lightweight slabs are a versatile, environmentally friendly alternative to conventional concrete. They are used in residential, commercial and infrastructure projects that need a lower weight or increased thermal insulation.

The main difference between lightweight and normal weight concrete is the water-cementitious material ratio (WCR). Concrete with a WCR of less than about 0.408 consumes more water than it can use, leading to dry concrete, shrinkage cracks, and failure to gain strength.

As an alternative, a mix can be designed with prewetted lightweight aggregate that replaces some of the fine or intermediate aggregate. This process is called internal curing and it reduces the need for additional water in the mix.

In addition to internal curing, lightweight concrete can be cured externally by placing the slab on an enclosed, climate controlled space, or in an ambient area with less moisture. This enables a lighter concrete slab to be constructed and cured in a shorter time than if it were constructed in an unclimated environment.

Other lightweight options include insulated slabs, and post-tensioned slabs that incorporate steel cables/metal tendons. These are more durable and offer greater strength than traditional concrete.

Insulated slabs are a popular choice for buildings with hot or cold floors, and may be particularly suitable for sites with high temperatures or cold soil conditions. They also reduce the amount of heat lost through the concrete, making them energy efficient.

The slab underside should be insulated, either by expanding foam boxes or ground-coupled alternatives, such as systems that use recycled tyres or detergent bottles filled with water, grouped together as void formers. This reduces the overall weight of the slab and can be particularly suitable for taller structures.