Fire Behavior of Thin CFRP Pretensioned High-Strength Concrete Slabs

Abstract

More sustainable precast concrete structural elements are emerging from the research community utilizing high-strength, self-consolidating fiber-reinforced concrete (HPSCC) reinforced with noncorroding prestressed carbon-fiber-reinforced polymer (CFRP). An example of this is a new type of precast CFRP pretensioned HPSCC panel intended as load-bearing beams or columns for use in building envelopes. Such elements have recently been applied to architectural façade elements in Europe. A key issue in the implementation of these elements as load-carrying members in buildings is demonstrating satisfactory performance in fire. It is well known that the bond between FRP reinforcing bars and concrete deteriorates at elevated temperatures. It is also known that high-strength concrete is susceptible to explosive spalling when subjected to fire. Reductions in FRP reinforcement tensile and bond strength during fire, effects on the load-bearing capacity of prestressed concrete structures, and the explosive spalling response of HPSCC during fire all remain largely unknown. This paper provides insights into the fire behavior of CFRP prestressed HPSCC slabs through an experimental study on thin slabs exposed to a standard fire while subjected to sustained service loads. It is shown that the fire resistance of these elements is governed by fire-induced spalling or, if spalling is prevented by the use of high dosages of polypropylene microfibers in the concrete, by thermal splitting-crack-induced bond failure of the CFRP tendons in their prestress transfer zone. Neither reductions in tensile strength of the tendons nor reductions in bond strength due to resin softening at high temperature appeared to play critical roles for the tests described in this paper. Key areas for future research are highlighted.