Experimental investigation on tensile characteristics of 3D printed auxetic embedded cementitious composites and shear bonding behaviour to masonry

Auxetic cementitious composites (ACC) made of embedded auxetic materials into cementitious matrix are gaining attention due to their enhanced mechanical properties caused by using high shock absorbing auxetic metamaterials as reinforcing medium. 3D printed auxetics can be tuned to achieve the required properties of ACC, by using different printing filaments, and cell geometries. In this research, three different types of re-entrant chiral auxetic (RCA) geometries in the form of reinforcing meshes were developed by 3D printing using Polylactic Acid (PLA) and Thermoplastic Polyurethane (TPU) filaments. The effect of re-entrant cells orientation was investigated to select a suitable orientation by testing the RCA meshes under uniaxial tension. Based on which, the horizontally celled RCA meshes were employed to develop and characterise ACC samples. The ACC samples were prepared by embedding all three types of 3D printed RCA meshes into two different kinds of mortar matrices of low and high tensile strengths. The ACC made of high strength mortar embedded with TPU-RCA mesh with densest cell geometry exhibited highest tensile strength (11 MPa) and ductility (ultimate strain/cracking strain = 20). The shear bond characteristics of developed ACC was also investigated through testing ACC strips bonded with masonry substrate under shear lap testing arrangement. The ACC made of high strength mortar embedded with PLA-RCA mesh exhibited highest shear bond strength of 0.44 MPa. The RCA meshes did not de-bond from the ACC during the shear testing, and failure occurred due to extension or fracture of embedded RCA meshes. The results prove the applicability and benefit of employing ACC as protective strengthening materials for masonry and other cementitious structures.