This paper presents the results of research on high performance
concretes (HPC) modified by theaddition of polypropylene fibres
(PP
fibres). The scope of the research was the measurement of theresidual
transport properties of heated and recooled concretes: gas permeability
and surface waterabsorption. Seven types of concrete modified with
fibrillated PP fibres were tested. Three lengths: 6,12 and 19 mm and
three amounts of fibres: 0, 0.9 and 1.8 kg/m3 were used. The research
programmewas designed to determine which length of fibres, used in which
minimum amount, will, after thefibres melt, permit the development of a
connected network and pathway for gases and liquids.