Auswahl der wissenschaftlichen Literatur zum Thema „Calcite reactivity monitoring“

γ-Dicalcium silicate (γ-C2S) is known for its strong carbonation reactivity by which it can capture atmospheric carbon dioxide (CO2), thus, it can be used in construction industries. This paper aims to study the effects of γ-C2S on the properties of ground granulated blast-furnace slag (GGBFS) containing cement mortar and paste in natural and accelerated carbonation curing. The compressive strength of 5% γ-C2S (G5) added to GGBFS cement mortar is higher compared with the control one in natural carbonation (NC) and accelerated carbonation (AC) up to 14 days of curing, but once the curing duration is increased, there is no significant improvement with the compressive strength observed. The compressive strength of AC-cured mortar samples is higher than that of NC. The scanning electron microscopy (SEM) images show that the AC samples exhibited compact, uniform, and regular morphology with less in porosity than the NC samples. X-ray diffraction (XRD) and Fourier transform infra-red (FT-IR) results confirmed the formation of calcium carbonate (calcite: CC) as carbonated products in paste samples, which make the surface dense and a defect-free matrix result in the highest compressive strength. The decomposition of AC samples around 650–750 °C revealed the well-documented and stable crystalline CC peaks, as observed by thermogravimetry analysis (TGA). This study suggests that γ-C2S added to concrete can capture atmospheric CO2 (mostly generated from cement and metallurgy industries), and make the concrete dense and compact, resulting in improved compressive strength.

The oxidation of pyrite is one of the near field processes of the chemical evolution of clay rock planned to host a deep geological radioactive waste repository during operation. Indeed, this process can lead to transitory acidic conditions in the medium (i.e., production of sulphuric acid, carbonic acid) which may influence the corrosion kinetics of the carbon steel components of some disposal cells. In order to improve the geochemical modelling of the long-term disposal, the oxidation of pyrite in contact with clays and carbonates at 100 °C must be evaluated. In this study, special attention was paid to the pyrite oxidation rate thanks to an original experimental set-up, involving several pyrite/mineral mixtures and a reactor coupled to a micro gas chromatograph (PO2 and PCO2 monitoring). Although thermodynamic modelling expects that hematite is the most stable phase in a pure pyrite heated system (low pH), experiments show the formation of native sulfur as an intermediate product of the reaction. In the presence of calcite, the pH is neutralized and drives the lower reactivity of pyrite in the absence of native sulfur. The addition of clay phases or other detrital silicates from the claystone had no impact on pyrite oxidation rate. The discrepancies between experiments and thermodynamic modelling are explained by kinetic effects. Two laws were deduced at 100 °C. The first concerns a pure pyrite system, with the following law: r P y = 10 − 4.8 · P O 2 0.5 · t − 0.5 . The second concerns a pyrite/carbonates system: r P y + C a = 10 − 5.1 · P O 2 0.5 · t − 0.5 where PO2 corresponds to the partial pressure of O2 (in bar) and t is time in seconds. Different mechanisms are proposed to explain the evolution with time of the O2 consumption during pyrite oxidation: (i) decrease of the specific or reactive surface area after oxidation of fine grains of pyrite, (ii) decrease of O2 pressure, (iii) growing up of secondary minerals (Fe-oxides or anhydrite in the presence of calcium in the system) on the surface of pyrite limiting the access of O2 to the fresh surface of pyrite, and (iv) change in the pH of the solution.

Four (04) different types of clays from Burkina Faso were studied for their potential applications in the production of calcined clays as substitution materials for Portland cement. The study aimed at analyzing the factors affecting their reactivity. The untreated clays were subjected to various tests to highlight the intrinsic properties that can influence their reactivity. After the treatment by calcination, the clays were subjected to various pozzolanicity tests and microstructural analysis in order to evaluate their influence on the microstructure of the cement paste. The results showed that the reactivity of calcined clays is strongly related to the intrinsic properties of the raw clays, such as the content and the structure of kaolinite: disordered kaolinite reacts better than ordered kaolinite. After the calcination, the reactivity depends on the amorphous phase (amorphous content) of the clays, which influences the strength activity index. This study established a correlation between different parameters to easily identify the main properties of calcined clays that can influence their pozzolanic reactivity. All the results showed that the kaolinite content is a determining factor in the reactivity of clays before calcination. However, the study showed that the amorphous content of kaolinite is the determining parameter of the reactivity of calcined clays, as calcination can lead to the recrystallization of kaolinite.

Availability of aluminosiliceous materials is essential for the production and promotion of geopolymer concrete. Unlike fly ash, which can only be found in industrial regions, clays are available almost everywhere but have not received sufficient attention to their potential use as a precursor for geopolymer synthesis. This study investigates the effectiveness of calcined clay as a sole and binary precursor (with fly ash) for the preparation of geopolymer mortar. Fly ash-based geopolymer containing between 0 and 100% low-grade calcined clay was prepared to investigate the effect of calcined clay replacement on the geopolymerization process and resultant mortar, using a constant liquid/solid ratio. Reagent-grade sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) were mixed and used for the alkali solution preparation. Six different mortar mixes were formulated using sand and the geopolymer binder, comprising varying fly ash-to-calcined clay ratios. The combined effect of the two source materials on compressive strength, setting time, autogenous shrinkage, and porosity was studied. The source materials were characterized using XRD, SEM, FTIR, and XRF techniques. Isothermal calorimetry was used to characterize the effect of low-grade calcined clay on the geopolymerization process. The addition of calcined clay reduced the surface interaction between the dissolved particles in the alkali solution, leading to slow initial reactivity. Geopolymer mortar containing 20% calcined clay outperformed the reference geopolymer mortar by 5.6%, 17%, and 18.5% at 7, 28, and 91 days, respectively. The MIP analysis revealed that refinement of the pore structure of geopolymer specimens containing calcined clay resulted in the release of tensional forces within the pore fluid. Optimum replacement was found to be 20%. From this study, the mutual reliance on the physical and inherent properties of the two precursors to produce geopolymer mortar with desirable properties has been shown. The findings strongly suggest that clay containing low content of kaolinite can be calcined and added to fly ash, together with appropriate alkali activators, to produce a suitable geopolymer binder for construction applications.

This research study evaluated the effects of adding Scottish canal sediment after calcination at 750 °C in combination with GGBS on hydration, strength and microstructural properties in ternary cement mixtures in order to reduce their carbon footprint (CO2) and cost. A series of physico-chemical, hydration heat, mechanic performance, mercury porosity and microstructure tests or observations was performed in order to evaluate the fresh and hardened properties. The physical and chemical characterisation of the calcined sediments revealed good pozzolanic properties that could be valorised as a potential co-product in the cement industry. The results obtained for mortars with various percentages of calcined sediment confirmed that this represents a previously unrecognised potential source of high reactivity pozzolanic materials. The evolution of the compressive strength for the different types of mortars based on the partial substitution of cement by slag and calcined sediments showed a linear increase in compressive strength for 90 days. The best compressive strengths and porosity were observed in mortars composed of 50% cement, 40% slag and 10% calcined sediment (CSS10%) after 90 days. In conclusion, the addition of calcined canal sediments as an artificial pozzolanic material could improve strength and save significant amounts of energy or greenhouse gas emissions, while potentially contributing to Scotland’s ambitious 2045 net zero target and reducing greenhouse gas emissions by 2050 in the UK and Europe.

Formamide has been recognized in the literature as a key species in the formation of the complex molecules of life, such as nucleobases. Furthermore, several studies reported the impact of mineral phases as catalysts for its decomposition/polymerization processes, increasing the conversion and also favoring the formation of specific products. Despite the progresses in the field, in situ studies on these mineral-catalyzed processes are missing. In this work, we present an in situ UV-Raman characterization of the chemical evolution of formamide over amorphous SiO2 samples, selected as a prototype of silicate minerals. The experiments were carried out after reaction of formamide at 160 °C on amorphous SiO2 (Aerosil OX50) either pristine or pre-calcined at 450 °C, to remove a large fraction of surface silanol groups. Our measurements, interpreted on the basis of density functional B3LYP-D3 calculations, allow to assign the spectra bands in terms of specific complex organic molecules, namely, diaminomaleonitrile (DAMN), 5-aminoimidazole (AI), and purine, showing the role of the mineral surface on the formation of relevant prebiotic molecules.

Cement manufacture contributes about 5–7% of the global carbon dioxide emission. The fastest short-term remedy is to replace parts of ordinary Portland cement (OPC) in concrete with supplementary cementitious materials (SCMs) to reduce CO2 emissions. Calcined clay and limestone filler have proven to be potential substitutes to good quality SCMs such as fly ash and slag because of their abundance, low cost, and potential reactivity to calcium hydroxide to form calcium silicate hydrates (C-S-H) which are responsible for the strength and other mechanical properties of concrete. A life cycle assessment (LCA) to evaluate the environmental impact of mortar with calcined clay and limestone filler in reinforced concrete (RC) column retrofitting is carried out using data from a multi-purpose complex project in Rizal province in the Philippines. A total of four retrofitting methods are evaluated based on two retrofitting techniques (RC column jacketing and steel jacketing) with two material alternatives (pure OPC-based mortar and mortar with partial replacements). Results show that RC column jacketing using patched mortar with partial replacement of calcined clay and limestone fillers is the least environmentally damaging retrofit option. The use of these SCMs resulted in a 4–7% decrease in global warming potential and a 2–4% decrease in fine particulate matter formation. Meanwhile, RC column jacketing decreased the effect on human carcinogenic toxicity by 75% compared to steel jacketing.

Arundo donax is a plant native to Asia and is considered an invader species in the Mediterranean region and many tropical zones in the world. These invader plants can be collected to produce a biomass, which can be converted to ash by combustion. The scope of the study is to assess the use of these ashes (Arundo donax straw ash [ADSA]) as supplementary cementing material due to their relatively high silica content. Electron microscopy studies on dried and calcined samples of different plant parts (cane, sheath leaf and leaf) were carried out. Some different cellular structures were identified in the spodogram (remaining skeleton after calcination). Major silica content was found in leaves and sheath leaves. The main element in all the ashes studied, together with oxygen, was potassium (22 to 46% depending on the part of the plant). Chloride content was also high (5–13%), which limits their use to non-steel reinforced concrete. The pozzolanic reactivity of ADSA was assessed in pastes by thermogravimetric analysis and in mortars with ordinary Portland cement based on compressive strength development. Excellent results were found in terms of reactivity.

Few studies focus on the co-valorization of river dredging sediments (DS) and residual waste glass (RWG) in alkali-activated binders. This study investigates the use of DS as an aluminosilicate source by substituting a natural resource (metakaolin (MK)), while using RWG as an activator (sodium silicate source). Suitable treatments are selected to increase the potential reactivity of each residue. The DS is thermally treated at 750 °C to promote limestone and aluminosilicate clays’ activation. The RWG (amorphous, rich in silicon, and containing sodium) is used as an alkaline activator after treatment in 10 M NaOH. Structural monitoring using nuclear magnetic resonance (29NMR and 27NMR), X-ray diffraction, and leaching is conducted to achieve processing optimization. In the second stage, mortars were prepared and characterized by determining compressive strength, water absorption, mercury porosimetry and Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM-EDS). Results obtained show the great advantage of combining RWG and DS in an alkali-activation binder. The treated RWG offers advantages when used as sodium silicate activating solution, while the substitution of MK by calcined sediments (DS-750 °C) at 10%, 20%, and 30% leads to improvements in the properties of the matrix such as an increase in compressive strength and a refinement and reduction of the pore size within the matrix.

Abstract Carbon dioxide (CO2) is the main contributor to greenhouse gases that affect global warming. The industrial sector is the third largest producer of CO2 and the cement industry is one of the industries that consistently produces the most significant CO2 emissions. The cement industry produces 5–8% of global CO2 emissions. Several methods for reducing specific CO2 emissions have been reported in the cement industry, including calcium looping, which uses the reversible reaction between calcination [calcium carbonate (CaCO3) decomposition] and carbonation [CO2 capture by calcium oxide (CaO)]. This work investigates calcium looping employing limestone obtained directly from several cement factories in Indonesia to observe the carbon-absorption characteristics of limestone from different mining locations. The experiment was carried out using a tube furnace equipped with a controlled atmospheric condition that functions as a calciner and a carbonator. X-ray diffraction and scanning electron microscopy with energy-dispersive x-ray spectroscopy characterization were conducted to analyse the changes in the experimental samples. The results demonstrated that the reactor configuration was capable of performing the calcination process, which converted CaCO3 to calcium hydroxide [Ca(OH)2], as well as the carbonation process, which captured carbon and converted it back to CaCO3. Parametric analysis was performed on both reactions, including pressure, temperature, duration, particle size and reaction atmosphere. The results show that the limestone obtained from all sites can be used as the sorbents for the calcium-looping process with an average reactivity of 59.01%. Limestone from cement plants in various parts of Indonesia has the potential to be used as carbon sorbents in calcium-looping technology. With a similar CO2 concentration as the flue gas of 16.67%, the experimental results show that Bayah limestone has the maximum reactivity, as shown by the highest carbon-content addition of 12.15 wt% and has the highest CO2-capture capability up to >75% per mole of Ca(OH)2 as a sorbent. Similar levels of the ability to capture CO2 per mole of Ca(OH)2 can be found in other limestones, ranging from 14.85% to 34.07%. The results show a promising performance of raw limestones from different mining sites, allowing further study and observation of the possibility of CO2 emission reduction in the sustainable cement-production process.

La précipitation et la dissolution de la calcite sont des processus primordiaux dans les roches carbonatées et le fait de pouvoir les surveiller in situ est un enjeu majeur. Les méthodes hydrogéophysiques sont fondées sur le développement de techniques géophysiques appropriées pour le suivi des processus hydrologiques et biogéochimiques de manière non-intrusive et à faible coût. Parmi les techniques existantes, les méthodes électriques ont déjà prouvé leur capacité à surveiller de tels processus. Pour cette raison, les méthodes du potentiel spontané (PS) et de la polarisation provoquée spectrale (PPS) ont été choisies pour investiguer les processus de dissolution et de précipitation de la calcite. La PS est une technique passive consistant à mesurer le champ électrique naturel généré par les flux d’eau et les gradients de concentration, tandis que la PPS est une méthode active mesurant la conductivité électrique complexe aux basses fréquences (mHz-kHz). Ses composantes réelle et imaginaire peuvent être reliées respectivement à la microstructure et à l’état de surface des minéraux le constituant. Cette thèse présente des développements expérimentaux et théoriques afin d'améliorer l’interprétation des méthodes PS et PPS. Un nouveau modèle de conductivité électrique est développé et montre un bon ajustement avec les résultats numériques de dissolution et de précipitation. Des données PS remarquables ont été obtenues et ont pu être reliées quantitativement grâce à de la modélisation de transport réactif. Les résultats PPS nourrissent la réflexion sur les mécanismes responsables des variations de polarisation engendrés par la réactivité de la calcite<br>Precipitation and dissolution of calcite are key processes in carbonate rocks and being able to monitor them in situ is a major issue. Hydrogeophysical methods are based on the development of appropriate geophysical techniques for monitoring hydrological and biogeochemical processes in a non-intrusive and low-cost manner. Among the existing techniques, electrical methods have already proven their ability to monitor such processes. For this reason, the methods of self-potential (SP) and spectral induced polarization (SIP) were chosen to investigate the processes of dissolution and precipitation of calcite. SP is a passive technique consisting in measuring the natural electric field generated by water flows and concentration gradients, while SIP is an active method measuring the complex electrical conductivity at low frequencies (mHz-kHz). Its real and imaginary components can be related respectively to the microstructure and surface state of the minerals constituting it. This thesis presents experimental and theoretical developments in order to improve the interpretation of SP and SIP methods. A new electrical conductivity model is developed and shows a good fit with the numerical results of dissolution and precipitation. Remarkable SP data have been obtained and could be quantitatively linked through reactive transport modeling. The SIP results provide further insights into the mechanisms responsible for the polarization variations caused by the reactivity of calcite