Fire induced concrete spalling in combination with size effects

Abstract

The size effect has its origin in fracture mechanics and describes the formation as well as propagation of cracks in brittle and solid materials in dependence of the specimen size. However, the size effect in concrete spalling describes the damage behaviour on a macroscopic scale for different sized specimens in case of fire. Concrete spalling is a very complex and yet not fully understood phenomenon. To reduce the effort of fire tests to analyse the spalling behaviour of concrete mixtures, this study investigates the susceptibility to spalling for six different concrete mixtures and three specimen sizes. The sizes were divided in full scale slabs (1.8 m × 1.2 m × 0.3 m), intermediate scale cuboids (0.6 m × 0.6 m × 0.3 m) and small scale cylinders (Ø0.15 m × 0.3 m). For this purpose, a novel test set-up was built to test six intermediate scale or twelve small scale specimens simultaneously to ensure a similar heating regime for every specimen. All specimens were fire exposed on one side and remained unrestrained. A size effect occurred for four of the six concrete mixtures. Compared to the full scale specimens the spalling was reduced significantly for all smaller specimen sizes. Additionally, spalling did not occur for the small scale specimens. The results show that the specimen size is an essential parameter to investigate the susceptibility to spalling of a concrete mixture. For future investigations the testing conditions must be adjusted for the intermediate scale specimens to recreate the conditions of the slabs.

The influence of the physical and chemical properties of hardened cement paste on the heat‐induced explosive spalling of concrete

“…According to Juknat et al 28 and Klimek et al, 29 the spalling behavior observed when testing small‐sized concrete specimens does not always correspond to the spalling characteristics of large concrete specimens. It was therefore considered important to validate the observations from the PTM tests through tests on larger specimens.…”

Physical, Mechanical, and Microstructure Characteristics of Ultra-High-Performance Concrete Containing Lightweight Aggregates

“…When exposed to high temperatures, concrete spalls are likely influenced by various factors, such as concrete materials, aggregate type, aggregate size, specimen dimensions, heating rate, loading conditions, and testing methods [ 36 , 37 ]. Although UHPC possesses remarkable mechanical properties and durability, it is more susceptible to explosive spalling than conventional concrete under elevated temperatures [ 38 , 39 ].…”