Emmanuel Keita

Emmanuel Keita
Gustave Eiffel University · Laboratoire NAVIER

PhD
Researcher in material science

About

49
Publications
16,092
Reads
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876
Citations
Additional affiliations
October 2016 - present
Gustave Eiffel University
Position
  • Researcher
Education
September 2009 - September 2010
September 2006 - September 2009
École Polytechnique
Field of study

Publications

Publications (49)
Article
Full-text available
The rapid development of 3D concrete printing now offers mechanical efficiency and freedom to push the limits of construction design. The digital manufacturing process holds potential for reducing carbon footprints through design optimization. Printable concrete, which is a mix of cement (based on ordinary Portland cement), aggregates, and admixtur...
Article
This study addresses the imbibition kinetics of finite water amounts in kaolinite plasters. Using an X-ray tomograph with in-situ liquid addition, 2D radiograph images precisely measure the water imbibition and distribution. Two distinct regimes are observed in the presence of a limited water reservoir. Following a classical penetration scaling wit...
Article
Full-text available
With the overall aim of supporting the development of new construction techniques and materials that are more economical and less carbon intensive, RILEM has decided to launch three new technical committees on earth construction in 2022. One of these committees will focus on the manufacturing processes used in earth construction (TC PEM). The aim o...
Article
Full-text available
We study here the imbibition of a nanosilica-based product in a hardened cement-based material along with the consequences of the product on transport properties. We use X-ray microtomography to assess the liquid ingress in the cement-based matrix as a function of time. We moreover measure the consequences of the nanosilica treatment on water absor...
Article
Full-text available
Besides the fact that concrete recycling allows to avoid landfills disposal and contributes to a closed-cycle economy, such option may be very much in demand in war struck regions such as Ukraine, which after the end of the war, are faced with the problem of rebuilding and reconstructing. Beyond this emergency, even in peacetime extensive parts of...
Article
Download this paper within the next 50 days: https://authors.elsevier.com/c/1efyH21ISlG4A ________ This paper focuses on material-process interactions in particle bed binding. After a classification of particle bed binding techniques currently available for cement-based materials, the most important material-process interactions and their underlyin...
Article
This paper deals with the control of the net geometry of a printed object in the case of powder-bed or particle bed binding technologies. We first measure and compare water penetration in one-dimensional experiments for various powder-beds. Our results, despite the simplicity of the experimental set-up, show a feature that has not been reported in...
Chapter
The comprehending of the processes’ physics is a prerequisite for the purposeful design and optimization of digital fabrication systems, as well as their efficient and robust process control. This chapter presents an overview of the underlying physics relevant to an understanding of the processing of cement-based materials during various production...
Conference Paper
The restoration, the protection, or the creation of earthen buildings require improving the mechanical strength of the material. The first way to do that is to use inorganic additives, but these additives change the structural properties of earth and have a high carbon footprint. In contrast, the other way to consolidate is the use of organic addit...
Article
Full-text available
The drying of porous media is a ubiquitous phenomenon in soils and building materials. The fluid often contains suspended particles. Particle deposition may modify significantly the final material, as it could be pollutants or clogging the pores, decreasing the porosity, such as in salt, in which particles and drying kinetics are coupled. Here, we...
Article
Full-text available
Currently, the largest among the earth excavation sites in Europe are located in the Paris region. The soils excavated from these sites are often considered waste and are not valorized. With an increasing focus on sustainable development, the demand for low-carbon building materials is rising. Although construction using raw earth is a vernacular t...
Article
This paper compiles selected predictive analytical and numerical tools which can be used to model and understand the mechanisms of importance at different stages during and immediately after extrusion-based 3D printing of cementitious materials. The proposed toolbox covers different aspects of the process including mixing, material transportation,...
Article
Full-text available
Increasing environmental concern has put forward the use of flax fibers instead of glass fibers in composite materials. However, durability performances of these bio-fibers remain one of their main issues. This study focuses on the hydrothermal aging of flax fibers. Flax tows were immersed in distilled water at a temperature of 80 °C for different...
Article
Earth plasters are a very interesting solution for the coating of earthen construction, in terms of embodied energy, technical efficiency, while keeping the hygroscopic properties of the wall, unlike very little permeable coatings, as the cement-based ones. An experimental campaign has been conducted on several earth plasters which differs by their...
Article
Full-text available
Earth-based building material processing is a challenge for new constructions. Moreover, field measurements to obtain the rheological properties of fresh materials are required in building applications. However, existing field-oriented tests were designed for more flowable materials, and new protocols for stiff materials are rarely available. In th...
Article
Polymer-modified mortars are cementitious materials that integrate polymers from 5 to 20 wt.%. Those materials are widely used for protecting and/or repairing concrete surfaces among which building facades, civil engineering structures, or sewage networks. In this context, polymer-modified mortars are applied into thin layers of about 1–3 cm. Howev...
Article
Full-text available
In the present work, we aim at improving our understanding of the effect of synthetic flexible fibers on the rheology of fresh cement-based suspensions. We first measure the way that synthetic fibers do increase the yield stress of various fresh cement pastes and mortars. We then measure, using micro CT, the way these fibers are deformed in a fresh...
Article
Full-text available
Recycled Concrete Aggregates are highly porous and may therefore absorb more water than natural aggregates. Several methods allow for the measurement of water absorption requiring drying at temperature above ambient conditions. We show here that, for temperatures above the ambient temperature (> 30°C) and at low relative humidity, the drying of rec...
Chapter
3D extrusion-based additive manufacturing is known as the most widely applied printing strategy for digital fabrication of civil engineering materials. This construction method does not only require specific rheological properties and structural build-ups rates, but also mechanical properties comparable to conventional materials. In the current wor...
Chapter
Powder-bed 3D printing technology is attractive as it allows to build complex structures and optimize cost and time. The liquid is sprayed to bond the powder bed at pre-determined positions layer by layer. After print, the non-bonded particles are removed during post-processing. From a material point of view, it is crucial to understand the interac...
Article
Full-text available
We study the impact, on the drying rate, of the presence of suspended elements, such as calcium sulfate ions, in the interstitial fluid of a porous medium. In order to single out this process in the complexity of a porous medium, we study it through drying in a simple capillary exhibiting characteristics such that it reproduces some critical aspect...
Article
Full-text available
Requirements on material properties for extrusion-based additive manufacturing mostly focus on the rheological behavior of the cementitious material being printed. The layer interface strength is therefore often considered to result from a proper mixing or remixing of two consecutive layers induced by the deposition process itself and therefore fro...
Conference Paper
Full-text available
Major component of raw earth construction, natural and reusable material, clays have amazing properties. They act as a binder in earthen materials and have enabled the building of cities since the beginning of the Neolithic revolution. However, their high sensitivity to the environment impacts the durability of clay-rich materials such as earthen o...
Article
Full-text available
In this paper, we compare the drying of non-reactive materials (glass beads packing) with the one of fresh mortars. Through the sample drying process, the existing literature on the general underlying physical processes involved in drying of porous media allows for the identification of two distinct regimes. These regimes drive the drying kinetics....
Article
Full-text available
From direct observations and MRI measurements we demonstrate that during the drying of a direct (oil in water) emulsion the whole system essentially concentrates homogeneously, which leads to shrinkage, without air penetration. The structure and mechanical strength (i.e. the elastic modulus) of this concentrated bulk are not significantly different...
Article
Full-text available
Assessment of the so-called "saturated-surface-dried" state shows a strong dependency on the test operator in the case of fine porous aggregates. This leads to low reliability and reproducibility of water absorption measurement for this family of particles. Evaporative methods for water absorption measurements seem to be a promising alternative. In...
Article
We focus in this paper on the bleeding of cement pastes. Our experimental results suggest that bleeding cannot be simply considered as the consolidation of a soft porous material but is of an obvious heterogeneous nature. It indeed leads to the formation of preferential water extraction channels. We measure here the existence of an induction period...
Article
Full-text available
The desiccation of porous materials encompasses a wide range of technological and industrial processes and is acutely sensitive to the hierarchical structure of the porous materials resulting in complex dynamics which are challenging to unravel. Macroscopic observations of the surface and geometry of model colloidal gels during desiccation under co...
Article
Full-text available
Polymers suspended in granular packings have a significant impact on water retention, which is important for soil irrigation and the curing of building materials. Whereas the drying rate remains constant during a long period for pure water due to capillary flow providing liquid water to the evaporating surface, we show that it is not the case for a...
Article
Full-text available
We look at the drying process in a simple glass channel with dominant capillary effects as is the case in microfluidics. We find drying kinetics commonly observed for confined geometry, namely a constant period followed by a falling rate period. From visualization of the air/water interface with high resolution, we observe that the drying rate decr...
Article
Full-text available
Direct observations of the surface and shape of model nano-colloidal gels associated with measurements of the spatial distribution of water content during drying show that air starts to significantly penetrate the sample when the material stops shrinking. We show that whether the material fractures or not during desiccation, as air penetrates the p...
Article
Full-text available
We show that the drying rate of plaster pastes is significantly lower than that expected for a pure liquid evaporating from a simple homogeneous porous medium. This effect is enhanced by the air flow velocity and the initial solid/water ratio. Further tests under various conditions and with the help of additional techniques (MRI, ESEM, Micro-tomogr...
Article
Full-text available
Drying of building materials and soils plays a major role in their final properties and is a main economics and environmental issue. In this thesis, we study the drying of complex porous media to better understand the impact of particles in the interstitial fluid. With a clear scale separation between the sample, pores and particles sizes, we obser...
Article
Full-text available
After drying colloidal particles suspended in a porous medium a concentration gradient appears. Using ^{1}H MRI we propose a protocol to observe simultaneously the distributions of air, liquid, and colloid through the unsaturated solid porous structure. Thus we show that the above phenomenon comes from a receding-front effect: The elements migrate...

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