STRATEGIES TO IMPROVE SHRINKAGE RESISTANCE OF CEMENT-BASED MATERIALS FOR EXTRUSION-BASED 3D PRINTING
"The main objective of this study is to develop new generation of shrinkage-resistant 3D printable mortar mixtures. To this end, the research work was carried out to: i) identify key material and processing parameters that affect printability; ii) investigate the influence of water-to-cement ratio, superplasticizer dosage, and welan gum content on mortar printability; iii) propose a “printability window” where rheological properties and desorptivity can secure successful printing; iv) investigate effect of shrinkage mitigation materials (expansive agent (EA), pre-saturated lightweight sand (LWS), superabsorbent polymers (SAP), and shrinkage reducing admixture) on printability and shrinkage performance of mortar; and v) evaluate the effect of EA, LWS, steel and synthetic fibers on chloride-induced corrosion and transport properties of concrete. The research work indicated that: i) in addition to rheology and printing parameters, desorptivity (the rate of fluid filtration during extrusion) can also present a significant influence on printability; ii) for extrusion speed of 2.5 mm/s, extruder capacity of 135 N, and nozzle size of 9 mm, the printability window encompasses yield stress of 100-470 Pa, plastic viscosity of 10-60 Pa.s, and desorptivity values < 3x10 -3 s-0.5; iii) the use of welan gum can enable development of print materials that are most suitable for 3D printing. The addition of welan gum (up to 0.6%) significantly reduced the desorptivity, which enabled extrusion of print material with yield stress > 400 Pa and contributed to lower mass loss due to plastic shrinkage; and iv) the use of SAP is effective at reducing desorptivity and such polymers with slower absorption and desorption kinetics are more effective to ensure shape stability and efficient internal curing of print materials"--Abstract, p. iv
3D printing, Extrudability, Fluid filtration, Printability window, Rheology, Shrinkage, Civil and Environmental Engineering, Civil Engineering, Engineering
Missouri University of Science and Technology
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