Micro and macro-structural effects of high temperatures in Prada limestone: Key factors for future fire-intervention protocols in Tres Ponts Tunnel (Spain)

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Title: Micro and macro-structural effects of high temperatures in Prada limestone: Key factors for future fire-intervention protocols in Tres Ponts Tunnel (Spain)
Authors: Martínez-Ibáñez, Víctor | Garrido, M. Elvira | Hidalgo Signes, Carlos | Tomás, Roberto
Research Group/s: Ingeniería del Terreno y sus Estructuras (InTerEs)
Center, Department or Service: Universidad de Alicante. Departamento de Ingeniería Civil
Keywords: Thermal damage | Physical and mechanical properties | Cracks | Tunnel fire | Limestone | Correlations
Knowledge Area: Ingeniería del Terreno
Issue Date: 7-Jun-2021
Publisher: Elsevier
Citation: Construction and Building Materials. 2021, 286: 122960. https://doi.org/10.1016/j.conbuildmat.2021.122960
Abstract: Temperature and cooling methods strongly affect the stability of tunnels drilled in rock masses and so condition interventions for fire emergencies. Samples from two horizontal boreholes drilled in Prada limestone during the design stage of the Tres Ponts Tunnel in the Catalan south Pyrenean zone (Spain) are heated from 105 to 600 °C, and subsequently cooled with air or water to simulate fire extinguishing interventions. Changes in chemical composition and microstructure, physical properties (open porosity, volume, dry total weight, P and S-wave velocity), and mechanical properties (uniaxial compressive strength, elastic modulus, and Poisson’s ratio) are analysed. Rock weakening is observed even at low temperatures (T < 300 °C). The influence of the cooling method appeared at intermediate temperatures of 300-400 °C and open porosity, P and S-wave velocities, and elastic modulus show greater variation for water-cooled samples. A temperature of 500 °C is of paramount importance for ‘Prada’ limestone as it leads to a dramatic increase in porosity and a notable decrease in P and S-wave velocities under both cooling methods. Trans-granular micro-crack progression is observed at 500 °C using scanning electron microscope (SEM), and water-cooled samples show a greater loss in uniaxial compressive strength (UCS), and this is due to micro-crack connections and growing fissures. Thermal damage at 600 °C is also greater when samples are quickly cooled. An ANOVA and a simple regression analysis are performed to discard the influence of the natural location of the borehole samples in the obtained experimental results. Finally, correlations to predict UCS and elastic modulus from volume, open porosity, and P-wave velocity after thermal treatment are proposed using simple exponential and potential functions to help make preliminary decisions after a tunnel fire. These predictive results on the effects of fire on Prada limestone will be considered for the definition of future fire intervention protocols in the Tres Ponts Tunnel.
Sponsor: This research was partially supported by the Vice-Rector of Research and Knowledge Transfer at the University of Alicante through projects UAUSTI19-25 and UAUSTI20-20, and by the Departamento de Ingeniería del Terreno at the Universitat Politècnica de València.
URI: http://hdl.handle.net/10045/113802
ISSN: 0950-0618 (Print) | 1879-0526 (Online)
DOI: 10.1016/j.conbuildmat.2021.122960
Language: eng
Type: info:eu-repo/semantics/article
Rights: © 2021 Elsevier Ltd.
Peer Review: si
Publisher version: https://doi.org/10.1016/j.conbuildmat.2021.122960
Appears in Collections:INV - INTERES - Artículos de Revistas

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