NiTiNb Shape Memory Bars for Concrete Prestressing Applications

Nickel–titanium (NiTi)–based shape memory alloys (SMAs) have been widely studied for concrete prestressing applications due to their high recovery stress and commercial availability. In previous studies, small 1–2 mm Nickel-titanium-Niobium (NiTiNb) wires were utilized, but the necessity for larger-diameter NiTiNb bars is increasing for broader applicability. This technical note presents the thermomechanical properties of a hot-rolled 6.4-mm-diameter NiTiNb bar (No. 2 bars) that is suitable for real-world prestressing applications. The prestrained bar is activated (stressed) via heating using a thermal chamber and electric heating. The bar maintains a steady recovery stress (prestress) at room temperature of 280 MPa when heated to a temperature of 225°C.