On Portland Metro and Pacific Northwest plans, cellular concrete and cellular grout often show up as “lightweight fill” or “foam concrete” with no number attached. That leaves the producer guessing and the acceptance criteria soft. The number that belongs on the plans is cast density at placement, in pounds per cubic foot (pcf).
This note is for engineers and contractors writing or reading that line item. It is not a mix design and not a substitute for the engineer of record.
What “cast density” actually means
Cellular concrete is cement slurry plus preformed foam. The foam creates a stable matrix of air cells. After hydration, you get a hardened cellular mass — light, flowable when fresh, cementitious when set.
Cast density is the wet unit weight measured at the point of placement (typically at the hose). It is the primary field quality-control variable. Hardened in-place density is similar but can shift slightly with hydration and moisture. Avoid ambiguous “dry density” language on geotech specs unless you truly mean a lab oven-dry value — that is not what the truck controls day of pour.
Industry guidance (ACI 523.1R and related geotech practice) treats many lightweight cellular fills as controlled by cast density first. Strength, when required, is a second acceptance criterion tied to age (for example, 28-day psi).
Why density comes before strength on most geotech jobs
Strength generally rises as density rises — more paste matrix, less air. At geotech densities, compressive strengths are low compared with structural concrete but often several times stronger than compacted soil. That is useful. It is also easy to over-specify.
ACI guidance publishes minimum 28-day floors by maximum cast density (for example, about 40 psi at 30 pcf and 160 psi at 50 pcf). Those are floors, not typical producer averages. Real mixes at a given density can land well above the minimum depending on cement content, foam quality, sand, and curing. Do not invent a psi table from memory for a Portland job.
Practical rule for plans:
- Write the target cast density (pcf) as the primary number.
- Add a minimum strength at a stated age only when the engineer needs it for the design.
- Say permeable or non-permeable — they are different products, not a field switch.
Volume Concrete’s Cellular Backfill range starts at about 27 pcf and is dialed upward (toward about 100 pcf) when the engineer specifies higher density. The 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. That is the design Volume stands behind when that mix is ordered. For planning interpolations across neat-cement and sanded bands, use the on-site density explorer — an Aerix manufacturer reference for planning. Volume designs and guarantees the mix delivered to your project specs.
Industry density bands (planning ranges, not your project number)
Typical industry bands (your plans still need the project pcf):
- About 20–30 pcf — maximum load reduction; soft-soil and approach fills where buoyancy is designed
- About 25–40 pcf — many pipe/culvert abandonments, annular / slip-liner grouting, tank and void fills
- About 30–50 pcf — foundation, abutment, and retaining-wall backfill when load reduction matters
- About 50–100+ pcf — higher-strength or sanded fills; less lightweight benefit toward conventional flowable-fill weights
Neat cement emphasizes the lightest, most pumpable band (often ~20–60 pcf in manufacturer literature). Fine sand raises density and strength. Sand vs neat is a second knob — orthogonal to permeable vs not.
Buoyancy: density vs water
Fresh water is about 62.4 pcf. Any fill cast well below that is lighter than the water it can displace. In a flooded excavation, pipe, or tank, lightweight cellular fill can float or lift if placement is not staged and anchored as designed.
Treat buoyancy as a design item whenever specified density is well below 62.4 pcf. Higher cast density is one lever; cover weight, anchors, and geometry are others. Do not assume “lightweight” automatically works under the water table without that check.
Fluid pressure while plastic, and lifts
While plastic, cellular concrete exerts full fluid hydrostatic pressure (cast density × depth). Forms, 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.
Placement is usually done in lifts — typically about 4 feet unless the foam system and the engineer allow more. Lower cast density only lowers the magnitude of fluid pressure while plastic; it does not remove it.
What to write on the plans (and what to collect before dispatch)
A useful cellular call usually includes:
- Target cast density (pcf) — required
- Permeable or non-permeable — required
- Minimum strength only if required (and at what age)
- Volume (yd³) or geometry we can estimate
- Application — pipe, annular / slip-liner, tank, foundation, abutment, void
- Pump access — staging, hose run, elevation, lift limits
- Water table / buoyancy concerns
- 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.
Volume estimating for pipes, annular spaces, and common tanks: use the site calculators. Optional overage covers hose waste and irregular voids — agree on it before dispatch. For density planning across mix families, open the density explorer.
Field QC: measure at the hose
Day-of placement, cast density at the point of placement is usually more decisive than waiting for 28-day breaks. Producers adjust foam-to-slurry ratio to stay on the target. If cylinders are required, low-density specimens are fragile: industry practice uses 3×6 in. cylinders, careful handling (do not rod like normal concrete), and ASTM C495-type prep — not oven-drying before crush. Put the acceptance method in the documents if the job depends on it.
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.
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 a cellular fill spec and the documents only say “lightweight” or “cellular,” add the cast density in pcf — then permeable vs not, volume, and access. Same facts sit on the calculators, density explorer, and related notes on permeable vs non-permeable, pipe/tank abandonment, foundation/abutment backfill, and cellular vs CLSM.