Mix design and testing improvements for 3D printable concrete mixtures with fibers

Vertical concrete construction primarily relies on formwork filled with a flowable concrete mixture. This is simple and effective, but formwork is costly. There has been a recent body of research and small industry in vertical concrete construction using a filament 3D printing technique for small structures, thus eliminating formwork. Instead of traditional rebar, many researchers and companies have used fibers distributed throughout the concrete mix for tension reinforcement. The work presented in this paper was part of a project with the Army Corps of Engineers and Missouri S&T to explore concrete 3D printing with worldwide locally available materials, notably local cementitious materials and local natural fibers. The technique could then have military applications such as barracks construction, drastically reducing equipment and materials shipping. Construction would only require bringing printing equipment and any specialized ingredients such as admixtures. The UMKC team’s part in this project was to be exploring fiber sourcing, developing a small-scale 3D printer, and testing a range of mixes with addition of most common natural fibers. The project changed course after the fiber sourcing stage, as a baseline mix proved difficult to develop for consistent printability even with only basic ingredients. The authors shifted to exploring what factors make a mix printable and measuring these factors with simple and robust field tests. The authors developed a new design philosophy for 3D printing concrete mixes, focused around paste thickness on aggregate particles. Printability of a mix was measured by overall mix shear, using a custom-designed head for a pocket vane shear test. Finally, the authors created a baseline printable mix and tested increasing fiber dosages, maintaining paste thickness and adding admixtures as needed to bring overall mix shear back into printable range. The printed samples were cured for 28 days and tested for compressive and flexural strength.

Name thesis:degree_name

M.S. (Master of Science)

Level thesis:degree_level

Masters

Discipline thesis:degree_discipline

Civil Engineering (UMKC)

Grantor

University of Missouri--Kansas City

Year dc:date.issued

2024

Author dc:creator

• Unruh, Nathan G.

Advisor dc:contributor.advisor

• Kevern, John T.

Handle dc:identifier.uri

https://hdl.handle.net/10355/106974

OAI identifier oai:identifier

oai:mospace.umsystem.edu:10355/106974