Original Research Article On reliable predicting risk and nature of thermal spalling in heated concrete Dariusz Gawin a, * , Francesco Pesavento b , Angel Guerrero Castells c a Łódź University of Technology, Department of Building Physics and Building Materials, Al. Politechniki 6, 90-924 Łódź, Poland b University of Padova, Department of Civil, Environmental and Architectural Engineering, via Marzolo 9, 35131 Padova, Italy c Ignia, Cl. Aragón 67, Ibiza, Baleares, Spain 1. Introduction Reliable prediction of durability and safety of concrete structures during a fire is of great practical importance, especially when designing concrete elements of high rise buildings or concrete lining of tunnels [1–3]. During heating of such structures, especially with a high rate, their integrity is endangered by the so-called thermal spalling. This paper addresses some issues concerning numerical simulations and prediction of this phenomenon (i.e. the interpretation and application of the numerical results), providing some possible solutions. The phenomenon of spalling is briefly described in Section 2. To assess the risk of thermal spalling occurrence for a concrete structure exposed to heating under given condi- tions, the evolutions of temperature, moisture content, pore a r c h i v e s o f c i v i l a n d m e c h a n i c a l e n g i n e e r i n g 1 8 ( 2 0 1 8 ) 1 2 1 9 – 1 2 2 7 a r t i c l e i n f o Article history: Received 15 July 2017 Accepted 18 January 2018 Available online Keywords: Thermal spalling Heated concrete Numerical simulations Energetic analysis Porous media mechanics a b s t r a c t Thermal spalling is a deterioration phenomenon which is of fundamental importance during durability analysis of concrete structures exposed to high temperature, e.g. during a fire. To assess the risk of this damage mechanism for a real concrete structure, numerical simulations are usually applied since experimental tests are very costly. Some aspects related to predicting thermal spalling by means of numerical modelling of chemo-hygro- thermal and damage processes in heated concrete, are presented in this work. First, we propose a spalling index, validate it with some experimental results and show how it can be used in the quantitative assessment of spalling risk. Then, the results of numerical simula- tions of a slab, made of two types of concrete (NSC and HPC), heated with three different rates, are discussed from the energetic point of view in order to indicate the main physical causes and predict the nature of thermal spalling: slow, rapid or violent. The presented results allow to assess the contribution of energy due to constrained thermal strains and compressed pore gas into the thermal spalling for different types of concrete heated with different rates. © 2018 Politechnika Wrocławska. Published by Elsevier Sp. z o.o. All rights reserved. * Corresponding author. E-mail addresses: dariusz.gawin@p.lodz.pl (D. Gawin), francesco.pesavento@dicea.unipd.it (F. Pesavento), agc@ignia.es (A.G. Castells). Available online at www.sciencedirect.com ScienceDirect journal homepage: http://www.elsevier.com/locate/acme https://doi.org/10.1016/j.acme.2018.01.013 1644-9665/© 2018 Politechnika Wrocławska. Published by Elsevier Sp. z o.o. All rights reserved.