Fiber-reinforced mortar with 100% recycled fine aggregates: A cleaner perspective on 3D printing

The huge labour-consumption, construction and demolition (C&D) waste pollution, and shortage of river sand have become increasingly serious problems facing the construction industry. Therefore, the possibility of fully replacing natural fine aggregates (NFA) with recycled fine aggregates (RFA) for fiber-reinforced 3D mortar printing (3DMP) was carefully evaluated by Digital Image Correlation (DIC) technique, mechanical testing, and microscopic analysis in this study. The results show that the 100% replacement of RFA had very limited impact on the failure pattern of the 3D printed (3DP) specimen, while the addition of 1% polyethylene (PE) fibers would change the failure pattern of specimens from brittle to ductile. This study also defines the parameter of anisotropic degree to reflect the anisotropy. It is found that the anisotropic degree of 3DP specimens was different under various loading conditions and obviously affected by both RFA and fibers. The microscopic analysis indicated that the effect of RFA on the 3DP specimens was mainly due to the porous structure and the existence of initial micro-cracks, while the effect of fibers was mainly due to the interfacial bond between PE fibers and matrix. This study also found that after reinforcing with appropriate fibers, the 3DP mortar mixed with 100% RFA has higher mechanical properties and better deformation ability than the fiber-free mortar with 100% NFA. It is believed that the 100% replacement of RFA is applicable in 3DMP, which will bring significant benefits to the cleaner production and sustainable development of the construction industry.