LWFC stands for Lightweight Foamed Concrete, which is an alternative name for cellular concrete. Cellular concrete is a type of controlled low strength material (CLSM). CLSM generally refers to flowable fill or mix designs specifically formulated for relatively low, but predictable, strengths. The “foamed” in LWFC refers to the preformed cellular concrete foam used to generate the material. Instead of sand and stone aggregate, the Low Density Controlled Low Strength Material has uniformly-distributed air bubbles. Sometimes sand is used, but it’s at much lower quantities per cubic yard than traditional CLSM. This lowers unit weight significantly. Foaming is done either through truck batching or continuous generation.
Types of Lightweight Foamed Concrete
LWFC can be either pervious or non-pervious. We generate non-pervious material using Aerlite preformed cellular concrete foam, this is manufactured by Aerix Industries. We use Aquaerix preformed cellular concrete foam to generate pervious material. Both types start with the same base 0.5 water : cement ratio slurry.
Uses for LWFC
The primary driver of Lightweight Foamed Concrete use instead of standard CLSM is load reduction. Applications range from abandoning pipes to void filling below bridge abutments, reducing loads on underground utilities and reducing settlement without the use of deep foundations.
Typical Neat Mix Designs
Neat mix LWFC is generated using a straight slurry, usually 0.50 water : cement ratio. For applications which need to be poured on slopes, 0.45 water : cement ratio slurry can be used. The slurry is blended onsite with pre-formed foam such as Aerlite, either in a ready mix truck or in-line, depending on the project volume & other constraints.
Cellular concrete typically ranges from 20lb/cuft wet cast density up to around 90lb/cuft. These densities provide strengths from around 50psi to greater than 1,000psi. Density is effectively infinitely variable within that range. There’s a relatively linear relationship between density and compressive strength.
Relatively common mixes are 20PCF, 30PCF and 70PCF. 20PCF wet cast density is the go-to mix design for maximum load reduction. Pervious LDFC is used in areas where low unit weights are required and buoyancy can’t be balanced by overburden. 30PCF is a relatively common mix for pipe abandonments, annular space grouting and other utility-related work.
70PCF material is also used to provide weight reduction compared to traditional CLSM or other fill materials when buoyancy must be absolutely avoided. Pervious LWFC must be protected from adjacent soils with geotextile fabric. CJGeo uses 68PCF wet cast density material in cases where pervious cellular concrete can’t be used, and buoyancy is a concern. 1,000psi compressive strength is required for some annular space grouting work. CJGeo uses 70PCF west cast density material to meet this specification.
Typical Sanded Mix Designs
Sanded mixes are used to economically achieve high wet cast densities. The base slurry for sanded LWFC consists of around 2,000 pounds of sand per cubic yard, 600 pounds of cement and around 800 pounds of water.
Sanded base mixes can be used to absolutely ensure no buoyancy of cured material; the oven dry density of 75lb/cuft LWFC is 68lb/cuft, ensuring that regardless of how dry an environment is, there are no chances of material buoyancy. 75lb/cuft sanded lightweight foamed concrete breaks around 200psi at 7 days and 300psi at 28 days.
A limitation of using sanded mixes is pumpability; sanded cellular concrete can’t be pumped nearly as easily as neat mix cellular concrete. When specifying lightweight foamed concrete, it’s best to leave the mix design up to the specialty contractor. Typically, specified characteristics are a wet cast density that’s +/- 5lb/cuft, and a minimum strength in psi at 28 days.