Fire experiments of thin-walled cfrp pretensioned high strength concrete slabs under service load

Sustainable precast concrete elements are emerging utilizing high-performance, self-consolidating, fibre-reinforced concrete (HPSCC) reinforced with high-strength, lightweight, and non-corroding prestressed carbon fibre reinforced polymer tendons. One example of this is a new type of precast carbon FRP pretensioned HPSCC panel intended as load-bearing panels for glass concrete building facades. It is known that the bond strength between both steel and FRP reinforcing tendons and concrete deteriorates at elevated temperature and that high strength concrete tends to an explosive spalling failure mode when subjected to a fire. The bond strength reductions in fire, their impacts on the load-bearing capacity of prestressed concrete structures, and the spalling behaviour of high-strength concrete remain poorly understood. This paper gives insight in the fire behaviour of filigree CFRP prestressed HPSCC slabs and presents selected results and analysis of an experimental fire test series on 45 mm and 60 mm thin-walled slabs with and without an additional external mineral fire protection coating. The main findings are that the fire resistance of the slabs is determined by spalling of the HPSCC or - if spalling can be avoided by the use of 5 kg/m³ PP microfibers in the concrete - by the thermal splitting-crack induced bond failure of the CFRP tendons in their prestress transfer zone.