Effectiveness of large-volume Class-F fly ash as a replacement for sand in foam concrete using an environment-friendly foaming agent

The scarcity of fine aggregate from natural resources has caused researchers to search for alternative materials to replace conventional river sand and manufactured sand. The disposal of fly ash is one of the challenges thermal power plants face, even though a part has been utilized in cement production. The current study is undertaken to address the issues mentioned above. The novelty of this study is the use of i) high-volume fly ash (Class F) as a replacement for fine sand up to 100% and ii) foam generated using a natural and environment-friendly plant species in foam concrete for design densities ranging from 900 kg/m³ to 1500 kg/m³. The foam was generated using soapnut, a plant-based foaming agent. The paper reports the effectiveness of large-volume fly ash as a replacement for sand in terms of workability, dry density, compressive strength, pore-size distribution, water absorption, sorptivity, and drying shrinkage of foam concrete. The inclusion of fly ash in foam concrete prevented the coalescence of bubbles by providing a protective layer around bubbles and enhanced the concrete properties. Using fly ash as a sand replacement at a constant foam volume enhanced the compressive strength through pore-refinement, which was confirmed through microscopic studies. An increase in the fly-ash replacement leads to an increase in sorptivity and shrinkage due to the rise in paste volume, consequent to the reduction in the requirement of foam volume.