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• The fresh and hardened properties of one-part alkali-activated slag (AAS) with rice straw ash (RSA) are investigated. • The Si provided by RSA reduces the early-age reaction rate and contributes to the gel growth. • The pore structure of one-part AAS becomes coarser upon the addition of RSA. • The autogenous and drying shrinkage of one-part AAS are mitigated by RSA mainly due to the internal curing effect of RSA. In this paper, fresh (setting and rheology) and hardened properties (strength and shrinkage) of one-part alkali-activated slag (AAS) with and without rice straw ash (RSA) are comprehensively investigated. The reaction kinetics and microstructure of the mixtures are characterized by a series of experimental techniques. The results reveal that RSA plays dual roles in AAS, as a precursor (though not fully reactive) and an internal curing agent. The reactive K and Si in RSA participate in the formation of C-(A)-S-H gel and the alkaline groups dissolved from the ash facilitate the hydrolysis of slag. Besides, the porous RSA absorbs liquid in the first day and releases it afterwards, thus providing internal curing to the matrix. The consistency index of the paste becomes higher with the incorporation of RSA. Both autogenous and drying shrinkage of AAS, which are considered as two problematic issues for this material, are mitigated by RSA. [ABSTRACT FROM AUTHOR]

• The time varying characteristics of rheological properties was investigated. • High fluidity-retaining has a positive effect on the interlayer bonding. • Extending the time interval has a negative effect on the interlayer bonding. • The plane porosity of interlayer zone is related to interlayer bonding strength. Proposed special requirements exist for the rheological properties and time-varying characteristics of 3D printing cementitious materials (3DPC). In this study, high-dispersion polycarboxylate superplasticizer (HD-PC) and fluidity-retaining polycarboxylate superplasticizer (FR-PC) were used to control the rheological behaviors of 3DPC. The correlation of the time interval, the time varying characteristics of the rheological properties and the interlayer bonding strength were investigated. The results indicated that FR-PC improved the fluidity-retention ability and thixotropy of the fresh pastes. The thixotropic hysteresis loop area and reflocculation rate (R thix) of FR-PC were 101.9% and 80.4% higher than those of HD-PC, respectively. Furthermore, the FR-PC polymer has a positive effect on the interlayer bonding and may reduce the negative effect caused by extending the time interval. During the time interval of 20 s to 30 min, the interlayer bonding strength with FR-PC decreases by 14.1%, while that with HD-PC decreases by 50.0%. [ABSTRACT FROM AUTHOR]

• Flow behaviors of cementitious materials through nozzles with different geometric parameters was investigated. • Increasing of the area ratio of outlet to inlet and direction of material deposition will reduces the extrusion pressure. • Changing the direction of material deposition is a critical means for controlling the printing pressure. • Increasing of nozzle aspect ratio and decreasing of direction of material deposition will reduces the deformation rate of deposited filament. Nozzle geometric parameters are important to control the flow and deformation behaviors of printed filament. Choosing the right nozzle geometric parameters before the printing process is critical and requires considerable attention. In this study, nozzles with various geometric characteristics were designed and fabricated. Experiment and computational fluid dynamics (CFD) simulation were used to investigate the flow and deformation behaviour of printing ink via these nozzles. The results indicated that increasing of the area ratio of outlet to inlet AR (A outlet / A intlet) and direction of material deposition θ will reduce the extrusion pressure. Changing the direction of material deposition θ is a critical means for controlling the printing pressure. Increasing of nozzle aspect ratio Ψ (W n / H n) and decreasing of direction of material deposition θ will reduces the deformation rate of deposited filament. This study may provide a theoretical guidance for the design and selection of nozzle before printing process. [ABSTRACT FROM AUTHOR]