Cellular concrete properties and the effect of synthetic and protein foaming agents

• Thirteen mix designs of cellular concrete (6–35% air) were prepared and tested.
• The type of foam used in cellular concrete influences sorptivity coefficient.
• Protein foam resulted in smaller isolated spherical air bubbles compared to air voids produced with synthetic foam.
• Concrete thermal conductivity was less sensitive to change in air content produced by synthetic foam compared to protein foam.

Cellular concrete consists of cement, water, aggregate and air voids. Cellular concrete can have between 10% and 70% air, which results in a material that is lightweight but may compromise the compressive strength and durability properties. Although it has been shown in the literature that less connected air voids yield a lower reduction in compressive strength, few studies have reported a detailed characterization of the microstructure of cellular concrete. It is critical to understand the impact of the microstructure and its implications on the development of strength, elastic modulus and transport properties in order to fully benefit from the lightweight properties, and this is the focus of this paper. Thirteen batches of cellular concrete were designed, prepared and tested. The air content varied, ranging from 6% to 35%. Three different foaming agents were used, one of which was protein-based and the other two were synthetic. Fresh properties such as slump, plastic air content and plastic density were measure for each batch of concrete as well as other properties, including hardened density, compressive strength, static elastic modulus, sorptivity, hardened air void distribution and thermal resistance. Key outcomes revealed that cellular concrete has good potential to be used for lightweight structural applications owing to its evolution of mechanical properties, transport properties and thermal resistance, but it is very sensitive to the type of foaming agent that is used. Outcomes showed that the foaming agent type had a noticeable effect on the thermal resistance and sorptivity coefficient but less of an effect on the mechanical properties. This is significant because the type of foaming agent used will directly influence the applications for which cellular concrete can be used. For example, cellular concrete designed with foaming agent B, which yields the greatest capillary pore volume is least suited for outdoor applications where the concrete may be exposed to moisture and or ions.