Combined Effect of Loading and Cold Temperature on the Stiffness of Glass Fiber Composites

Because of the short construction season and cold winters in Alaska, the prestressed concrete decked bulb-tee bridge system is very popular. However, the concrete deck is an integral part of the bridge superstructure and cannot be easily replaced when it deteriorates. Obviously, there is merit in combining durable “premanufactured” fiber-reinforced polymer (FRP) composite deck with stiffer prestressed concrete girders in cold regions. However, the effects of long-term exposure to extreme temperature variations and various moisture conditions typical of cold regions on the performance of FRP composite materials are not fully understood. This paper summarizes the combined effect of low-temperature and deformation strain levels on the longitudinal modulus of glass fiber-reinforced polymer (GFRP) samples. The modulus of elasticity of GFRP laminate coupons was tested at various temperatures down to −31 °F $\left(-35°\text{C}\right)$ by temporarily subjecting the samples to three strain levels of 1,000, 2,000, or 3,000 microstrains. Both biaxial and uniaxial samples subjected to a deformation of 1,000 microstrains showed an increase in stiffness when tested at increasingly colder temperatures, and no noticeable change in stiffness was seen when the samples were retested after being equilibrated to room temperature. However, samples subjected to a predetermined elevated strain level did show significant stiffness degradation after room temperature equilibration. The degree of degradation was noticeably larger for samples subjected to the low temperatures than for control samples that were subjected to the equivalent number of cycles at room temperature. It was also noted that the degradation due to load cycles or temperature coupled with load cycles was noticeably less for uniaxial samples than for biaxial samples.