Cellular grout 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 “cellular” in cellular grout refers to the preformed cellular concrete foam used to generate the material. Instead of sand and stone aggregate, cellular 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 Cellular Grout
Cellular grout can be either pervious or non-pervious. We generate non-pervious material using Aerlite-iX preformed cellular concrete foam, this is manufactured by Aerix Industries. We use Aquaer-iX preformed cellular concrete foam to generate pervious material. Both types start with the same base paste, which can be as low as 0.45 w:c ratio, and as high as 0.80 w:c ratio.
Uses for Cellular Grout
There are two primary drivers for using lightweight cellular grout: load reduction and placement characteristics. 25lb/cuft wet cast density material is the most common lightweight fill material. It will cure to 20.5lb/cuft. On the placement characteristics side, cellular grout is used due to economics in utility grouting applications in that it can be pumped very far (thousands of feet) at very low pressures. This facilitates annular space grouting and abandonments of much longer runs compared to traditional grout materials.
Typical Neat Mix Designs
High w:c ratios facilitate longer placement times and actually increase compressive strengths. Low w:c paste (0.45) facilitates sloped placements up to 4%. 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 cellular grout 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.
Need to displace water? If placing into pipes, material below 62.4PCF can still displace water. For mass placements directly into water, 65lb/cuft is the recommended minimum density.
Typical Sanded Mixes
Sanded slurry is most economical for tremied placements displacing water. The base slurry for sanded cellular grout consists of around 2,000 pounds of sand per cubic yard, 600 pounds of cement and around 800 pounds of water.
75lb/cuft sanded lightweight foamed concrete breaks around 200psi at 7 days and 300psi at 28 days. With an oven dry density of 68lb/cuft, buoyancy is not a concern.
Sand makes material significantly more difficult to pump.
Specifying Cellular Grout
Cellular grout is a whole different beast from traditional concrete or grout. For example, at most densities, increasing w:c ratio actually increases UCS. When specifying cellular grout, 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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