Contribution à l’étude des transferts hydriques et colloïdaux dans les milieux poreux : cas d’application aux matériaux cimentaires

The existence of porosity inside concrete allow transport of aggressive substance that lead to the degradation of the concrete structure. The remaining possible solutions to extend life expectancy of the structure are either its protection or reparation. A nanosilica-based technology is applied as a reparation solution for existing structures. This solution was promoted from the uses of nanosilica in formulation of high performance concrete. However, reparation or protection mechanisms of nanosilica in existing concrete remain little studied. The aim of this study is to define the physical framework when a suspension of nanosilica particles is applied on top of a cementitious matrix and to develop a methodology to assist during the application process.During imbibition of cement paste and mortar, we identify the existence of a critical depth where the flow regime of nanosilca decelerate drastically in the cementitious matrix. We show the probabilistic nature of this critical depth and its similarities to clogging like its dependency to the nanosilica volume fraction and porosity size of the medium. After nanosilica treatment, we assess the effect of treatment and the decrease of water transfers preceded by an induction period. An overclogging ratio is built upon the acquired knowledge of clogging and durability tests that measure the thickness of the formed silica layer. Based on the overclogging ratio, we develop a method that could assist when surface treating with nanosilicaLa présence de porosité à l’intérieur du béton permet le transport de substances agressives favorisant la dégradation de la structure en béton. Selon l’état de la structure, on peut envisager sa protection ou sa réparation afin de prolonger sa durée de vie. Une solution technologique à base de nanoparticules de silice est appliquée comme solution de réparation de structures existantes. Cette solution est inspirée de l’utilisation de la nanosilice lors de la formulation des bétons à hautes performances. Néanmoins, les mécanismes de réparation ou protection de la nanosilice sur des bétons existants restent peu étudiés. L’objectif de cette thèse est de comprendre les procédés physiques mis en jeu lors de l’application de nanosilice sous forme de suspension sur une matrice cimentaire durcie et de proposer une méthodologie adaptée lors de l’application.Lors de l’imbibition de pâtes de ciment et de mortiers par la nanosilice, nous identifions l’existence d’une profondeur critique qui caractérise un régime d’écoulement ralenti. Nous montrons le caractère probabiliste de cette profondeur critique. Le mécanisme à l’oeuvre peut s’apparenter à un colmatage et nous montrons sa dépendance à la fraction volumique de la nanosilice et à la taille de porosité. Après traitement à la nanosilice, nous montrons que les transferts hydriques sont réduits et nous étudions la période d’induction qui résulte de ce traitement. Sur la base des connaissances acquises et des résultats de durabilité, nous définissons un ratio de surcolmatage qui permet d’évaluer l’épaisseur de la croute de silice formée. À l’aide du ratio de surcolmatage, nous proposons une méthode qui permet d’assister lors de l’application de la nanosilice sur chantie

Contribution to the understanding of aqueous and colloid transfers in porous media : application to cementitious materials

La présence de porosité à l’intérieur du béton permet le transport de substances agressives favorisant la dégradation de la structure en béton. Selon l’état de la structure, on peut envisager sa protection ou sa réparation afin de prolonger sa durée de vie. Une solution technologique à base de nanoparticules de silice est appliquée comme solution de réparation de structures existantes. Cette solution est inspirée de l’utilisation de la nanosilice lors de la formulation des bétons à hautes performances. Néanmoins, les mécanismes de réparation ou protection de la nanosilice sur des bétons existants restent peu étudiés. L’objectif de cette thèse est de comprendre les procédés physiques mis en jeu lors de l’application de nanosilice sous forme de suspension sur une matrice cimentaire durcie et de proposer une méthodologie adaptée lors de l’application.Lors de l’imbibition de pâtes de ciment et de mortiers par la nanosilice, nous identifions l’existence d’une profondeur critique qui caractérise un régime d’écoulement ralenti. Nous montrons le caractère probabiliste de cette profondeur critique. Le mécanisme à l’oeuvre peut s’apparenter à un colmatage et nous montrons sa dépendance à la fraction volumique de la nanosilice et à la taille de porosité. Après traitement à la nanosilice, nous montrons que les transferts hydriques sont réduits et nous étudions la période d’induction qui résulte de ce traitement. Sur la base des connaissances acquises et des résultats de durabilité, nous définissons un ratio de surcolmatage qui permet d’évaluer l’épaisseur de la croute de silice formée. À l’aide du ratio de surcolmatage, nous proposons une méthode qui permet d’assister lors de l’application de la nanosilice sur chantierThe existence of porosity inside concrete allow transport of aggressive substance that lead to the degradation of the concrete structure. The remaining possible solutions to extend life expectancy of the structure are either its protection or reparation. A nanosilica-based technology is applied as a reparation solution for existing structures. This solution was promoted from the uses of nanosilica in formulation of high performance concrete. However, reparation or protection mechanisms of nanosilica in existing concrete remain little studied. The aim of this study is to define the physical framework when a suspension of nanosilica particles is applied on top of a cementitious matrix and to develop a methodology to assist during the application process.During imbibition of cement paste and mortar, we identify the existence of a critical depth where the flow regime of nanosilca decelerate drastically in the cementitious matrix. We show the probabilistic nature of this critical depth and its similarities to clogging like its dependency to the nanosilica volume fraction and porosity size of the medium. After nanosilica treatment, we assess the effect of treatment and the decrease of water transfers preceded by an induction period. An overclogging ratio is built upon the acquired knowledge of clogging and durability tests that measure the thickness of the formed silica layer. Based on the overclogging ratio, we develop a method that could assist when surface treating with nanosilic

Innovative Cutting and Valorization of Waste Fishing Trawl and Waste Fishing Rope Fibers in Cementitious Materials

International audienceThe valorization of waste fishing trawl (WFT) and waste fishing rope (WFR) fibers in cementitious materials (CMs) has gained attention in recent years; however, the lack of information on the cutting and cleaning techniques for these fibers hinders their widespread commercial utilization. Existing research primarily relies on manual cutting, which proves to be impractical for large-scale production due to its time-consuming nature and lack of industrial feasibility. This research is a component of the VALNET project and introduces an innovative technique that utilizes the cutting mill to convert WFT and WFR into fibers to effectively overcome the constraints of earlier methodologies. By employing a rotor with blades, this apparatus enables efficient and precise cutting of WFT and WFR, eliminating the need for labor-intensive manual cutting. The sustainable cleaning of WFT and WFR was carried out utilizing rain and wind by placing them outside for a certain period of time. The advancements presented in this study provide a pathway for an efficient and scalable valorization of WFT and WFR fibers in CM. The study focused on analyzing the impact of varying fiber sizes and percentages on the mechanical properties of CM. Different sizes obtained from the cutting machine and different fiber percentages were examined to gain a better understanding of their influence. The fibers obtained by the utilization of a 20 mm sieve yield optimal outcomes, while the incorporation of fibers at a volume fraction of 0.5% yields the most favorable results. Furthermore, the study presents evidence of a noticeable rise in porosity resulting from the incorporation of WFT and WFR fibers, regardless of their size and proportion. Porosity slightly increases as the fiber length increases, but the rise in fiber proportion leads to a significantly greater increase in porosity

Nanosilica-based post-treatment of hardened cement-based materials: The underlying physics

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 absorption and chloride penetration. Our results suggest that nano-silica imbibition in cement-based materials involves some deep particle clogging and, in turn, some phase separation in the porous cement-based material. As a consequence, the effective local concentration of nano-silica increases in a clogged zone located between a critical clogging depth and the surface. In this zone, the silica concentration level in the porosity allows for the formation of a physical barrier inside the material, which can, in turn, affect transport properties