PSI - Issue 78

Han Liu et al. / Procedia Structural Integrity 78 (2026) 1759–1766

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2.2. Fabrication Process

A standardized mixing protocol was used to prepare specimens and maintain consistent rheological properties. As illustrated in Figure 1, two types of Sikacrete composites including conductive Sikacrete composite and normal Sikacrete composite were produced. To fabricate the conductive Sikacrete composites, Sikacrete powder, G, MCMF, and CCMF were first dry-mixed using a spatula for two minutes to break up particle agglomerates. Subsequently, 50 wt% of the designed total mixing water was added, and the mixture was blended with a handheld electric mixer at 200 rpm for 2 minutes. The remaining 50 wt% of the water was then introduced to achieve a water-to-binder ratio (w / b) of 0.26, followed by an additional 3-minute mixing cycle at the same speed to produce a homogeneous and printable cementitious composite. The fabrication of the normal Sikacrete followed the same procedure, excluding the addition of any conductive fillers, and was prepared with a lower w / b ratio of 0.23 to account for the absence of conductive additives.

Fig. 1: Fabrication process of the conductive cementitious composites: (a) combination of cement, G, and CMF; (b) dry mechanical mixing of material; (c) adding water and following with standard mixing procedure; (d) feed-in composites mixture; and (e) mounting on pump and printing paste.

To investigate the percolation behavior of the conductive Sikacrete composites, a series of cube specimens were prepared using various mixture proportions, with three replicates fabricated for each formulation. Specifically, graphite (G) powder was introduced at an initial dosage of 1 wt% and incrementally doubled up to 16 wt%. Similarly, MCMF was incorporated starting at 0.03125 wt% and doubled in each subsequent mixture until reaching 0.25 wt%, with the same stepwise approach applied to CCMF. The water-to-binder (w / b) ratio was held constant at 0.40 across all mixtures. Specimen labels begin with a numeric prefix indicating the weight percentage (wt%) of conductive filler relative to the weight of Sikacrete powder. A hybrid composition consisting of 2 wt% G, 0.25 wt% MCMF, and 0.062 wt% CCMF, referred to as 2G250M62CCMF, was ultimately selected as the mix design for fabricating the conductive Sikacrete composite in this study. This selection was informed by the percolation behavior observed in the tests, as detailed in Section 4, as well as by practical considerations to ensure su ffi cient workability for layer-by-layer extrusion and adequate buildability to support the 3D printing process. An extrusion-based commercial 3D clay printer (3D Potter 7) was used for the 3DP process, and the overall setup is shown in Figure 1. The freshly mixed Sikacrete composite was manually loaded into the extruder tube in three consecutive pours, in which the first pour consisted of conductive Sikacrete composite, while the second and third pours contained the normal Sikacrete mix. A circular nozzle with a diameter of 8 mm was attached to the extruder, and the stand-o ff distance between the nozzle and the printing platform was set at approximately 4 mm. A hollow beam specimen featuring a diagonal reinforcement pattern and overall dimensions of l × w × h = 320 × 120 × 55mm 3 was designed and sliced in Cura into 15 layers, each with a layer height of 3.66 mm. The specimen was printed at an extrusion rate of 320 mm 3 / s and a printing speed (the movement speed of the printer platform) of 120mm / s. Six steel drop-in anchors were embedded as electrodes at equal intervals of 46 mm along the left side of the third layer. Additionally, three #2 reinforcement bars (diameter of 6.35 mm) were placed longitudinally in the