Cross‐comparison of screening tests for fire spalling of concrete

Abstract

Concrete spalling is an important phenomenon to consider when evaluating the fire behavior of concrete, as this can sometimes have an impact on the structural capacity of the studied element. Spalling can be assessed experimentally using screening tests although it is influenced by the size, geometry, and boundary conditions of the tested element, among other factors. No standardized and systematic methods are yet available to assess concrete spalling sensitivity by testing. Plus, comparative results between screenings tests (small and medium scale) and full-scale tests to evaluate their representativity remain scarce in the literature. In this study, five different spalling tests-with different geometries and boundary conditions-that are used as screening tests were investigated. A concrete mix known to be sensitive to spalling was used to evaluate the representativity of two types of screening tests (material screening tests and intermediate-scale screening tests). The representativity of these test setups was evaluated by comparing the measured spalling depths to the spalling measured on a full-scale slab test using the same concrete mix. This comparative study confirmed that the presence of load and/or restraint was essential for a good representativity for a screening test but should always be implemented in large enough specimens.

Fire induced concrete spalling in combination with size effects

“…Thus, several research groups investigated the spalling behaviour including size effects, whereas only three displayed publications considered all three specimen sizes (full scale members, intermediate scale slabs, small scale specimens) [14][15][16]. All these studies show more severe spalling due to an increase of the specimen size for the same concrete mixture.…”

“…Unfortunately, the difference of specimen sizes and spalling volumes are too large to interpret and an intermediate scale specimen size is needed to improve the significance to the size effect [17,18]. The research of Mohaine et al [15] investigated the spalling behaviour of four different specimen sizes including passive restraints on the small scale specimens to create similar stress conditions compared to the center of a large concrete member. Small cylinders (Ø0.1 m; h = 0.22 m), two types of round specimens restrained by a steel ring with sizes of Ø0.3 m; h = 0.11 m and Ø0.61 m; h = 0.3 m as well as members that have a similar size to the full scale member of this paper (1.7 m 9 0.98 m 9 0.2 m) were tested.…”

“…For instance, the water-cementratio, the porosity as well as the permeability, the presence of reinforcement, polypropylene fibres and the type of aggregate can influence the impact of the thermal induced damage [26]. Additionally, external factors, for instance external restraints [15] or loads [19], increase the spalling of a member compared to a concrete that can expand freely.…”

Editorial for special issue on Interflam 2019: Mass timber and fire resistance

“…An innovative material screening test method, with concrete molded in steel pipes to create a restraint during testing, is illustrated using a comparative study. 8 This seems to be a promising test setup, although it appears that the size of the specimen is critical. In the second article on fire spalling of concrete, it is shown that addition of even relatively small amounts of polypropylene fiber to the fresh concrete mix can reduce fire spalling.…”