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 use Aerlite-iX preformed cellular concrete foam to generate non-pervious material. We use Aquaerix preformed cellular concrete foam to generate pervious material. Both types start with the same base cement & water 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
A straight slurry around 0.60 water : cement ratio typically generates neat mix LWFC. For applications which need to be poured on slopes, 0.45 water : cement ratio slurry can be used. The site crew blends the slurry with pre-formed foam such as Aerlite, either in a ready mix truck or in-line, depending on the project volume & other constraints. In-line generation is significantly faster.
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 25PCF, 30PCF and 70PCF. 25PCF wet cast density CJFill-UL is the go-to mix design for maximum load reduction. 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 absolutely must be avoided. Use non woven geotextile to protect pervious LWFC from adjacent soils. The non woven geotextile helps prevent soil from fouling the permeable matrix. CJGeo uses 68PCF wet cast density material in cases where pervious cellular concrete can’t be used, and buoyancy is a concern. Some annular space grouting work requires 1,000psi compressive strength. CJGeo uses 70PCF west cast density material to meet this specification.
Typical Sanded Mix Designs
High wet cast densities are mot economical with sanded mixes. 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. Someone can’t pump sanded cellular concrete 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.
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