Design and Function of Thermoresponsive-Ultrafast Stiffening Suspension Formulations for 3D Printing
Presented By: Gaurav Sant
Affiliation: University of California, Los Angeles
Description: An inability to accurately control the rate and extent of solidification of cementitious suspensions is a major impediment to creating geometrically complex structural shapes via 3D printing. In this work, we have developed a thermoresponsive rapid stiffening system that will stiffen suspensions of minerals such as quartz, limestone, portlandite, and Ordinary Portland Cement (OPC) over a wide pH range. When exposed to trigger temperatures between 40 °C and 70 °C, the polymer binder system undergoes a thermally triggered free radical polymerization (FRP) reaction, leading to an ultrafast stiffening of the suspension at an average rate on the order of 1 kPa/s and achieving MPa-level strength in less than a minute. The cured composites exhibit flexural strength and strain capacity far greater than OPC-based composites (s_f ~ 25 MPa, ?_f >1 %). We successfully demonstrated 3D printing using these engineered slurries, showcasing their thermal response, thermal latency, and printability, thereby validating our design approach and its potential for diverse applications. These thermoresponsive slurries facilitate freestyle printing, non-horizontal printing, and the creation of complex geometries with high overhangs. This approach provides a means to surmount the significant limitations of extrusion-based 3D printing using particulate suspensions and open up new possibilities in integrating design and production.
Monitoring of the E-modulus of 3D Concrete Made with Recycled Aggregates From Very Early Ages to the Hardened State through Oscillatory Rheology, Penetration Tests, and EMM-ARM
Presented By: Claudia Pomahuallca Chahua
Affiliation: Pontificia Universidad Catolica Del Peru
Description: The main objective of this research project is to propose and validate a methodology to collect quantitative data about the evolution of concrete E-modulus from very early ages, i.e., immediately after mixing up, to the hardened state (7 days of age). The methodology is composed of concrete penetration tests (ASTM C403/C403M-23) and novel techniques such as oscillatory rheology tests and E-moduli Monitoring through the Ambient Resonance Method (EMM-ARM). The proposed tests will allow monitoring of the concrete E-modulus in the liquid, transition, and hardened states. This methodology will be validated by analyzing two printable concretes: concrete with natural aggregates and concrete with recycled aggregates. The impact of the research project is significant as a useful framework to monitor the E-modulus evolution over time will be validated. This tool can be applied to study the buildability of a wide range of printable concretes and evaluate the effectiveness of chemical admixture for improving it, such as accelerating admixtures and viscosity modifiers.
Early Age Fracture Behaviour of Self Compacting FRC for Tunnel Retrofitting: Material Characterization and Structural Transient Design Verification
Presented By: Liberato Ferrara
Affiliation: Politecnico di Milano
Description: The automation of construction implies that concrete will be subjected since very early ages to combination of actions which may be close to the persistent design situations. In the case of concrete, the determination of mechanical properties and design parameters in early ages may henceforth be crucial with respect to both, the design of the automated construction process and to check the strength and stability at various stages. Vertical and horizontal slip-forming are a remarkable and nowadays quite common examples of a situation in which concrete at a mere few hours of life is called to withstand the self-weight of the just built structural parts and of those progressively interacting with it. In this paper the case study is presented of a new slip-forming technique for tunnel retrofitting and/or new construction, in which, due to the scheduled productivity of the system, Fibre Reinforced Concrete (FRC) tunnel linings of a mere few hours age has to start withstanding their self-weight as well as interacting with the existing lining. A tailored material characterization has been undertaken for the purposely designed extrudable FRC, whose design parameters, as per fib Model Code 2010, have been identified at 4 hours, 8 hours, 24 hours, 72 hours and 7 days, together with more “customary” 28 day deadline. A “stabilization” of the toughness properties of the material has been observed after 24 hours, together with a remarkable deflection hardening. The design parameters identified as above has been henceforth employed to construct design Moment-Axial force interaction domains and moment-curvature sectional diagrams. These have allowed to design the transient design stages of tunnel linings of varying thickness and identify the progressively evolving level of safety for transient design situations in which the same lining has to withstand its self-weight and start interacting with existing lining to allow the construction to proceed as scheduled.
3D-Printed Polymer Concrete Mix Design Optimization: Insights from Early-Age Rheological and Mechanical Properties
Presented By: Mahmoud Reda Taha
Affiliation: University of New Mexico
Description: 3D-printed concrete has gained rapid growth and adoption due to design flexibility, reduced waste, and faster build times compared with traditional construction methods. While cement-based concrete has limitations such as low tensile strength and brittle behavior, polymer concrete (PC) offers advantages like enhanced flow control, improved buildability, and superior structural integrity, making it an ideal material for specialized 3D-printing applications. A key factor in achieving high-quality 3D printing—ensuring stable prints without structural collapse—requires a good understanding of the early-age rheological and mechanical properties of 3D-printed PC. This research characterizes the early-age rheological and mechanical properties of PC and investigates their relationship with the 3D-printing process and PC mix design. An experimental study has been conducted to measure slump, early-age gel strength and rheological behavior, unconfined uniaxial compressive strength, elastic modulus, and shear strength of 3D-printed PC. The findings were used to establish correlations between the early-age properties and the PC mix components, providing valuable insights for developing future 3D-printed PC mix design guidelines.
Influence of Cellulose Nanofiber and Limestone Filler on Early-Age Properties of Mixtures for 3D Concrete Printing
Presented By: Ala Douba
Affiliation: American Concrete Institute
Description: Cellulose nanofibers (CNF) are biodegradable materials gaining interest in the 3D printing of concrete, particularly for their ability to modify the rheological properties of cementitious mixtures. This capability positions CNF as a sustainable and economical viscosity modifier for the 3D printing applications. Additionally, recent studies reported on additional benefits of incorporating CNF in concrete, including acceleration of hydration and enhancement of mechanical properties. Similarly, limestone filler is also increasingly used as a partial cement substitute to reduce clinker content in blended cements. This presentation will cover the rheological properties, printability and buildability of 3D-printing mixtures containing CNF and limestone filler. The influence of these materials on early-age hydration kinetics and mechanical properties of these mixtures will also be presented. The proposed mixtures demonstrated improved rheology and mechanical properties, and thus offer a sustainable and cost-effective choice for 3D concrete printing applications.
Modeling Fluid Absorption in Anisotropic 3D-Printed Cement-Based Materials
Presented By: Luiz Antonio de Siqueira Neto
Affiliation: Oregon State University
Description: This presentation will introduce a finite element modeling approach based on first principles to simulate water absorption in layered cement-based materials. The model is first validated by accurately predicting the moisture uptake of mortar samples during a ponding experiment. The same experiment is simulated with layered geometries replicating those of 3D-printed structures, emphasizing substantial heterogeneity between filament and interfacial regions. Results reveal the highly anisotropic nature of moisture transport in these systems, showing how specific layer arrangements can facilitate or inhibit absorption. Additionally, the study analyzes the role of porosity, pore connectivity, and pore size distribution on the directionality of moisture transport through the layered structures, providing insights into how the materials in and the geometries of these systems can be designed to control water absorption.