Construction, testing, and analysis of a shape-optimised concrete beam with stay-in-place CFRP textile formwork

Reducing carbon emissions from the construction sector is vital amid the climate emergency. Shape-optimisation can reduce concrete usage compared to prismatic designs, but formwork and reinforcement need unconventional solutions when curved and complex geometries are required. This study proposes dual-purpose formwork with CFRP textile, serving as both the reinforcement and a part of the formwork, for shape-optimised concrete beams. A prototype shape-optimised concrete beam with a stay-in-place CFRP textile formwork is constructed and tested, and an analysis method is developed to estimate the Ultimate Limit State capacity. Pouring concrete onto dry CFRP textile and resin-curing post-hardening concrete created a promising bond between the concrete surface and formwork. The CFRP textile showed no observable debonding from the concrete surface under load testing to failure, and overall strain behaviour aligned well with the analysis method presented. The prototype beam experienced a premature brittle flexural failure initiated by rupture in CFRP textile due to stress concentrations, but still reaching 75 % of the predicted ultimate capacity. Stay-in-place participating formwork with CFRP textile is a promising construction method for shape-optimised beams without internal reinforcement, however, further research is needed to provide further insights on deformability, stress concentrations, and bond behaviour.