Abstract

When exposed to fire, concrete is liable to fracture and spalling owing to thermo-hygro-mechanical
phenomena. It is challenging to gain a deep and systematic understanding of high temperature
induced cracking in concrete due to the interplay of several physical phenomena, some of which
are non-linear. In particular, spalling is widely considered to be highly dependent on the mi-
gration, evaporation and condensation of internal moisture content. Numerical modelling may
be the only viable method for studying high temperature concrete fracture phenomena, as the
real time observation of moisture propagation, evolution of vapour content and induced pore
pressure, and mechanical strain in 3D are difficult or infeasible to obtain by experimentation.

The model presented in this study simulates coupled thermal and multi-phase moisture dif-
fusion, and the induced mechanical deformation and fracture owing to thermal gradients and
build-up of pore pressure. Studies in this area are usually limited to 1D or 2D problems, despite
the fact that cracking is inherently a 3D phenomenon. PDS-FEM was used as the numerical
method since it provides a numerically efficient treatment for simulating crack propagation in
large 3D models. The model was validated against experimental data [1] by comparing with the
measured pressure and temperature at varying depths, where good qualitative agreement was
met. Using the validated model, a full 3D simulation was conducted in order to explore and
compare the simulated fracture pattern with available visual data [2].

As a result of the observed results, we speculate that a build-up of moisture inside the macro-
cracks may be a key mechanism responsible for spalling. Therefore, we also introduce a mech-
anism by means of an additional boundary condition for the release of moisture into the opened
cracks. This has laid the groundwork for estimation of the additional macroscale pressure ex-
erted on the concrete skeleton inside the cracks themselves.
Keywords: Concrete, High temperature, Fracture, 3D simulation, Particle-Discretisation Scheme
Finite Element Method, High Performance Computing.

References

[1] Kalifa, P., Menneteau, F. D., & Quenard, D. (2000) Spalling and pore pressure in HPC at high
temperatures. Cement and concrete research 30(12), 1915–1927.
[2] Mindeguia, J. C., Pimienta, P., Carr ́e, H., & La Borderie, C. (2009) Experimental study on the
contribution of pore vapour pressure to the thermal instability risk of concrete. 1st International
Workshop on Concrete Spalling due to Fire Exposure