Characterizing the Mechanical Performance of Topology-Optimized Low-Weight Reinforced Concrete Beams
Presented By: Jackson Jewett
Affiliation: MIT
Description: Topology optimization (TO) is a design optimization method known to generate high-performing structures with a limited volume of material. TO is particularly powerful because it does not require an initial layout of structural members from the user. Rather, it places material freely inside a defined design space with known forces and boundary conditions, so the method can algorithmically derive highly efficient results. TO has enormous potential for impact in the construction industry because it can help reduce the use of building materials, which produce approximately 10% of greenhouse gasses worldwide.
Within existing research on TO for construction, tailoring algorithms specifically to reinforced concrete (RC) design has received considerable attention. RC is an important structural system for research because it is ubiquitous in the construction industry. It can also be easily formed into shaped molds, allowing it to be adapted to complex optimized geometries. A common approach for TO of RC uses continuum elements that are stiff in compression to represent the placement of concrete struts, and truss elements that are stiff in tension to place steel ties. These two components come together to create a truss-like RC structure following the strut-and-tie method.
This research will present a new framework for topology optimization of RC. Continuum and truss elements will be used together as in [3], but the locations of the nodes of the truss elements will be controlled by design variables, and able to move during the optimization process. Also, SIMP penalization schemes will not be used on the continuum elements, so that their respective design variables can take intermediate values between 0 and 1. These values will be interpreted as varying thickness in the final design, following the Variable Thickness Sheet method. Several numerical design examples will be presented using this new framework, and mid-scale designs (~1 meter spans) will be fabricated and tested
Improving the Confinement of Concrete Structural Members with Steel Auxetic Truss Lattice Reinforcement
Presented By: Thomas Vitalis
Affiliation: University of Massachusetts Amherst
Description: When auxetics are embedded in an interpenetrating phase composite (IPC) matrix to fabricate auxetically reinforced composite materials, the same mechanism that provides beneficial mechanical properties to a bare truss lattice can be harnessed to increase the confinement pressure acting upon the composite matrix. The development of mismatch strains between the matrix and the truss lattice phase, under sufficient elastic contrast of the two constituents, allows additional confinement pressure buildup, adding to the passive confinement pressures generated by the expansion of the effectively confined matrix core. Furthermore, the presence of auxetic truss lattices inside a composite matrix increases the hydrostatic compression of the matrix while also suppressing crack openings, assuming the two phases are adequately bonded. Thus, the peak stress and ductility of an IPC can be tailored and remarkably enhanced compared to unconfined or traditionally confined specimens. In this work, we study the influence of using auxetic reinforcement for confining structural members through experimental prototyping, analytical and computational means. Specifically, two re-entrant families of structures with varying geometrical features and relative densities of ?*=5%, are studied in IPCs. Explorative parametric computations are utilized combined with a Voigt model to determine promising candidate architectures based on the percentage increase of the confinement pressure they provide in a wide range of transverse moduli. The laser powder bed fusion method is utilized, along with a precipitation hardening 15-5 stainless steel pre-alloyed powder to manufacture truss lattice specimens. Truss lattice-reinforced structural member prototypes are manufactured and employed for studying the behavior of auxetic IPCs in cubes, columns, and beams. A cementitious mortar mix design is specifically designed to cast the composite matrix. Comparisons between unconfined specimens, conventionally reinforc
Performance of Steel Fiber Reinforced 3D Printed Concrete Mixtures Including Coarse Aggregates
Presented By: Caleb Lunsford
Affiliation: Cornell University
Description: The inclusion of steel fiber reinforcement in 3D printed concrete (3DPC) has been shown to increase the mechanical performance of printed structures. Orientation of these fibers, as well as their adherence with cementitious matrix have significant influence on the overall performance that could be achieved from their use. These factors are influenced by the printing method and composition of the concrete mixture being used. Here, 3DPC mixtures containing straight steel fibers and varying size of maximum aggregate sizes were developed for use in a 1-stage in-house built gantry style printer. To evaluate the performance of the mixtures developed and printing method employed, both 3D printed and casted samples were prepared. Orientation of the fibers and the properties of the fiber-matrix interface were determined by conducting microscopic analyses, and mechanical performance was examined through compression and bending tests. Based on the experimental observations, the effects of changing the aggregate size and production method on the performance of fiber reinforced 3DPC mixtures are identified in various aspects. Identifying trends in the interaction between larger aggregates and steel fibers, as well as the fibers and cementitious matrix within the confines of extrusion-based 3D printing allows for continued mix optimization and the refinement of 3DPC’s mechanical performance.
Using Nature-Inspired Patterns to Enhance Flexural Performance of Architected Polymer Reinforced Cementitious Composite
Presented By: Parsa Namakiaraghi
Affiliation: Drexel University
Description: Over millions of years of evolution, living organisms have developed specific architectural elements with unique geometries, such as cellular and hollow structures in plants, to enhance the mechanical properties of their structures. Integrating these nature-inspired architectures, which offer distinct mechanical advantages, into the layout of concrete reinforcement has the potential to enhance mechanical responses and optimize mass in reinforced concrete. Moreover, it can strengthen the bond between the reinforcement and the matrix by increasing the contact area between these components. This research aims to explore the potential improvement in the mechanical properties of reinforced cement-based materials by introducing nature-inspired architected polymeric reinforcements. Polymeric 3D-printed elements, featuring various nature-inspired architectures like cellular and hollow structures, were created as reinforcements for a cement-based matrix and embedded in mortar beams. The design of each architected element maintained a constant reinforcement ratio, determined based on the experimental material properties of the 3D-printed polymer. The flexural behavior of these mortar beams was examined through 3-point bending tests, assessing parameters such as maximum load capacity, modulus of rupture, deflection, toughness, and fracture propagation patterns. The results indicate that the incorporation of nature-inspired architectures with advanced mechanical characteristics into the reinforcement design enhances the flexural behavior of cement-based materials and can be further fine-tuned to meet specific mechanical requirements.
Fracture Mechanics of Tough and Ductile Nacre-like Cementitious Composites
Presented By: Shashank Gupta
Affiliation: Princeton University
Description: Enhancing fracture toughness and ductility of brittle materials such as concrete remains a challenge. Nature offers numerous solutions to enhance fracture toughness without sacrificing strength using purposeful designs of materials architecture. Here, we propose a bioinspired “nacre-like” brick-and-mortar arrangement from mollusk shells, enabled by laser processing and periodic tabulating of cement paste laminated with limited amounts of elastomeric interlayers. These new “nacre-like” architected composites reproduce tablet sliding and interlayer deformation toughening mechanisms that are present in natural nacre and promote higher fracture toughness but absent in human-made brittle and quasi-brittle materials such as cement paste and concrete. By engineering laser-induced defects and tabulated arrangements of hard-soft materials, we produce interlayer deformation, tablet sliding, and tortuous crack propagation as toughening mechanisms such that both fracture toughness and ductility are significantly enhanced, by one order of magnitude, compared to the constituent brittle cement paste. These toughening mechanisms also promote rising R-curves in “nacre-like” composites compared to the flat brittle response of monolithic cement paste. We leverage bio-inspired design principles to program toughening into internal schemes of these hard-soft cementitious composites. The findings of this research can help develop a strategy to enhance the toughness of concrete materials by harnessing internal flaws and incorporation of small amounts of soft hyperelastic materials. This approach could lead to generate flaw-tolerant and impart crack-resistant characteristics in brittle cementitious material at large scale, for example using largescale lamination or additive manufacturing techniques.
3D Printable Magnesium Oxysulfate Cement Composite with Enhanced Seawater Resistance Using Hybrid Metakaolin-Fly Ash-Silica Fume Mixture
Presented By: Hanbin Cheng
Affiliation: Pennsylvania State University
Description: Extensive utilization of portland cement in concrete manufacturing significantly contributes to global CO2 emissions. A recent heightened focus on reducing the carbon footprint in sustainable construction calls for alternative binding materials. One alternative is magnesium oxysulfate cement (MOSC). This work delineates the development of 3D printable MOSC that is seawater-resistant. This was achieved by a combination of MOSC with metakaolin and the hybrid addition of metakaolin and fly ash. An exploration of the impact of these supplementary cementitious materials on the mechanical properties, water resistance, and volume stability of MOSC was conducted. The enhancement mechanism was revealed by using XRD, SEM, FTIR, TG/DSC, and MIP. In addition, a clear and precise distribution of the hydration products in well-cured MOSC specimens was demonstrated with the X-ray mapping technique. These investigations result in the optimal proposition of the MOSC formulation, characterized by heightened water resistance and enhanced mechanical performance. Subsequently, the proposed MOSC formulation was adapted for 3D concrete printing technology by incorporating silica fume. An examination of silica fume's influence on the rheological parameters of the optimally designed MOSC was carried out, encompassing resting times. A broad battery of tests was undertaken to characterize the effects of silica fume on flowability, extrudability, open time, buildability, hydration, compressive strength, and air void content and distribution. Finally, the implementation of a laboratory-scale 3D printing setup was demonstrated.