Effects of modifying agent on rheology and workability of alkali-activated slag paste for 3D extrusion forming

•A green none-cement paste used for 3D-printting has been designed with alkali-activated slag.•CMS improved the printable AAS paste with good rheology and buildability.•The rheology of AAS paste related to 3D-printting was studied.•The effect of CMS on the physical–chemical properties of AAS were investigated.•The tailoring mechanism using AAS materials for 3D-printting was discussed. Improper rheological performances of alkali-activated materials (AAM) may bring about sagging, segregating or bleeding problems in its extrusion application, and subsequently lead to the degradation of durability and mechanical strength. Unfortunately, most Ordinary Portland Cement (OPC) based rheology modifying agents are ineffective for AAM system. In this study, sodium carboxymethyl starch (CMS) is chosen as a feasible viscosity modifying agent for alkali-activated slag (AAS). To in-depth explore the modifying mechanism of CMS, the evolution of rheological parameters including viscosity, yield stress and thixotropy were evaluated and correlated with the structural evaluation and reaction kinetics of AAS. It was found that CMS strongly enhanced the plastic viscosity, yield stress, thixotropy and recoverability of fresh AAS, imparting stable shear thinning behavior with essential properties for 3D extrusion forming requirements. CMS could hydrolyze into intertwined gel, which filled between the AAS particles to strengthen the solid–liquid cohesion. CMS possessed retarding effect, the maximum reaction heat flow decreased from 0.068 to 0.049 μV/mg. Results indicate that CMS has great sense to effectively govern the rheology of AAM, and is expected to contribute towards offering a workability improvement modifying agent for AAM for 3D extrusion forming.