Characterizing microstructural damage in cementitious composites reinforced with 3D-printed auxetic lattices using X-ray computed tomography

Cementitious materials are limited by its brittle nature, leading to the adoption of steel bars or fibers as reinforcement to improve ductility.With advances in additive manufacturing, 3Dprinted lattice structures have emerged as a promising alternative for reinforcing cementitious composites, enabling enhanced mechanical properties This study explores the incorporation of a three-dimensional lattice structure with negative Poisson's ratios (auxetic behavior) into cementitious composites.Uniaxial compression test showed that the densification energy could reach 170% times of reference cement mortar.Because of the lateral contraction tendency of auxetic lattices which would constrain the expansion of cementitious matrix, the peak strength for auxetic lattice reinforced cementitious composites was 1.4 times of their non-auxetic counterparts.To further disclose the interaction mechanisms between the 3D-printed lattice and the cementitious matrix, X-Ray computed tomography (X-ray CT) was utilized to analyze the internal damage under varying strain levels.Micro-CT characterization revealed distinct failure mechanisms for auxetic and non-auxetic lattice reinforced cementitious composites.Due to a larger lateral expansion tendency of the non-auxetic lattice structure, interfacial shear cracking was observed between the lattice reinforcement and cementitious matrix.In contrast, the opposing deformation pattern of auxetic lattices resulted in fewer cracks in the core area, more even stress distribution, and prevention of large crack formation, thus enhancing the composite's energy absorption capacity.Moreover, quantitative analysis from CT scans showed that the crack volume in the core of the auxetic lattice-reinforced composites was almost 60% lower than that of the non-auxetic samples at 2.5% strain.At 5% strain, the auxetic lattice continued to limit crack merging, but at 7.5% strain, although the total crack volume remained 20% lower, the ability to prevent crack coalescence diminished.These insights from micro-crack analysis provide valuable guidance for designing cementitious composites reinforced with auxetic lattice structures.