Styrke og rissutvikling i 3D-printet betong

Abstract

This master’s thesis was carried out at the University of Agder as part of the MSc in Civil Engineering program. The aim of the study is to investigate and compare the mechanical properties and crack development of 3D-printed concrete with reference concrete B45 MF40, which is commonly used in harsh and chloride-exposed environments. The experiments investigate the effects of print orientation and reinforcement on the behavior of 3D-printed concrete beams subjected to four-point bending. The research problem was defined through a literature study, and the following research question was formulated:

How does the strength and crack development of 3D-printed concrete compare to the reference concrete B45 MF40?

A total of 24 3DPC and B45 MF40 beams were produced, which include both unreinforced and reinforced specimens. The 3DPC beams were printed in two orientations (X and Y direction) to study the anisotropic effects. Four-point bending tests were performed to measure flexural tensile strength and maximal load capacity. Additionally, digital image correlation was applied to document crack formation and propagation during testing.

The results showed a clear influence of filament orientation with beams printed in Y-direction generally demonstrating higher flexural tensile strength than those printed in X-direction. The flexural tensile strength in both directions was weaker than for the casted specimens. The application of reinforcement in 3DPC significantly improved crack control and loadbearing capacity, although optimal bond between reinforcement and concrete remains a challenge as there is a possibility of the reinforcement moving.

The implementation of reinforcement resulted in higher average point loads for the printed specimens compared to the cast 3DPC specimens. This suggests that the 3DPC material is not well suited for casting, and that casting may not be the most appropriate method for evaluating the material’s true properties. The printed beams showed substantially more concentrated crack development compared to B45 MF40, where the main cause can be attributed to the fine aggregate in 3DPC.

The study concludes that 3DPC has the potential to be used as a supplement in structural applications, particularly in complex geometries and customized components. However, further development is necessary to optimize printer parameters and reinforcement strategies to fully meet the strict durability and strength requirements in the construction industry.