Foam concrete may be considered a two-phase system consisting of an aqueous foam and a base mix (paste or mortar). Foaming agents can be sourced from natural surfactants, obtained directly from plants, animals, and microbes through separation procedures like extraction, precipitation, and distillation, or synthetic surfactants, industrially produced using chemicals via various reactions. Traditional foaming agents used in foam concrete production are synthetic and petroleum-based, which can harm the environment. A range of proprietary foaming agents are available in the market, primarily derived from petrochemical sources. Further, saponin foaming agents derived from natural sources lack compatibility with cement due to sugar chains. This necessitates the identification of alternate foaming agents that are more sustainable than synthetic foaming agents and more compatible with other concrete constituents than natural saponin foaming agents.
Like many other agricultural sectors, the cashew industry generates significant waste throughout its production process, posing environmental and economic challenges. One of the major by-products is the Cashew Nut Shell Liquid (CNSL), which is used in several applications like the production of resins, paints, varnishes, and as a component in rocket propellants. However, despite these applications, a substantial amount of CNSL remains unutilized. CNSL contains various phenolic compounds, largely anacardic acid(s), cardol, and cardanol. The objectives of the present work are (i) to obtain an aqueous foam comprising the mixture of unsaturated anacardic acid(s) derived from cashew industry waste by identifying suitable alkali reagents, (ii) to enhance the foam stability using admixtures, viz., xanthan gum, guar gum, and carboxymethyl cellulose, and (iii) to investigate the feasibility of stabilized anacardate foam in producing foam concrete with OPC and geopolymer binders.