AN INVESTIGATION OF EXPLOSIVE SPALLING IN CONCRETE: IS PORE PRESSURE MORE IMPORTANT OR THERMALLY INDUCED STRESS

Concrete spalling under fire critically threatens structural safety. It is widely attributed to coupled
thermo-hygro-mechanical (THM) processes, but the relative roles of pore pressure and thermal stress remain
disputed. This study addresses the issue by combining a fully coupled peridynamic THM model with H-TRIS
fire tests on concrete slabs. The peridynamic framework couples heat, moisture and solid deformation with
temperature-dependent permeability and damage, and introduce a volume-averaged damage metric to separate
pore-pressure-driven and stress-driven contributions. Three-dimensional simulations directly reproduce crack
initiation, propagation and spalling depth. H-TRIS tests with systematically varied water–cement ratio,
in-plane restraint and polypropylene fibres show that high w/c and strong restraint produce the most violent
spalling, while fibres largely suppress explosive cover loss. The simulations capture these trends and the
observed damage morphologies. We found that for low-w/c concrete (w/c=0.3), damage and spalling is
controlled by thermally induced stresses, particularly under rigid in-plane restraint. For high-w/c concrete
(w/c=0.6), pore-pressure loading makes a substantial, though not dominant, contribution to damage, leading to
distributed microcracking that relieves pressure without violent fragment ejection. The combined
experimental–numerical framework clarifies spalling mechanisms and enables physics-based prediction of
fire-induced concrete failure.