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SynC · Editorial revision

Water-Retaining Concrete Structures

Revision1
EditedOct 12, 2026
StatusCurrent
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Current revision. This is editorial revision 1, the current text of this standard. Read it on the standard's page.

SynC Standards Team — Specifier (Platform Standards) ✓ OfficialDiscloses employment SynC (SynC Platform Team)
Initial publication

1 Scope

NOTE This standard governs what ACI 350 adds to the cast-in-place concrete of a structure that holds liquid, or keeps groundwater out, by the concrete and its joints alone: the durability limits on the mixture, the reinforcement and cover that hold cracks closed at a liquid face, the order and continuity of placement, the setting and grouting of the items cast into liquid-retaining walls, the form ties through those walls, the hydrostatic tightness test of the finished structure, the repair of what the test finds, and the backfill that waits for it. (1.1)
NOTE The structures in scope are the environmental engineering concrete structures of ACI 350: treatment basins and tanks, clarifiers, aeration and contact tanks, filter boxes, clearwells, wet wells and lift station structures cast in place, open and covered channels, digesters, equalization and holding tanks, sludge storage and thickening tanks, chemical containment, and the galleries, vaults, and pump rooms a plant designs to remain dry below groundwater. A structure is in scope whether its liquid is on the inside or the outside; what qualifies it is that the concrete is the barrier. (1.2)
NOTE A water-retaining structure is made tight by its concrete and its joints, not by a membrane. A membrane on the outside of a basin hides the leak that the concrete should have stopped, cannot be inspected or repaired once backfilled, and is absent at the one place the structure is most likely to leak, which is the joint. Every requirement in this standard exists to make the concrete itself the barrier, and the tightness test at the end is the proof that it is. (1.3)
NOTE The concrete standards on this platform are layered, and this standard sits above the material layer. The constituent materials, mixture qualification, production, delivery, placement, consolidation, weather protection, and strength acceptance of all concrete are governed by Cast In Place ConcreteCast-in-Place ConcreteResolves to the current adopted revision.sync/cast-in-place-concrete; the bars, their placement and splices, and the ACI 318 cover minimums by Concrete ReinforcementConcrete ReinforcementResolves to the current adopted revision.sync/concrete-reinforcement; the forms, ties as hardware, and tie-hole patching by Concrete FormworkConcrete Formwork and AccessoriesResolves to the current adopted revision.sync/concrete-formwork; curing methods and finishes by Concrete Curing And FinishingConcrete Curing and FinishingResolves to the current adopted revision.sync/concrete-curing-and-finishing; joint types, layout, spacing, the ACI 350 crack-width limit at liquid faces, waterstops, and sealants by Concrete Joints And WaterstopsConcrete Construction Joints and WaterstopsResolves to the current adopted revision.sync/concrete-joints-and-waterstops with the waterstop products under Concrete AccessoriesConcrete Accessories and EmbedsResolves to the current adopted revision.sync/concrete-accessories. This standard restates none of that; where the two conflict, the requirement of this standard governs the liquid-retaining members. (1.4)
NOTE The following are governed elsewhere and are outside this standard: (1.5)
  • the wall pipes, wall sleeves, seep rings, and collars cast into liquid-retaining walls, as products and as to their location, under Ductile Iron Process PipingDuctile Iron Process PipingResolves to the current adopted revision.sync/ductile-iron-process-piping, Steel And Stainless Process PipingSteel and Stainless Steel Process PipingResolves to the current adopted revision.sync/steel-and-stainless-process-piping, and Plastic Process PipingPlastic Process PipingResolves to the current adopted revision.sync/plastic-process-piping; this standard governs their blockouts, casting tolerance, and grouting
  • gate thimbles, embedded gate frames, and stop log guides as products, under Slide Gates And Stop LogsSlide Gates and Stop LogsResolves to the current adopted revision.sync/slide-gates-and-stop-logs; this standard governs their blockouts, casting tolerance, and grouting
  • the repair materials and methods for cracks, honeycomb, and leaking joints, under Concrete Repair And RestorationConcrete Repair and RestorationResolves to the current adopted revision.sync/concrete-repair-and-restoration; this standard governs when a repair is required and when the structure is retested
  • linings and coatings on concrete in wastewater, digester, or chemical service, under High Performance CoatingsHigh-Performance CoatingsResolves to the current adopted revision.sync/high-performance-coatings; this standard governs the sequence of the tightness test relative to the lining
  • the disinfection of a potable water structure before it is placed in service, under Disinfection Of Water SystemsDisinfection of Domestic Water SystemsResolves to the current adopted revision.sync/disinfection-of-water-systems
  • non-shrink grout as a material, under Non Shrink GroutNon-Shrink GroutResolves to the current adopted revision.sync/non-shrink-grout
  • excavation, dewatering, and backfill, under EarthworkEarthworkResolves to the current adopted revision.sync/earthwork; this standard governs only when backfill may begin
  • the special inspection agency and the statement of special inspections, under Special Inspections And TestingSpecial Inspections and Structural TestingResolves to the current adopted revision.sync/special-inspections-and-testing
  • drainage headwalls, trench walls, utility vaults, and detention structures that do not hold water by design, under Site Concrete StructuresCast-in-Place Site Concrete StructuresResolves to the current adopted revision.sync/site-concrete-structures and Stormwater Management SystemsStormwater Management and Detention SystemsResolves to the current adopted revision.sync/stormwater-management-systems; a cast-in-place detention vault designed under ACI 350 to hold water is in scope
  • precast wet wells, precast manholes, and precast vaults, under Sanitary Sewer SystemsSanitary Sewer Systems (Site)Resolves to the current adopted revision.sync/sanitary-sewer-systems and Utility Manholes And HandholesUtility Manholes and HandholesResolves to the current adopted revision.sync/utility-manholes-and-handholes
  • membrane waterproofing of occupied below-grade building space, under Below Grade WaterproofingBelow-Grade WaterproofingResolves to the current adopted revision.sync/below-grade-waterproofing
  • prestressed and wire-wound circular tanks under AWWA D110 and AWWA D115: Water Storage TanksWater Storage TanksResolves to the current adopted revision.sync/water-storage-tanks
  • cathodic protection: Cathodic ProtectionCathodic ProtectionResolves to the current adopted revision.sync/cathodic-protection
  • chemical storage tanks and chemical feed systems, which are not yet owned by a SynC standard
  • the structural design of the structure, including the environmental durability factors of ACI 350 and the seismic design under ACI 350.3, which the Engineer of Record performs and records on the structural drawings
NOTE On a treatment plant, pump station, or industrial process project this standard is read with Common Work Results ProcessCommon Work Results for Process EquipmentResolves to the current adopted revision.sync/common-work-results-process, which carries the submittal register, the manufacturer field service and witnessed test policy, nameplates, spare parts, and the anchorage basis shared by every process scope; nothing it carries is restated here. (1.6)
1.7 Liquid-retaining members shall comply with ACI 350 in addition to the requirements of Cast In Place ConcreteCast-in-Place ConcreteResolves to the current adopted revision.sync/cast-in-place-concrete.
1.8 The locations, extents, dimensions, and design liquid levels of each structure shall be as indicated on the structural and process drawings.
1.9 Where the contract documents, the adopted code, and a referenced standard impose conflicting requirements on the same subject, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.

2 Referenced Standards

2.1 Materials, construction, and testing shall comply with the latest adopted edition of each of the following unless a specific edition is cited.
2.2 Where referenced standards conflict, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.
Standard Title
ACI 350 Code Requirements for Environmental Engineering Concrete Structures and Commentary
ACI 350.1 Specification for Tightness Testing of Environmental Engineering Concrete Containment Structures
ACI 350.3 Seismic Design of Liquid-Containing Concrete Structures and Commentary
ACI 350.4R Design Considerations for Environmental Engineering Concrete Structures
ACI 350.5 Specifications for Environmental Concrete Structures
ACI 301 Specifications for Concrete Construction
ACI 318 Building Code Requirements for Structural Concrete and Commentary
ACI 117 Specification for Tolerances for Concrete Construction and Materials
ACI 224R Control of Cracking in Concrete Structures
ACI 212.3R Report on Chemical Admixtures for Concrete
ASTM C150/C150M Portland Cement
ASTM C595/C595M Blended Hydraulic Cements
ASTM C1157/C1157M Performance Specification for Hydraulic Cement
ASTM C494/C494M Chemical Admixtures for Concrete
ASTM C1107/C1107M Packaged Dry, Hydraulic-Cement Grout (Nonshrink)
ASTM C1218/C1218M Water-Soluble Chloride in Mortar and Concrete
ASTM C1585 Measurement of Rate of Absorption of Water by Hydraulic-Cement Concretes
AWWA C652 Disinfection of Water-Storage Facilities

3 Submittals

3.1 Action Submittals

3.1.1 The Contractor shall submit the following for review and acceptance before concrete is ordered for any liquid-retaining member:
  • The mixture design for each liquid-retaining mixture class, submitted under Cast In Place ConcreteCast-in-Place ConcreteResolves to the current adopted revision.sync/cast-in-place-concrete and identified here as satisfying the water-cementitious materials ratio, strength, air content, supplementary cementitious material, cement type, and chloride limits of this standard
  • Product data for any permeability-reducing admixture, with the dosage, the test data establishing its performance under the hydrostatic head of the structure, and the producer's statement of compatibility with the other admixtures of the mixture
  • A placement sequence plan for each structure, showing the base slab segments, the wall segments, the order and the interval in which they will be placed, the location of every construction joint keyed to the joint layout accepted under Concrete Joints And WaterstopsConcrete Construction Joints and WaterstopsResolves to the current adopted revision.sync/concrete-joints-and-waterstops, the placement rate for each wall segment, and the concrete delivery rate that supports it
  • Shop drawings of every blockout, showing its dimensions, the embedded item it will receive, the reinforcement displaced or added around it, the surface preparation, the waterstop at its perimeter, and the grout
  • Product data for the form ties to be used in liquid-retaining walls, showing the water seal feature, the break-back dimension, and the tie-hole treatment
  • Product data for the blockout grout
  • A tightness test plan for each structure, identifying the compartments to be tested and the condition of each adjacent compartment, the test criterion, the water source and its conveyance, the fill rate, the measurement method and its resolution, the evaporation correction, the stabilization and measurement periods, the dewatering to be maintained, the disposal of the test water, and the party witnessing each reading
Action Submittals Requiredcheckbox
☑ Liquid-retaining mixture designs identified against this standard
☐ Permeability-reducing admixture product data and performance data
☑ Placement sequence plan for each structure
☑ Blockout shop drawings
☑ Form tie product data for liquid-retaining walls
☑ Blockout grout product data
☑ Tightness test plan for each structure
3.1.2 Concrete shall not be placed in any liquid-retaining member until the placement sequence plan for that structure has been reviewed and accepted.
3.1.3 A structure shall not be filled for a tightness test until the tightness test plan for that structure has been reviewed and accepted.

3.2 Informational Submittals

3.2.1 The Contractor shall submit the following before the first tightness test:
  • The name and qualifications of the person who will take the test readings, and the calibration record of the measuring device
  • The placement record for each wall segment, giving the date, the start and finish time, the delivery tickets, and any interruption longer than 30 minutes
  • The curing record for each liquid-retaining member, giving the method, the start date, and the end date
Informational Submittals Requiredcheckbox
☑ Test reader qualifications and measuring device calibration
☑ Wall segment placement records
☑ Curing records for liquid-retaining members

3.3 Closeout Submittals

3.3.1 The Contractor shall submit the following before a structure is accepted:
  • The tightness test report for each structure and each compartment, giving the dates, the liquid levels at each reading, the evaporation and precipitation readings, the computed loss as a percentage of volume per 24 hours, the visual inspection record of every exterior face and joint, and the result against the criterion
  • A map of every damp spot, leak, and crack found during the test, with the repair performed at each and the retest result
  • The grouting record for each blockout, giving the date, the grout, the ambient temperature, and the curing
  • The record of groundwater observations where a structure designed to exclude groundwater was inspected empty
Closeout Submittals Requiredcheckbox
☑ Tightness test reports for each structure and compartment
☑ Leak and repair map with retest results
☑ Blockout grouting records
☐ Groundwater exclusion inspection record

4 Quality Assurance

4.1 Pre-Placement Conference for Liquid-Retaining Structures

4.1.1 A pre-placement conference shall be held for each structure before its first liquid-retaining member is placed, in addition to the conference required by Cast In Place ConcreteCast-in-Place ConcreteResolves to the current adopted revision.sync/cast-in-place-concrete or combined with it where the schedule allows.
4.1.2 The conference shall be attended by the Contractor's superintendent, the concrete producer's technical representative, the formwork and reinforcement foremen, the trades furnishing wall pipes, gate thimbles, and other embedded items, the testing agency, and the Engineer of Record.
4.1.3 The conference agenda shall cover the placement sequence plan, the wall segment lengths and rate of rise, the embedded items in each segment and the party setting each, the blockouts, the form tie type and tie-hole treatment, the waterstop continuity at every joint in the segment, the curing method and its duration, and the schedule from the last placement to the tightness test.
NOTE Most tightness test failures are traced to one of four things, and every one of them was decided before the first truck arrived: a horizontal cold joint in a wall, a void under a wall pipe collar, a tie hole patched from the wrong side, and a construction joint whose waterstop was not continuous around a corner. The conference is where those four are settled with every trade that touches them in the room. (4.1.4)

4.2 Tightness Test Witness and Readings

4.2.1 The tightness test of each structure shall be witnessed by the Engineer of Record or a representative the Engineer of Record designates in writing, and every reading shall be taken in the witness's presence.
4.2.2 The Contractor shall give the Engineer of Record not less than 48 hours notice of the start of filling and of each reading.
NOTE Acceptance of a tightness test rests with the Engineer of Record; the testing agency and the witness record the readings and do not accept or reject the structure. (4.2.3)

4.3 Special Inspection of Liquid-Retaining Members

4.3.1 Special inspection of the reinforcement, cover, embedded items, and concrete placement of liquid-retaining members shall be performed under the statement of special inspections administered by Special Inspections And TestingSpecial Inspections and Structural TestingResolves to the current adopted revision.sync/special-inspections-and-testing.
4.3.2 The special inspector shall verify, before each wall segment is placed, that the waterstop is continuous through the segment and spliced at every corner and intersection, that every embedded item is set within the tolerance of this standard, and that the cover at the liquid face is not less than this standard requires.

5 Structure Classification and Service

NOTE ACI 350 covers the structure by the liquid it holds and the exposure the liquid creates. Potable and raw water are mild; wastewater generates hydrogen sulfide that becomes sulfuric acid on every surface above the waterline; digesters add heat, gas, and sulfides; chemical containment adds whatever the chemical does to cement paste. The service of the structure is therefore the first decision, because it fixes the sulfate class, the cement type, the chloride limit, the lining, and the test water. (5.1)
5.2 The service of each structure shall be as indicated in the datasheet, and where a project has structures in more than one service the datasheet shall be completed for each.
Contained Liquid Serviceselect
Potable or finished water
Raw water, settled water, or filter effluent
Reclaimed water or treated plant effluent
Raw, screened, or settled wastewater
Mixed liquor, return sludge, or aerated process
Primary, digested, or thickened sludge
Digester contents with gas space
Chemical solution or chemical containment
Stormwater or combined flow held by design
Groundwater excluded from a dry structure
NOTE Potable and clean water service asks the concrete only to be impermeable and to keep its own chlorides below the limit, so the mixture decisions reduce to the water-cementitious materials ratio and the cement. Wastewater and sludge service add biogenic sulfuric acid attack in the vapor space, which the mixture cannot resist alone and which is why those structures carry a lining above the waterline; raw and screened wastewater also carries sulfate into the sulfate class. A digester adds elevated temperature and a gas-tight requirement at the cover. Chemical containment is governed by the chemical, and the cement type, the admixtures, and the lining are chosen against it rather than against water. A dry structure below groundwater is a water-retaining structure turned inside out: the same crack width, cover, and tightness test apply, with the water on the outside. (5.3)
5.4 The design liquid level and the maximum liquid level, including overflow, of each structure shall be as indicated on the process hydraulic profile.
5.5 Where the base slab of a structure lies below Seasonal High Groundwater ElevationSeasonal High Groundwater ElevationParameterEach project supplies its own value.seasonal-high-groundwater-elevation, the structure shall be regarded as both liquid-retaining and groundwater-excluding, and the requirements of this standard for exterior faces and for the empty condition apply to it.
NOTE The structural design, including the environmental durability factors of ACI 350, the crack-width analysis, and the seismic design under ACI 350.3 for Seismic Design CategorySeismic Design CategoryParameterEach project supplies its own value.seismic-design-category, is performed by the Engineer of Record and recorded on the structural drawings; this standard specifies the construction of what that design shows and adds no design requirement. (5.6)

6 Durability Requirements for Liquid-Retaining Concrete

6.1 Water-Cementitious Materials Ratio and Strength

6.1.1 The maximum water-cementitious materials ratio for each liquid-retaining mixture shall be the lesser of the value indicated in the datasheet and the value ACI 350 requires for the exposure of the member.
Water-Cementitious Materials Ratio, Liquid-Retaining Concreterange
0.360.380.40.420.45
Default: Not more than 0.42
6.1.2 The specified compressive strength of liquid-retaining members shall be not less than the value indicated in the datasheet, and where the structural drawings show a higher strength for a member the higher strength shall govern that member.
Specified Compressive Strength Floor, Liquid-Retaining Membersrange
psi
4000450050006000
Default: Not less than 4000 psi
NOTE ACI 350 fixes 4,000 psi as the floor for environmental structures and ties the water-cementitious materials ratio to the exposure, with 0.45 the limit for concrete that must be impermeable and lower values where freezing, deicing chemicals, or chlorides act on the member. Most environmental specifications settle on 0.42 for every liquid-retaining mixture rather than carrying two limits through a structure that has a wet face, a frozen top of wall, and a chloride-bearing splash zone all in one wall. Below about 0.40 the mixture bleeds almost nothing, the finishing window closes, and the top of wall and slab surfaces crack in the plastic state unless curing starts at once. (6.1.3)
NOTE The specified compressive strength of each member remains the output of the structural analysis and is recorded on the structural drawings under Cast In Place ConcreteCast-in-Place ConcreteResolves to the current adopted revision.sync/cast-in-place-concrete. The floor here is the ACI 350 value below which no liquid-retaining mixture may be proportioned, whatever the structural demand; it is not a strength for any member. (6.1.4)

6.2 Air Entrainment

6.2.1 Air entrainment in liquid-retaining concrete shall be as indicated in the datasheet, and where air is entrained the content shall be that required by ACI 318 Table 19.3.3.1 for the member's freeze-thaw exposure class and the nominal maximum aggregate size.
Air Entrainment in Liquid-Retaining Concreteradio
○ All liquid-retaining concrete air-entrained
○ Air-entrained only where the freeze-thaw exposure class assigned under cast-in-place-concrete requires it
NOTE Entraining air in every liquid-retaining mixture improves workability and reduces bleeding at the low water-cementitious materials ratios these structures use, and it protects the top of a wall and the walkway edge of a basin that freeze wet every winter while the bulk of the structure sits below the liquid. Limiting it to the members whose exposure class requires it recovers the strength the air costs and avoids blistering on a hard-troweled slab, at the price of a wall whose top foot has a different mixture than its base or no air at all. (6.2.2)

6.3 Cement Type

6.3.1 Hydraulic cement in liquid-retaining concrete shall be limited to the types indicated in the datasheet, within the types permitted under Cast In Place ConcreteCast-in-Place ConcreteResolves to the current adopted revision.sync/cast-in-place-concrete.
Cement Types Permitted in Liquid-Retaining Concretecheckbox
Any of:
☐ Portland cement Type I under ASTM C150/C150M
☑ Portland cement Type II under ASTM C150/C150M
☑ Portland cement dual-certified as Type I and Type II under ASTM C150/C150M
☐ Portland cement Type V under ASTM C150/C150M
☐ Portland-limestone cement Type IL under ASTM C595/C595M
☐ Portland-limestone cement Type IL(MS) under ASTM C595/C595M
☐ Blended cement Type IS(MS) or IP(MS) under ASTM C595/C595M
☐ Blended cement Type IS(HS) or IP(HS) under ASTM C595/C595M
☐ Hydraulic cement Type MS or HS under ASTM C1157/C1157M
6.3.2 Cement for members in wastewater, sludge, or digester service, and for members whose sulfate exposure class is S1 or higher, shall carry a moderate or high sulfate resistance designation as the assigned class requires under ACI 318 Table 19.3.2.1.
NOTE Moderate sulfate resistance is the norm for environmental structures because the wastewater and the soil are both sources of sulfate and the cost of Type II over Type I is negligible. A high-sulfate-resistance cement is reserved for the S2 and S3 soils of the geotechnical report, where it is a code requirement rather than a preference. Portland-limestone cement is now the ordinary cement at many plants, and its MS grade carries the same sulfate designation as Type II. (6.3.3)

6.4 Supplementary Cementitious Materials

6.4.1 The content of each supplementary cementitious material in liquid-retaining concrete, expressed as a percentage by mass of total cementitious materials, shall not exceed the values indicated in the datasheet.
Fly Ash Content, Liquid-Retaining Concreterange
%
035
Default: Not more than 25 %
Slag Cement Content, Liquid-Retaining Concreterange
%
065
Default: Not more than 50 %
Silica Fume Content, Liquid-Retaining Concreterange
%
010
Default: Not more than 8 %
Total Supplementary Cementitious Material Content, Liquid-Retaining Concreterange
%
065
Default: Not more than 50 %
NOTE Supplementary cementitious materials are the mechanism by which a liquid-retaining mixture reaches the permeability its water-cementitious materials ratio promises: fly ash and slag cement refine the pore structure, and silica fume closes it. ACI 350 caps them at the same values ACI 318 uses for deicing exposure, 25 percent fly ash and 50 percent slag, and most environmental specifications adopt those caps for every liquid-retaining mixture because the top of every outdoor wall is a deicing-class surface in winter. Beyond the caps the early strength and the curing demand both move, and a wall that is to be tested at 28 days is the member that notices. (6.4.2)

6.5 Permeability-Reducing Admixture

6.5.1 A permeability-reducing admixture shall be used in liquid-retaining concrete only as indicated in the datasheet.
Permeability-Reducing Admixtureradio
● None
○ Permeability-reducing admixture for non-hydrostatic conditions
○ Permeability-reducing admixture for hydrostatic conditions, crystalline
6.5.2 Where a permeability-reducing admixture is used, it shall be an ASTM C494/C494M Type S admixture, its dosage shall be that used in the trial batches that qualified the mixture, and the mixture design submittal shall show its effect on setting time, air content, and strength.
6.5.3 Where a permeability-reducing admixture for hydrostatic conditions is used, the product data shall include water penetration or absorption test results under a head not less than the design liquid depth of the structure, and the admixture shall not be used as grounds for relaxing any other requirement of this standard.
NOTE A low water-cementitious materials ratio, the right supplementary cementitious materials, and complete curing produce a concrete tight enough to pass the ACI 350.1 test without an admixture, and that is the basis of nearly every environmental structure built. A damp-proofing class admixture reduces absorption and is a surface-moisture measure, not a barrier against a head. A crystalline class admixture grows crystals into capillaries and small cracks in the presence of water and can seal a hairline crack after the fact, which is the case for it in a structure that cannot be drained to repair; its cost is a dosage that varies by product, an interaction with air entrainment and set time that has to be qualified, and the temptation to treat it as a substitute for the joint and reinforcement detailing it does not replace. (6.5.4)

6.6 Chloride Limit

6.6.1 The maximum water-soluble chloride ion content of liquid-retaining concrete, by mass of cementitious materials and determined by ASTM C1218/C1218M at the age ACI 350 states, shall be as indicated in the datasheet.
Water-Soluble Chloride Ion Content, Liquid-Retaining Concreterange
% by mass of cement
0.060.10.150.3
Derived — the reinforcement type and whether the member is exposed to chlorides in service, per ACI 350 Table 4.4.1 (by default)
6.6.2 Admixtures containing intentionally added chlorides shall not be used in liquid-retaining concrete.
NOTE ACI 350 holds chlorides lower than ACI 318 because the structure is permanently wet, and a wet reinforced member with chlorides at the bar corrodes without the drying cycles that protect a building. The limit is a lookup rather than a choice: prestressed members take the tightest value, reinforced members that will see chlorides from the liquid, the soil, or a coastal site take the middle value, and reinforced members in clean water that are dry on the outside take the loosest. (6.6.3)

6.7 Sulfate Exposure from the Contained Liquid

6.7.1 Where the contained liquid service is wastewater, sludge, digester contents, or a chemical solution, the sulfate exposure class assigned under Cast In Place ConcreteCast-in-Place ConcreteResolves to the current adopted revision.sync/cast-in-place-concrete for the liquid-retaining members shall account for the sulfate of the contained liquid as well as of the soil and groundwater, and shall be not less than S1.
NOTE The geotechnical investigation samples the soil and the groundwater, and that is where the sulfate class of a building comes from. In a wastewater structure the sulfate is also in the liquid the structure is built to hold, and the base slab and lower walls sit in it for the life of the plant; a class assigned from the soil alone can leave the inside of the tank at S0 while the outside is S1. (6.7.2)

7 Crack Control and Reinforcement at Liquid Faces

NOTE ACI 350 controls leakage through the concrete by keeping flexural and shrinkage cracks at the liquid face narrow enough to self-heal, and it does this with the environmental durability factor that inflates the design loads, with the crack-width limit at liquid faces that Concrete Joints And WaterstopsConcrete Construction Joints and WaterstopsResolves to the current adopted revision.sync/concrete-joints-and-waterstops carries, and with more shrinkage and temperature reinforcement than a building wall gets, placed closer together and in both faces. The reinforcement ratio rises with the distance between movement joints because a longer segment shrinks more against the same restraint. (7.1)
7.2 The shrinkage and temperature reinforcement ratio in liquid-retaining walls and slabs, in each direction, shall be not less than the value indicated in the datasheet.
Shrinkage and Temperature Reinforcement Ratio, Liquid-Retaining Membersrange
0.0030.0040.0050.006
Derived — the length between movement joints shown on the joint layout drawings and the bar grade, per ACI 350 Table 7.12.2.1 (by default)
7.3 The center-to-center spacing of shrinkage and temperature reinforcement in liquid-retaining members shall not exceed the value indicated in the datasheet.
Bar Spacing of Shrinkage and Temperature Reinforcementrange
in
689101218
Default: Not more than 12 in
7.4 Shrinkage and temperature reinforcement in liquid-retaining walls thicker than 10 in. shall be placed in each face, and the reinforcement in each face shall be not less than half of the total required.
7.5 Shrinkage and temperature reinforcement shall be continuous through construction joints and shall terminate only at movement joints shown on the joint layout.
7.6 Concrete cover to reinforcement at faces in contact with liquid, and at formed faces in contact with earth, shall be not less than the value indicated in the datasheet, and shall govern over the ACI 318 minimum of Concrete ReinforcementConcrete ReinforcementResolves to the current adopted revision.sync/concrete-reinforcement where greater.
Concrete Cover at Liquid and Formed Earth Facesrange
in
1.522.53
Default: Not less than 2 in
7.7 Concrete cover to reinforcement at faces cast against earth shall be not less than the value indicated in the datasheet.
Concrete Cover at Faces Cast Against Earthrange
in
33.54
Default: Not less than 3 in
NOTE Cover is the barrier between the liquid and the bar, and in a structure that is wet for its life the barrier is working every day. ACI 350 sets 2 in. at liquid faces for every bar size where ACI 318 allows 1-1/2 in. for small bars, and the ratio and spacing requirements above keep the cracks that cross that cover narrow. A larger cover widens the surface crack for the same bar strain, so cover above 2 in. at a liquid face is paired with closer bar spacing rather than added alone; a wastewater vapor space takes its protection from the lining, not from an extra inch of cover that the acid consumes at the same rate. (7.8)
NOTE Bar size, grade, splices, placement tolerance, and the pre-placement inspection of reinforcement are governed by Concrete ReinforcementConcrete ReinforcementResolves to the current adopted revision.sync/concrete-reinforcement; the cover and spacing above apply to liquid-retaining members in addition to that standard. (7.9)

8 Placement Sequence and Continuity

8.1 Base Slabs

8.1.1 Each base slab shall be placed in the segments shown on the placement sequence plan, and each segment shall be placed in one continuous operation between the joints shown on the joint layout accepted under Concrete Joints And WaterstopsConcrete Construction Joints and WaterstopsResolves to the current adopted revision.sync/concrete-joints-and-waterstops.
8.1.2 The base slab of a structure, or the segment of it that supports a wall, shall be placed and shall have reached the strength the formwork design requires before the wall on it is placed.
8.1.3 A base slab shall not be placed on a subgrade that holds standing water, and dewatering shall hold the groundwater below the bottom of the slab, and below the bottom of any underdrain or sump beneath it, from the start of placement until the structure is released for backfill under this standard.
8.1.4 The order in which the base slab and the walls of each structure are placed shall be as indicated in the datasheet.
Base Slab and Wall Placement Orderradio
● Base slab first, walls on a construction joint with waterstop above the slab
○ Base slab with an integral wall starter curb, walls on a construction joint above the curb
○ Walls and base slab monolithic at the structures the Engineer of Record designates
NOTE A wall placed on a hardened slab through a waterstopped construction joint is the sequence nearly every basin uses, because the slab gives the wall forms a floor to bear on and the joint is at the point of maximum restraint where it can be detailed. Casting a short starter curb with the slab raises that joint above the floor, keeps the joint out of the standing water the base of a wall collects, and gives the first wall form a cast edge to clamp to, at the cost of a second waterstop plane and a curb that has to be placed and consolidated with the slab around it. A monolithic slab and wall removes the joint but demands a form that can be filled from the top of the wall while the slab is still plastic, and it is reserved for small structures and for the channels and sumps where the Engineer of Record has drawn it. (8.1.5)

8.2 Walls

8.2.1 Liquid-retaining walls shall be placed as indicated in the datasheet.
Wall Placement Heightradio
● Full height in one continuous placement, no horizontal construction joint
○ Horizontal construction joints permitted above the maximum liquid level only
○ Horizontal construction joints permitted below the liquid level where shown on the joint layout, with waterstop
NOTE A horizontal joint in a liquid-retaining wall is a leak path across the whole length of the wall, and it is the one feature of the structure the tightness test finds most reliably. Placing the wall full height in one operation removes it, and walls to 25 or 30 ft are placed that way routinely with a pump and lifts that keep the surface alive. Permitting a joint above the maximum liquid level lets a tall wall or a wall with a walkway curb be placed in two operations where the joint is never wetted. Permitting a joint below the liquid level, waterstopped and prepared as a construction joint, is the position for a wall taller than the forms, the pump, or the delivery can serve in one placement, and it trades a tested joint for a cold joint nobody planned. (8.2.2)
8.2.3 Each wall segment shall be placed in one continuous operation between the vertical joints shown on the joint layout, with each lift covering the full length of the segment before the preceding lift reaches initial set, and the lift depth and vibrator practice of Cast In Place ConcreteCast-in-Place ConcreteResolves to the current adopted revision.sync/cast-in-place-concrete apply.
8.2.4 The rate of rise of concrete in each wall segment shall be not less than the value indicated in the datasheet, and not more than the rate the formwork design accepted under Concrete FormworkConcrete Formwork and AccessoriesResolves to the current adopted revision.sync/concrete-formwork allows.
Rate of Rise in Liquid-Retaining Wallsrange
ft/hr
23456810
NOTE The rate of rise is bounded from two sides. Below it the surface of the lift reaches initial set before the next lift arrives and a cold joint forms across the wall; above it the lateral pressure exceeds what the form was designed for. The lower bound depends on the set time of the mixture at the placement temperature, so it is set with the mixture, the haul, and the season in view rather than from a table, and a retarder dosed for the placement is the usual way to open the window. (8.2.5)
8.2.6 Where placement of a wall segment is interrupted long enough that the surface of the last lift reaches initial set, the Contractor shall stop the placement at that lift, shall notify the Engineer of Record before placement resumes, and the Engineer of Record shall direct either that the surface be prepared as a construction joint under Concrete Joints And WaterstopsConcrete Construction Joints and WaterstopsResolves to the current adopted revision.sync/concrete-joints-and-waterstops with a waterstop added, or that the lift be removed.
8.2.7 A cold joint below the liquid level that is not prepared and waterstopped shall be regarded as defective work.
8.2.8 The sequence of wall segments within a structure shall be as indicated in the datasheet.
Wall Segment Sequenceradio
○ Alternate segments first, infill segments after the interval indicated
○ Consecutive segments in one direction, each after the interval indicated
○ Any sequence the Contractor elects, each segment after the interval indicated
8.2.9 The interval between placing a wall segment and placing the segment adjacent to it shall be not less than the value indicated in the datasheet.
Interval Before Placing an Adjacent Wall Segmentrange
days
1235714
NOTE Placing alternate segments and infilling later lets each early segment shrink against nothing before its neighbors restrain it, which is the sequence ACI 350 commentary describes for long walls with contraction joints and the one that produces the fewest shrinkage cracks between joints. Consecutive placement keeps the forms moving in one direction and shortens the schedule at the cost of each new segment restraining the one before it while that one is still shrinking. Leaving the sequence to the Contractor is honest where the segments are short and the joints are expansion joints that carry no restraint; the interval then does the work. (8.2.10)

8.3 Consolidation at Waterstops and Embedded Items

8.3.1 Concrete at every wall pipe, sleeve, gate thimble, and embedded frame shall be placed from one side of the item and vibrated so that the air beneath each horizontal collar, seep ring, and flange is driven out toward the opposite side, and the vibrator shall be inserted on both sides of the item.
8.3.2 Where a collar or seep ring is wider than 6 in. or is set in a wall thinner than three times the collar projection, a vent or an inspection opening shall be provided in the form above the collar so that complete filling beneath it can be confirmed.
NOTE A horizontal collar on a wall pipe is a shelf, and concrete placed from above traps a pocket of air under it that no vibrator reaches from the top. The pocket is a void against the one surface whose purpose is to lengthen the leak path along the pipe, and it is the most common point of leakage at a wall penetration. Placing from one side and vibrating on both chases the air out from under the shelf. (8.3.3)
NOTE Consolidation around waterstop flanges is governed by Concrete Joints And WaterstopsConcrete Construction Joints and WaterstopsResolves to the current adopted revision.sync/concrete-joints-and-waterstops. (8.3.4)

8.4 Curing of Liquid-Retaining Members

8.4.1 Liquid-retaining members shall be cured by the method indicated in the datasheet, in accordance with Concrete Curing And FinishingConcrete Curing and FinishingResolves to the current adopted revision.sync/concrete-curing-and-finishing.
Curing Method, Liquid-Retaining Membersradio
○ Water curing by continuous moisture on every surface
○ Sheet curing with absorptive cover kept wet under the sheet
○ Membrane-forming curing compound, removed before any lining or coating
8.4.2 The curing period for liquid-retaining members shall be not less than the value indicated in the datasheet, and shall govern over the duration selected under Concrete Curing And FinishingConcrete Curing and FinishingResolves to the current adopted revision.sync/concrete-curing-and-finishing where longer.
Curing Period, Liquid-Retaining Membersrange
days
7101421
8.4.3 Forms shall remain in place on liquid-retaining walls, or the wall shall be covered and kept wet immediately on stripping, for the full curing period.
8.4.4 The curing period shall not be shortened on account of early strength.
NOTE The permeability that the mixture was proportioned for exists only in concrete that stayed wet long enough to hydrate the paste through, and ACI 350 therefore holds the structure to at least 7 days of moist curing above 50°F, with a longer period where slag cement or fly ash carries a large share of the cementitious materials or where low permeability governs. Water curing is the method that meets the requirement without question on a wall or a slab that will be wet anyway; a curing compound is permitted but must come off before a lining goes on, and its film is what a lining manufacturer will blame for a disbonded floor. (8.4.5)

9 Embedded Wall Pipes, Thimbles, and Frames

NOTE The wall pipes, wall sleeves, gate thimbles, and embedded frames are furnished and located by the piping and gate standards; what the concrete trade owns is the moment they become part of the wall. An item cast in place with the wall can never be moved; an item set in a blockout can be set to the gate or the pipe that will bolt to it, at the price of a second concrete interface the test has to prove. This article governs that choice, the tolerance, and the grout. (9.1)
9.2 Wall pipes and wall sleeves furnished under Ductile Iron Process PipingDuctile Iron Process PipingResolves to the current adopted revision.sync/ductile-iron-process-piping, Steel And Stainless Process PipingSteel and Stainless Steel Process PipingResolves to the current adopted revision.sync/steel-and-stainless-process-piping, and Plastic Process PipingPlastic Process PipingResolves to the current adopted revision.sync/plastic-process-piping shall be set by the method indicated in the datasheet.
Setting Method for Wall Pipes and Sleevesradio
● Cast in place with the wall placement
○ Set in a formed blockout and grouted after the wall is placed
9.3 Gate thimbles, embedded gate frames, and stop log guides furnished under Slide Gates And Stop LogsSlide Gates and Stop LogsResolves to the current adopted revision.sync/slide-gates-and-stop-logs shall be set by the method indicated in the datasheet.
Setting Method for Gate Thimbles and Embedded Framesradio
● Cast in place with the wall placement
○ Set in a formed blockout and grouted after the wall is placed
NOTE A wall pipe cast with the wall is a single concrete interface, which is why nearly every treatment structure sets its wall pipes that way; the price is that its location, elevation, and end connection are fixed the day the wall is placed and the piping has to fit it. A gate thimble cast with the wall is the same bargain, and most are cast in, but a thimble set in a blockout can be plumbed and trued to the gate after the wall has moved through its early shrinkage, which is the case for it where the gate's seating tolerance is tighter than the wall tolerance. A blockout adds a grouted joint around the item, a hydrophilic strip to seal it, and a second item for the test to find. (9.4)
9.5 Each embedded item shall be set within the tolerance of its location and elevation indicated in the datasheet, measured to the centerline of a pipe or sleeve and to the face of a thimble or frame, and within the plumb, level, and flatness tolerance the gate manufacturer publishes under Slide Gates And Stop LogsSlide Gates and Stop LogsResolves to the current adopted revision.sync/slide-gates-and-stop-logs for an item that receives a gate.
Position Tolerance of Embedded Itemsrange
in
0.1250.250.3750.5
Default: Not more than 0.25 in
9.6 Each embedded item shall be braced to the formwork, or to a template independent of the reinforcement, so that placement and vibration do not move it, and the bracing shall be checked by the special inspector immediately before placement.
9.7 Reinforcement interrupted by an embedded item shall be replaced by the bars shown on the structural drawings around the opening, and no bar shall be cut or bent in the field to clear an item without the Engineer of Record's written direction.
9.8 No pipe, conduit, or sleeve other than the wall pipes and sleeves shown shall be embedded in a liquid-retaining wall or slab below the maximum liquid level, and conduit shall not be embedded in a liquid-retaining member at all.
9.9 Where an item is set in a blockout, the blockout shall be formed with a clearance of not less than the value indicated in the datasheet around the item, with its sides sloped or keyed so that the grout is locked in, and with a hydrophilic waterstop strip installed around the full perimeter of the blockout at mid-depth of the wall before grouting.
Blockout Clearance Around the Embedded Itemrange
in
2346
Default: Not less than 3 in
9.10 The surfaces of a blockout shall be roughened to expose aggregate, cleaned of laitance and debris, and brought to a saturated surface-dry condition before grout is placed.
9.11 Blockouts shall be filled with the grout indicated in the datasheet, placed from one side so that air is displaced ahead of it, and consolidated or pressure-grouted so that the blockout is completely filled beneath every collar and flange.
Blockout Groutradio
● Non-shrink cementitious grout under ASTM C1107/C1107M
○ Epoxy grout
○ Concrete of the liquid-retaining mixture with a shrinkage-compensating admixture
NOTE Non-shrink cementitious grout is the material of nearly every blockout, because it bonds to the concrete, is placed by the concrete trade, and is covered as a material by Non Shrink GroutNon-Shrink GroutResolves to the current adopted revision.sync/non-shrink-grout. Epoxy grout is chosen where the item will see vibration or where the blockout is in a chemical service the cementitious grout cannot survive, and it brings a cure that is temperature sensitive and a thickness limit that a deep blockout exceeds. Concrete with a shrinkage-compensating admixture suits a blockout large enough to be a placement in its own right, where a bagged grout would be placed in too many lifts. (9.12)
9.13 Grouted blockouts shall be cured as liquid-retaining members, and a structure shall not be filled for the tightness test until the grout in every blockout has reached its specified strength.

10 Form Ties in Liquid-Retaining Walls

NOTE A form tie passes through the wall at every point it holds, and a wall that must hold water cannot have a hole through it; so the tie in a liquid-retaining wall is selected for what it leaves behind. The hardware, the tie working load, the break-back, and the patching are specified under Concrete FormworkConcrete Formwork and AccessoriesResolves to the current adopted revision.sync/concrete-formwork; this article adds the water seal and the sequence. (10.1)
10.2 Form ties in liquid-retaining walls shall carry the water seal indicated in the datasheet.
Form Tie Water Sealradio
● Integral waterstop washer or plate on the tie at mid-wall
○ Removable rod in a sleeve, with the sleeve removed and the hole sealed full depth
○ Threaded tie with a cone at each face, the cone recess plugged and sealed
NOTE A waterstop washer or plate welded to the tie at mid-wall lengthens the path water would have to travel along the tie, in the same way a seep ring does on a wall pipe, and it is what nearly every snap tie or coil tie in a basin wall carries. A removable rod leaves a clean hole that is sealed through the full thickness, which is the tightest result and the most labor. A taper tie with cones leaves a cone recess at each face and the tie body in the wall, and it depends on the recess being sealed rather than merely patched. (10.3)
10.4 The ends of form ties in liquid-retaining walls shall be broken back or removed to the depth indicated in the datasheet below the concrete surface.
Tie Break-Back Depthrange
in
0.7511.52
Default: Not less than 1 in
10.5 Tie holes on the liquid face shall be filled before tie holes on the opposite face, and both shall be filled with the non-shrink material and method of Concrete FormworkConcrete Formwork and AccessoriesResolves to the current adopted revision.sync/concrete-formwork before the structure is filled for the tightness test.
10.6 Through-ties that remain in the wall without a water seal, and ties whose patched recess is the only barrier, shall not be used in liquid-retaining walls.
NOTE A tie hole filled from the dry side first is filled against the air that will later be the water; the plug is pushed out from behind by the head. Filling the liquid face first puts the plug where the pressure holds it in. (10.7)

11 Hydrostatic Tightness Testing

11.1 Structures and Compartments Tested

11.1.1 Each structure that holds liquid by design shall be tightness tested under ACI 350.1 before it is placed in service, and each compartment that can be isolated by a wall shall be tested as an independent unit.
11.1.2 A compartment shall be tested with each adjacent compartment empty, so that the dividing wall carries the full differential head during the test.
11.1.3 Open channels shall be tested by installing temporary bulkheads furnished by the Contractor and filling to the design water surface elevation of the channel.
11.1.4 A structure designed to exclude groundwater shall be tightness tested by filling, where it can be filled, and shall in every case be inspected empty under the article on groundwater exclusion below.
NOTE A structure that cannot be filled, such as a gallery or a dry pit, shall be inspected empty under the article on groundwater exclusion below, and the inspection is its tightness test. (11.1.5)

11.2 Condition of the Structure at Test

11.2.1 The tightness test shall not begin until every liquid-retaining member of the structure has attained its specified compressive strength, every blockout has been grouted and cured, every tie hole has been filled, every pipe and gate opening has been closed with a blind flange, a bulkhead, or the gate itself, and the curing period of this standard has ended.
11.2.2 The tightness test shall be performed before any lining, coating, or surface treatment is applied to the concrete, and before any backfill is placed against a wall to be inspected, except as the test timing selected in the datasheet provides.
11.2.3 The test shall be made with every exterior face and every exterior joint accessible for inspection, unless the test timing selected in the datasheet provides otherwise.
NOTE A lining applied before the test hides the leak the test exists to find and bonds to a surface that may later be cut for repair; a test made after a lining is applied proves the lining, not the concrete. (11.2.4)

11.3 Test Timing Relative to Backfill

11.3.1 The tightness test of each structure shall be made at the time indicated in the datasheet.
Test Timing Relative to Backfillradio
● Before backfill, with every exterior face exposed for inspection
○ After backfill, by volume loss only, where the Engineer of Record accepts in writing
NOTE Testing before backfill is the ordinary sequence, because the exterior face of the wall is the only place a damp spot can be seen and the only place a repair can be made from the pressure side; it also means an excavation held open and dewatered through the test. Testing after backfill is accepted where flotation, a shoring system that cannot wait, or a wall cast against shoring leaves no exterior face to inspect, and the test then rests on the volume loss alone, with any leak found later repaired from the inside. (11.3.2)
11.3.3 Where the structure is tested before backfill and its base slab lies below Seasonal High Groundwater ElevationSeasonal High Groundwater ElevationParameterEach project supplies its own value.seasonal-high-groundwater-elevation, dewatering shall be maintained to hold the groundwater below the base slab throughout the test and until the structure is released for backfill.
11.3.4 A structure shall not be left empty below the groundwater level at any time unless the structural drawings show it designed for the empty condition under that groundwater, or dewatering is maintained.

11.4 Test Criterion

11.4.1 The structure shall be accepted as tight only where the volume loss over the measurement period, corrected for evaporation and precipitation, does not exceed the criterion indicated in the datasheet.
Tightness Test Criterionradio
● HST-050, loss not exceeding 0.050 percent of the volume in 24 hours
○ HST-025, loss not exceeding 0.025 percent of the volume in 24 hours
○ HST-NML, no measurable loss
NOTE ACI 350.1 names its criteria by the allowable loss. HST-050 is the criterion for the general run of basins, tanks, and channels, and in a 20 ft deep tank it allows a drop of about 1/8 in. a day, which is at the edge of what a hook gauge resolves. HST-025 halves that and is selected where the liquid is potable water that would be lost to the ground, where the groundwater is to be protected from the contents, or where the structure sits on a soil that a small seepage would soften. HST-NML is reserved for hazardous contents and for secondary containment, where any loss at all is a release; it demands a measurement period long enough that the instrument's resolution bounds the loss, and it is rarely met on the first fill. (11.4.2)
11.4.3 The volume loss shall be computed from the drop in liquid level over the measurement period, the surface area of the liquid at the test level, and the volume of the structure at that level, and expressed as a percentage of volume per 24 hours.

11.5 Visual Acceptance of Exterior Faces

11.5.1 In addition to the volume criterion, the exterior faces and joints of the structure shall satisfy the visual criterion indicated in the datasheet throughout the measurement period, and a structure that fails the visual criterion shall be repaired and retested regardless of its volume loss.
Visual Acceptance of Exterior Facesradio
○ No visible dampness on any exposed exterior face or joint
○ Damp spots permitted where moisture cannot be picked up on a dry hand
○ Damp spots permitted provided no water flows or drips from any point

11.6 Filling

11.6.1 The structure shall be filled at a rate not exceeding the value indicated in the datasheet, and filling shall be stopped at any point where a flow of water appears on an exterior face.
Fill Raterange
ft/hr
123468
11.6.2 The structure shall be filled to the maximum liquid level shown on the process hydraulic profile, including the overflow level where an overflow is provided, and not merely to the normal operating level.
NOTE A slow fill lets the wall take up its load and the concrete absorb water gradually, and it stops at a level where a flowing leak can still be found and repaired before the full head is on it; a fast fill is what a test crew wants when the water source is a truck. The rate is set by how fast the exterior faces can be walked and inspected as the level rises, and by the source, so no one rate suits every structure. (11.6.3)
11.6.4 Test water shall be from the source indicated in the datasheet.
Test Water Sourceselect
Potable water from the site water service
Raw water from the plant intake or well
Treated plant effluent or reclaimed water
Water transferred from a structure already tested
Water delivered by truck
11.6.5 A structure in potable or finished water service shall be tested with potable water and shall be disinfected under Disinfection Of Water SystemsDisinfection of Domestic Water SystemsResolves to the current adopted revision.sync/disinfection-of-water-systems after the test, before it is placed in service.
NOTE Potable water from the service is the source where the plant is a water plant or the site main is large enough to fill a tank in a working day, and it leaves nothing to dechlorinate but itself. Raw water or plant effluent is the source at a wastewater plant, where potable water is a metered purchase and effluent is free, at the cost of a disposal that may need a permit and a structure that will need cleaning before a lining. Transferring water from the last structure tested saves the water and the disposal and is the sequence a multi-basin plant plans around. Trucked water is the source where there is no other and sets the fill rate by the truck cycle. (11.6.6)
11.6.7 The cost of test water, its conveyance to the structure, and its disposal shall be borne by the party indicated in the datasheet, and the cost of water for every retest after a failed test shall be borne by the Contractor.
Test Water Furnished Byradio
○ Owner, from a source on the site at no charge
○ Contractor
11.6.8 Test water shall be disposed of at the test water disposal point shown on the civil drawings, dechlorinated where it is potable water discharged to a receiving water, and discharged at a rate and through an outlet that causes no erosion and no flooding of adjacent work.

11.7 Stabilization and Measurement

11.7.1 After the structure is filled to the test level, the level shall be held for a stabilization period not less than the value indicated in the datasheet before the measurement period begins, with the structure topped up to the test level at the end of it.
Stabilization Period Before Measurementrange
days
12357
Default: Not less than 3 days
11.7.2 The measurement period shall be not less than the value indicated in the datasheet, and shall be extended until the drop the criterion allows over the period is not less than four times the resolution of the measuring device.
Measurement Periodrange
days
12357
Derived — the test criterion, the liquid depth, and the resolution of the measuring device, extended until the allowable drop is measurable (by default)
NOTE New concrete absorbs water for the first several days it is wet, and a reading taken during that absorption records the concrete drinking rather than the structure leaking; ACI 350.1 holds the structure full for a stabilization period before the clock starts for that reason. The measurement period then has to be long enough that the loss the criterion permits is larger than the instrument can mistake, which in a shallow channel at HST-025 can mean several days. (11.7.3)
11.7.4 The liquid level shall be measured by the method indicated in the datasheet, at not fewer than two fixed points in each compartment, with a device readable to 1/16 in. or finer, and each reading shall record the time, the liquid temperature, and the ambient conditions.
Liquid Level Measurement Methodselect
Hook gauge at a fixed reference point
Fixed staff gauge read at the meniscus
Submerged pressure transducer with a logged record
Surface-reading electronic level sensor with a logged record
NOTE A hook gauge reads a change of a few thousandths of a foot from a fixed point and is the instrument ACI 350.1 was written around; it needs a still surface, a reference that does not move with the wall, and a person at the tank for every reading. A staff gauge is cheap and everyone can read it, and its resolution is what makes the measurement period long. A transducer or an electronic sensor logs continuously and catches the diurnal swing that single readings miss, at the cost of a calibration that has to be proved before the test and a temperature correction that has to be applied. (11.7.5)
11.7.6 The loss shall be corrected for evaporation and precipitation by the method indicated in the datasheet.
Evaporation and Precipitation Correctionradio
○ Calibrated pan floating in the structure, read with each level reading
○ Structure covered for the test, no correction
○ No correction, loss taken as measured
Derived — whether the structure is open or covered; an open structure takes the floating pan (by default)
NOTE A floating pan filled from the structure sees the same sun, wind, and rain as the liquid surface and is the correction ACI 350.1 specifies for an open structure; the loss from the pan over the period is subtracted from the drop in the structure. A roofed structure needs no correction. Taking the loss as measured is conservative in dry weather and wrong after rain, and it is tolerable only on a covered structure or in a test short enough that the weather did not change. (11.7.7)

11.8 Retest After Repair

11.8.1 A structure that fails the volume criterion or the visual criterion shall be drained to the extent repair requires, repaired under the leak repair article of this standard, and retested from the beginning of the stabilization period, and the cycle shall be repeated until the structure passes.
11.8.2 Where a structure fails the criterion on two successive tests, the Engineer of Record shall direct an investigation of the cause before a third test, and the Contractor shall bear its cost.
11.8.3 Every retest shall be witnessed and reported as the first test was.

12 Groundwater Exclusion

12.1 A structure designed to exclude groundwater shall, after any filled test is complete and after dewatering is discontinued, be inspected empty for a period not less than the value indicated in the datasheet with the groundwater at or above its seasonal level, and every interior face, joint, tie hole, and penetration shall be examined for inflow.
Empty Inspection Period for Groundwater Exclusionrange
days
1235714
Default: Not less than 3 days
12.2 Any flow of water into the structure at any point, and any damp spot on an interior face that will be lined, coated, or occupied, shall be a leak and shall be repaired and the inspection repeated.
12.3 Where the groundwater is below its seasonal level at the time of the inspection, the Engineer of Record shall determine whether the inspection is to be repeated at a later date, and the Contractor's obligation to repair a leak found at that later inspection shall survive acceptance for the warranty period of this standard.

13 Leak Repair

13.1 Every leak, flowing water, and damp spot that fails the visual criterion shall be located and marked on the leak map before the structure is drained, and the Contractor shall report the map to the Engineer of Record before any repair begins.
13.2 The Engineer of Record shall direct the repair method for each leak from the methods of Concrete Repair And RestorationConcrete Repair and RestorationResolves to the current adopted revision.sync/concrete-repair-and-restoration, and no leak shall be repaired, patched, coated, or concealed before that direction is given in writing.
13.3 Repairs to cracks and joints in liquid-retaining members shall be made from the liquid side where the liquid side is accessible, and a repair made from the dry side alone shall be accepted only where the Engineer of Record directs it in writing.
13.4 A leak attributable to a honeycomb, a cold joint, a void beneath a collar, a tie hole, or a discontinuous waterstop shall be repaired at the Contractor's expense, together with the cost of draining, refilling, and retesting the structure.
13.5 Where the parties disagree whether a crack is a construction defect or a design matter, the Engineer of Record shall make the initial determination.
NOTE A crack that passes water on the first fill and stops within the stabilization period has healed itself: the water carries calcium hydroxide into the crack and deposits it as calcium carbonate, which is the mechanism ACI 350 relies on when it limits the crack width at liquid faces. A crack that keeps flowing is wider than that mechanism can close, or is moving, and it is repaired by injection from the pressure side so that the head holds the repair in rather than pushing it out. (13.6)

14 Linings, Coatings, and Surface Treatments

14.1 Where a lining or coating is scheduled for a liquid-retaining member under High Performance CoatingsHigh-Performance CoatingsResolves to the current adopted revision.sync/high-performance-coatings, it shall be applied only after the tightness test of the structure has been accepted and the concrete has reached the moisture condition the lining manufacturer requires.
14.2 Curing compound, form release agent, and laitance shall be removed from every surface that is to receive a lining, by the surface preparation High Performance CoatingsHigh-Performance CoatingsResolves to the current adopted revision.sync/high-performance-coatings requires, and the removal shall be verified before the lining is applied.
NOTE The lining of the vapor space of a wastewater or sludge structure protects the concrete from the sulfuric acid that forms there; it is not a tightness measure, and a structure that depends on its lining to hold water has failed this standard. (14.3)

15 Backfill

15.1 Backfill shall not be placed against any wall of a structure until the tightness test of that structure has been accepted in writing by the Engineer of Record, except where the after-backfill test timing is selected in the datasheet.
15.2 Backfill against liquid-retaining walls shall be placed under EarthworkEarthworkResolves to the current adopted revision.sync/earthwork in lifts brought up uniformly on all sides of the structure, and the difference in backfill elevation between any two walls of a structure shall not exceed 2 ft unless the structural drawings show the wall designed for the unbalanced condition.
15.3 A structure shall be either filled with water or held dewatered, as the structural drawings require for the backfill condition, while backfill is placed.
NOTE Backfilling before the test buries the only face of the wall that can be inspected, and it buries the repair access with it. Backfilling one side of a basin ahead of the other puts a soil load on a wall that was designed to be held by the water or by the slab on the other side, and it is the way a wall that would have passed every test is cracked before the test begins. (15.4)

16 Warranty

16.1 The Contractor shall warrant each structure constructed under this standard against leakage through the concrete, its joints, its tie holes, and its embedded items for the period indicated in the datasheet, measured from the date of substantial completion, in addition to the warranties of the material standards this standard is read with.
Watertightness Warranty Periodrange
years
1235
Default: Not less than 1 years
16.2 A leak appearing within the warranty period shall be repaired by the Contractor at no cost to the Owner, under the leak repair article of this standard, including the cost of draining and refilling the structure, of a lining disturbed by the repair, and of a retest where the Engineer of Record requires one.
16.3 Where the parties disagree whether leakage within the warranty period is a construction defect, a design matter, or the result of service beyond the design basis, the Engineer of Record shall make the initial determination.
16.4 Work repaired under the warranty shall carry a renewed warranty running from the date the repair is accepted, for the full original period or for the remainder of the original period, whichever ends later.
NOTE Leakage through a crack caused by settlement beyond the design basis, by a liquid or a temperature the structure was not designed for, or by a load the Owner applied is a design or operating matter rather than a construction defect; leakage at a tie hole, a cold joint, a blockout, or a joint whose waterstop was found discontinuous is the Contractor's. (16.5)