Properties and microstructure of extrusion-based 3D printing mortar containing a highly flowable, rapid set grout

In this study, a highly flowable, rapid set crack repair grout powder (CRG) was used to facilitate mix design of 3D printing mortar. Various mortar mixtures with different amounts of CRG were evaluated for setting time, flowability, and printability. For the first time, pore/micro-structures of printed filaments and their bonds were examined in detail. The results have provided a better understanding of the anisotropic mechanical behavior of printed mortar. Plausible explanations have been made for the observations that printed samples displayed lower compressive but higher flexural strength than cast samples. It is demonstrated that CRG can be simply used as a raw material component to expedite the 3D printing concrete mix design process since finding the balance among various admixtures (e.g., water-reducing agent, thixotropic agent, accelerator, etc.) is not required.