PSI - Issue 78

Antonella D’Alessandro et al. / Procedia Structural Integrity 78 (2026) 1887–1894

1888

of sustainable material formulations (Sanjayan & Nematollahi (2019); Bhattacherjee et al. (2021); Song & Li (2021); Yu et al. (2021)). Despite these advantages, 3D-printed cementitious (3DPC) structures present specific challenges, particularly related to the anisotropic nature of the material, which leads to variability in mechanical properties (Gebhard et al. (2021); Zhao et al. (2022)). This anisotropy can compromise interlayer bonding, material homogeneity, and influence the structural performance and durability of printed elements (Wolfs et al. (2019); Nodehi et al. (2022)). The incorporation of conductive fillers into cement-based materials can impart piezoresistive behavior to the composite (Laflamme et al. (2023)), enabling its use as a smart material for strain sensing applications. These fillers include a wide range of conductive materials, such as carbon nanotubes (D’Alessandro et al. (2016); Wang & Pang (2020); Yahya et al. (2020)), carbon fibers (Ding et al. (2023); Hao et al. (2023)), graphene (Guo et al. (2021); Sevim, Jiang, and Ozbulut (2022)), and graphite (Papanikolaou et al. (2020)). While this field is already well-developed, its integration with 3DPC has recently emerged as a promising research direction (Sousa et al. (2024)). Such integration enables the design of structural elements with embedded sensing capabilities, facilitating real-time monitoring and contributing to the development of intelligent infrastructure systems (Liu et al. (2024); K.C. et al. (2025)) . Despite recent advances in this field, several research gaps remain to be addressed, particularly concerning the influence of printing path strategies on damage detection in 3DPC elements. This study aims to investigate the effect of different printing patterns on the damage-sensing capabilities of 3D-printed cement-based beams doped with carbon fibers. The experimental program involves the comparison between two cement pastes with carbon microfibers, printed with distinct paths, as well as the evaluation of different performances of a mortar and a cement paste, both with carbon microfibers and produced using the same printing pattern. These comparisons are intended to assess both the impact of printing strategy and the influence of material composition on damage-sensing performance. 1.1. Sample fabrication Two different cement-based mixes were produced: a cement paste and a mortar, both incorporating 0.4 wt.% of chopped carbon microfibers (CCMF) SIGRAFIL® C M150-4.0/240-UN. The cement used in both mixtures was Portland CEM II/B-M (P-LL) 42.5R. The paste consisted of cement, water, and fibers, with a water-to-cement (w/c) ratio of 0.39. The mortar included fine siliceous river sand with a maximum particle size of 1 mm, combined with cement and fibers, using a 1:1 sand-to-cement ratio and a w/c ratio of 0.53. For the mortar mix, cement, sand and CCMF were manually mixed until a uniform dry consistency was achieved. In the case of the paste, only cement and CCMF were combined during this stage. Water was then incorporated in two steps: first, 80% of the total water volume was added, followed by the remaining 20%, with continuous manual mixing until homogenization (Figure 1). Samples were printed using a WASP 40100 LDM printer equipped with a manually fed extruder. Printing parameters were consistent for both paste and mortar samples, except for print speed. An 8 mm nozzle was used, with a 6 mm standoff distance (the vertical distance between the nozzle tip and the printing bed) and 100% infill. The paste was printed at a speed of 12 mm/s, while the mortar required a higher speed of 16 mm/s. All samples had printed dimensions of 160 × 40 × 40 mm 3 (Figure 2). The paste mixes were printed in two directions: longitudinal (along the long axis of the specimen) and transverse (parallel to the short side), with one sample printed for each orientation, while the mortar was printed only in the longitudinal direction, with one sample produced. Stainless steel nets were used as electrodes and positioned at the ends of each printed specimen, as shown in Figure 3. Despite the predefined dimensions, the final printed samples exhibited dimensional deviations. The mortar printed in the longitudinal direction resulted in dimensions of 17.5 × 7.0 × 4.4 cm³, whereas the paste printed in the same direction presented dimensions of 15.5 × 4.5 × 4.5 cm³. The paste printed in the transversal direction maintained dimensions close to the intended design (15.5 × 4.5 × 4.5 cm³).