Disadvantages of Lightweight Concrete Blocks

Mix

• The aggregate in lightweight concrete absorbs some of the water that is added, but the amount it will absorb is difficult to determine in advance. Builders often pre-wet the aggregate to help reduce the extent of this problem. Nonetheless, this absorption can reduce the water content and make it more difficult to correctly determine the amount of each ingredient needed. Pre-wetting may also not be possible in cold weather, especially if temperature-controlled storage facilities are not available.

Curing

• Lightweight concrete has a higher total moisture content, so it tends to dry more slowly than normal concrete. This means builders must wait longer before they apply the floor covering material. Even once the concrete is dry, finishing it can be challenging, because if particles are drawn out of or removed from the surface, the resulting low-surface density may compromise resistance to frost and de-icing agents.

Strength

• The gravel particles in the aggregate for normal-weight concrete are stronger than the particles found in lightweight concrete. When a crack forms in the concrete, the particles at the tip of the crack may break also, allowing the crack to extend deeper into the block. The particles in normal-weight concrete, by contrast, are better at stopping cracks. Consequently, lightweight concrete is more fragile than the normal-weight equivalent and more likely to break into fragments.

Considerations

• These disadvantages are not the only features to bear in mind when considering lightweight concrete, however. Although lightweight is more fragile than normal weight, lightweight concrete still has high compressive strength, and its chief advantage is the way it combines the durability of concrete with a lower weight-to-volume ratio. Whether lightweight concrete is the most appropriate choice depends on the application -- the amount of load that structural elements can bear, the strength and durability required and the stresses to which the concrete will be exposed.