Slip-lining and casing work leave an annular space — the gap between a new carrier pipe and the host pipe, casing, or tunnel. On Portland Metro and Pacific Northwest jobs that gap is often filled with cellular grout (cement slurry plus preformed foam) so the liner stays bedded, the void does not collapse or migrate, and groundwater does not short-circuit along the annulus.
This note is for engineers and contractors writing annular / slipline fill into the documents. It is not a mix design and not a substitute for the engineer of record.
Why cellular grout belongs in the annulus
The annulus is long, thin, and irregular. Conventional sand slurry or heavy CLSM can work, but it is denser, harder to pump long distances at low pressure, and adds more weight on the carrier. Cellular grout is built for that geometry:
- Flowable and self-consolidating — fills irregular rings with little or no vibration
- Pumpable — hose placement from limited access points is normal
- Lightweight — cast densities in the mid-20s to mid-40s pcf are common industry practice for many annular jobs, so the fill itself does not pile unnecessary load onto soft ground or the liner
- Controlled density — foam content is the primary dial; QC is cast density at the hose
“Cellular concrete” and “cellular grout” are the same product family here. Trade language often says grout when the job is pipe, annular, or void fill.
Do not treat everyday “CLSM / flowable fill” as the same line item unless density and foam are confirmed. Heavy sand–cement slurry and lightweight foamed fill behave differently in a long annulus.
Cast density still comes first
Write cast density at placement in pcf. “Lightweight,” “cellular,” and “grout” are not numbers.
Cellular Backfill starts at about 27 pcf and is dialed upward (toward about 100 pcf) when the engineer specifies higher density or strength. Volume’s featured packet example is about 38 pcf, non-permeating, with packet maturity on the order of 104 / 144 / 180 psi at 7 / 14 / 28 days for that specific mix — the design Volume stands behind when that mix is ordered.
Industry practice often parks many annular and abandonment fills roughly in the mid-20s to mid-40s pcf when load reduction and pumpability matter. Your plans need the project number. If minimum strength is also required, write the age and the psi. Density still comes first. Use the on-site density explorer for Aerix chart interpolations when you are planning; Volume designs and guarantees the mix delivered to your project specs.
Neat cement mixes emphasize the lightest, most pumpable band. Fine sand raises density and strength when the engineer wants a sanded family. Sand vs neat is a second knob — orthogonal to permeable vs not.
Buoyancy of the liner (and of the fill)
Fresh water is about 62.4 pcf. Cellular fill cast well below that is lighter than the water it can displace. In a flooded host, that matters two ways:
- The carrier / liner can float during or after grouting if the annular fill and water loads are not staged as designed. Lightweight annular grout is often chosen partly because it reduces the uplift push of a heavy sand slurry — but it does not remove buoyancy as a design item.
- The fresh cellular mass itself can float or lift in a flooded excavation or flooded host if placement is not sequenced and vented correctly.
Treat buoyancy as a design and field-control item whenever specified density is well below 62.4 pcf, or whenever the host can hold water. Put water-table and dewatering assumptions in the documents, not only in a phone call.
Permeable vs sealed annulus
Most annular / slipline jobs want a non-permeable (closed-cell) fill so the annulus does not become a drain path along the carrier. That is the usual Cellular Backfill call for sealed abandonment and sealed annular space.
Specify permeable (PLDCC / open-cell) only when drainage through the set mass is part of the design. Those are different foam chemistries, not a field switch on the same truck. If the documents are silent, ask before the foam generator starts. Related detail lives in the permeable vs non-permeable note.
Closed-cell annular fill is not automatic waterproofing of the host or the carrier. Joints, bulkheads, and drainage outside the annulus still follow the structure’s design.
Placement: bulkheads, vents, lifts, fluid pressure
Annular work is placement geometry as much as mix design:
- Bulkheads at ends and staged intervals keep the grout where it belongs and let you work in controlled segments on long runs
- High-point vents let air and water escape so the annulus actually fills; pump until material returns at vents when that is the acceptance method
- Pressure monitoring protects thin liners and host pipes — cellular grout pumps at relatively low pressure compared with heavy sand slurry, but “low” is not “zero”
- Lifts — a typical starting point is about 4 feet of lift height unless the foam system and the engineer allow more. Deep or tall segments are staged, not poured as one uncontrolled column by default
While plastic, cellular concrete exerts full fluid hydrostatic pressure (cast density × depth). Bulkheads, liners, and thin walls must resist that load during placement. After set (often within roughly 8–24 hours depending on conditions), that fluid pressure drops for permanent design purposes.
Dewater as practical before fill. Follow producer and engineer of record means-and-methods — this is not a contractor playbook.
Spec sheet: collect this before dispatch
A useful annular call usually includes:
- Target cast density (pcf)
- Permeable or non-permeable (required — do not leave blank)
- Minimum strength only if required (and at what age)
- Geometry — host ID, carrier OD, length, or a volume we can estimate (use the site annular calculator when helpful)
- Application — slipline, casing, tunnel annulus, or related void
- Pump access — staging, hose run, elevation, segment / lift limits
- Water table / buoyancy concerns and dewatering plan
- Sand or neat if the engineer cares about mix family
- Testing / submittals expected (cast-density logs, cylinders, foam or cement certs)
Phone for dispatch: (971) 219-8604.
Optional overage covers hose waste and irregular voids — agree on it before dispatch. Pipe and tank abandonment notes that share bulkhead and vent language are here.
Standards awareness — not a certificate wall
Literature and test methods cellular specs often cite include ASTM C495, ASTM C796, ASTM C869, and ACI 523.1R. Volume’s Cellular Backfill mixes are developed in accordance with ACI 301 and ASTM C685, C1602, C150, and C1600.
That is standards awareness, not a wall of invented certificates. If the job needs cylinders or a named acceptance criterion, put it in the documents. Field QC of cast density at the hose is usually more decisive on placement day than waiting for a 28-day break alone.
How we cover the Portland Metro and PNW
Cellular Backfill is a product line of Volume Concrete LLC. Production uses volumetric trucks and mobile silos — Type IL cement (Ash Grove Durkee OR in the featured packet), Aerix foam systems, sand optional, permeable and non-permeable as specified. Everyday ready-mix stays in Greater Portland Metro; cellular jobs travel the Pacific Northwest when this product is on the ticket. Home base is Estacada, Oregon (city only — no plant street published here).
Confirm the jobsite on the call. Service area details live on the service area page.
Public NAP (billing / postal, not a plant street):
Volume Concrete LLC
4230 SE King Rd. #211
Milwaukie, OR 97222
(971) 219-8604
If you are writing an annular or slipline fill and the open questions are density, sealed vs draining, and how the liner behaves in water, put those numbers in the documents — then call with geometry, access, and buoyancy assumptions. Same facts sit on the calculators, density explorer, and related notes on pipe/tank abandonment, foundation/abutment backfill, and cellular vs CLSM.