Mechanical anisotropy evolution of 3D-printed alkali-activated materials with different GGBFS/FA combinations

The mechanical anisotropy of 3D-printing concrete is a crucial factor limiting the application of this technology. This study focuses on the evolutions of mechanical anisotropy and interlayer pore structure in the 3D-printed alkali-activated materials (3DPAAMs) with different precursors combinations of grounded granulated blast-furnace slag (GGBFS) and fly ash (FA), aiming to elucidate the relationship of mechanical anisotropy evolution and precursor selections. The pores generated by the printing process were quantitatively characterized with X-ray computed tomography (X-CT) tests using image processing methods. Results show that the mechanical anisotropy coefficient (I-Mechanical) of 3DPAAMs mitigates with the curing age since the formed reaction products fill the pores generated by the printing process. With the curing age extension from 3 to 28 days, the I-Mechanical of GGBFS-based 3DPAAMs decreased 51.1%, 60.9%, and 71.1% for compressive, flexural and split tensile strengths, respectively. Over-high FA incorporation (50 and 75%) yields lower mechanical strengths and aggravated anisotropy. Compared with GGBFS-based 3DPAAMs, the addition of 75% FA increases the I-Mechanical at 28 days by 274%, 236% and 274% for compressive, flexural and split tensile strengths, respectively. The low activation reactivity of FA and the higher thixotropy of FA-incorporated mixtures coarsen the interlayer pore structure, contributing to a higher mechanical anisotropy.

Automated summary

This study investigates the evolutions of mechanical anisotropy and interlayer pore structure in 3D-printed alkali-activated materials with different precursor combinations. Results show that the mechanical anisotropy decreases with curing age and over-high fly ash incorporation leads to lower mechanical strengths and aggravated anisotropy.