Pumice concrete is a lightweight concrete in which pumice stone is used as aggregate instead of gravel. It is lighter than normal concrete and offers good thermal insulating properties, making it a popular choice for non-structural walls, roof screeds and other applications where reduced weight and improved insulation are important.
Composition and properties
Pumice concrete, or “bimsbeton” in Dutch, is made by mixing cement, water and pumice granules in place of the conventional gravel or crushed stone aggregate found in standard concrete. The porous nature of pumice introduces millions of tiny air pockets into the finished mix, which is what gives the material both its low density and its insulating capacity.
A typical pumice concrete has a dry density of roughly 800 to 1,400 kilograms per cubic metre, compared with around 2,300 kilograms per cubic metre for normal-weight concrete. The thermal conductivity is considerably lower as well, often in the range of 0.20 to 0.55 W/mK, depending on the density and the proportion of pumice in the mix.
Applications
Pumice concrete blocks are widely used for interior partition walls and the inner leaf of cavity walls. Their light weight makes handling easier on site and reduces the load on foundations, which can lead to cost savings in the substructure. In flat-roof construction, pumice concrete is poured as a lightweight screed to create falls for rainwater drainage without adding excessive weight to the roof structure.
Pre-cast pumice concrete elements, such as lintels and wall panels, combine structural function with built-in insulation. Some manufacturers add additional air-entraining agents or expanded clay to the mix to further reduce density and improve performance.
Limitations
Because pumice concrete is less dense, its compressive strength is lower than that of conventional concrete. It is therefore generally unsuitable for heavily loaded structural members such as columns or foundation beams. The porous surface also absorbs moisture, so external faces should be rendered, painted or otherwise protected from prolonged water exposure.
Related terms
- Pumice
- Concrete
- Lightweight concrete
- Insulation
- Aggregate
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