International audienceThe aim of this paper is primarily experimental and is intended to analyse the behaviour of two cementitious materials, before and after heat treatment: one unreinforced (i.e. without fibres) and the other reinforced (with polypropylene fibres).At room temperature and after heating up to 500 °C, the bending strength is improved by the presences of fibres. The residual young modulus is slightly higher for the fibres reinforced samples.As the temperature increases, the strength gain due to fibres inclusion is reduced. Beyond 500 °C, the bending strength is lower for the fibre reinforced cementitious material compared to those without fibres. Fracture energy is also improved for the fibre mortars at room temperature. At 400 °C this improvement decreases gradually with the introduction of polypropylene fibres. Beyond this temperature and due to the introduction of polypropylene fibres, the fracture energy is reduced.Another test is developed: rapid heating due to exposure to a flame. The temperature in the front side reaches in few seconds 1000 °C. At this temperature and after one hour of exposure, the opposite side reached 140 °C. After cooling, the punching shear strength of the fibre mortar is definitely weaker than of the mortar without fibre

International audienceThe advantage of steel fibres in cement based materials vis-à -vis mechanical reinforcement is widely recognized in the field of construction. This paper considers the behaviour of materials under extreme conditions in terms of temperature (e.g. fire). To this end, a comparison is made of the mechanical behaviour of mortars reinforced with steel fibres, polypropylene fibres and a hybrid fibre combination. These mortars are subjected to various heat exposures and then tested mechanically. Protection mechanisms of steel fibres and polypropylene are analyzed. SEM observations of steel fibres show oxidation at high temperatures; this oxidation impairs the protective effect of steel fibres. L'intérêt des fibres d'acier dans les matériaux cimentaires vis-à-vis du renforcement mécanique est reconnu dans le domaine de la construction. Nous nous intéressons ici au comportement de ces matériaux dans des conditions extrêmes du point de vue de la température (par exemple un incendie). Pour cela, nous comparons le comportement mécanique de mortiers renforcés avec des fibres d'acier, des fibres de polypropylène et des mortiers hybrides. Ces mortiers ont été soumis à divers traitements thermiques puis testés mécaniquement. Les mécanismes de protection des fibres d'acier et de polypropylène sont analysés. Des observations au MEB des fibres d'acier mettent en évidence une oxydation aux hautes températures. Cette oxydation compromet l'effet protecteur des fibres d'acier

ABSTRACT. The advantage of steel fibres in cement based materials vis-à-vis mechanical reinforcement is widely recognized in

Properties of fibre mortars after exposure to high temperaturesResults obtained by testing mechanical behaviour and microstructure of fibre mortars and standard mortars after exposure to high temperatures are presented in the paper. A flame test using propane gas was developed to enable the best possible simulation of fire conditions. The testing was conducted on three different mortars: standard mortar, steel fibre mortar, and hybrid mortar (with equal proportion of steel fibres and polypropylene fibres). The addition of fibres ensured greater ductility of mortar at temperatures from 400 to 700°C. These observations served as a basis for explaining the loss of strength. Svojstva vlaknima ojačanih mortova nakon izlaganja visokim temperaturamaU radu su prikazani rezultati mehaničkog ponašanja i mikrostrukture vlaknastih i standardnih mortova nakon izlaganja visokim temperaturama. Da bi se što vjernije simulirali uvjeti požara, razvijeno je ispitivanje plamenom primjenom plina propana. Ispitivanje je provedeno na tri različita morta: na standardnom mortu, na mortu s čeličnim vlaknima te na hibridnom mortu (s jednakim omjerom čeličnih vlakana i polipropilenskih vlakana). Pri temperaturama od 400 do 700°C dodavanjem vlakana postignuta je veća duktilnost morta. Navedena opažanja poslužila su kao podloga za objašnjavanje gubitka čvrstoće.Ključne riječi: čelična vlakna, polipropilenska vlakna, mort, visoka temperatura, ispitivanje plamenom, savojna čvrstoća