Foaming Agents Used in Concrete

Foaming agents are chemical additives that produce a foam in the concrete mix which creates a light weight cellular structure. Foam concrete is typically used in geotechnical applications due to its low density and good shear resistance, limiting the risk of damage to soils and other sub-grade materials [2].

The type of foaming agent is important as it determines the characteristics of the foamed product such as stability, water absorption and frost resistance. Several foaming agents are available, including a range of straight synthetic (SS) and protein-based products. It is recommended that any chosen foaming agent be laboratory tested with local materials to confirm expected compatibility.

The pore size distribution and porosity of the foam are also important in foam concrete. The pore sizes are influenced by the foaming agent and aggregates. A broader distribution of smaller pores enhances the strength and reduces drying shrinkage. The pore size is determined by the foaming agent, so the use of a more aggressive foaming agent increases the pore size and improves the strength.

Using different types of aggregates is also important in foam concrete. The aggregate type influences the overall pore size and the strength of the material. Gencel et al. showed that RCA increased the pore size and reduced the compressive strength of foamed concrete. Pasupathy et al. found that RCA reduces the strength of foamed concrete, probably because the aggregate particles are less strong than sand.

Adding silica fume to the foam concrete increases the dry density and compressive strength, as well as the thermal conductivity. In addition, it is reported that granulated blast furnace slag is useful for reducing the hydration heat and temperature development in foam concrete.