PSI - Issue 64

H. Varela et al. / Procedia Structural Integrity 64 (2024) 1427–1434 Varela et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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For printability evaluation, trials were done using a manual extrusion device and a robotic 3D printer. Prismatic 4x4x16 cm 3 specimens were manufactured both using conventional steel molds and 3 layers 3DP specimens produced with the manual extruder for hardened evaluation. Several physical parameters were evaluated, as apparent density, open porosity (accessible to water) (Fig. 2c-ii). Apparent density ( D ap ) and open porosity ( P op ), accessible to water, were calculated using a hydrostatic balance and 4x4x4 cm 3 3DP and conventional specimens, measuring dry, saturated and submerged weight. Capillary water absorption index ( i ) was assessed placing the same samples dehydrated in contact with water. Water weight absorbed by mortars was measured over time in all samples, according to Liu et al. (2023) and Puentes et al. (2015). Besides, compressive and flexural strength tests were carried out at 14 days on 4x4x16 cm 3 (Fig. 2c-i). 3. Results and discussion Figure 3 plots the experimental results of the rheological characterization obtained with FTT and CPT from 10 to 90 minutes on stirred samples and the correlation between and CPT penetration depth. SF produced a reduction of of FTT final diameter, showing the reference mortar (M0) the highest initial value (277 mm) and the highest SF volume fraction (M3) the lowest diameter (245 mm). However, FTT final diameter over time showed a behavior similar to samples with 13mm length fibers (M1, M2, and M3) progressively decreasing up to 90 minutes. On the other hand, M4 (SF 6.5 mm length) presented initially and over time a lower reduction of final diameter, even lower than M0 at 90 minutes (232 and 222 mm, respectively), according to previous studies by Bohuchval et al. (2020) and Varela et al. (2023b).

Fig. 3. Rheological evaluation results: a) final diameter over time of FTT; b) penetration over time of CPT; c) correlation between both tests.

Regarding CPT initial penetration depth, M3 showed the highest value (38mm), which corresponded to the lowest shear yield stress. Mortars M1, M2 and M3 followed a similar behavior among them decreasing over time. In this case, M4 followed the same evolution as the reference mortar (M0). When FTT final diameter and CPT depth penetration were compared, a good correlation with a statistical coefficient of determination (R 2 ) value of 0.85 was obtained, as pointed out in Varela et al. (2023b). Figure 4 summarizes the printability evaluation carried out with a manual extrusion system and a robotic 3DP system. Figure 4a shows the manual extrusion system and the production of a 4x4x16 cm 3 3DP specimen. All mixtures were properly extruded with the manual system and prismatic specimens were obtained for all designed mortars, although samples with higher fibers VF required larger force to be extruded, as explained by Varela et al. (2023b).