Foam Concrete and Its Foam Making Agent

Foam concrete is a new form of construction material that combines sand, aggregates and cement with foam making agent to produce lightweight, self-compacting and durable concrete. It is poured into a mould or a form and can be cut to different sizes for use in structural elements such as beams, slabs and walls. Foam concrete can be used in place of traditional forms or mortar and is much lighter than conventional concrete because of its thixotropic properties (ability to flow like a milkshake) that are derived from the interaction between the foam bubbles and the sand and aggregates in the mixture.

The workability of foam concrete depends on the water-cement ratio and type of aggregates. The higher the water-cement ratio, the more fluid the concrete is and the easier it is to pour. However, when the w/c ratio is above the optimal limit, foam concrete with thin-walled and irregular pores develops. This affects the compressive strength because the pores are subjected to stress concentrations [5,15]. Using supplementary binder components improves the workability. These include fly ash, geocement and alkaline Portland cement. Fly ash is the most widely used as it reduces the amount of cement used and its hydration temperature, which leads to an increase in the workability. In addition, the spherical shape of fly ash increases the flowability of the concrete and its hydration reaction.

The use of RCA as a replacement for sand enhances the workability and mechanical properties of the foam concrete, and also increases porosity due to its empty texture. However, it has a negative effect on drying shrinkage and water absorption.