Clay Resources Research Articles

Clay resource estimation using a geostatistical approach in Tam Binh district, Vinh Long province, Viet Nam

ABSTRACT Clay is an essential resource for improving the brick and ceramic industries. However, the demand for clay needs to grow. Estimating industrial mineral reserves requires an optimal and unbiased statistical tool. Geographical information systems and geostatistics are two promising tools that could be used to predict clay resources. The study objective was to apply these two tools to compare the performance of the methods for spatial clay resource prediction, considering clay thickness and spatial distribution. The demonstration site is in Tam Binh district, Vinh Long Province, Viet Nam. The results show that the Gaussian variation model at a 600 × 400 m distance is good for sampling and extrapolating clay thickness. This is based on 240 geolocated samples with different densities. Projected clay reserves match measurements, and the spatial statistical method is more accessible and valuable than the traditional method. The interpolated method’s total selected soil borehole number was optimized for clay resource estimation, and geostatistics can help manage and plan clay resources and save money. Future research should examine various spatial interpolation techniques and approaches in management, land use, and topography to improve the accuracy of calculations.

Fly Ash and Rice Husk Ash Utilization to Enlarge Clay Brick Dimension

Burnt clay bricks, mostly used as non-structural wall unit materials in Indonesia, contain only clay in Bengkulu Province. A large amount of clay is used during clay brick production as a shrinkage effect of burning, while clay is a limited natural resource. Available non-plastic materials that can withstand combustion contraction are required to reduce the use of clay. Ash materials like fly ash and rice husk ash are non-plastic materials. The purposes of this research are to reduce clay usage, enlarge dimensions, and improve brick performance at the same time by adding coal fly ash (FA) and rice husk ash (RHA). This research is an experimental study of FA clay brick (FCB) and a combination of 50% FA and 50% RHA clay brick (FRCB). The ash was added to the mixture at weights of 10%, 20%, and 30% of clay. The factory-specified production method was used to create bricks. After the materials and water meltdown process to produce plastic material, bricks were molded, dried, and burned. Green and burnt brick measurements and weights were gathered. The Brick Indonesian Standard Code (SNI 15-2094-2000) was used while determining the bricks' compression strength and absorption. The mean values of the quantitative data were used after being analyzed through coefficient of variation values less than 10%. The result shows that the compressive strengths and absorption of 10% and 20% of the ash content of FCB meet the Indonesian code. Both brick volumes expand as the ash content increases. FRCB volume weight is 11%, 7.8%, and 8.1% lighter than FCB for 10%, 20%, and 30% ash content, respectively. Both brick varieties meet the ASTM code for nonload-bearing concrete masonry units. The use of FA and a mixture of FA and RHA enhances shrinkage, increases brick dimensions, and simultaneously lowers brick weight. Using lighter and larger bricks for the walls helps to recycle waste, reduce the mass of the building, and reduce the use of clay resources. Application 10% and 20% fly ash is recommended for increasing the size of clay bricks in Bengkulu Province, Indonesia.

Insight into hemostatic performance and mechanism of natural mixed-dimensional Attapulgite clay

Clay minerals have attracted wide attention as biomedical materials due to the unique crystal structure, abundant morphology and good biocompatibility. However, the relevant studies on the abundant natural mixed clay deposits were scarcely reported. Herein, the hemostatic performance of natural mixed-dimensional attapulgite clay (MDAPT) composed of one-dimensional attapulgite and multiple two-dimensional clay were systematically investigated based on the structural evolution using oxalic acid for different time. The results of hemostatic evaluation showed that MDAPT leached by oxalic acid with 1 h presented the shortest clotting time (134 ± 12.17 s), a 15.09 % and 41.74 % reduction of relative hemoglobin absorbance at 180 s and 120 s when compared with the control group, respectively, and an increase of 19.45 % of the blood clotting index in vitro, as well as MDAPT obtained the shortest bleeding time (158.5 ± 6.9 s), nearly 66 % and 31 % reduction blood loss as compared to the blank group and the YNBY group in vivo. This improvement was primarily ascribed to the synergistic effect of lamellar non-expandable illite, and nano rod-like attapulgite. Furthermore, the rapid hemostasis of MDAPT was also due to the joint effect of superhydrophobic property toward blood, minimizing blood loss, surface negative charge, metal ions from MDAPT structural skeleton, promoting an average increase of 21 % for platelet activation. The results suggested that MDAPT could be served as a promising efficient inorganic hemostatic materials, which provided a feasible strategy to realize the high-valued utilization of natural mixed clay resources.

Research on the in-situ flocculation behavior of polyferric silicate for enhancing the lithium leachability in lithium-rich clay

The expansion of global lithium demand urgently requires efficient extraction technologies for lithium-rich clay recourse. However, the encapsulation of polysilicate products in the acidic leaching system impedes the migration of lithium from the mineral to the solution, resulting in a low recovery rate of lithium. Here, this study proposes an in-situ flocculation mechanism of Fe3+ on the polysilicate to reconstruct the surface structure, enhancing the leaching efficiency of lithium. Results showed that the flocculation of Fe3+ approaches the Si-O surface and reacts with silicate to form the polyferric silicate (Fe3Si2O5(OH)4). This special configuration eliminates the wrapping and adsorption effect of polysilicate while promotes the diffusion of Li+. Increased FeCl3 concentration and higher leaching temperature are beneficial for the leaching efficiency of Li. Under optimized conditions, the Li leaching efficiency in the FeCl3 leaching system reaches up to 92.81 %. This work introduces Fe3+ to overcome the limiting effect of polysilicate during acidic leaching, and affords extraordinary recovery of lithium from clay resources.

Enhancing reactivity in muscovitic clays: Mechanical activation as a sustainable alternative to thermal activation for cement production

The use of calcined clays in the construction industry is thriving. However, muscovitic or illitic clays, which constitute a large portion of the available clay resources, are hardly activated by thermal processes. This work aims to enhance the reactivity of raw muscovitic clay through mechanical activation. Various combinations of milling time and rotation speed were evaluated. The results confirmed that a highly amorphous material was obtained through mechanical activation, while thermal activation led to muscovite dehydroxylation without inducing amorphisation, resulting in the formation of crystalline dehydroxylated muscovite. The reactivity of the activated clays as a potential precursor for cement production was assessed through pozzolanic activity measurements and Si and Al potential availability. Both confirmed that mechanically activated muscovitic clay presented significantly higher reactivity than calcined muscovitic clay, obtaining an excellent pozzolanic material or an alternative cement precursor. Accordingly, mechanical activation of muscovitic clays could effectively introduce these types of clay in the cement industry.

Comparative analysis of energy performance between clay-based and conventional building materials: A case study in Moroccan semi-arid climate

The environmental challenges arising from using traditional construction materials, such as cement, along with their rapid depletion, underscore the necessity of employing environmentally friendly building materials derived from natural resources. In this context, this study presents a comparative analysis of the energy performance of conventional building materials and clay-based materials. Focusing specifically on the Beni Mellal region, adobe bricks reinforced with straw, at weight percentages of 0%, 2%, and 4%, were manufactured. First, the physicochemical properties of the investigated clay were characterized. Subsequently, the thermophysical properties of the fabricated bricks were determined. Annual simulations were conducted using the TRNSYS software, considering a typical meteorological year (TMY) for Beni Mellal City, located in the semi-arid climatic zone. The energy performance of various passive energy efficiency measures was evaluated and discussed, facilitating a thermal analysis to assess the energy needs for heating and cooling inherent to each building material. The results demonstrate that clay bricks, particularly those reinforced with 4% wheat straw, outperform conventional materials in terms of energy efficiency, highlighting their potential for sustainable construction. This study emphasizes the significance of local clay resources and natural reinforcements in enhancing energy efficiency and provides insights into their application in eco-friendly construction practices, thereby contributing to sustainable development goals

Investigating the Late Chalcolithic pottery production and consumption at Valencina de la Concepción (Seville, SW-Spain): An archaeometric analysis using petrographic and LA-ICP-MS techniques

This paper discusses the results of an archaeometric analysis carried out on undecorated Late Chalcolithic ceramics from Valencina de la Concepción, which is one of the largest and most important Chalcolithic settlements in the southern Iberian Peninsula. The purpose of the study is to contribute to the debate on the socio-economic organization and exchange networks of the site during the third millennium BCE in the Lower Guadalquivir Basin. Petrographic and chemical analysis by LA-ICP-MS of compressed ultrafine powder pellets were used to analyze selected ceramic samples (n = 42) from Valencina and reference clay samples (n = 62) from different locations in the Aljarafe plateau. This study sheds light on possible raw material sources, the choice strategy of raw materials, and certain aspects of production technologies employed for Late Chalcolithic ceramics found at Valencina de la Concepción.The archaeometric analysis revealed that a significant portion of the ceramics, especially plates and platters manufactured primarily using coarse clays, are largely non-local production. However, there was also a limited availability of local production. This study emphasizes the central role of Valencina in the exchange network of the Lower Guadalquivir Basin during the Late Chalcolithic period. This study further demonstrates the wide variety of clay resources available throughout the Aljarafe region and provides solid reference material for further archaeometric analyses of ancient ceramic materials in this region.

Comprehensive utilization of blast furnace slag, municipal sludge and kaolin clay in building brick manufacture: Crystalline transformation, morphology observation and property assessment

At present, the comprehensive utilization of bulk industrial solid waste has attracted wide attention. The recycling of industrial solid waste in building materials not only provides valuable insights for the management of solid waste, but also alleviates the over-exploitation of natural clay resources in the construction industry. In this study, municipal sludge (MS) and blast furnace slag (BFS) were incorporated into kaolin clay (KC) to synthesize sustainable composite bricks, and the sintering effects and engineering properties of bricks were adjusted by changing BFS dosages. The results indicated that the addition of BFS would promote liquid glassy phase production in bricks due to the higher content of alkali/alkaline-earth metal oxides, and the ingredient, viscosity and content of liquid glassy phases could also be regulated through varying the dosage of BFS (0-15%), thereby affecting the pore structure, particle arrangement/consolidation and performance of bricks. Among all synthesized bricks, the optimum dosages of BFS, MS and KC for satisfying the building standard thresholds were 10%, 40% and 50%, with corresponding linear shrinkage, porosity, density, water absorption, compressive and flexure strengths of 12.97%, 18.15%, 1.83 g/cm3, 0.82%, 15 MPa and 38 Mpa, respectively. Finally, mechanism analysis further demonstrated that the formation and evolution of liquid glassy phases were the key responsibility for adjusting the brick micromorphology and performance. Based on this study, using MS and BFS in brick manufacturing benefited the value-added utilization of industrial solid wastes, clean protection of environments and sustainable production of building materials, providing a reference for the process optimization and potential application of MS and BFS wastes in masonry construction.

Study on the relationship between permeability coefficient and porosity, the confining and osmotic pressure of attapulgite-modified loess

This study investigated attapulgite-modified loess as an efficient and cost-effective method for creating an impermeable liner for landfills in regions with scarce clay resources. Laboratory permeability tests were conducted using a flexible wall permeameter to determine the permeability of compacted loess and attapulgite mixtures under varying osmotic conditions. The relationship between the permeability coefficient, attapulgite dosage, radial pressure, and osmotic pressure was analyzed. Nuclear magnetic resonance and scanning electron microscopy were also used to observe the microstructure of the modified loess. The results showed that attapulgite dosage significantly reduced the permeability coefficient, but the effect became limited when the content surpassed 10%. The decrease of the permeability coefficient of the modified loess is mainly due to the filling of pores between the loess by attapulgite, which makes the pore size and throat size of the modified loess smaller. The modified loess displayed a sheet structure that contributed to an increased permeability coefficient due to increased radial pressure. This study provides valuable insights into using attapulgite-modified loess as a material for landfill lining in regions with scarce clay resources.

PHYSICAL CHARACTERIZATION OF EXCAVATED SOILS IN DIAMNIADIO-SENEGAL

The building is an object of concern in terms of health, energy consumption and environmental impacts. With more than 40 % of the worlds energy consumption and high CO2 emissions, the building sector is among the most energy-intensive sectors. An in-depth analysis of the building sector shows that Concrete, the material currently most used in Senegal is unsuited to the climatic conditions of Sahelian countries. In addition, cement production consumes a lot of energy and is a source of greenhouse gas emissions. Faced with environmental and energy concerns, the choice of appropriate materials is a key to limiting environmental impact and ensuring a healthy and comfortable indoor environment. This is how a sustainable approach using local clay resources for the production of clay bricks was implemented. However, the use of swelling clays is the source of significant problems in construction. Thus for a good prediction of the mechanical and thermal behavior of a material, it is important to determine its physical properties. This is why our study focuses on the physical characterization of the excavated soils of Diamniadio.

Developing fired clay bricks by incorporating scrap incinerated waste and river dredged sediment

The global extraction of several billions of clean clay resources, which destroy millions square meters of land, is triggering environmental problems. Incorporating different dosages of incinerated waste or dredged sediment in bricks production has been studied by many researchers. Research articulating the combined effect of incinerated waste material (IWM) and river dredged sediments (RDS) addition on the performance of bricks is scarce. This paper aims to present findings on the engineering performance of fired bricks developed with the addition of IWM and RDS. In this regard, bricks were made with 5 wt% IWM and different dosages of RDS (i.e., 0 – 15 wt%). Physical, durability, mechanical, thermal and microstructure of the developed bricks is examined. Bricks’ shrinkages were found meeting quality performance criterion in the 1.42 – 4.11% range. The highest bulk density of 1.85 g/cm3 permit to classify bricks obtained as lightweight. Water absorptions were mostly within the acceptable 20% tolerance level postulating the developed bricks high durability standard. Compressive strength reductions, which were confined within 5.28 and 21.57 MPa, showed the developed bricks applicability to structural weight-supporting construction as well as specialized engineering construction works. The 40.5% thermal conductivity reduction in WB15 bricks (at 800 °C) theorized its suitability for thermal insulation construction. Mineralogical and morphological analyses of fired bricks clearly showed kaolinite polymorphic phase transformation, which contributed to the different morphologies in the brick matrices. Consequently, reuse of IWM and RDS offered a chance to advance sustainable use of scarce clay resources in lightweight and thermal insulation brick production.

Physico–mechanical and durability performances of compressed earth blocks incorporating quackgrass straw: An alternative to fired clay

In developing countries such as Benin, the use of clay soils to produce fired clay bricks can be confronted with the problems of availability of the energy required for firing. The present study assesses the possibility to use these clay resources to produce compressed earth blocks (CEB) as alternative to fired clay. CEBs were produced by physically stabilizing a highly clayey soil with 0/5 granite dust, followed by chemical stabilization with 8wt% cement and the incorporation of 0 to 1.5wt% quackgrass straw. This resulted in dimensional stability of CEB, despite a slight swelling of 16.33 mm/m upon immersion observed only on CEB containing 1 and 1.5wt% straw. The coefficients of resistance to abrasion are well improved above the standardized minimum threshold of 2cm2/g, i.e. 29.7 to 7.72cm2/g for straw contents of 0 to 1.5%. Moreover, the maximum erosion depth of the CEB of 32.6mm/h, is well below the limit of 120mm/h, despite using a water pressure 10times higher than the standard pressure of 50kPa. These results testify to the durability of stabilized CEB. However, the dry and wet compressive strength decreased from 5.1 to 2.84MPa and from 3 to 1.02MPa, respectively, with the straw content of 0 to 1%. This does not hinder the use of these CEB for sustainable building construction, as the values of their compressive strength in dry and wet conditions were respectively above the required values of 2MPa and 1MPa.

Combined effects of biomass bottom ashes and spent charcoal on characteristics of fired clay bricks

Among the diversity of solid waste produced, biomass by-products stand out due to their synergizing role in energy savings during brick firing process and impact on mitigating sustainability issues of fired clay brick production. Therefore, this study accentuates on assessing the characteristics of fired clay bricks made by replacing clay with both biomass bottom ashes (BBA) and spent charcoal from 8 to 20 wt% in order to minimize non-renewable resource use and enhance brick performance. In total, bricks from 6 mixture series were prepared to ascertain the effect of 5 wt% BBA incorporation and 3 – 15 wt% spent charcoal addition on the physical, durability, mechanical and thermal properties of the produced fired clay bricks. Parameters such as linear shrinkage, dried weight, dried and fired apparent densities, water absorption, open porosity, thermal conductivity and compressive strengths were examined at spent charcoal increasing inclusion in the brick bodies. The produced bricks showed linear shrinkage values within the safe limits of 7%. Water absorption values were also within acceptable levels of 16.33%. Thermal conductivity significantly reduced from 0.76 W/mK to 0.58 W/mK and this reduction meant improvement in the thermal efficiencies of the bricks. Bricks containing 5 wt% BBA and 9 wt% of spent charcoal exhibited compressive strengths of 10.40 MPa in accordance with standards required for structural construction. These results were authenticated from mineralogical and microstructural analyses. Consequently, utilization of up to 20% wastes in a brick body is a crucial step in point of economic growth, environmental cleanliness, natural clay resources conservation and innovation in the fired clay bricks product development.

Structural and Mechanical Properties of Non-Glazed Ceramic Tiles Developed from Selected Mineral Deposits in Uganda

Uganda is well endowed with clay resources; however, comprehensive knowledge about the composition, structure and suitability of these clays for ceramic tile production is lacking. In this study, we provide a comprehensive characterisation of locally sourced clays in Uganda and their suitability for ceramic tile production. In the study, we developed ceramic tiles using feldspar, kaolin, ball clay and sand from four different sites in Uganda. We focused on analysing the surface morphology, crystallographic structure and mineralogical composition of the raw materials. In addition, we examined the mechanical properties of the developed tiles with the different mixture ratios of the clay types. The surface morphology of the raw materials was analysed by using a scanning electron microscope. The structural analysis of the raw clay materials was done using X-ray diffraction. The mineralogical composition of the raw materials was investigated using energy dispersive X-ray spectroscopy and X-ray fluorescence spectroscopy. The results indicated that the strength and rapture modulus are influenced by the composition of kaolin and feldspar. We concluded that the selected mineral deposits can be used in the production of ceramic tiles in Uganda.

Use of waste husk from millet grain cultivation in the production of fired clay bricks

AbstractThe consumption of colossal quantities of materials in the building industry has advanced the swift depletion of clean clay reserves. The use of organic additives in brick production is conserving clay resources. In addition, in some cases, it can lead to improvements in some material properties, such as decreasing thermal conductivity and increasing the capacity of the ceramic material in terms of thermal insulation. In the present investigation, waste millet husk (WMH) was incorporated in different proportions to clays to ascertain its influence on the fired brick properties. The raw materials were characterized for their physical, chemical, and thermal properties and found suitable for use in fired brick production. Additionally, the prepared modeled brick samples were tested for their physico‐mechanical properties. The results indicated that linear shrinkage and weight loss increased, whereas bulk density decreased from 2.06 to 1.58 g/cm3 depending on WMH incorporation amount in the clays and firing temperature. Similarly, compressive strength reduced by up to 68%. Thermal conductivity beneficially reduced by 42% with the addition of 16 wt.% of WMH. The best results in terms of mechanical properties were obtained with 4 wt.% of the WMH. In terms of thermal insulation, the best results were exhibited in the samples admixed with 16 wt.% of WMH. The results showed that porosity and bulk density were critical determining factors that directly influence the bricks physico‐mechanical properties.

Sustainable Composites from Waste Sulfur, Terpenoids, and Pozzolan Cements

Sulfur cements have drawn significant attention as binders because sulfur is a byproduct of fossil fuel refining. Sulfur cements that can be formed by the vulcanization of elemental sulfur and plant-derived olefins such as terpenoids are particularly promising from a sustainability standpoint. A range of terpenoid–sulfur cements have shown compressional and flexural properties exceeding those of some commercial structural mineral cements. Pozzolans such as fly ash (FA), silica fume (SF), and ground granulated blast furnace slag (GGBFS) and abundant clay resources such as metakaolin (MK) are attractive fines for addition to binders. Herein, we report 10 composites prepared by a combination of sulfur, terpenoids (geraniol or citronellol), and these pozzolans. This study reveals the extent to which the addition of the pozzolan fines to the sulfur–terpenoid cements influences their mechanical properties and chemical resistance. The sulfur–terpenoid composites CitS and GerS were prepared by the reaction of 90 wt% sulfur and 10 wt% citronellol or geraniol oil, respectively. The density of the composites fell within the range of 1800–1900 kg/m3 and after 24 h submersion in water at room temperature, none of the materials absorbed more than 0.7 wt% water. The compressional strength of the as-prepared materials ranged from 9.1–23.2 MPa, and the percentage of compressional strength retained after acid challenge (submersion in 0.1 M H2SO4 for 24 h) ranged from 80–100%. Incorporating pozzolan fines into the already strong CitS (18.8 MPa) had negligible effects on its compressional strength within the statistical error of the measurement. CitS-SF and CitS-MK had slightly higher compressive strengths of 20.4 MPa and 23.2 MPa, respectively. CitS-GGBFS and CitS-FA resulted in slightly lower compressive strengths of 17.0 MPa and 15.8 MPa, respectively. In contrast, the compressional strength of initially softer GerS (11.7 MPa) benefited greatly after incorporating hard mineral fines. All GerS derivatives had higher compressive strengths than GerS, with GerS-MK having the highest compressive strength of 19.8 MPa. The compressional strengths of several of the composites compare favorably to those required by traditional mineral cements for residential building foundations (17 MPa), whereas such mineral products disintegrate upon similar acid challenge.

Green synthesis of nano-H-ZSM-5 zeolite single-crystal aggregates via an in situ reconstruction of the topology of natural clay

The synthesis of zeolites from natural aluminosilicate minerals is environmentally sustainable. However, the preparation of nano-ZSM-5 zeolite single crystals via the facile “silica–alumina homologation” of natural clay remains challenging. This paper highlights a novel strategy for the synthesis of defect-free, highly crystalline nano-H-ZSM-5 with a uniform morphology through the kinetically controlled in situ reconstruction of the topology of natural clay within a solid-state-like system. Crystal nucleation and growth were decoupled by aging to control the crystal size. The “homogeneous silica–alumina” property of natural clay was found to be directly inherited by nano-H-ZSM-5 to provide uniformly distributed acidic sites for catalysis. This was demonstrated by methanol-to-propylene conversion, wherein the performance of the obtained crystals was superior to that of commercial ZSM-5. This strategy promotes the development of natural silica–aluminate clay resources and allows the scalable production of high-quality nano-H-ZSM-5 single crystals for heterogeneous catalysis.

Study on Preparation and Properties of Sintered Brick from Multi-Source Solid Waste

The recycling of construction waste and the use of a new sintering process in the field of sintered bricks can greatly solve the problems of clay resource depletion, soil structure destruction, and high CO2 emissions that always limit the development of the sintered brick field. The study was carried out using an orthogonal experiment to derive the optimal mix ratio for the preparation of sintered bricks, and subsequently, the sintered bricks were prepared using the optimal mix ratio. The experimental results show that the maximum compressive strength of construction waste sintered brick (MRB sintered brick) prepared using high-temperature sintering is 8.1 MPa, and the water absorption is 11. When the waste glass slag is mixed with 10%, it can show a better fluxing effect in the preparation of sintered bricks by mixing construction waste with waste glass slag (MGB sintered bricks), so that the MGB sintered bricks have a higher densification. The compressive strength is 32.9% higher and the water absorption is 3.5% lower than that of MRB sintered brick. MGS sintered bricks were prepared by mixing Yellow River sedimentary sand into MGB sintered bricks. The strength of MGS sintered bricks increased with the replacement rate of Yellow River sedimentary sand, and when the replacement rate of Yellow River sedimentary sand reached 16%, the strength of the MGS sintered bricks increased by 88.9%, and the water absorption rate was reduced by 4.6% compared with the MGB sintered bricks. The sintering mechanism had significant effects on the compressive strength, weathering resistance, and frost resistance of the sintered brick. The microwave sintering process has the characteristics of high efficiency, uniform heating, selective heating, and low thermal inertia, which can increase the compressive strength of MGS sintered brick by 4.6%, reduce the water absorption by 12.9%, shorten the sintering time by 43.6%, and improve the frost resistance.

Characterization, technological properties, and ceramic applications of Kastamonu alluvial clays (Northern Turkey) in building materials

This research investigates two unexploited Pınarbaşı (PC) and Küçüksu (KC) alluvial clays from Kastamonu province in the Black Sea region (Northern Turkey) and studies their potential applications in building materials. We have characterized the samples regarding their chemical and physical properties, spectrometry, thermal behavior, phase, and microstructure. This study also explores the technological features of heated clays at 900–1100 °C (such as ceramic properties and color), dilatometry, phase, and microstructural analyses. The results show that both clays contain quartz, kaolinite, illite, and calcite as dominant phases and some clayey minerals as minors. The chemical analysis indicates that the deposits are siliceous clays with the principal oxides of SiO2(48.43–51.58 wt%), Al2O3(17.92–20.87 wt%), and Fe2O3(5.93–6.91 wt%). The KC clay shows a notably high surface area of 88.51 m2/g after N2-physisorption analysis. The characterization of heated clays demonstrates that the densification occurs by forming mullite and anorthite, which are responsible for the increased mechanical strength (24.84–32.85 MPa) above 1000 °C. The overall results reveal that both clays possess suitable technological characteristics, making them favorable low-cost sustainable raw materials in producing red-fired construction and building parts. Study shows that these reserves are typical representatives of other distributed natural clay resources in the area, which generally contain high iron or high carbonate substances. It is formidable that this work is helpful to cover a part of insufficient investigations on the clayey deposits of the Black Sea region.

An Investigation on the Synthesis of Alkali Activated Materials from Thermally Modified Clays

The sustainability and economic competitiveness of alkali activation technology greatly depends on expanding the raw materials database with locally available resources. Therefore, a notable trend has been witnessed toward the exploitation of common clays as alternatives to well-established solid aluminosilicate precursors due to their availability and wide geographical distribution. However, common clays are complex and dedicated research is needed to tailor synthesis procedures and mix designs for different clay resources. This paper describes the outcomes of a study conducted to investigate the influence of several synthesis parameters (solid-to-liquid ratio, NaOH molarity, Si availability, and curing conditions) on the properties of alkali activated binders produced from different thermally modified clays. Optimal synthesis conditions for benchmark metakaolin systems have been identified and binders were produced with progressive dosages of metakaolin replacement by common local clays. Fundamental physical and mechanical properties such as apparent density, open porosity, water absorption, and compressive strength were examined at different curing ages, and X-ray diffraction (XRD) was used to provide complementary mineralogical insights. By combining the effects of the parameters studied, mortar specimens were produced with the developed binders, reaching compressive strength values exceeding 28.2 ± 0.1 MPa, a bulk density as low as 1.78 ± 0.0 g/cm3, and open porosity and water absorption values lower than 15% and 8%, respectively. These properties are comparable to those of conventional hydraulic products, which presents them as interesting candidates for construction. Ultimately, this work aims to contribute with valuable insights toward the valorization of a large group of unexploited clay precursors by demonstrating the feasibility of producing technologically competitive alkali activated materials with little or no use of the prime precursors, thus adding to the extant knowledge and contributing to future scientific and industrial developments in this field.