Synergistic effect of fly ash and polyvinyl alcohol fibers in improving stability, rheology, and mechanical properties of 3D printable foam concrete

Foam concrete, a lightweight cellular cementitious mixture has gained significant attention globally due to its multifunctional properties. Employing such multifunctional material to additive manufacturing helps in reducing the material wastage, time for construction and cost of production. However, there are various challenges encountered in employing such material with conflicting attributes in 3D concrete printing technology. Therefore, it is important to address these challenging requirements (i.e. stability along with printability). In this study, fly ash and polyvinyl alcohol fibers are employed as sand replacement and reinforcing material respectively to improve stability, rheology and mechanical characteristics of 3D printable foam concrete. Initially, printability of the mixture is achieved through moderation of slump and slump flow. Further, these mixtures are studied for fresh density, rheological properties and buildability. Essential hardened properties like oven dry density, compressive strength, flexural strength, bond strength, and thermal conductivity are studied. Later, microstructural studies are conducted to analyze the variations in hardened properties. Results show that replacement of sand with fly ash has significant influence (more than 100%) in improving the printability (for both 1300 and 1000 kg/m3 densities), however it has negative impact on the stability of foam. Stability of foam concrete could be counteracted by adding the fibers which forms networks with the foam bubbles and reduced the breakage and coalescence. Nonetheless, addition of fly ash increased the mechanical performance and thermal conductivity, but the dry density is increased due to bubble breakage. Addition of fibers reduced dry density with significant reduction in thermal conductivity and minimal compromise in mechanical performance.