materialThe patches are failingRestoration to original repair condition is needed

BACK

Walls

Peeling repair patch

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Summary Walls Roof Floor Recommendations Conclusions

Roof Concrete EvaluationPetrographic analysis:

Concrete properly consolidated and curedExcellent overall strength propertiesPortland cement sufficiently hydratedDepth of concrete carbonation:

exterior is moderateinterior is minor

Large crack contained some fractured aggregateConcrete compressive strength:6,210 psi and 6,590 psi (design 3,500 psi)

BACK

Roof

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Summary Walls Roof Floor Recommendations Conclusions

Roof ExteriorLarge cracks (~1/32 inch)observed on roofCracks are thru-thickness

Cracking pattern observed for roof exterior-northwest corner of tank-

BACK

Roof

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Summary Walls Roof Floor Recommendations Conclusions

Roof Exterior

Core #4BACK

Roof

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Summary Walls Roof Floor Recommendations Conclusions

Roof InteriorMinor hairline cracking inlocations of large positivebendingCorrosion product visible insome locations

Typical cracking pattern observed for roof interior-northwest corner of tank-

BACK

Roof

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Summary Walls Roof Floor Recommendations Conclusions

Roof Interior

BACK

Roof

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Summary Walls Roof Floor Recommendations Conclusions

Slab on GroundTypical cracking runningnorth-to-southLocations of previouslyrepaired cracksUn-repaired cracks are alsovisibleCracking at surface extendsthrough depth of slab

Typical cracking pattern observed for tank floor-northeast corner of tank-

BACK

Floor

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Summary Walls Roof Floor Recommendations Conclusions

Tank FloorPrevious repairs

Floor

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Summary Walls Roof Floor Recommendations Conclusions

Tank FloorUnfinished repairs

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Summary Walls Roof Floor Recommendations Conclusions

Through thickness crack

Core F1

Tank Floor

BACK

Floor

Tank floor crack – no repairs initiated

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Summary Walls Roof Floor Recommendations Conclusions

Roof Reinforcement

Roof

Continuous reinforcement at contraction joints

Longitudinal reinforcement ratio provided: 0.0036

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Summary Walls Roof Floor Recommendations Conclusions

Roof Deck Reinforcement RequirementsCrack spacing and width control is accomplished throughreinforcement ratio and control joints

Roof control joints spaced at about 30 feet

Roof transverse reinforcement ratio of 0.36%

Minimum horizontal reinforcement ratio of 0.5% per ACI 350R.01Table 7.12.2.1

Restraint requires additional reinforcement (ACI 350-06)

BACK

Roof

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Summary Walls Roof Floor Recommendations Conclusions

SeepageSeepage measured from underdrain (more precise testingrecommended)~98 gallons measured in 4.5 hours = 520 gallons/dayFor 10MG tank = 0.005% loss/dayACI/AWWA: 0.1% loss/day generally acceptable

BACK

Floor

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Summary Walls Roof Floor Recommendations Conclusions

Contraction JointsAlso known as control joint, and classified as a subset ofmovement joints

BACK

Source: ACI 350-06

Roof

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Summary Walls Roof Floor Recommendations Conclusions

ACI 350-06 – Reinforcement With ConstraintAdditional shrinkage constraints require increased reinforcement

Source: ACI 350-06

Walls

BACK

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Summary Walls Roof Floor Recommendations ConclusionsWalls

400 MPa = 58 ksiBACK

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Summary Walls Roof Floor Recommendations Conclusions

ACI 350-06 – Reinforcement With ConstraintAdditional shrinkage constraints require increased reinforcement

Source: ACI 350-06

Roof

BACK

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Summary Walls Roof Floor Recommendations Conclusions

400 MPa = 58 ksi

Roof

BACK

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Summary Walls Roof Floor Recommendations Conclusions

Shrinkage of ConcreteConcrete is subject to shrinkageCaused by loss of moistureDecrease in volumeRestraints inhibit movement inducing tensile stresses inconcreteCracking when concrete tensile capacity is exceededCracking is controlled with proper amount of reinforcement

Walls

BACK

Roof

Roof slab cracking Floor slab cracking

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Summary Walls Roof Floor Recommendations Conclusions

ACI 350-06 – Minimum Reinforcement

Source: ACI 350-06

Roof

BACK

Walls

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Summary Walls Roof Floor Recommendations Conclusions

ACI 224R-01

BACK

Walls