Evaluation of fresh and mechanical properties and shrinkage of hydrophobic mortar containing microfiber for 3D printing technology

This study investigated the development of hydrophobic mortar tailored for three-dimensional (3D) printing applications by incorporating calcium stearate (CS) and polypropylene (PP) microfiber. CS was used as a partial hydraulic cement replacement at 10, 12.5, and 15% by binder weight, while 6-mm PP microfibers were added at 0.2 and 0.4% by volume. The water-to-binder (W/B) ratio was adjusted to achieve a flowability of 180–190 mm. The research evaluated the fresh properties, mechanical performance, shrinkage, and microstructural characteristics of the 3D-printed mortars. The results indicate that increasing the CS content delayed the setting time and reduced the compressive strength, whereas the addition of PP microfiber effectively enhanced the compressive strength. Notably, the use of 15% CS resulted in a significant 91% reduction in water sorptivity and a water contact angle of up to 142°, imparting hydrophobic and dust removal ability to the mortar surface. Plastic shrinkage was reduced by 53% with the inclusion of CS, and a further reduction was observed with the inclusion of PP microfiber. The combination of 15% CS and 0.2% PP microfiber achieved the greatest suitability for 3D printing applications, improving both printability and structural stability. Microstructural analysis revealed that CS increased pore generation within the matrix. However, this did not adversely affect water absorption as the presence of CS on pore surfaces, confirmed by a high proportion of carbon detected by EDS analysis, led to the development of hydrophobic properties. • Calcium stearate and PP fibers were used to produce 3D printable hydrophobic mortar • 15% CS reduced water sorptivity by 91% and increased contact angle to 142° • PP fibers improved compressive strength and buildability of printed mortar • Plastic shrinkage was reduced by 53% using 15% CS and 0.2% PP microfiber • Optimized mix achieved clean surface, high stability, and good print quality