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This study investigates the use of fly ash, limestone calcined clay (LC2), and RESIN8 (from recycled plastics) fine aggregate for sustainable 3D concrete printing. Four different printable mixes were formulated and tested for their fresh, rheological, and hardened mechanical properties and evaluated for extrudability and buildability performance. They are the control (C), which is a fly ash-cement-based mix, LC2-cement-based mix (LC), and two mixes with RESIN8 replacing the sand by 10% vol., yielding CR (control + 10% RESIN8) and LCR (LC2 + 10 RESIN8). The findings from this study show that both LC2 and RESIN8 mix improved the fresh properties for printability – reduced slump, increased yield stress and its evolution, shape retention, and buildability. The LC2 has dual benefits of improving the pumpability and buildability, which are opposing printable materials' requirements. Furthermore, the use of LC2 in 3DPC causes the fresh material to be susceptible to increased deformation under sustained load, which can be improved with the addition of RESIN8. Incorporating 10% RESIN8 into C- and LC-printed concrete systems reduced the workability by 3.8% (CR) and 1.9% (LCR) and enhanced buildability performance from 46 (C) to 59 (CR) and 74 (LC) to 90 (LCR) number of layers. Contrary to LC2, which improves the hardened properties and interlayer bond strength in flexure, the use of RESIN8 causes strength reduction and decreased void topology (28% for LCR) and significantly increased porosity by 210% and 259% for CR and LCR, respectively.
Babafemi et al. (Sat,) studied this question.