ABSTRACT
Three-dimensional (3D) printing with foam concrete, which is known for its distinct physical and mechanical properties, has not yet been purposefully investigated. The article at hand presents a methodological approach for the mixture design of 3D-printable foam concretes and a systematic investigation of the potential application of this type of material in digital construction. Three different foam concrete compositions with water-to-binder ratios between 0.33-0.36 and densities of 1100 to 1580 kg/m³ in the fresh state were produced with a prefoaming technique using a protein-based foaming agent. Based on the fresh-state tests, including 3D printing as such, an optimum composition was identified, and its compressive and flexural strengths were characterized. The printable foam concrete showed low thermal conductivity and relatively high compressive strengths of above 10 MPa; therefore, it fulfilled the requirements for building materials used for load-bearing wall elements in multi-story houses. Thus, it is suitable for 3D-printing applications, while fulfilling both load-carrying and insulating functions.
ABSTRACT
Surfaces of carbon fibre roving were modified by means of a low temperature plasma treatment to improve their bonding with mineral fines; the latter serving as an inorganic fibre coating for the improved mechanical performance of carbon reinforcement in concrete matrices. Variation of the plasma conditions, such as gas composition and treatment time, was accomplished to establish polar groups on the carbon fibres prior to contact with the suspension of mineral particles in water. Subsequently, the rovings were implemented in a fine concrete matrix and their pull-out performance was assessed. Every plasma treatment resulted in increased pull-out forces in comparison to the reference samples without plasma treatment, indicating a better bonding between the mineral coating material and the carbon fibres. Significant differences were found, depending on gas composition and treatment time. Microscopic investigations showed that the samples with the highest pull-out force exhibited carbon fibre surfaces with the largest areas of hydration products grown on them. Additionally, the coating material ingresses into the multifilament roving in these specimens, leading to better force transfer between individual carbon filaments and between the entire roving and surrounding matrix, thus explaining the superior mechanical performance of the specimens containing appropriately plasma-treated carbon roving.
