Student Projects – Fall 2018-2019

Orientation of functionalised gold nanoplatelets in magnetic fields (LC3)

Responsible: Paul Bowen, paul.bowen@epfl.ch

In this project we propose to study the synthesis of a gold nanoplatelets suspension system to define and optimize its constituents for reversible platelet orientation by use of weak magnets.

After synthesis and functionalization of the platelets, suspension system candidates will be selected based on their aging properties. The candidate systems will thereafter be studied to optimize the ordered/disordered state and the transition time. Therefore the interaction between platelet solid load, viscosity, film thickness and the magnet intensity on the transition time and the orientation will be studied.

Characterisation of the platelets before and after functionalisation will be carried out using electron microscopy (SEM), dynamic light scattering (DLS) and laser doppler electrophoresis (for zeta potentials). Possible applications could be of interest to the watch, composite or ceramics industries.

Chloride binding of Limestone Calcined Clay Cements (LC3)

Responsible: François Avet, francois.avet@epfl.ch

Concrete is the most produced material in the world. Due to its massive production, cement and concrete are responsible for about 7% of man-made CO2 emissions. We do not have any magic solution today to fully replace cement. The most promising approach is to partially replace it by Supplementary Cementitious Materials (SCMs). These SCMs are aimed to keep the properties of conventional cements while reducing their cost and economic impact. Limestone Calcined Clay Cements (LC3) were developed at LMC, EPFL. In LC3, half of cement is replaced by a combination of calcined clay and limestone. About 30% of CO2 emissions are prevented using LC3 at a lower cost than plain cement.

In terms of mechanical properties, LC3 behaves better than plain cement from 7 days onwards even using clays with quite low amount of kaolinite. Durability is also an important concern for concrete, especially its resistance against chloride ingress. Chloride resistance depends on the porosity of the material as well as its binding capacity.

In this project, the binding capacity of LC3 will be characterized, varying the kaolinite content of clay. Several NaCl solutions will be used, and the amount of bound chloride will be determined by titration. Moreover, the microstructure will be studied. Phase assemblage will be characterized by X-Ray Diffraction (XRD) and Thermogravimetric Analysis (TGA). The chloride distribution in the microstructure will be studied by Scanning Electron Microscopy (SEM-EDX).

Concrete and cementitious materials in Haiti

Responsible: Elise Berodier, elise.berodier@epfl.ch

This study is part of a large project on understanding the use of concrete in developing countries in collaboration with the University of Port-au-Prince and the Swiss Cooperation.

This semester project aims to characterize the concrete samples collected in different construction sites in Port-au-Prince area. Samples will be received from different locations such as close to the sea, near quarries or rivers, places isolated from transportation and countryside locations which can limit the access to concrete materials. The analysis will give insights on how concrete-making and materials are depend on the location of the construction site. The results will be combined with strength data provided by the local team from University of Port-au-Prince and the Swiss Cooperation in Haiti.

X- Ray Diffraction and Scanning Electron Microscopy will be the major techniques to characterize the materials.

Tracking the early stage formation of Alkali Silica Reaction

Responsible: Solène Barbotin, solene.barbotin@epfl.ch

Alkali-Aggregate Reaction (AAR) and more specifically Alkali-Silica Reaction (ASR) is an endogenous chemical reaction happening in concrete material. It is one of the most important degradation mechanism affecting concrete structures.

As mentioned in numerous books and publications, three conditions are necessary for the alkali-silica reaction to occur :

  • presence of reactive silica, coming from the aggregates
  • presence of water or moisture, mainly from the pore solution, but also from external water supply during the structure life
  • alkali ions, primarily coming from the cement

Metastable silicates present in aggregates are dissolved by hydroxyl groups OH- in the alkaline pore solution. The degrading silica structure then bonds mainly to water, calcium and alkali ions. Due to the water uptake, the reaction products expand, leading to stress in the aggregates and subsequent cracking of the structure.

In Switzerland, several hundreds of structures are affected and it is a major concern in the field, especially for structures where mechanical properties and dimensions must be stable over time, like bridges and dams.

So far, only the second stage ASR product has been studied, and information about the initial formation of the product and its evolution is of prior interest.

Goal of the project : Be able to localize ASR early stage formation and follow its formation with time (composition, product morphology, crack opening…) using Scanning Electron Microscopy (SEM)

Concerning the techniques, you will mainly learn how to use a SEM, and be able to operate it by yourself, as well as the preparation steps.

Understanding and modelling chloride diffusion in porous cement systems

Responsibles: William Wilson, william.wilson@epfl.ch / Shiyu Sui, shiyu.sui@epfl.ch

Chloride-induced corrosion represents the most important threat to reinforced concrete structures exposed to de-icing salts and/or marine environments. Modern concrete incorporating supplementary cementitious materials (SCMs) can now be designed to prevent the chloride ions to reach the reinforcing bars before several decades. Nevertheless, the fundamental understanding of the different mechanisms responsible for chloride penetration still require further research to accurately model the service life of concrete exposed to chlorides.

In this semester project, the mission of the student will be to investigate the link between the multi-scale porosity of hydrated cement systems and the chloride diffusion capacity. A series of blended-cement systems will be investigated, with varying water-to-binder ratios and incorporating novel SCMs, such limestone calcined clay cements (LC3). More precisely, the student will work in collaboration with our research team using advanced experimental methods such mercury intrusion porosimetry, pore solution extraction and characterization, and the SIMCO chloride migration cell (an electricity-accelerated test to investigate chloride diffusion). Ultimately, the aim will be to improve the prediction of the long-term resistance to chloride-induced corrosion of real concrete structures, using the collected experimental data as input for chloride transport modelling with the STADIUM software.

Preparation of different ordering of silica plate by heating and the effect of aluminum on the dissolution rates of the prepared samples at high pH

Responsible: Mahsa Bagheri, mahsa.bagheri@epfl.ch

Alkali-silica reaction (ASR), as a worldwide durability concern for concrete structures, causes cracks and damage in concrete structures, creating remarkable costs to repair or to reconstruct. ASR is a long-term chemical reaction between amorphous silica (from reactive aggregates) and alkalis (mainly from pore solution of cement paste), producing ASR products, which form an expansive gel in the presence of water.

Addition of Supplementary cementitious materials (SCMs) to Portland cement (PC) has been introduced to reduce or even stop expansion of ASR. Especially, alumina rich SCMs such as fly ash have been indicated to be more efficient in avoiding ASR. Chappex and Scivener in 2012 showed the decrease in the rate of silica dissolution due to adsorption of aluminum on the reactive silica surface.

Among various parameters, the degree of ordering and also structural defects have noticeable effects on the dissolution kinetics.

The main goal of the present project is preparation of different ordering of silica plates by heating, and then the role of aluminum on the silica dissolution rates will be investigated at high pH. Inductively Coupled Plasma/Optical Emission Spectrometry (ICP-OES) will be used to determine the ion concentrations, and also to track the change of the morphology, Scanning Electron Microscope (SEM) will be used.