Lightweight concrete is a mix of water, Portland cement, and aggregate. It is classified as structural or non-structural depending on its strength and degree of compression. Structural lightweight aggregate concrete is used for high-strength applications, while non-structural lightweight concrete is used for lighter applications. The aggregates used vary, and insulation is often a factor in choosing an aggregate. It is important to consult a qualified engineer or architect when considering lightweight concrete for a construction job.
Lightweight concrete, similar to normal weight concrete, is a mix of water, Portland cement or ordinary Portland cement (OPC), and aggregate. It is classified as structural or non-structural concrete depending on its strength and degree of compression, usually determined by the type of aggregate material used in the concrete mix. Lightweight aggregate concrete uses a variety of aggregates with lower density than normal weight concrete.
Structural concrete, either an approved lightweight concrete or normal weight concrete, is used for applications that require a high level of strength and compression. These could be highway overpasses, bridges, high-rise buildings and construction in earthquake-prone areas. The benefits of structural lightweight aggregate concrete with a correspondingly reduced weight load include reduced dead loads or weight of the structures used to build and more efficient transportation.
While not approved for many structural applications, non-structural lightweight concrete is used where a normal or denser structural lightweight mix would not be practical. Lightweight concrete tiles are lighter in weight and require less robust truss systems. The combination of strength, weather resistance, and low weight often make lightweight aggregate concrete and lightweight blocks a good choice for non-traditional residential buildings.
The aggregates used to produce lightweight aggregate concrete vary. Expanded shale, slate and clay, often fired in a kiln to increase porosity, are among the aggregates used for structural lightweight concrete. Other porous material is often used, such as air-cooled blast furnace slag.
Insulation is often a factor in choosing an aggregate for lightweight non-structural concrete. A lightweight aerated concrete can be used to make both lightweight panels and lightweight blocks suitable for a variety of constructions, including some foundation shaft walls. Lightweight aerated concrete can be made in a variety of ways, such as forcing air into a slurry of OPC and a porous material, or using a stable foam product as aggregate.
Perlite and vermiculite are naturally occurring minerals which, when heat treated, can be mixed with OPS to produce lightweight non-structural aggregate concrete. The product is often used for decorative treatments in concrete, roof tiles and other light applications. This lightweight concrete is often used in jobs that require heat and sound insulation.
Structural lightweight aggregate concrete might typically require a density or unit weight of 90 to 115 lb/ft³ or (1440 to 1840 kg/m³) and a compression ratio of 2500 psi or (1700 MPa), which is about 65 % of the density or unit weight of normal concrete. Non-structural lightweight concrete might have a density or unit weight of 35 lb/ft³ or (561 kg/m³). When considering lightweight concrete for a construction job, it is generally a good practice to consult a qualified engineer or architect for specifics.
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