Calcaire | EPFL Graph Search

vignette|Calcaire perforé, Prádena de la Sierra, Ségovie, Espagne. vignette|La lecture du paysage révèle les différentes formations géologiques qui s'expriment par leurs morphologies : les calcaires, roches cohérentes, forment ici des falaises abruptes qui, à l'affleurement, présentent des strates plus ou moins épaisses et déformées. Les niveaux plus tendres donnent des vires boisées au niveau desquelles les roches plus friables subissent une érosion mécanique qui se manifeste par un fort ravinement. La photo représente la Dent de Crolles et les Rochers du midi dans le Massif de la Chartreuse. thumb|Blocs de calcaire bruts de sciage de carrière. thumb|Bloc de calcaire en région lyonnaise (Bloc erratique de Saint-Fons). Les calcaires sont des roches sédimentaires, tout comme les grès ou les gypses, facilement solubles dans l'eau (voir karst), composées majoritairement de carbonate de calcium CaCO, mais aussi de carbonate de magnésium MgCO. Ces roches carbonatées ont une grande importan

Limestone Addition in Cement

Olga Agata Chowaniec

Addition of fine limestone provides an excellent means to reduce the amount of clinker in cement. It is now well accepted that limestone partially reacts in cementitious systems with C3A to produce hemi- and monocarboaluminate phases and as a consequence more sulfate is available to form ettringite and the total volume of hydrates increases. The mechanism by which limestone affects the hydration is crucial in understanding its influence on the properties of cementitious materials. Laboratory and Commercial Cements with two different types of clinker, low and high C3A with different gypsum and limestone addition, were investigated. Hydrated pastes and mortars were investigated in terms of kinetics, phases assemblage, microstructure development, porosity, mechanical properties and durability (sulfate attack and sorptivity). An improvement in sample preparation for XRD measurement was made, which allows preferential orientation to be avoid and improves Rietveld Analysis quantification. The elastic modulus was found to correlate well with compressive strength and could be used as a nondestructive method to measure compressive strength. Monocarboaluminate formation was found to increase with increasing C3A. For high C3A cement it is visible at 2 days of hydration and at 720 days 4.5% of monocarboaluminate is measured in the system. For Low C3A cement it is visible at 7 days of hydration and at 720 days 1.6% of monocarboaluminate is measured in the system. Mc is formed only after all gypsum, which is more reactive than limestone is consumed to produce ettringite. No monosulfate is observed in the limestone systems. The optimum gypsum, was found to have as much effect at early ages on the hydration as 10% of limestone addition. Consequently variations in the gypsum level were investigated but it was difficult to quantify differences between samples with increasing gypsum addition. Studies of behavior in sulfate solution indicated that C3A is the dominant factor. Limestone addition produces slight changes in the form of degradation but do not fundamentally change whether deterioration takes place or not.

EPFL2012

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

Hydration and dimensional stability of calcium aluminate cement based systems

Julien Bizzozero

Calcium aluminate cements (CAC) are often used in combination with calcium sulfate and Portland cement for special applications where rapid setting, rapid drying and shrinkage compensation are required. A growing fraction of the clinker, which has the highest CO2 intensity, is being replaced by supplementary cementitious materials (SCM). These SCM are usually from industrial by-products such as slag, fly ashes or can simply be raw materials such as limestone. This project aims at replacing the Portland cement and fraction of the CAC in ternary binders with such SCM. Indeed, the understanding of their interactions, both physical and chemical, with calcium aluminate cements and calcium sulfate is fundamental for the development of innovative products. This thesis focuses first on the hydration of systems with and without SCM, slag or limestone, from the first hours up to two years of hydration. Second, this study focuses on the expansion of these systems and on the mechanisms underlying the dimensional stability. The influence of the ratio between calcium sulfate and calcium aluminate on the hydration of the cement, on the reaction of SCM, and on the expansion is highlighted. This study indicated that the calcium sulfate reacts with CAC from the first hours of hydration and, only when sulfate is exhausted, does slag or limestone react with aluminate phases. Moreover, this research brings new insights on the main parameters influencing the dimensional stability of the studied systems and on the mechanisms governing expansion. Pore solution analyses showed that supersaturation with respect to ettringite increases with the calcium sulfate content, which results in an increase of the crystallization pressure. The supersaturation determines the minimum pore size in which crystals can grow. Therefore, with increasing supersaturation a larger pore volume can be accessed by ettringite crystals exerting pressure. This could explain the critical amount of calcium sulfate leading to high expansion. Both the confinement in nanometer size pores and the supersaturation of ettringite are necessary for expansion to occur.

EPFL2014