Papers presented in this session will cover the most significant aspects of early age behavior of 3D printed concrete. Specifically, the focus will be or the behavior of mixes from the time of extrusion from the nozzle to about 7 days of age. Due to their unique composition, processing methods, and microstructure resulting from layer-by-layer deposition, these mixtures may exhibit higher potential for early-age shrinkage, cracking, and creep. The rate of strength development may also be different compared to mixtures placed using traditional casting methods as it may be affected by the rate of drying and development of bond between the printed layers.
Learning Objectives:
(1) Review recent research progress in controlling the early age properties of 3D printed concrete;
(2) Develop knowledge on the influence of ink composition and printing parameters on the the properties of 3DPC;
(3) Discuss mechanical behavior of concrete during the 3D printing process;
(4) Recognize the challenges of controlling volumetric stability and bond strength in the early age 3D printed concrete.
Novel Fresh Properties and Plastic Strength Behavior of 3D Printed Concrete
Presented By: Benjamin Manaugh
Affiliation: University of Illinois Urbana-Champaign
Description: The 3D concrete printing (3DCP) industry has relied on cement-rich mortar to facilitate pumping and ensure rapid development of strength; however, to improve the sustainability and shrinkage performance of printed concrete there must be a transition to mixes with coarse aggregate. To evaluate the printability of these concrete mixes, we used fresh property tests which replicate the effects of pumping, extrusion, and layer build-up. We begin by the applying the ICAR flow tests, which was used to measure the bulk and interfacial rheology for prediction pipe flow. Next, extrusion testing, which was employed to quantify the impact of pipe reducers, stop-starts, and nozzle extrusion. We then characterize the mix stability under pumping particularly the bleed rate. Finally, we the fresh-state strength development was measured with both an ICAR and a handheld shear vane to determine limits on layer height and overlap time. Through collaboration with a 3DPC contractor, these fresh property tests and new mix design principles are connect full-scale 3DPC structures
Fresh State Properties of 3D-Printing Bioactive Concrete for Marine Applications
Presented By: Nestor Fabian Rodriguez Buitrago
Affiliation: National Renewable Energy Laboratory
Description: This presentation will explore updates to 3D printed concrete mixtures needed to successfully construct under water, including utilizing seawater as mixing water. Our approach draws inspiration from natural processes, focusing on biohybrid strategies utilizing a specifically design carbonic anhydrase enzyme to facilitate rapid carbonate precipitation to enhance interlayer bonding and structural properties. Bioactive marine printing has the potential to unlock rapid construction opportunities needed for coastal development and repairs needed for future industrial and energy applications.
Evaluating Early-Age Interlayer Bond Development in 3D-Printed Concrete Using Ultrasonic Testing
Presented By: Zahra Miri
Affiliation: University of Waterloo
Description: 3D Concrete Printing (3DCP) offers a groundbreaking method for construction, depositing concrete layer-by-layer via a nozzle mounted on a gantry or robotic arm. By removing the need for formwork, 3DCP enhances cost efficiency, accelerates project timelines, and promotes sustainability in construction practices. However, 3DCP faces technical challenges, particularly the formation of weak interlayer bonds between deposited layers, which can lead to anisotropy and impact structural integrity.
This research focuses on applying ultrasonic testing (UT) to detect weak interlayer bonds at early ages in 3D-printed concrete. Ultrasonic pulse measurements were performed concurrently with splitting tensile tests to monitor bond development at ages 1, 3, and 7 days. Specimens (100 mm cubes) were prepared using commercially available printable concrete, cast in two layers with a 1-hour time gap between them—matching the final setting time of the material. Two interlayer conditions, dry (exposed to air) and wet (misted with water before the second layer), were examined to study the impact of moisture conditions on bond strength; these samples were then compared to a control scenario without any interlayer. By employing ultrasonic measurements, this study seeks to identify weak interlayer bonds early, providing critical insights into the role of interlayer moisture conditions in bond formation. The results will help refine bonding strategies in 3DCP, improving structural performance and consistency in 3D-printed concrete applications. This work highlights ultrasonic frequency analysis as a key non-destructive testing technique for assessing interlayer bond quality in early-age concrete, supporting industry-wide efforts to enhance the reliability and durability of 3D-printed structures.
Magnesium Oxysulfate Binders for Additive Construction Applications
Presented By: Hunain Alkhateb
Affiliation: The University of Mississippi
Description: Further research is essential for exploring in-space additive construction applications that leverage in-situ resource utilization to minimize material transport and costs in space. The use of indigenous materials to enhance cement-like mortars with lunar regolith is a critical area of study for 3D printing technologies applicable to space exploration. This paper centers on characterizing both the fresh and hardened properties of magnesium oxysulfate (MOS) composites with various molar configurations. The research team presents proof of concept demonstrating the viability of an MOS binder for 3D printing in both terrestrial and extraterrestrial additive construction settings. We assessed the fresh and hardened characteristics of optimized binders mixed with lunar simulants and polypropylene fibers, successfully reducing shrinkage cracks in the MOS mortar. The integration of artificial intelligence plays a vital role in enabling real-time adjustments during the printing process and predicting performance-related properties. Our simulation results closely match experimental outcomes, and statistical analysis reveals that artificial neural networks (ANNs) can effectively predict compressive strength, flow, and initial setting time, thereby improving the efficiency of MOS mix design.
Exploring Application of Self-Healing Capabilities in 3D-Concrete Printing and Evaluating its Effectiveness
Presented By: Adam Biehl
Affiliation: Clemson University
Description: 3D Concrete Printing (3DCP) construction differs from traditional concrete construction due to 3DCP’s elevated binder content, anisotropic behavior, and interlayer joints, which increase the likelihood of cracking and a loss of watertightness. Repairing these cracks is a tedious process as the concrete continues to shrink and form additional cracks. An autonomous solution to heal those cracks through the inclusion of self-healing agents is a possible pathway but could display reduced levels of effectiveness along interlayer joints where the self-healing agents are unlikely to be in sufficient concentration. This study uses bacteria-based self-healing agents in 3DCP to evaluate their effectiveness in healing cracks formed under restrained shrinkage. The self-healing efficiency of bacterial-based self-healing agents was assessed at a two- and four-percent replacement of the total binder content against a control to independently assess the influence of autonomous and autogenous self-healing in 3DCP. Initial tests compared crack morphology and stress generation in 3DCP through the traditional and a modified version of the restrained shrinkage ring test. The cracks were then evaluated through a water transmission test under constant water head to determine the crack width. After curing to allow for self-healing, the crack widths were then assessed again utilizing the water transmission test, with the reduction in water transmission/crack width determining the effectiveness of the self-healing.