CJGeo installs two types of lightweight fill: cellular concrete, and geotechnical/structural polyurethane. Lightweight fills are materials which provide adequate bearing capacities at much lower unit weights than traditional fill materials, such as flowable fill, compacted soils or stone.
CJFill is a cement-based product which is essentially flowable fill with exceptionally high air entrainment (generally greater than 50%). CJGrout geotechnical polyurethanes are some of the lightest weight fill materials available, with unit weights as low as two pounds per cubic foot.
Uses for Lightweight Fill
There are two broad uses of lightweight fill:
Axial Load Reduction
Axial load reduction applications for lightweight fill allow for reducing dead loads over compressible soils and underlying structures. This includes building walls & sites over compressible soils, or over structures such as pipes, tunnels, and basements.
Lateral Load Reduction
Lateral load reduction applications for lightweight fill allow reduce loads on walls and structures to facilitate building more economically. For example, filling between a permanent slope and a wall with 25lb/cuft CJFill-Ultra Lightweight cellular concrete effectively eliminates passive earth pressure after the CJFill has set, which takes just a few hours.
Low density fills are an economical way to reduce or compensate for the loads of a structure. This allows for smaller foundation footprints, reductions in anticipated settlements, and avoidance of expensive deep foundations.
Cellular concrete is a lightweight backfill frequently used for MSE wall backfill to reduce settlement of bridge approaches. Pervious cellular concrete is used for reducing the load on retaining walls. It allows water to freely drain to avoid building up hydrostatic pressure.
For buildings, undercutting unsuitable soils and filling the excavations with stone or flowable fill is a common practice. Cellular concrete can be used in this application to further reduce the loads of the underlying unsuitable soils, while maintaining adequate strength for structural loads.
As the use of less suitable land increases in urbanized areas, land which was frequently left undeveloped due to extensive geotechnical concerns is placed into service. Lightweight fill can provide an economical alternative to deep foundations in these situations.
Types of Lightweight Fill
There are three broad categories of low density fills.
- Cementitious, including cellular concrete and lightweight aggregate concrete,
- Plastics, which includes high density polyurethanes, and expanded polystyrenes, and
- Aggregates, including foamed glass, expanded shale, and expanded clay
CJGeo specializes in installing cellular concrete (also called Foamed Concrete) as a cement-based lightweight fill, and high density polyurethanes as a plastic-based lightweight fill.
Cellular concrete consists of Portland, water & air bubbles. Occasionally, sand or fly ash is added to cellular concrete mixes to achieve higher densities. However, this also the strength of the material. Densities of cellular concrete start around 16 pounds per cubic foot and increase to around 50 pounds per cubic foot. Bearing capacities start at 50psi and increase to around 950psi for neat mixes. Autoclaved Aerated Concrete is similar to cellular concrete, but isn’t appropriate for mass lightweight fills.
Geotechnical polyurethanes are rigid cellular plastics, placed as liquids which then expand and cure. Depending on the application, densities are as low as 2.0 pounds per cubic foot, and increase to around 10 pounds per cubic foot. Bearing capacities start at 3,000PSF and increase with density. High density polyurethanes can either be sprayed or poured, depending on the application. Vertical applications are generally sprayed, horizontal applications are typically poured, but may also be sprayed.
Other Types of Lightweight Fill
Learn more about the other types of lightweight fill here.
Limitations of Lightweight Fill
Lightweight fills such as CJFill Ultra Lightweight cellular concrete and CJGrout geotechnical polyurethanes are generally not suitable for load distribution in uses such as footing construction or as traffic able surfaces such as roadways, parking lots or sidewalks.
Below 63 pounds per cubic foot, lightweight fills are buoyant. Therefore, attention must be paid during the design phase to ensure that the weight of the structure bearing on the lightweight fill is greater than the buoyancy. To counteract buoyancy, pervious cellular concrete can be used. Pervious cellular concrete allows water to inundate the matrix of the lightweight fill without flotation, and then freely drain out as water levels recede. However, when the pervious cellular concrete becomes saturated, the loads on underlying soils/structures increase.
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