Heat exposure tests on various types of fibre mortar

Abstract

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

High temperature behaviour of polypropylene fibres reinforced mortars

“…At the high temperatures, two types of damage appear: (1) the physicochemical modifications and 2cracking of the cementing matrix [11,19,20]. Results from a previous study showed that the polypropylene fibres had more effect on the reduction of cracking than on the reduction of the physicochemical modifications [21]. From 170°C, the polypropylene fibres melt and create a connected porosity [22].…”

Behaviour of recycled tyre polymer fibre reinforced concrete at elevated temperatures

“…By this mean the specimen was heated up in an electric furnace with a constant heating rate until the target temperature was reached. The most commonly used heating rate ranges from 1 to 10 °C/min, such as 1 °C/min [2,9], 2 °C/min [45], 4 °C/min [46], and 10 °C/min [14,18,47]. A higher heating rate can significantly speed up the pore pressure buildup inside concrete due to a higher induced thermal stress [8].…”

Thermo-mechanical properties and stress-strain curves of ordinary cementitious mortars at elevated temperatures

“…The previous considerations hold for both hot conditions [14][15][16]21] and residual conditions [12,13,17,18,20,21], with the tests carried out at high temperature and past cooling, respectively. Note that the compressive strength in ordinary conditions spans from 4.5-16 MPa in [13][14][15]20] to [35][36][37][38][39][40][41][42][43][44][45] MPa in [17,18] and 55-60 MPa in [11,12,16].…”

“…Mortar structure has been investigated both at the micro-and meso-level [10,28,34], with specific attention to thermo-hygral phenomena [11,35,36], to the inclusion of polymeric, metallic, inorganic and hybrid fibres [37][38][39], to the replacement of cement with alkaliactivated materials (geopolymers [40]), and to fracture energy [21,41]. In [38] polypropylene fibres are shown to be very effective in preventing thermal spalling in both autoclaved and water-cured high-strength mortars.…”