Elevated Temperature Effects on 3D Printed Ultra-High-Performance Concrete (2023-01)¶

3D printing of ultra-high performance fiber reinforced concrete (3DP-UHPFRC) enables the construction of thin and lightweight concrete members with complex geometries. However, due to their low permeability, UHPFRCs are vulnerable to explosive spalling when exposed to fire. This study investigated the response of 3DP-UHPFRC to high-temperature exposure conditions ranging from 200 ◦C to 1000 ◦C. Several mixtures were developed with various combinations of hybrid fibers (steel and polymer fibers). Results showed that the interlayer delamination failure was more predominant than spalling in 3DP-UHPFRC specimens. The low incidences of explosive spalling were attributed to the porous interlayers. The residual compressive strength of 3DP-UHPFRC specimens increased after exposure to 400 ◦C temperature, then rapidly decreased after exposures up to 800 ◦C, and plateaued beyond 800 ◦C until 1000 ◦C at 25–30 % of the control strength. The anisotropy of strengths observed in the specimens became insignificant following exposures to 800 ◦C and above. The outcomes were further validated using thermal analysis and microscopic investigations of the test specimens.