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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Nomenclature 3DP

3D printing CBM Cement based materials CPT Cone-penetration test D ap Apparent density F c Compressive strength F f1

Flexural strength at first crack

Flexural strength remaining after first crack

F f2

FTT

Flow table test

Capillary water absorption index Open porosity (accessible to water) Coefficient of determination

i

P op R 2 SF VF w/c

Sisal fiber

Volumetric fraction Water to cement ratio

1. introduction 3D printing (3DP) with cement-based materials (CBM) technology is a hot topic in the construction field due to its advantages as faster cast-in place, digitalization, material efficiency and architectural design autonomy, as reported by Flatt et al. (2022). Nevertheless, this technology still presents some issues related to reinforcing and sustainability of material compositions, as described by Flatt et al. (2022) and Li et al. (2024). CBM requires to control rheological parameters to obtain proper printable capacity and vertical constructability. Shear yield stress and cohesion have to be initially tailored to control printability. Then, structural build up over time have to grow to avoid a plastic collapse of the printing piece, as explained by Varela et al. (2023a), Roussel (2018) and Wolf et al. (2019). The use of fibers in 3DP mortars can address these issues, as proposed by Li et al. (2024) and Varela et al. (2023b). Particularly, vegetal fibers could be a good opportunity to take advantage of their reinforcing capacity and also to improve mortar sustainability due to its natural and renewable origin, according to Fidelis et al. (2013), Varela et al. (2023b) and Bohuchval et al. (2020). The irregular cross-section, high flexibility, high strength, and water adsorption capacity of Sisal fiber (SF), pointed out by Toledo Filho et al. (2009), Silva et al. (2008), Ren et al. (2022) and Castoldi et al. (2024), makes this natural fiber a good option for printable mortar reinforcement. All these properties could help to improve rheology and hardened properties of material. 3DP process, which it is totally different to conventional concrete production, also creates differences in material hardened properties, as described by Wolfs et al. (2019). Extrusion casting process causes a particle squeezing which can induce changes in physical and mechanical properties, as reported by Liu at al. (2023); Puentes et al. (2015). Besides, layered vertical structure and layers ’ orientation can modify hardened behavior of 3DP elements, reducing bearing capacity as noted by Wolfs et al. (2019) and Van Overmier et al. (2023). On the other hand, extrusion can also produce fibers alignment, affecting hardened properties as flexural strength, described by Hamback (2016). The aim of this study was to assess fresh and hardened properties of 3DP mortars reinforced with sisal fibers, considering their use for architectural applications. Sisal fiber was introduced in three volume dosages (0.5, 1 and 1.5 %) and two different length sizes (13 and 6.5 mm). An evaluation of rheology, printability and hardened properties throughout several experimental methods was carried out to get a better understanding of sisal fibers behavior in a 3DP mortar. 2. Materials and methods Figure 1 summarizes the design criteria used for the mortar compositions used in this study. A reference mixture (M0) contained CPII-F40 cement (similar to CEM II/A-L European cement type), natural sand (0-0.6mm), with a