Fire spalling sensitivity of high-performance concrete in heated slabs under biaxial compressive loading

Abstract

Explosive spalling of concrete exposed to fire consists in the violent expulsion of shards from the hot surface due to the interaction between cracking and pore pressure build-up. Fire spalling relevantly increases the overall thermal damage of a structure exposed to fire, thus leading to much higher costs in the repair intervention, and in some cases it can even jeopardize the structural stability due to loss of reinforcement protection and reduction of the bearing cross-sections. High-performance concrete is particularly sensitive to spalling phenomenon due to inherent material features, such as the unstable fracture behaviour and the low permeability (favouring high values of pore pressure). In this context, an experimental campaign has been carried out on high-performance concrete (f c & 60 MPa with silico-calcareous aggregate), without or with one of three different fibre types (steel fibre, monofilament or fibrillated polypropylene fibres). Tests were performed by means of a special test setup developed at Politecnico di Milano, based on slabs (800 9 800 9 100 mm) subjected to Standard Fire at the bottom and to biaxial compressive loading in the mid-plane, while monitoring pore pressure, temperature and deflection. Explosive spalling was observed in both plain concrete slabs and in one of the two slabs with steel fibre, this casting some doubts on the use of steel fibre alone against spalling. No detachment was observed when polypropylene fibre was added to the mix.

Fire induced concrete spalling in combination with size effects

“…tunnel linings. All these concrete mixtures are prone for spalling in case of fire [1][2][3][4]. Spalling leads to an increase of the concrete temperature in deeper parts of the member.…”

Failure characteristics of reinforced concrete circular slabs subsequently subjected to fire exposure and static load: An experimental study

“…The literature contains many studies that have investigated the effect of fire on RC structural members, such as beams, [25][26][27][28][29][30] slabs, [31][32][33][34] or tunnel linings. [35][36][37][38] Despite all the research available, new recommendations and approaches for the design and assessment of concrete structures and structural components to protect against fire are still being published to this day.…”

Feasibility Study of Digital Image Correlation in Determining Strains in Concrete Exposed to Fire

“…Additionally, the thermocouples are placed at different depths in the concrete section to measure the temperature development inside the concrete element. Sometimes, the tests are enriched by further measurements; for example, embedded gauges placed at different distances to measure the pore pressure changes inside the concrete or linear voltage displacement transducers (LVDTs) installed at the exterior side of the element to monitor the deformation of the concrete element (especially the deflection) [8].…”