Ciment Portland | EPFL Graph Search

thumb|right|280px|Sacs de ciment Portland. Les ciments Portland sont des liants hydrauliques composés principalement de silicates de calcium hydrauliques qui font prise et durcissent en vertu d'une réaction chimique à l'eau appelée hydratation. Lorsqu'on ajoute la pâte (ciment, air et eau) aux granulats (sable et gravier, pierre concassée ou autre matériau granulaire), elle agit comme une colle et lie ensemble les granulats pour former une masse semblable à de la pierre, le béton, le matériau artificiel le plus polyvalent et le plus répandu qui existe. thumb|, un des lieux historiques de la fabrication sous franchise du ciment Portland aux États-Unis thumb|Un moulin à ciment de 10 MW d'une capacité de 270 tonnes/h. le moulin à ciment est l'équipement qui sert à moudre le clinker dur et nodulaire du four à ciment en la fine poudre grise qui est le ciment. Le ciment est broyé dans des broyeurs à boulets. Jusqu'au début du , la manière de faire le mortier a presque toujours été laissée aux ouvriers. Avec le , une bataille s'engage entre pays pour la suprématie économique. Les progrès réalisés par l'industrie exigent la construction de nouvelles infrastructures portuaires, militaires dont l'édification peut désormais être guidée par la technique. Les progrès de la chimie, qui depuis le Moyen-Âge est passée du statut de technique empirique à celui de science exacte au , permettent de scruter les comportements de la matière comme jamais auparavant. Des architectes, des ingénieurs et de brillants inventeurs s'attellent donc à l'amélioration des mortiers et plus particulièrement ceux faisant prise sous eau. Les Romains obtenaient de tels mortiers en ajoutant à de la chaux grasse des tuileaux ou de la pouzzolane naturelle, et cet état de connaissance est celui qui prévaut encore à la fin du . La thèse qui s'impose alors est que c'est l'argile qui confère à la chaux la propriété de se solidifier sous eau, mettant fin à une tradition qui voulait que ce soient les calcaires les plus purs qui donnent les meilleures chaux.

Precipitation, Characterization, Kinetic, and Thermodynamic Modelling of Synthetic C-S-H Systems (C-S-H, CASH, CSH+$)

Maya Nicole Harris

This thesis investigates the effects of aluminates, sulfates, and heterogeneous substrates on the nucleation and growth of synthetic calcium-silicate-hydrates (C-S-H) produced by dropwise precipitation. The use of synthetic C-S-H, separate from other cementitious phases, allows formation mechanisms and kinetics effects to be investigated in a simplified system. The addition of other ions and substrates then allows an approach to the more complicated, multi-phase system of cement and concrete. The first goal of this thesis was to reproducibly synthesize single-phase C-S-H with Ca:Si from 1 to 2. Guidelines were described for collection, drying, and handling of the precipitates to prevent the formation of Ca(OH)2 during synthesis and minimize carbonation. Interlayer spacing in precipitates was studied by transmission XRD to compare the effects of Ca:Si, relative humidity, and time, using the 14Å tobermorite structure as a baseline for synthetic C-S-H. The growth and nucleation kinetics of C-S-H were then investigated with the combined thermodynamic and population balance equation model (PBEM). The surface characteristics of C-S-H, C-A-S-H, and C-S-H +

were investigated by acoustophoresis to compare the effects of Ca:Si, washing, and dispersion media on zeta potential measurements. Results showed the necessity of full characterization of both solutions and precipitates in order to understand and compare acoustophoresis results. In the final section of the thesis C-S-H, C-A-S-H, and C-S-H +

were grown on the surface of heterogeneous substrates, quartz and calcite, to approach C-S-H growth in real systems. Overall, the results from this thesis provided helpful information on synthetic C-S-H, C-A-S-H, and C-S-H + $ at the full range of Ca:Si molar ratios, particularly ratios above 1.5, as observed in Portland cement. As we get closer to understanding and controlling C-S-H in real systems, this work will help provide insight as to how heterogenous substrates and aluminates introduced by SCMs, in addition to sulfates, commonly added to cement via gypsum, affect the early age strength and kinetics of C-S-H formation.

EPFL2022

Nanoscale modelling of ionic transport in the porous C-S-H network

Khalil Ferjaoui

To reduce the CO2 footprint of construction materials, concrete producers blend their cement with Supplementary Cementitious Materials (SCMs). SCMs such as fly ash or blast furnace slag are mostly the byproducts of other industries. And while SCMs are chosen to match the properties of the common Ordinary Portland cement (OPC), their addition to the cement recipe may alter the chemistry of the system. These changes may lead to different mechanical and transport properties of the cement-based structure which may, in turn, affect its long-term resistance to harmful external agents. Therefore, understanding the relationship between cementâs microstructure and the degradation mechanisms is key for optimizing the design of new cementitious materialsIn this context, chloride attack is the most common reason for steel rebars to corrode especially when exposed to external chloride (seawater, deicer saltsâŠ). At low w/c ratios (typically 13) pore solution, the C-S-H surface develops a negative surface charge density. Electrostatic interactions between the surface and the ions in the pore solution result in a redistribution of the ionic species in two layers of charge at the interface of the solid i.e. the Electrical double layer (EDL). In nanoscopic pores, the EDL is dominated by atomic phenomena which are thought to interfere with the mobility of ions and chloride in particular. In order to understand and quantify the surface effects and their influence on ionic transport, we firstly propose an atomistic model of the EDL formation based on the use of the Metropolis Monte Carlo algorithm. This model is used to compute the ionic distributions and electrochemical potentials of electrolytes at equilibrium in nanoscopic pores. These quantities constitute the main driving forces of ionic transport at the pore scale. The microstructure parameters including the surface charge density of C-S-H, the ionic strength (and pH) of the pore solution, and the pore size are equally investigated and their effect on chlorideâs behavior quantified. Among the other parameters, the model also provides quantitative information on the effect of calcium ions which are thought to play a major role in the binding of chloride on C-S-H. The next step consists in using the calculated atomic-scale properties of the EDL in order to resolve the transport problem at the pore scale and compute microscopic diffusivities of chloride. This is achieved by using the molecular computations from the Monte Carlo (MC) engine in order to implement a modified version of the classical Poisson-Boltzmann system. The method is compared to the classical Finite element analysis of the Poisson-Nernst-Planck (PNP) equations and the data are discussed in the light of established experimental results in the literature.

EPFL2022

Hydration and durability of fast hardening binders incorporating supplementary cementitious materials

Sarra El Housseini

The use of supplementary cementitious materials (SCMs) is widely considered the most promis-ing approach to reduce CO2 emissions relative to cement production. SCMs are not commonly present in binders used for special applications. On the other hand, due to their low reactivity at early age, cements incorporating SCMs such as Limestone calcined clay cement (LC3) exhibit low early age strength when compared to PC. This could restrict their field of applications and therefore solutions have to be found.This thesis focused on two main axes: The first one is to lower the CO2 footprint of ternary blends composed of Portland cement (PC), calcium aluminate cement (CAC) and calcium sulfate (Cs) using calcined clay as clinker substitute. The hydration of simple systems composed of PC with an increas-ing amount of CAC and Cs with and without calcined clay from 3 hours up to 90 days of hydration helped to understand and identify the contribution of each component. The results showed that in-creasing the CAC and Cs content in a PC system with and without calcined clay led to an increase of the ettringite content and a decrease of the portlandite content due to the portlandite consumption to form ettringite. The C3S hydration was not delayed in presence of CAC and Cs. However, the pres-ence of CAC, Cs and calcined clay led to slightly lower degree of hydration especially at later ages. The hydration and strength of a more realistic system "a fixing mortar formulation" with and without calcined clay was investigated. Overall, results showed that calcined clay can replace Portland cement by up to 20% with acceptable strength results. The second aspect on which this thesis focused was the influence of incorporating CAC and Cs as limestone substitute in LC3. The effect of the C/A molar ratio of the used CAC and its content were the main parameters investigated. The incorporation of 10% (CAC, Cs) improved the strength com-pared to LC3 at all ages. The massive ettringite formation during the first hours of hydration explained the early age strength improvement. Results showed that the C3S hydration was hindered when the C/A ratio of the CAC is equal to 1.7. The calculation of saturation indices indicated that a super satu-ration with respect to portlandite is likely needed to trigger the C3S hydration. The high late age strength in LC3-CAC blends was explained by a high volume occupied by hydrates in comparison with LC3 blends. In terms of durability, the resistance to chloride ion penetration was investigated through the mini-migration method. LC3-CAC blends showed a better chloride resistance than LC3, which is mainly explained by the porosity refinement compared to PC, and the decrease of the total porosity in comparison with LC3. On the other hand, the natural carbonation study showed that LC3-CAC blends have a higher carbonation rate when compared to PC. Contrary to PC, accelerated car-bonation of LC3 and LC3-CAC blends resulted in a decrease of the strength. However, the strength of carbonated LC3-CAC specimens is still at least similar to the non-carbonated PC specimen.

EPFL2022

Precipitation, Characterization, Kinetic, and Thermodynamic Modelling of Synthetic C-S-H Systems (C-S-H, CASH, CSH+$)

Maya Nicole Harris

were investigated by acoustophoresis to compare the effects of Ca:Si, washing, and dispersion media on zeta potential measurements. Results showed the necessity of full characterization of both solutions and precipitates in order to understand and compare acoustophoresis results. In the final section of the thesis C-S-H, C-A-S-H, and C-S-H +

EPFL2022

Nanoscale modelling of ionic transport in the porous C-S-H network

Khalil Ferjaoui

EPFL2022

Hydration and durability of fast hardening binders incorporating supplementary cementitious materials

Sarra El Housseini

EPFL2022