Universit de Pau et des Pays de lAdour
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Université étatique, Parcourir ses opportunités similaires
Study of the behaviour at high temperature of earth-based materials: Effect of manufacturing method, water content and fibres.
Context of the study
The use of raw earth is booming as a solution to reduce the environmental impact of construction. This material, although used for thousands of years, still presents scientific challenges due to the need to ensure compliance with current regulations and new material developments. Among these issues is its fire behaviour which is one of the major issues in building safety. Earth has been fired for thousands of years to produce terracotta, which gives it much better water resistance and stability than raw earth. However, rapid heating, which is the case in a fire, of a wet clay, which is the case in certain environments, can lead to instabilities and then the complete destruction of a wall.
The work carried out in the SIAME laboratory of the UPPA in collaboration with the Civil Engineering laboratory of the Lebanese University has made it possible to study the behaviour of compacted earth bricks at high temperature (PhD of Rafik Abdallah). In the absence of cement stabilisation, these bricks showed risks of instability during heating of the building fire type (ISO 834-1 fire) for intermediate water contents (after conservation at 50 and 75 % R.H.). This work has highlighted the predominant effect of water, which influences both the mechanical strength and the thermal gradients that appear during heating.
This work will be carried out within the ConstrucTerr chair, which conducts research on the comfort and durability of raw earth materials. It is also part of a national and international dynamic through the participation of the holders in the national earth project and the RILEM working group on raw earth: https://www.rilem.net/groupe/mae-mechanical-performance-and-durability-a... .
The post-doctoral student will actively participate in these networks to disseminate the results of the research, to exchange with the Chair's partners involved in the studies and to participate in the setting up of projects.
Objectives of the study
Earth-based building materials are varied and the range of strengths involved is very wide. Compacted earth bricks, stabilised or not, already tested in the laboratory, have a compressive strength of 5 MPa. In order to complete this work, other types of materials with lower and higher strengths can be mentioned, such as adobe and earth concretes.
Previous work has shown the importance of the effect of the water content of bricks on the risk of instability. Indeed, large temperature gradients within the material can lead to moisture transfer due to the thermodiffusion phenomenon. The work in this study will involve both the measurement of temperatures and the study of moisture transfer during fire-type heating. The experimental measurements will then be compared with coupled heat and mass transfer models.
The fire behaviour of building materials is also influenced by the mechanical loading applied to the tested material during heating. Even very moderate compression (a few MPa) parallel to the heated face can strongly increase the risk of thermal instability of concrete. This effect is even more important in the case of biaxial compression, compared to uniaxial compression. The design of a new test for assessing the risk of spalling on a medium scale (50 cm diameter plate) has been developed: the modified ring test. Through the use of this test, the present study will also highlight the effect of peripheral confinement on the risk of instability for one of the materials studied.
The main objectives of the study are therefore:
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