Internal prestressing of ultra-high performance concrete using shape memory fibers

Using shape memory fibers to reinforce concrete is a novel concept in civil engineering. Pre-stretched fibers are brought into concrete and after activating the shape memory effect, a compressive prestress state is introduced. The present work investigates this method numerically. A brief introduction to the relevant behavior of shape memory alloys is given. Fiber activation is modeled by an empirical phase transition model. Simulations are carried out by applying the Finite Element Method to solve the CAUCHY-FOURIER equations. Results of studies are presented for single-fiber, improved single-fiber and multi-fiber configurations. Special focus is put on the geometric type of strain release. Key findings are that compressive stresses can be introduced into the concrete, however, local tension will occur. By altering the fiber geometry and applying an elastomeric coating, these regions can be eliminated. Furthermore, when using multiple fibers, there are synergies between regions of compression.