Search

Micro-silica fume (MSF)-modified self-consolidating concrete (MSC) is generally employed to achieve good mechanical properties resulting from pore refinement. Nevertheless, the relationship between the pore fractal dimension (PFD) and MSC's fresh and hardened properties are unclear. Herein, both solid waste MSF and high-purity MSF were employed to produce MSC with various weight fractions. The PFD of MSC was calculated from low-field nuclear magnetic resonance test results. With the increase in both kinds of MSF content, all the values of compressive, splitting tensile strength, and drying shrinkage achieved a peak, with the proportion of MSF substituted cement reaching 1/3. But at this point, fresh MSC's flowability, air content, and total porosity were all at the bottom. The porosity and air content displayed a negative linear correlation with micro-PFD, meso-PFD, and macro-PFD while drying shrinkage displayed a positive linear correlation with micro-PFD. Multiple linear formulas were also developed to predict compressive and splitting tensile strength based on PFD at various scales. The properties of concrete are enhanced by both solid waste and high-purity microsilica fume (MSF), albeit with different effects. High-purity MSF refines the microstructure more effectively owing to its increased silica content and reactivity, thereby reducing porosity and improving mechanical properties, such as compressive and tensile strength. Although it requires a greater energy input and incurs higher production costs, it also confers superior long-term durability. Conversely, solid-waste MSF exhibits slightly higher porosity and less significant strength improvement owing to its reduced reactivity resulting from impurities. Nevertheless, it substantially enhances concrete performance while offering economic and environmental benefits through the recycling of industrial waste, thereby presenting a sustainable construction option.These findings provide critical insights for practitioners in the construction industry, enabling them to optimize the use of micro silica fume in concrete mixtures to enhance mechanical performance while managing flowability and porosity, ultimately leading to more efficient and sustainable construction practices. Self-consolidating concrete mixtures for complex structures must balance strength, shrinkage control, and flowability for long-term durability and low maintenance costs. The results can be used to improve their design.

Past experimental results have shown that the use of nozzle trowels can enhance the interlayer strength of 3D printed cement paste. In this study, the design is further optimized by introducing concave and convex shapes onto the nozzle trowel design. A technique for accurate simulation of the interlayer stresses with the influence of nozzle trowels is established, and it is found that the nozzle trowels double the maximum shear stress and increase the maximum pressure by about 114 %. Moreover, the concave and convex nozzle trowels with removal of interlayer notch further increase the interlayer strength by 35 %. A theoretical model is also proposed to predict the interface geometry and then validated by the experimental observations on the concave and convex trowels. These findings not only result in 3D printed cement paste with much higher interlayer strength, but also emphasize the importance of nozzle designing with optimal interlayer stresses and interface geometries in the application of 3D concrete printing (3DCP).