Corpus sync: neutrality remakes, note hygiene, datasheet relocation, transformer-split cross-refs
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title: Cast-in-Place Site Concrete Structures
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## Several adjacent standards own work that is easy to conflate with this Standard: building structural concrete belongs to [[sync/cast-in-place-concrete]]; isolated mechanical and electrical equipment pads belong to [[sync/concrete-pads]]; site retaining walls carrying significant retained-soil surcharge belong to [[sync/retaining-walls]]; precast manholes, vaults, and box culverts supplied from a plant belong to [[sync/utility-manholes-and-handholes]]; storm pipe, inlet sizing, and network layout belong to [[sync/storm-drainage]]; and the excavation and backfill operations around these structures belong to [[sync/earthwork]]. {note}
−## Where a single structure is part cast-in-place and part precast, the Contract Documents shall identify unambiguously which portions are governed by this Standard and which by [[sync/utility-manholes-and-handholes]]. {note}
+## Where a single structure is part cast-in-place and part precast, the Contract Documents shall identify unambiguously which portions are governed by this Standard and which by [[sync/utility-manholes-and-handholes]].
## Catch basin collars and adjustment rings poured onto precast base units are the common mixed case; combining cast-in-place forming procedures with precast plant tolerances on the same element produces conflicting requirements, and the scope split must be explicit on the drawings so the requirements do not collide. {note}
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# Concrete Materials and Mix {toc}
−## Compressive strength shall be selected from the structural design and the governing exposure class, not chosen uniformly across all site concrete; for lightly loaded site walls and aprons 3,000 psi is adequate, the 80% case for buried utility vaults and headwalls is 3,500 psi, walls subject to vehicular surcharge or severe freeze-thaw warrant 4,000 psi, and specifying 5,000 psi across all site concrete without an exposure or load basis is a common overspecification that raises mix cost and - because the higher cementitious content increases heat of hydration - can actually increase cracking in thin site walls; all strengths are verified at 28 days by ASTM C39. {note}
+## Compressive strength shall be selected from the structural design and the governing exposure class, not chosen uniformly across all site concrete; for lightly loaded site walls and aprons 3,000 psi is adequate, the usual strength for buried utility vaults and headwalls is 3,500 psi, walls subject to vehicular surcharge or severe freeze-thaw warrant 4,000 psi, and specifying 5,000 psi across all site concrete without an exposure or load basis is a common overspecification that raises mix cost and - because the higher cementitious content increases heat of hydration - can actually increase cracking in thin site walls; all strengths are verified at 28 days by ASTM C39. {note}
### The specified compressive strength shall be not less than the minimum required by the governing exposure class in ACI CODE-318-25 Table 19.3.2.1.
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```
−## Supplementary cementitious materials improve durability and reduce heat of hydration; replacing a portion of the portland cement with Class F fly ash (ASTM C618) reduces permeability, improves sulfate resistance, and lowers the heat of hydration that drives early cracking in thicker pours; a 15 to 25% Class F replacement by weight of cementitious material is the 80% case; Class C fly ash up to 25% is acceptable where sulfate exposure is low but is less effective against sulfate attack and should not be the choice for S2/S3 soils; slag cement and silica fume are alternatives where specified by the mix designer. {note}
+## Supplementary cementitious materials improve durability and reduce heat of hydration; replacing a portion of the portland cement with Class F fly ash (ASTM C618) reduces permeability, improves sulfate resistance, and lowers the heat of hydration that drives early cracking in thicker pours; a 15 to 25% Class F replacement by weight of cementitious material is the usual range; Class C fly ash up to 25% is acceptable where sulfate exposure is low but is less effective against sulfate attack and should not be the choice for S2/S3 soils; slag cement and silica fume are alternatives where specified by the mix designer. {note}
+## The supplementary cementitious material and replacement percentage, if any, shall be specified based on the governing sulfate exposure class and durability requirements.
+
```datasheet
label: Supplementary Cementitious Material
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# Jointing and Waterstops {toc}
−## Construction joints in below-grade structures shall be waterstopped because an unstopped cold joint is the most common leak path in site concrete; a construction joint is the planned interface between two placements, and below grade that interface is a direct path for groundwater infiltration into a vault or junction chamber and for exfiltration out of a water-conveying structure; a waterstop cast into the joint blocks that path; a flat PVC dumbbell waterstop, minimum 6 in. wide, is the standard for accessible joints; a hydrophilic swellable rubber strip (typically 3/4 in. by 3/8 in.) is the alternative for joints too tight or congested to place a PVC stop, and it expands on contact with water to seal the joint. {note}
+## Construction joints in below-grade structures shall be waterstopped because an unstopped cold joint is the most common leak path in site concrete; a construction joint is the planned interface between two placements, and below grade that interface is a direct path for groundwater infiltration into a vault or junction chamber and for exfiltration out of a water-conveying structure; a waterstop cast into the joint blocks that path; a flat PVC dumbbell waterstop, minimum 6 in. wide, is the standard for accessible joints; a hydrophilic swellable rubber strip (typically 3/4 in. by 3/8 in.) is the alternative for joints too tight or congested to place a PVC stop, and it expands on contact with water to seal the joint.
### Construction joints in below-grade structures shall receive a continuous waterstop.
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−## The annular space between a pipe and its sleeve shall be sealed because an unsealed annular gap is the primary infiltration path through a vault wall; a pipe passing through a sleeve leaves a ring-shaped gap, and left open that gap is the main way groundwater enters a vault or escapes a water-carrying structure; the closure must be designated explicitly - a non-shrink grout pack for fixed pipes, or a modular mechanical link-seal where the pipe needs to articulate or where a positive, gasketed seal is required; leaving the annular closure unspecified guarantees a leak. {note}
+## The annular space between a pipe and its sleeve shall be sealed because an unsealed annular gap is the primary infiltration path through a vault wall; a pipe passing through a sleeve leaves a ring-shaped gap, and left open that gap is the main way groundwater enters a vault or escapes a water-carrying structure; the closure must be designated explicitly - a non-shrink grout pack for fixed pipes, or a modular mechanical link-seal where the pipe needs to articulate or where a positive, gasketed seal is required; leaving the annular closure unspecified guarantees a leak.
### The annular space between each pipe and its sleeve shall be sealed by non-shrink grout or a modular mechanical link-seal as scheduled.
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## This Standard covers a family of cast-in-place site structures formed with job-built or modular forms; the configurations below share materials and execution but differ in geometry and in which features apply - a headwall needs wingwall flare and surface sealer, a vault needs a lid pocket and waterstopped joints, an apron needs integral curbs and energy dissipation; the structure type drives which of the optional features in this Standard are invoked. {note}
+## The structure type shall be specified for each cast-in-place site structure, and the optional features this Standard invokes for that type shall be provided.
+
```datasheet
label: Structure Type
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## Headwalls and wingwalls are formed at the outlet end of a culvert or storm outfall with the wingwalls flared to retain the embankment and guide flow; a headwall caps the pipe end and supports the embankment while the wingwalls flare out from it to hold back the fill and direct the discharge; the flare angle is a hydraulic and grading decision, with 30° and 45° being the common values; headwalls are fully exposed and so invoke the air-entrainment and surface-sealer requirements of this Standard, and they are formed with job-built forms or reusable proprietary headwall form systems. {note}
+## Where a headwall with wingwalls is specified, the wingwall flare angle shall be specified based on the hydraulic and grading requirements of the outfall.
+
```datasheet
label: Wingwall Flare Angle
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## Cast-in-place utility vaults are rectangular below-grade structures with a lid or frame pocket, pipe penetrations, and a floor sump; pull, splice, and meter vaults are box structures formed in place where a precast unit will not fit the configuration or the site constraints; they invoke the full below-grade feature set of this Standard - waterstopped construction joints, sealed pipe penetrations, and cast-in hardware for the lid frame and any grounding or conduit; a floor sump is provided so water that does enter can be pumped or drained rather than standing on equipment. {note}
+## Where a cast-in-place utility vault is specified, the floor sump configuration shall be specified based on the site's drainage and pumping requirements.
+
```datasheet
label: Vault Floor Sump
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```
−## Exposed site concrete shall receive a penetrating surface sealer because unprotected concrete in wet-dry and freeze-thaw cycling degrades quickly; headwalls, aprons, curbs, and exposed wall faces live in repeated wetting and drying and, in cold climates, freeze-thaw with deicing salts; unsealed, they carbonate and admit chlorides and the surface scales and spalls; a penetrating silane or siloxane sealer soaks into the surface and repels water without changing the appearance and is the standard protection for exposed site concrete; for below-grade vaults where watertightness is the priority, a crystalline waterproofing admixture batched into the mix is the alternative - it grows crystals that block water through the concrete body rather than at the surface. {note}
+## Exposed site concrete shall receive a penetrating surface sealer because unprotected concrete in wet-dry and freeze-thaw cycling degrades quickly; headwalls, aprons, curbs, and exposed wall faces live in repeated wetting and drying and, in cold climates, freeze-thaw with deicing salts; unsealed, they carbonate and admit chlorides and the surface scales and spalls; a penetrating silane or siloxane sealer soaks into the surface and repels water without changing the appearance and is the standard protection for exposed site concrete; for below-grade vaults where watertightness is the priority, a crystalline waterproofing admixture batched into the mix is the alternative - it grows crystals that block water through the concrete body rather than at the surface.
### Exposed surfaces of headwalls, aprons, curbs, and walls shall receive a penetrating silane or siloxane sealer after curing is complete.
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### Concrete shall be deposited in horizontal layers and shall not be allowed to free-fall in a manner that causes segregation.
−## Backfill against walls shall not begin until the concrete has reached minimum age or strength because premature backfill can crack or overturn a wall that has not yet reached working strength; a freshly poured wall has little strength to resist lateral load, and heavy compaction equipment working against the wall transmits lateral pressure that can crack the wall or push it off its footing before the concrete is strong enough to act as designed; within 3 ft of the wall, only hand compaction is permitted until the structure reaches full strength; backfill material and the earthwork operation itself are governed by [[sync/earthwork]] and, for drainage behind the wall, by [[sync/foundation-drainage]]. {note}
+## Backfill against walls shall not begin until the concrete has reached minimum age or strength because premature backfill can crack or overturn a wall that has not yet reached working strength; a freshly poured wall has little strength to resist lateral load, and heavy compaction equipment working against the wall transmits lateral pressure that can crack the wall or push it off its footing before the concrete is strong enough to act as designed; within 3 ft of the wall, only hand compaction is permitted until the structure reaches full strength; backfill material and the earthwork operation itself are governed by [[sync/earthwork]] and, for drainage behind the wall, by [[sync/foundation-drainage]].
### Machine compaction of backfill against structure walls shall not begin until the concrete is a minimum of 7 days old or has reached 75% of the specified f'c, confirmed by field-cured cylinders.
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default: 1
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