Link to Latest Report : Coming Soon.
Background :
Recent advancements in 3D construction printing technology have the potential to revolutionize the construction of concrete structures. Many 3D printers are now on the market and have been utilized in different project applications and scales. However, while popularity has grown, there still remain barriers to widespread adoption, especially in bridge and highway construction. Some of the reasons for this include lack of skill or workforce experience with 3D printers, very little data to support long-term performance, and no guidance on structural design or specifications for 3D printed concrete, among others.
Using 3D concrete printing technology for building reinforced structural concrete elements can undoubtedly be complex and risky to an engineer. On the other hand, the potential in using 3D concrete printing to perform concrete repair may be an easier barrier to overcome due to the inherently lower risk and often more “relaxed” specifications compared to structural class concrete, especially horizontal concrete elements. Often these specifications only require high-early strength for reopening and low shrinkage for preventing/mitigating early-age cracking. However, few studies (if any) have been aimed at creating a high-early strength 3D printed concrete for repair. In addition, a 3D concrete printer intended for concrete repair can substantially increase safety on jobsites by reducing the number of personnel needed to complete the work. Moreover, a mobile 3D concrete printer can further increase the capacity, volume and application of concrete repair work that can be done on concrete bridges.
Objective :
This project will have three primary objectives:
- Evaluate the feasibility of fabricating a rapid, high-early strength concrete using a mobile 3D printer for concrete bridge repair.
- Evaluate and characterize key engineering properties including early-age strength and shrinkage.
- An assessment of the technical and logistical challenges in scaling 3D mobile printing for large infrastructure repair projects will be documented.
Scope :
Task 1 – Synthesis of Published Literature
The objective of this task is to synthesize literature on the state-of-the-art and state-of-the-practice for 3D concrete printing. While all types of 3D concrete printing applications will be sought, a particular focus will be in finding literature on success with 3D concrete printers in transportation infrastructure applications. Additionally, information on material properties, mix designs, and the challenges associated with printing technology in the construction industry will be sought. This will provide a foundation for understanding how to optimize mixtures for 3DCP to ensure the best success within this research project.
The research team will conduct an extensive literature review to document the current state of knowledge on the following topics:
- 3DCP Material Properties: This includes key considerations for fresh and hardened concrete properties in 3D printing processes, such as workability, setting time, strength development, and shrinkage control.
- Mix Design Optimization: Evaluating various proportions of cement, aggregates, and additives that yield concrete mixtures suitable for 3DCP, ensuring proper flowability, buildability, and constructability.
- Durability Considerations: Focus on the long-term durability of 3D printed concrete, particularly in terms of resistance to cracking, shrinkage, and exposure to environmental factors such as moisture and temperature fluctuations.
- Technology Challenges: Reviewing the key technological hurdles associated with 3DCP, including printing speed, nozzle design, layer bonding, and the implications of rapid curing on final 3D concrete integrity.
- Case Studies and Standards: Examine previous 3DCP projects, particularly in transportation applications, to gather insights into successful practices and lessons learned from the field.
Task 2 – 3D Mobile Printer Optimization for High-Early Strength Concretes.
The first phase of this task will involve designing and installing a set of hose lines within the 3D mobile printer system. These hoses will be connected to automated admixture dispensers, allowing for the rapid and controlled introduction of chemical additives such as retarders and accelerators into the concrete mix during the printing process.
In parallel with the addition of admixture capabilities, this task will also focus on the enhancement of the printer’s real-time monitoring system. New sensors and data logging equipment will be integrated into the printer to track and record vital properties of the concrete during the printing process.
The final component of the modification will involve optimizing the user interface for the printer’s control system, making it easier for operators to adjust mix properties based on the real-time data collected from the monitoring sensors.
Task 3 – High-Early Strength Mixture Design and Optimization.
A laboratory program will be developed to initially screen potential HESC materials and mixture designs (e.g., cements, mixture proportions, rheological properties, constructability/placement techniques). This project will focus on optimizing a high-early strength mixture using a high early-strength Type III cement combined with varying amounts of chemical admixtures (e.g., superplasticizer, set modifiers, etc.). A Type IL (10) will also be used as a control to compare and contrast early- and later age performance (i.e., strength and shrinkage). Additionally, an overarching objective of this task will be to explore the use of a beletic calcium sulfoaluminate (BCSA) cement capable of providing faster early-age strengths and lower shrinkage potentially reducing the risk of cracking in 3D printed samples.
Task 4 – Proof of Concept Testing and Characterization
In Task 4, the research team will conduct proof of concept testing using larger, lab-scale prints to assess the feasibility and challenges of utilizing high-early strength concrete systems in 3D mobile printing. The primary focus of this task will be on horizontal applications, specifically for projects like bridge deck and pavement repair, where printed concrete is deposited horizontally in layers. This task will evaluate the printability, workability,andperformance of the high-early strength concrete mixtures developed in Tasks 2 and 3 when scaled up to real-world application sizes. The ultimate goal is to assess how well these materials can be printed in practical, large-scale scenarios that resemble the actual challenges of in-situ repairs or installations.
The research team will submit timely quarterly reports and present annually at the Research Days meeting. A final paper will be written that summarizes the methods used and the findings reached during the project.
Research Team :
Principal Investigator : Fred Aguayo, PhD.