The mechanical properties of 3D-printed metakaolin/fly ash-based geopolymer mortars containing multi-walled carbon nanotubes exposed to freeze-thaw

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Abstract This study examined the mechanical properties of 3D‐printed geopolymer mortars (GPMs) containing multi‐walled carbon nanotubes (MWCNTs) subjected to freeze–thaw (F‐T). The fly ash (FA) and metakaolin (MK) were used as binders in the 3D‐printed geopolymer composites (GPCs). MWCNT was used at 0%, 0.25%, 0.5%, and 0.75% rates in the mixtures. The rheological characteristics of the mixtures were ascertained through experiments conducted on viscosity, buildability, and flow. After this stage, samples with dimensions of 40 × 40 × 160 mm were manufactured using a 3D printer and cured for 28 days at a laboratory temperature of 20 ± 2°C. Then, 3D‐printed geopolymer (3DPG) samples were subjected to the F‐T in accordance with the TS EN 15177 standard. Finally, the weight loss (WL), compressive strength (CS), flexural strength (FS), and ultrasonic pulse velocity (UPV) of 3DPG specimens exposed to F‐T were determined. Additionally, scanning electron microscopy (SEM), x‐ray powder diffraction (XRD), and energy dispersive x‐ray spectroscopy (EDX) analyses were carried out on specimens. The results of this investigation showed that 3D‐printed GPM containing 0.25% MWCNT had the highest FS, UPV, and CS. Furthermore, this study demonstrated that the 3D‐printed GPM with 0.25% MWCNT has a strong resistance to F‐T with a CS retention rate of 95.86%.