RESIDUAL PROPERTIES OF SEVEN-WIRE LOW RELAXATION PRESTRESSING TENDON SUBJECTED TO EXTREME TEMPERATURES

The use of cold-drawn prestressing steel as reinforcement in concrete is common among bridge design throughout the world. This composite material is particularly useful for designs consisting of large spans where the dead load will cause significant cracking and deflection. Unlike mild steel reinforcement, prestressing steel is stressed and cause a compression force within the concrete. This prevents cracking and increases the structure’s capacity. A prestressed concrete member will also have a longer life expectancy due to the prevention of cracks. Without cracks the steel will not be exposed to the environment and therefore will be at a reduced risk of corrosion. The increased capacity, ability to sustain longer spans, and durability make this type of material an advantageous choice of construction. This paper investigates the residual properties of seven wire, uncoated, 0.5 in. (12.7 mm) and 0.375 in. (9.5 mm) diameter low relaxation grade 270 ksi (1862 MPa) prestressing tendon subjected to extreme temperature. The temperatures selected for the study were 500°F (260°C), 800°F (427°C), 1000°F (538°C), 1200°F (649°C), and 1300°F (704°C). The upper limit was defined by the furnace’s capability at Missouri S&T. In addition, control specimens were tested for each strand size. A control was defined as exposure to approximately 68°F (20°C). Two cooling methods were also investigated, namely inside the furnace and outside the furnace. Test results presented include visual observations, yield stress, ultimate load, and elastic modulus.