Efeito de fibras de sisal em compósitos cimentícios impressos em 3D submetidos a elevadas temperaturas

Abstract

When exposed to high temperatures, 3D-printed cementitious composites (3DP-CC) often exhibit delamination and poor interlayer bonding. This study aims to develop a 3D-printable cementitious composite reinforced with sisal fibers (3DP-SFCC) and to experimentally evaluate the impact of elevated temperatures on the mechanical, physical, and microstructural behavior of both printed and cast specimens. The 3DP-SFCC mixtures were developed with appropriate buildability for extrusion-based printing systems, incorporating sisal fibers of 6 mm and 12 mm in length at volumetric contents of 0,5% and 1,0%. The mixes also included limestone filler and metakaolin. Extrudability, rheological properties, and green strength were evaluated, and physical, mechanical, and microstructural properties were assessed before and after exposure to 200, 400, 600, and 800 °C. The heat propagation through the printed composites was evaluated using thermocouples installed at eight different points of blocks heated to 400 and 600 °C. Incorporating sisal fibers improved green strength but reduced the mechanical performance of unheated 3DP-SFCC in the hardened state. However, at high temperatures, tests demonstrated that sisal fibers prevented interlayer adhesion loss up to 400 °C, while fiber-free mixtures showed a ~37% reduction in interlayer adhesion at the same temperature. Sisal fibers significantly reduced the losses in compressive strength with heating. Between room temperature and 600 °C, the compressive strength decreased by 34% in REF-C and by only 0.3% in SF05%12 in the Y direction. The damage caused by heating was mitigated, especially with the use of 12 mm fibers, and the impact of heating on the anisotropy induced by the 3D printing process was reduced, reinforcing that 3DP-SFCC exhibits improved performance in environments prone to elevated temperatures. The incorporation of sisal fibers altered the heat propagation through the printed composites, modifying the preferential heat transfer path from the interlayer region to the intralayer region, thereby reducing the thermal gradient across the material and minimizing its effects.