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1
Cracking and Leakage at ReinforcedConcrete Pomona Reservoir 5C
Piotr D. Moncarz, Ph.D., P.E.Patxi Uriz, Ph.D., P.E.
Reservoir 5C
2
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
3
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
4
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
5
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
6
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
14
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
15
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
20
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
24
Summary Walls Roof Floor Recommendations Conclusions
Roof Interior
BACK
Roof
25
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
26
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
29
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
31
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
32
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
34
Summary Walls Roof Floor Recommendations ConclusionsWalls
400 MPa = 58 ksiBACK
35
Summary Walls Roof Floor Recommendations Conclusions
ACI 350-06 – Reinforcement With ConstraintAdditional shrinkage constraints require increased reinforcement
Source: ACI 350-06
Roof
BACK
36
Summary Walls Roof Floor Recommendations Conclusions
400 MPa = 58 ksi
Roof
BACK
37
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
38
Summary Walls Roof Floor Recommendations Conclusions
ACI 350-06 – Minimum Reinforcement
Source: ACI 350-06
Roof
BACK
Walls
39
Summary Walls Roof Floor Recommendations Conclusions
ACI 224R-01
BACK
Walls