- Université Gustave Eiffel
- Research Field
- ChemistryChemistry » Physical chemistryEngineeringEngineering » Materials engineering
- Researcher Profile
- First Stage Researcher (R1)
- Application Deadline
- Type of Contract
- Job Status
- Hours Per Week
- Is the job funded through the EU Research Framework Programme?
- H2020 / Marie Skłodowska-Curie Actions COFUND
- Marie Curie Grant Agreement Number
- Is the Job related to staff position within a Research Infrastructure?
Raw earth construction has experienced a new boom in recent years with ambitious architectural projects and under the pressure imposed by the urgency to save natural resources and to reduce the carbon footprint of the construction sector. Raw earth construction, although decarbonised, is still a sign of 'poverty' and associated with poor sustainability properties. While the usual lime and cement addition improves the earth mechanical performance and its water resistance, their manufacture emits greenhouse gases. However, earthworks in some countries already proposed an alternative soil treatment for road construction by replacing lime/cement by an enzyme-rich solution (i.e. a bio-sourced macromolecule). Although treatments with various marketed products lead to a global reduction of CO2 emissions and contribute to the development of roads without bituminous coatings, this technique remains not widespread in temperate countries such as France. Indeed, obtaining an efficient treatment requires a rigorous and bonding application protocol. In other words, the treatment does not work in all cases.
In this context, the PhD thesis will apply enzymatic treatments on natural soils to produce improved compressed earth bricks (CEB) for building construction with low environmental impact. Compared to earthworks that use complex and variable in-situ soils, CEB manufacturing platforms use homogeneous stock of soil and tools that allow the control and the optimization of the granular skeleton and mineralogical composition of the material.
The enzyme treatment should strengthen the soil for use in self-supporting structures and reduce the broken bricks during transport. At the same time, the reinforcement should not induce negative effects on the properties of CEB, such as hygro-thermal properties or material durability through particle loss due to wind erosion or after contact with liquid water (by rebound effect of raindrops or during superficial rain runoff). Note that the effects of water vapor in contact with CEB and liquid water in contact with treated soil in earthwork will have to be compared to better understand the action mode of enzymes.
To achieve previous objectives, experimental tests will be set up in the laboratory at brick scale, complemented by a 1:1 application in Sence city equipex (corresponding to a 400 m2 climate chamber with environmental sensors and with housing small buildings submitted to durability test) as well as a life cycle assessment (LCA) calculation to estimate the real benefit of the enzymes addition.
The PhD student will use both material (geomaterials) and geotechnical approaches (proctor compaction test compared with factory compaction tools, soil identification such as methylene blue value or Atterberg limits complemented by X-ray diffraction quantitative mineralogical analysis and chemical tests to characterize surface or bulk material).
In this context, issues requiring developments in the PhD thesis are the following:
- A wide variety of enzymes exist in nature but can it be identified whether all enzymes improve the mechanical properties of soils or only a particular class of molecules. If so, what are the characteristics of these molecules?
- The conditions to improve the mechanical properties remain unclear as well as the explanation of why a fine fraction, in particular clays (and swelling clays) or organic matter are usually required. Only one process or several must be involved and it is questionable whether the molecule can act by itself or is its role limited to catalysis. Hypothetically, enzyme may act for example by a exchange reaction (using the cation exchange capacity of clays) or by adsorption on soil particles by electrostatic interaction using the surface charge. A modification of the wettability of soil mineral surfaces, particularly clays, could also explained enzyme action, if this macromolecule has a surface-active property (surfactant effect). The latter can act on water property in the soil porosity and thus induce a porosity rearrangement, which modifies the suction and the soil cohesion. Of course, the catalytic effect as expected with enzyme, must be explored but in this case, the involved reaction has to be identified and does such a reaction use mineral/organic species and/or micro-organisms at the origin of the precipitation of "binding" products allowing the soil reinforcement. The different scenarios from literature will have to be studied and validated using various soil compositions (clay minerals such as illite, kaolinite, montmorillonite with more or less organic matter). Adsorption tests at the solid/liquid interface complemented by the measurement of the variation in surface tension or contact angle before and after treatment will be used, as well as X-ray diffraction to monitor the size of interlayer space, a characteristic of swelling clay minerals. Coupled effects with other compounds in soil (i.e. iron oxides) or additives (dispersing, flocculating agents...) should be explored.
- Finally, the degree of soil compaction also has an important impact on the treatment efficiency. The soil microstructure should therefore be studied qualitatively by scanning electron microscopy, but also quantitatively by mercury intrusion porosimetry and other measurement methods. The pore structure and the degree of physical or chemical bonding between particles (their organization/aggregation) will be used to explain and optimize the formulation of an improved CEB.
After preparation until the obtaining of optimized formula (to be compared with the recommendations proposed by enzyme suppliers), the treatment efficiency will be assessed using a compressive strength test as well as a swelling test in an oedometer cell (or by a water immersion/dispersion test). The resistance to erosion will be given by the modified MOJET test (a home-made device developed in the laboratory for in situ testing by using controlled liquid water jets). Between the effect of a highly compacted microstructure and/or the action of enzymes, the main explanation of the soil water resistance enhancement will have to be found.
Finally, the PhD thesis proposes a multi-scale study of raw earth material ranging from the particle scale to the use properties. After the demonstration of the treatment efficiency under well-established conditions, collaboration with a manufacturer of enzymes and a CEB factory using soils excavated from the Grand Paris train line is planned to test the treatment at industrial scale and the long-term durability of manufactured bricks will be monitored on walls in Sence city platform.
- Research Field
- Education Level
- Bachelor Degree or equivalent
- At the time of the deadline, applicants must be in possession or finalizing their Master’s degree or equivalent/postgraduate degree.
- At the time of recruitment, applicants must be in possession of their Master’s degree or equivalent/postgraduate degree which would formally entitle to embark on a doctorate.
- High-quality doctoral training rewarded by a PhD degree, delivered by Université Gustave Eiffel
- Access to cutting-edge infrastructures for research & innovation
- Appointment for a period of 36 months based on a salary of 2 700 € (gross salary per month)
- Job contract under the French labour legislation in force, respecting health and safety, and social security: 35 hours per week contract, 25 days of annual leave per year
- International mobility will be mandatory
- An international environment supported by the adherence to the European Charter & Code
- Access to dedicated CLEAR-Doc trainings with a strong interdisciplinary focus, together with a Career development Plan
Applicants must fulfil the following eligibility criteria :
- At the time of the deadline, applicants must be in possession or finalizing their Master’s degree or equivalent/postgraduate degree
- At the time of recruitment, applicants must be in possession of their Master’s degree or equivalent/postgraduate degree which would formally entitle to embark on a doctorate
- At the time of the deadline, applicants must be in the first four years (full-time equivalent research experience) of their research career (career breaks excluded) and not yet been awarded a doctoral degree. Career breaks refer to periods of time where the candidate was not active in research, regardless of his/her employment status (sick leave, maternity leave etc). Short stays such as holidays and/or compulsory national service are not taken into account
- At the time of the deadline, applicants must fulfil the transnational mobility rule: incoming applicants must not have resided or carried out their main activity (work, studies, etc.) in France for more than 12 months in the 3 previous years
- One application per call per year is allowe
- Applicants must be available full-time to start the programme on schedule (November 1st 2023)
- Application rules are enforced by the French doctoral system which specifies a standard duration of 3 years for a full-time PhD together with the MSCA standards and the OTM-R European rules as follows
- Citizens of any nationality may apply to the programme
- There is no age limit
- Please refer to the Guide for Applicants available on the CLEAR-Doc website: https://clear-doc.univ-gustave-eiffel.fr/how-to-apply/useful-documents/
- The first step before applying is contacting the PhD supervisor. You will not be able to apply without an acceptation letter from the PhD supervisor
- International mobility: Please contact the PhD supervisor for any additional detail on the international mobility.
- Please contact the PhD supervisor for any additional detail on job offer
- There are no restrictions concerning the age, gender or nationality of the candidates Applicants with career breaks or variations in the chronological sequence of their career, with mobility experience or with interdisciplinary background or private sector experience are welcome to apply
- Support service is available during every step of the application process by email: firstname.lastname@example.org
- Website for additional job details
- Number of offers available
- Université Gustave Eiffel
- Postal Code
- 5, Boulevard Descartes
Where to apply
- 5, Boulevard Descartes
- Postal Code