Creep Rupture Performance of Basalt Fiber-Reinforced Polymer Bars

Fiber reinforced polymer (FRP) composite bars are suitable substitutes for steel reinforcement in structural concrete because of their light weight and high specific strength and stiffness. Sustained load on FRP composites over the entire service life of the structure can cause failure by creep rupture at loads much smaller than those corresponding to static transient loads. Creep rupture test methods used by several researchers are presented, and a suitable loading arrangement and test method were selected for this study. The creep rupture properties of basalt FRP bars were determined using sustained loading applied to the test specimens simultaneously with an alkaline solution at an elevated temperature. The tests were based on the method specified by the American Concrete Institute (ACI) in a standard. The ultimate creep rupture strength coefficients for basalt FRP bars were determined to be approximately 18% for 50 year service life and 28% for 5 year service life. The corresponding one million hour creep coefficient was estimated to be 13%. One standard specified that creep rupture stress limits are constant regardless of the duration of the service life of the structure. Such an approach leads to conservative designs, particularly for structures with short service lives. It is recommended that time-dependent creep rupture stress limits be used in the design of structures with short service life so as to utilize the strength of FRP bars more effectively. Design creep rupture stress limits for basalt FRP bars are suggested based on the test results of this study and varying safety factors that are dependent on the duration of service life