A novel highly compressible auxetic cementitious composite (ACC) is developed in this work. Contrary to conventional cementitious materials, such as plain concrete and fiber reinforced concrete, the ACC shows strain-hardening behavior under uniaxial compression: the stress continuously increases with strain up to approximately 40 % strain. On one hand, in the early compression stage, the ACC exhibit highly recoverable deformability of 10 % strain under cyclic loading (20 times higher than the constituent cementitious material). In addition, the ACC shows fatigue damage until the stiffness/strength and energy dissipation plateau values are reached after 500 cycles. At 2.5 % strain amplitude, the plateau stiffness/strength is approximately 120 MPa/3 MPa, while these values are only 25 MPa/1.2 MPa at 5 % strain amplitude. In contrast, the energy dissipation plateau of the ACC is independent from the amplitude and remains at 0.05 J/cm3. On the other hand, due to the strain-hardening behavior, the ACC exhibits significantly improved energy dissipation capacity compared to both the conventional cementitious materials and the auxetic frame. This behavior is achieved by a tailored composite action: integrating cementitious mortar with 3D printed thermoplastic polyurethane (TPU) auxetic frame. A rotating-square auxetic mechanism was designed for the TPU frame for the ACC to achieve the tailored cracking behavior. The horizontal ACC cells enable large deformability by enlarging the crack width under the confinement of the auxetic frame, while the vertical cells work as stiffening phase to ensure load resistance. Owing to the outstanding mechanical properties, the ACC shows great potential to be applied in engineering practice where high compressive deformability is required, for instance yielding elements for squeezing tunnel linings.

中文翻译：

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拉胀超弹性框架实现水泥基复合材料的类弹簧行为


这项工作开发了一种新型的高可压缩拉胀水泥复合材料（ACC）。与普通混凝土和纤维增强混凝土等传统水泥材料相反，ACC 在单轴压缩下表现出应变硬化行为：应力随着应变不断增加，最高可达约 40% 应变。一方面，在早期压缩阶段，ACC 在循环荷载下表现出 10% 应变的高度可恢复变形能力（比胶凝材料高 20 倍）。此外，ACC 显示疲劳损坏，直到 500 次循环后达到刚度/强度和能量耗散平台值。在 2.5% 应变幅值下，平台刚度/强度约为 120 MPa/3 MPa，而在 5% 应变幅值下这些值仅为 25 MPa/1.2 MPa。相比之下，ACC 的能量耗散平台与振幅无关，并保持在 0.05 J/cm3。另一方面，由于应变硬化行为，与传统水泥材料和拉胀框架相比，ACC 表现出显着提高的能量耗散能力。这种行为是通过定制的复合作用实现的：将水泥砂浆与 3D 打印的热塑性聚氨酯 (TPU) 拉胀框架相结合。为 ACC 的 TPU 框架设计了旋转方形拉胀机构，以实现定制的开裂行为。水平 ACC 单元通过在拉胀框架的限制下扩大裂缝宽度来实现大变形，而垂直单元作为硬化相以确保负载阻力。 由于其出色的机械性能，ACC 在需要高压缩变形能力的工程实践中显示出巨大的应用潜力，例如用于挤压隧道衬砌的屈服元件。