High-strength foamed concrete for structural applications: Influence of metakaolin, superplasticizer, maximum fine sand particle size, and dry density

Aiming to minimize cement usage and carbon emissions while reducing the weight of structural elements, this work presents preliminary findings from ongoing experimental campaigns focused on foamed concrete for structural applications. This study explores the influence of dry density, superplasticizer dosage, maximum fine sand particle size, and metakaolin on the slump and mechanical properties, including flexural strength, compressive strength, and elastic modulus of foamed concrete. In detail, this experimental study involved the preparation of 90 prismatic foamed concrete specimens with fixed target densities between 1350 and 1600 kg/m3. All specimens were cured in water for 28 days and subsequently tested according to relevant UNI EN standards. The results show that mixtures containing metakaolin and higher dosages of superplasticizer demonstrate excellent flowability, a crucial characteristic for this type of material in structural applications, effectively eliminating the need for vibration. Additionally, the presence of metakaolin, smaller maximum particle size of aggregate, and higher superplasticizer content can enhance the mechanical properties of foamed concrete by promoting a denser and improved microstructure characterized by smaller micro-air-pore sizes. These conclusions are consistent with the finding related to elastic modulus. Specifically, the maximum compressive strength of the foamed concrete containing metakaolin at a target dry density of 1600 kg/m3 is approximately 58 MPa, with flexural strength exceeding 8 MPa and an elastic modulus around 20 GPa. The results are promising, in particular the compressive strength is found to be higher than that typical of lightweight aggregate concretes of the same density and is comparable to that of a conventional concrete with strength class C40/50. Additionally, these results underscore the material's strong potential for structural applications. The combination of favorable mechanical properties and reduced density can significantly enhance sustainability in the construction sector by lowering structural dead loads.