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1. On the Bonding Characteristics of Clays and Biopolymers for Sustainable Earthen Construction

   Mikofsky, R.A.; Armistead, S.J.; Srubar, W.V. (June 2023, International Conference on Bio-Based Building Materials)

   Amziane, S.; Merta, I.; Page, J. (Ed.)

   Sustainable earthen building materials provide a pathway to mitigating the environmental impacts of the modern construction sector. While the application of these materials has been limited due to the inherent heterogeneity, erosivity, and weak mechanical properties of soil, the physical and thermal properties can be improved through the addition of ubiquitous, non-toxic, sustainable biopolymers. Yet, the fundamental understanding of the physiochemical bonding mechanisms between clays and biopolymers in this system is limited. In this work, a ‘micro to macro’ methodological approach was applied to investigate the bonding characteristics of common clays and clay-stabilizing biopolymers. At the micro-scale, fundamental interactions of clays (i.e., kaolinite, bentonite) with biopolymer additives (i.e., xanthan gum, guar gum, sodium alginate, microcrystalline cellulose) were assessed through mineral binding characterization techniques, including Fourier-transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). The findings were used to interpret unconfined compressive strength (UCS) tests results for macro-scale soil-biopolymer composites samples (1% biopolymer by soil mass). The results from this study illustrate the utility of understanding the mechanisms of clay-biopolymer interactions for improving the design of strong and durable earthen materials and structures. 

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2. Quantification of age-related changes in the structure and mechanical function of skin with multiscale imaging

   https://doi.org/10.1007/s11357-024-01199-9  

   Woessner, Alan_E; Witt, Nathan_J; Jones, Jake_D; Sander, Edward_A; Quinn, Kyle_P (May 2024, GeroScience)

   Abstract The mechanical properties of skin change during aging but the relationships between structure and mechanical function remain poorly understood. Previous work has shown that young skin exhibits a substantial decrease in tissue volume, a large macro-scale Poisson’s ratio, and an increase in micro-scale collagen fiber alignment during mechanical stretch. In this study, label-free multiphoton microscopy was used to quantify how the microstructure and fiber kinematics of aged mouse skin affect its mechanical function. In an unloaded state, aged skin was found to have less collagen alignment and more non-enzymatic collagen fiber crosslinks. Skin samples were then loaded in uniaxial tension and aged skin exhibited a lower mechanical stiffness compared to young skin. Aged tissue also demonstrated less volume reduction and a lower macro-scale Poisson’s ratio at 10% uniaxial strain, but not at 20% strain. The magnitude of 3D fiber realignment in the direction of loading was not different between age groups, and the amount of realignment in young and aged skin was less than expected based on theoretical fiber kinematics affine to the local deformation. These findings provide key insights on how the collagen fiber microstructure changes with age, and how those changes affect the mechanical function of skin, findings which may help guide wound healing or anti-aging treatments. 

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3. Nano-Scale and Macro-Scale Characterizations of the Effects of Recycled Plastics on Asphalt Binder Properties

   https://doi.org/10.3390/buildings14030642  

   Al-Hosainat, Ahmad; Nazzal, Munir D; Kaya, Savas; Reza, Toufiq (March 2024, Buildings)

   This paper summarizes the results of one of the first comprehensive laboratory studies that was conducted to evaluate the effects of adding different contents of recycled polyethylene terephthalate (rPETE) as a modifier to an asphalt binder on the rheological and mechanical properties of the modified binder as well as on the agglomeration behavior between the rPETE and asphalt binder at a multiscale level. The high-temperature and low-temperature performances of the modified binder were investigated at the macro-scale and compared with those of the unmodified binder using dynamic shear rheometer (DSR) and bending-beam rheometer (BBR) rheological tests, as well as asphalt binder cracking device (ABCD) testing. The nano-scale evaluation of the binder properties, including the surface roughness, bonding energy, and reduced modulus, was accomplished using atomic force microscopy (AFM). The results indicated that the addition of rPETE enhanced the high- and intermediate-temperature rheological properties of the modified PG 64-22 binder. The low-temperature rheological properties and resistance to cracking decreased slightly with increasing rPETE content in the asphalt binder. However, this reduction was not remarkable when adding 4%, 8%, and 10% rPETE contents. The asphalt binder modified with 4% rPETE had a low-temperature grade of −22, similar to that of the unmodified binder, indicating that 4% rPETE can be added to the binder to improve its high- and intermediate-temperature properties without reducing its resistance to low-temperature damage. The AFM tapping-mode results indicated that the inclusion of rPETE in the asphalt binder improved the stiffness properties of the modified binder as compared with those of the control asphalt binder. In addition, the rPETE-modified binders showed rougher surfaces than the control binder. The addition of rPETE to the binder increased the values of the reduced modulus and bonding energy compared with those of the control binder. 

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4. Full-scale testing of precast tunnel lining segments under thrust jack loading: Design limits and ultimate response

   https://doi.org/10.1016/j.tust.2023.105446  

   Ouyang, Ziyan; Zheng, Haotian; Patmanidis, Constantine; Naito, Clay; Quiel, Spencer; Mooney, Michael (December 2023, Tunnelling and Underground Space Technology)

   In modern practice, precast segmental tunnel linings are typically installed via a tunnel boring machine (TBM), which advances by thrusting against the previously installed segmental ring. The forces applied through the thrust jack pads can induce significant bursting and spalling tensile stresses and strains in the segment, and improperly designed segments can suffer from cracking as a result. An experimental study has been conducted to evaluate the progression of damage from initial cracking to ultimate capacity for full-scale precast tunnel liner segments under thrust jack loading. The baseline segment design is composed of steel fiber reinforced concrete (SFRC), and the impact of supplemental conventional steel bar reinforcement and load application eccentricity were also investigated. Six full-scale tests were performed with a thrust jack load per pad up to 22.2 MN (which is ~3.8 times the maximum expected installation thrust force). At the maximum expected thrust jack load during installation (5.78 MN per pad), the segments were virtually undamaged, and hairline cracking initiated between the load pads on only one test. At the TBM’s ultimate jacking capacity (9.55 MN per pad) surface cracking was observed between and under the load pads; however, the crack width remained below 0.2 mm for all specimens. The formation of cracking limit states was accurately predicted by pre-test linear and nonlinear finite element (FE) models. At overload conditions, the baseline SFRC-only segment exhibited a radial bursting failure. The inclusion of supplemental conventional reinforcement does not reduce the level of cracking damage or strain development below the TBM’s ultimate jacking capacity; however, at overload conditions, the supplemental reinforcement mitigates cracking and prevents a radial bursting failure at 20.3 MN per pad. A load eccentricity of 38 mm towards the extrados surface increased the transverse strain and the formation of transverse cracking at a lower load level. 

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5. Mechanical properties of additively manufactured variable lattice structures of Ti6Al4V

   https://doi.org/doi.org/10.1016/j.msea.2021.140925  

   Traxel, Kellen; Groden, Cory; Valladares, Jesus; Bandyopadhyay, Amit (March 2021, Materials science engineering)

   null (Ed.)

   Engineered micro- and macro-structures via additive manufacturing (AM) or 3D-Printing can create structurally varying properties in a part, which is difficult via traditional manufacturing methods. Herein we have utilized powder bed fusion-based selective laser melting (SLM) to fabricate variable lattice structures of Ti6Al4V with uniquely designed unit cell configurations to alter the mechanical performance. Five different configurations were designed based on two natural crystal structures – hexagonal closed packed (HCP) and body centered cubic (BCC). Under compressive loading, as much as 74% difference was observed in compressive strength, and 71% variation in elastic modulus, with all samples having porosities in a similar range of 53 to 65%, indicating the influence of macro-lattice designs alone on mechanical properties. Failure analysis of the fracture surfaces helped with the overall understanding of how configurational effects and unit cell design influences mechanical properties of these samples. Our work highlights the ability to leverage advanced manufacturing techniques to tailor the structural performance of multifunctional components. 

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