We install 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.
Cellular concrete is a cement-based product which is essentially flowable fill with exceptionally high air entrainment (generally greater than 50%). 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
Lightweight 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 fill frequently used for MSE wall backfill to reduce settlement of bridge approaches. Pervious cellular concrete can be used for reducing the load on retaining walls, while also allowing 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 two broad categories of lightweight fill—cement based, which is further broken down into cellular concrete and lightweight aggregate concrete, and plastic based, which includes high density polyurethanes, and expanded polystyrenes. Concrete Jack 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, which are introduced through a proprietary foam injection system. Occasionally, sand or fly ash is added to cellular concrete mixes to achieve higher strengths, though this also increases the unit weight of the materials. 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. We do not install Autoclaved Aerated Concrete, which is similar to cellular concrete, but is produced differently and used generally for structural assembly in place of CMU.
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 cellular concrete and high density polyurethane 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.