Properties and microstructure of a low-carbon clinker-free cementitious binder and its extrusion-based printing performance

Abstract

The extensive use of cement binders in the construction industry limits the progress of carbon emission reduction. A low-carbon clinker-free cementitious binder (CFCB) was developed by using wet grinding to activate granulated blast furnace slag (GGBS), combining fly ash (FA) spheres as rheology-modified material and calcium carbide slag (CS) together with sodium metasilicate (NS) powder as the compound activator. The effects of FA content and CS/NS ratio on the hydration, performances, and microstructure were systematically investigated. The printability and mechanical anisotropy of extrusion-based printed CFCB were also analyzed. The results show that lower fly ash content and CS/NS ratio positively influenced the yield stress and improved rheology and thixotropy within a certain range. The compressive strength of the CFCB mortar reaches a maximum of 46.6 MPa at 28 days. At the same time, the decrease in the CS/NS ratio is conducive to the development of the hydration process, generating a higher amount of hydration and forming a denser microstructure. The FA20-CS18 group shows suitable extrudability, buildability, and shape retention ability with a height loss of only 0.8 %. The existence of interlayer property differences causes the extrusion-based printed mortar to exhibit anisotropic mechanical properties, with the highest flexural and compressive strength in the Z-direction. The anisotropy coefficient was below 0.25 before 7 days.