THE MODE OF ACTION OF POLYPROPYLENE FIBRES IN HIGH PERFORMANCE CONCRETE AT HIGH TEMPERATURES

摘要

It has been shown in fire tests that polypropylene fibres reduce or avoid explosive spallingrnof high performance concrete. In the critical temperature range up to 300 ℃ the permeabilityrnof HPC increases by using polypropylene fibre. Due to this the water vapour, which is thernmain reason for explosive spalling, can escape. There exist different theories in the literaturernconcerning the micro structural mechanisms, which cause an increase in the permeability.rnWithin the framework of an internal research project at BAM an innovative methodology wasrndeveloped for experimental verifying of existing theories and to get new insights into thisrnproblem. The methodology used is unique and has been undertaken here for the first time.rnThis consists of the combination of acoustic emission and ultrasonic measurement duringrntemperature loading and the non-destructive micro structural analysis of cooled downrnsamples with the aid of micro X-ray computed tomography. For the validation of the nondestructiverntest methods scanning electron microscopic images of prepared samples werernundertaken. The results show that due to the thermal decomposition of the polypropylenernfibres micro canals emerge. These are connected due to a simultaneous micro cack formation.