Date of Graduation
12-2024
Document Type
Thesis
Degree Name
Master of Science in Civil Engineering (MSCE)
Degree Level
Graduate
Department
Civil Engineering
Advisor/Mentor
Barry, Michelle L.
Committee Member
Murray, Cameron D.
Second Committee Member
Fernstrom, Eric
Keywords
3D printing; additive construction; civil engineering; concrete testing
Abstract
Additive construction (AC), also often referred to as 3D concrete printing (3DCP) represents an emerging technology in the concrete industry, employing specialized equipment and materials to systematically build structures through a controlled, layer-by-layer deposition process. Ongoing research is focused on gaining a deeper understanding of the behavior of AC concrete, as well as developing methods to measure and enhance its properties. The determination of the mechanical properties of nozzle-deposited concrete is the focus of this research and was conducted as a part of a larger program sponsored by the U.S. Army Corps of Engineers Engineer Research and Development Center (USACE-ERDC) which seeks to develop AC as a solution for horizontal infrastructure essential to combat missions.
This study consisted of evaluating conventional and novel material tests currently used in AC. A series of hardened property tests were performed on two AC mixtures to assess the mechanical behavior of AC concrete and determine the parameters needed to calibrate computational models for structural performance prediction. The findings showed that uniaxial compressive and indirect splitting tensile tests on nozzle deposited cylinders produced consistent results and are applicable to AC concrete. Triaxial shear tests exhibited increased variability, but this was likely due to the sampling method used which created voids and other defects in the specimens. The determination of elastic modulus and Poisson’s ratio using digital image correlation (DIC) is acceptable for AC if proper sample preparation and equipment are used.
To ensure that representative samples of AC material accurately evaluate the material’s performance, they must account for the specific conditions of the printing process. Multiple sampling methods were developed and evaluated, and it was determined that the deposited method produced more consistent results and reduced the number of visible voids in the samples. Significant improvement has been made in preparing sample surfaces for testing, but future research should aim to develop a permanent solution to this issue and remove inaccurate loading procedures as a source of error.
The evaluation of current sampling and testing methods for printed, layered specimens was also conducted to determine their applicability to AC concrete. A procedure for directional compression testing was developed and is effective in determining the differences between printed and mold-cast cubes, as well as evaluating the anisotropic properties of printed elements. Punching shear was also determined to be an appropriate method to assess the bonding behavior of printed concrete in the field when the layer interval time is high and proper testing procedures are carried out. Future research should also focus on the evaluation of direct tension testing of printed elements for bond strength to confirm the most appropriate testing protocol for capturing the effects of layering.
Citation
Nunez, T. (2024). Determining the Mechanical Properties of 3D Printed Concrete Mixtures. Graduate Theses and Dissertations Retrieved from https://scholarworks.uark.edu/etd/5600
