Porcelanite and chert are silica-rich sedimentary rocks composed of varying proportions of megaquartz, microcrystalline quartz, chalcedony, opal-CT, and opal-A. Both porcelanite and chert are characterized by their high silica purity, fine-grained texture, and distinctive porcelain-like sheen. Their scientific classification largely depends on the relative proportions of silica phases (opal-A/amorphous silica, opal-CT, cristobalite, tridymite, and quartz). Studying these materials is essential for reconstructing ancient sedimentary environments, understanding diagenetic processes including the general formation pathway involving the initial precipitation of amorphous silica followed by successive transformations from opal-A to opal-CT, then to cristobalite/tridymite, and ultimately to microcrystalline quartz, and tracing the evolution of the terrestrial biosphere.Furthermore, their diverse applications from archaeology to advanced technological industries make them subjects of multidisciplinary interest. This review aims to provide a comprehensive synthesis of current knowledge on silica-rich sedimentary rocks, with a focus on their formation processes, physicochemical properties, industrial uses, as well as ongoing scientific debates and future research directions. It also explores the main analytical techniques used (such as X-ray diffraction, chemical analysis, SEM, and optical petrography) in their investigation, highlights recent findings, and discusses the broader implications of these discoveries, particularly for the development of advanced ceramics, selected biomedical applications, wastewater filtration and treatment technologies, and innovations in the construction-material sector.

This study investigates the workability of an emerging cement based on calcined clay, considered one of the sustainable binders for reducing the carbon footprint of construction materials. Despite existing experimental data, no comprehensive analysis has been conducted. In the present paper, a literature-derived dataset was analyzed using CPM-based packing density computation and interpretable statistical analyses (distribution statistics and Pearson correlation-based projections). The novelty of this study lies in integrating the domain-knowledge-informed hierarchical analysis to identify packing density as a primary, sustainable lever to enhance LC3 fluidity while limiting reliance on superplasticizers. PCE superplasticizers (0-2.5 wt.% in the dataset) improve fluidity across packing densities; noticeable gains are observed even for low dosages (approximate to 0.5-1 wt.%) at packing 0.36-0.38. A paradigm shift is proposed through optimizing packing density by adjusting clay and limestone content in the mix. Prioritizing packing density, alongside conventional parameters, opens new avenues for sustainability by reducing reliance on organic fluidizers in low-carbon cements.

The thermal expansion behavior of the sodalite cage [Al12O24] in cubic ye'elimite, Ca-8[Al12O24](SO4)(2) with space group I (4) over bar 3m and Z = 1, was investigated using high-temperature X-ray powder diffraction. A split-atom model previously reported for 1073 K accurately represented the disordered crystal structures at 773-973 K. This model is characterized by the splitting of the O atoms coordinating to the S atom around the triad axes within the [Al12O24] cage structure. As the temperature increased from 773 to 1073 K, both the cage and the unit cell expanded steadily and continuously by 0.255 %, with a coefficient of linear thermal expansion of 8.5 (c) 10(-6) K-1. Two distinct thermal expansion processes were observed above and below approximately 923 K for the [Al12O24] cage. Between 773 and 873 K, the values of quadratic elongation and bond angle variance, which describe the distortion of the [AlO4] tetrahedron, increased continuously by 0.16 and 11.74 %, respectively, leading to a cage expansion of 0.073 %. Below approximately 923 K, the Al-O-Al angle of the apex-sharing [AlO4] tetrahedra remained nearly constant. However, as the temperature increased to 1073 K, this angle increased by 0.77 %, contributing to a further 0.182 % expansion of the cage. Thus, the total expansion of 0.255 % (= 0.073 + 0.182 %) for the [Al1(2)O(24)] cage was primarily due to the distortion of the [AlO4] tetrahedron below approximately 923 K and the mutual rotation of the apex-sharing [AlO4] tetrahedra above this temperature. This study identified, for the first time, the switching between these two distinct processes in the thermal expansion behavior of sodalite cages.

This study investigates the impact of atmosphere conditions on the thermal transformations of iron-enriched kaolin. Natural kaolin was chemically enriched with iron at two concentrations. Fine characterisation was conducted using X-ray diffraction, Mossbauer spectroscopy, solid-state nuclear magnetic resonance and electron dispersive spectroscopy. The samples were heat-treated at 1050 degrees C and 1400 degrees C under synthetic air and argon to assess the influence of these conditions on their transformations. Analyses revealed that presence of iron significantly influenced reaction kinetics. Under oxidizing atmosphere, the formation of mullite was facilitated by an equilibrium with hematite. The presence of iron accelerated the formation of secondary mullite and cristobalite, though the effect was not proportional to iron concentration. Conversely, under oxygen-deficient atmosphere, the reaction pathway diverged, leading to the formation of hercynite, tridymite (and after cristobalite) and mullite. Iron similarly promoted formation of these phases. No significant differences were observed for the pure kaolin sample under either atmosphere.

Calcined clays present a high water demand. Consequently, when used in mortars or concretes, calcined clays usually lead to a low workability. The origin of the increased water demand depends on the nature of the (calcined) clay. Hence, the aim of the present study is to determine the mineralogical and physical parameters of the calcined clays that affect the water demand. This paper presents some preliminary results on the characterization techniques implemented to characterize the mineralogy and physical parameters of calcined clays, and their rheological behavior when mixed with water.

This study focuses on ye'elimite, a versatile mineral compound of low carbon sulfo-aluminate cements. While stoichiometric ye'elimite typically exhibits orthorhombic symmetry, the introduction of foreign ions, especially iron, stabilizes a pseudocubic symmetry. This research advances the field by synthesizing highly pure cubic ye'elimite doped with iron and sodium, a unique combination not extensively explored. The study integrates Bayesian optimization to systematically enhance the purity of doped ye'elimite. The results demonstrate an impressive 83 wt.% phase purity achieved with optimal fractions of Ca3.6Na0.4Al5.65Fe0.35SO16 after only 16 experimental iterations, highlighting the effectiveness of Bayesian optimization in streamlining the synthesis process of highly pure materials with reduced experiments.

Understanding the transformations and interactions of kaolinite with secondary phases is a key point to control the physical and chemical properties of resulting materials. The production of ceramics involves multiple steps, among which, sintering is a critical step regarding the achievement of the target properties of use. The sintering environment and the surrounding atmosphere can significantly affect the transformation kinetics by changing heat transfer patterns and phase stability. Therefore, the challenge of the present study was to understand the effects of such modifications, especially on the physical and chemical transformations of kaolin- based ceramics regarding the presence of iron-enriched compounds. One typical kaolin was chosen as new material for this study: a kaolin denoted "CR" that was provided by Imerys company. The influence of chemically added iron oxide was studied according with reference to the Ellingham diagram. To this end, controlled additions of 5 and 10 wt% of added iron oxide were performed. The thermal behaviour of these samples was investigated from room temperature to 1400 degrees C under controlled atmosphere using air, argon, or nitrogen. DTA/TG, XRD and SEM analyses were performed to enhance the understanding of the phase transformations and interactions of kaolinite with iron oxide. The presence of iron in kaolin promoted the formation of secondary mullite at lower temperatures, followed by cristobalite formation under air. When the atmosphere was modified using argon or nitrogen (lower partial pressure of dioxygen) these effects were even more pronounced. In addition to decreasing the onset temperature of secondary mullite and cristobalite crystallisation, the reaction paths were modified.

Managing the vast quantities of waste constantly generated by mining activities is one of the major environmental and economic problems facing mankind today. Fluorapatite is separated from the associated gangue minerals by a series of crushing and screening, washing, and flotation processes. These processes produce a significant amount of phosphate sludge, which is stored on the mine site in drift rock and large surface ponds. One possible environmental option is to reuse it as an alternative raw material in ceramics and building materials. Consequently, two phosphate sludges from two different Moroccan towns, Youssoufia and Khouribga, were studied. Due to the complexity of these raw materials resulting from long geological processes, in-depth physical, chemical, mineralogical, and thermal characterization is required. Dry compressed powder pellets were sintered at 900 °C, 1000 °C, and 1100 °C for 2 h. The study focuses on the effect of sintering temperature on mineralogical transformations and ceramic properties such as apparent porosity, water absorption, and mechanical strength. At 1100 °C, a slight increase in density was observed for both phosphate sludges. Water absorption was reduced by 2.51 % in both sludges for pellets sintered at 1100 °C compared to those sintered at 900 °C. Mechanical strength improved significantly, with an increase of about 60 % for samples sintered at 1100 °C, recording 227 N for Youssoufia sludge and 247 N for Khouribga sludge. This work has provided new data on the physical, chemical, mineralogical, and thermal changes in ceramics as the sintering temperature increases. These data will be useful for the manufacture of high-value ceramics.

Siltation is a permanent threat to the operation of dams since it reduces its storage capacity. In Tunisia, the annual siltation of dams is estimated at 22 Mm3 / year. Sediments currently cover 20% of the total capacity of the reservoirs, which could be a national water security issue in the years to come. Considering that sediments contain the oxides, SiO2. Al2O3. Fe2O3 and CaO, as main chemical constituents, a partial replacement of the raw materials in the cement production is suggested. This work concerns dam sediments from different regions in Tunisia. Characterisation results show that studied sediments are suitable for a beneficial reuse in the clinker production. However, according to the chemical composition, the incorporation rate of sediments in the raw mix varies from one sediment to another but still relatively important, ranging between 9 and 27 wt%. The characterization of produced clinkers show that mineralogy depends on minor oxides contents, especially SO3. MgO and equivalent Na2O. It has been proven that it is possible to substitute natural materials with 27.4 %SS sediment. The obtained clinker is characterized by the presence of M1 C3S and orthorhombic C3A. The high free lime content associated to incomplete alite formation can be surmounted by increasing slightly the clinkerization temperature.

Calcium phosphate materials synthesized from apatite with atomic Ca/P ratios ranging from 1.50 to 1.67 (Ca 10- x (HPO 4 ) x (PO4) 6- x (OH) 2- x (0 ≤ x ≤ 1)) have very interesting applications in bone regeneration and in the environment field for the removal of toxic species. The physicochemical characteristics of synthetic calcium apatite change when the Ca/P ratio varies. In this study, two batches of apatite powder were prepared by precipitation in an aqueous medium at 25 °C with Ca/P molar ratios that were close to those of tricalcium phosphate (1.48, 1.50, and 1.52) and close to those of hydroxyapatite (1.65, 1.67, and 1.72). For dried and ceramized powders, the chemical composition, morphology, surface area, compacity, durability, and crystalline phases of prepared powders were studied. The result shows that the dried powders composed of nanocrystals are poorly crystallized. The sample with the lowest Ca/P atomic ratio (1.48) shows the lowest specific surface area (75 ± 5 m 2 /g) with good compaction ability and acceptable mechanical properties. While stoichiometric HAP (Ca/P = 1.67) has a large specific area (110 ± 5 m 2 /g), however, it has poor compaction properties. Calcined apatite (Ca/P = 1.65) at 900 °C composed of HAP with traces of tricalcium phosphate (Ca 3 (PO 4 ) 2 : βTCP) shows a higher compressive strength (78 ± 10 MPa). βTCP ceramic with Ca/P = 1.48 has the lowest optical gap (OG = 4.6 ± 0.4 eV). The result of this study shows how little changes in the Ca/P ratio had an impact on the granular properties of dried and calcined calcium phosphate materials. Apatite produced with slightly sub-stoichiometric calcium has the potential for promising future uses in the biological, catalytic, and environmental domains.

Brick production is a major contributor to the construction industry, but the process requires a significant amount of non-renewable clay. To address this, researchers have explored incorporating waste materials into clay bricks. This study investigates phosphate-washing sludge (PS-K) as an additive in clay bricks and evaluates its impact on physical, mechanical, and thermal properties. Laboratory and pilot-scale experiments were conducted to determine the optimal quantity of PS-K for waste reduction. Five compositions with PS-K percentages ranging from 0% to 50% were prepared in the laboratory based on the raw materials' chemical composition. The bricks were shaped using a humic method, underwent drying and cooking processes, and underwent physical analysis, including bulk density, apparent porosity, and water absorption tests. Microstructural analysis was performed using a scanning electron microscope, while thermal conductivity and compressive strength were evaluated. Results showed that increasing PS-K content led to higher open porosity and water absorption in the bricks. At 50% waste content, the open porosity reached 52%, and water absorption reached 32%. The relationship between waste content and porosity/water absorption was nonlinear, with greater increases observed at higher waste contents. Incorporating up to 30% sludge met standard brick requirements.Pilot-scale experiments using the optimal 30% PS-K content demonstrated similar porosity and water absorption trends as observed in the laboratory samples. The bricks' extrusion shaping process and final appearance after drying were successfully demonstrated.This research provides valuable insights into utilizing phosphate-washing sludge in clay bricks, offering a potential waste management solution and reducing clay consumption in brick production. The findings demonstrate the feasibility of incorporating PS-K into bricks while meeting industry standards, contributing to sustainable practices in the construction sector.

Pure powders of ye'elimite Ca4Al6-2xFe2xSO16 particles containing iron were synthesized by chemical route for the first time, the maximum of ye'elimite formed was obtained at 1250 degrees C for 1 h. The increase in iron content in the reaction system is accompanied by the increase on amount of the iron-stabilized cubic phase after calcination at sufficient temperature, at the expense of the orthorhombic phase until a concentration of x = 1.13 where only the cubic phase is detected. The presence of iron also causes the formation of ferritic phases. A protocol of elimination of the ferritic phases was proposed. This chemical treatment with sodium dithionite was applied to compositions containing a large majority of cubic ye'elimite and the isolation of cubic ye'elimite grains was successful. Thanks to very fine crystallographic analyses, the crystal structure of Ca4[(Al4.74Fe1.26)O12]SO4, a cubic ye'elimite doped only with Fe2O3, has been successfully determined for the first time.

Calcined clay cements have the potential to reduce the carbon footprint of the cement production sector. However, accurately predicting the engineering properties of this low carbon cement remains challenging due to the numerous parameters involved in formulation and hardening processes. Machine learning (ML) algorithms have shown promising prediction performance for Portland cement, and their effectiveness for calcined clay cement is expected due to their data-driven nature. In this study, the ML approach was leveraged to predict the influence of material composition and hardening conditions on the compressive strength of calcined clay cement. Seven supervised ML algorithms are employed, considering fourteen input features including clay, Portland cement, and limestone percentages, chemical composition expressed as reactivity ratios, clay calcination conditions, and hardening conditions. The targeted feature is the compressive strength. Through evaluation, the XGboost algorithm emerges as the most accurate predictor, yielding a mean absolute error of 2.5 MPa. The findings reveal that the alumina-to-silica ratio of clay significantly impacts the development of cement strength. Furthermore, the ML model predicts a decrease in strength above 920°C, consistent with experimental results reported in the literature. The developed ML model not only confirms previous experimental findings but also identifies promising potential formulations based on calcined clay for further experimentation. It is important to note that the carbon footprint of the compositions predicted by the ML model requires a comprehensive life cycle assessment, which goes beyond the specific research question of this paper.

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Cement production is a major contributor to global CO 2 (Carbon dioxide) emissions.To minimize its environmental impact while maintaining the required mechanical properties of cement, there is a pressing need for sustainable production processes.This paper focuses on developing sustainable cement production processes by optimizing the mechanical properties of limestone calcined clay cement (LC3) using data-driven models based on artificial intelligence.The study explores the use of data augmentation techniques, specifically the copulas method, to improve the performance of linear regression models for linking the compressive strength of LC3 with its mix design.While data augmentation using copulas can be useful in augmenting tabular data, its effectiveness in improving linear regression performance may depend on the statistical characteristics of the original data.The method successfully generated additional data that preserved the original statistical properties, but it did not always lead to significant improvements in linear regression performance.The research highlights the potential of data-driven models for optimizing cement materials properties and emphasizes the importance of considering the statistical characteristics of the original data when applying data augmentation techniques.