Clay Raw Materials Research Articles

Lightweight aggregates from waste materials: Reappraisal of expansion behavior and prediction schemes for bloating

There is a growing concern on lightweight aggregates (LWA) for recycling of waste materials: this manufacturing technology is considered a flexible tool to make it possible the conversion of large amounts of residues into building products. The main challenge for this purpose is the control on the technological behavior during firing of waste-bearing batches. The target is engineering the sintering and expansion of LWA in order to tailor bulk density, mechanical strength and water absorption on various possible applications (e.g., structural and non-structural lightweight concretes, lightweight mortars, filtration substrates, floriculture). The prediction of the aggregate expansion – and hence the batch design – is usually carried out utilizing the Riley’s and/or Cougny’s schemes, which are based on the bulk chemical composition of clay bodies. However, collecting the literature data on waste-based LWA and plotting them in the Riley’s and Cougny’s diagrams, no reliable discrimination turns out between expanding and non-expanding batches. In the same way, the attempt to modify the Riley’s and Cougny’s parameters, including elements present in wastes but not in natural raw materials, was unsuccessful. From this standpoint, a new approach to assess the batch expandability was developed through a deeper comprehension of mechanisms acting on sintering and expansion of LWA. A specific characterization protocol was set up, entailing hot-stage microscopy and determination of phase composition and microstructure. This implies a paradigm shift from batch (chemical composition) to vitreous phase (amount, chemical composition, and viscosity at high temperature). The vitreous phase plays a key-role for bloating, microstructure and physical properties of LWA. A working example is presented about new LWA based on waste glasses, ceramic tile polishing sludge and clay raw materials.

Clays of Wierzbka I deposit (northern margin of Holy Cross Mountains) for the production of clinker tiles

Abstract The paper presents results of research on the assessment of the suitability of the Wierzbka I Triassic clay raw materials, which are part of the Wierzbka deposit near Suchedniów, for the production of clinker tiles obtained by pressing. Red colour clays are often used in the production technology of clinker tiles. The high content of Fe2O3 in the composition of red clays promotes the sintering process and affects the colour of the resulting material, a typical characteristic of clinker materials. The raw materials used in this technology should have good sinterability, which guarantees a material with low water absorption, high chemical resistance and mechanical strength. Samples of the raw materials were taken from three different depths of the deposit, and subjected to analysis as follows: chemical composition, phase composition (XRD, thermal analysis DSC/TG), sintering shrinkage, sintering curve and the characteristic temperatures. The analysis of the microstructure was determined using scanning electron microscopy (SEM). The X-ray and thermal analysis of the studied clays revealed the presence of clay minerals such as: illite, kaolinite, illite/smectite, but also quartz and ferruginous minerals. There was no presence of calcium carbonate in the tested samples of the raw clay, which particularly distinguishes these materials as being suitable for use in the fast firing technology of clinker tiles. Samples of the raw materials were pressed under a pressure ranging from 21 to 42 MPa and then fired at temperatures in the range 1130 to 1220°C. The obtained sintered bodies were characterized by a high degree of sintering, an apparent density of 2.31g/cm3, an open porosity of less than 2.5% and water absorption below 1.0%. The results of this study indicate a high technological value of raw materials from the Wierzbka I deposit.

Application of hot-stage microscopy to evaluating sample morphology changes on heating

Investigations of the thermal properties of a raw material or a ceramic product under a hot-stage microscope allow, among others, determining the characteristic temperatures corresponding to the changes of the shape and the cross-section area of samples being heated. They are based on observing and analysing images of the sample recorded with the growth of its temperature. The pictures of changes allow establishing—for the raw materials with the ability of thermal expansion—the technological temperatures of sintering, softening, thermal expansion, melting and flowing. Their knowledge is necessary in determining optimum ranges of manufacture conditions for a number of ceramic processes. Considering some difficulties with precise determination of these characteristic temperatures and with the problem of measuring the coefficient of thermal expansion S of clay raw materials, the authors have proposed hereby a new method of measuring a sample cross-section area on heating under a hot-stage microscope. It has been invented and implemented in the Matlab software environment on the basis of an image analysis of the expanding sample. The changes of its cross-section area (i.e. an outline area visible under a hot-stage microscope) are continuously recorded on the film and can be converted after digital processing into sample volume changes. The method is applicable to precise measuring the coefficient of thermal expansion S of clay raw materials, among others those used in the manufacture of lightweight ceramic aggregates.

Production of Ceramic Brick Based on Aluminum-Silicate Wastes

The paper focuses on the production of ceramic brick based on aluminum silicate waste generated by thermal power plants. The grain size and chemical compositions of the raw material are investigated. Experimental studies are carried out to identify optimum operating parameters of the ceramic brick production. It is shown that the use of aluminum silicate waste, namely, 40–60 % ash together with clay raw material allows obtaining ceramic brick possessing 20–25 MPa compressive strength, 10–15 % water absorption, and frost resistance of over 60 cycles.

Montmorillonite colloids: II. Colloidal size dependency on radionuclide adsorption

Bentonite is a strong radionuclide (RN) adsorbent. As a consequence, it is proposed as one of the engineered safety barriers in many nuclear waste disposal concepts in granite formations. Despite the many beneficial effects of bentonite, in contact with groundwater of low ionic strength montmorillonite colloids may be released from the bentonite buffer and transported towards the biosphere carrying the RNs bound to it. During the transport of colloids in bedrock fractures, size separation of clay colloids may occur, which may further affect RN mobility. In this work, RN adsorption (Th(IV), U(VI), Np(V), Tc(VII) and Pu(IV)) onto size fractionated montmorillonite colloids was studied in a synthetic, carbonated groundwater. Fractionation was done by simple settling procedures and sequential centrifugation. We combined batch adsorption experiments and geochemical modelling for the adsorption studies. U(VI), Np(V) and Tc(VII) did not adsorb to montmorillonite in the synthetic groundwater. Adsorption of Th(IV) and Pu(IV) is strong but, within experimental uncertainties, not significantly affected by the fractionation process. Montmorillonite colloids obtained by fractionation of the raw clay material but in the presence of organic matter during the initial separation step present significantly reduced uptake of Th and Pu. Based on the results, implementation of an “average log KD” (i.e. average distribution coefficients) for all colloidal sizes in reactive transport modelling codes would be acceptable.

Influence of Homogenization of Clay Batch for Laboratory Test on the Structure of the Ceramic Samples

In this paper, we study the chemical and mineralogical composition of the Krasnoyarsk Kray clay used in the production of coarse ceramics. It is found that the fire –strength depends of method of preparation of clay paste. It is shown that the forced dissolution of the raw clay material effectively homogenizes clay paste. As a result, strength of the samples increased during firing. It is also justified by the influence of their mineralogical composition and there method of the preparation. It is proved that conditions of preparation and mineralogical composition affect equally.

Numerical Simulation and Experimental Characterization of Clay Paste under Loads for Energy Saving in Clay Materials Processing

Requirements for the respect of the environment encourage to reduce the impact of human activity on the nature. Civil engineering answers these requirements by the development of ecological construction materials. This paper deals with the transformation of clay raw materials which enable the processing of environmentally friendly construction materials: in addition to their biodegradability, the alveolar fired clay materials allow energy saving in home heating thanks to their thermal isolation properties. But their manufacturing is a high energy consumption process, in particular during compaction, drying and firing which contribute to the emission of greenhouse gases. The goal of this paper is to study the rheology of clay pastes in order to develop low energy in manufacturing processes. For this purpose, theoretical and experimental approaches were carried out on six clay varieties. In the theoretical approach, a finite element (FE) simulation model has been developed for pressing a non-rigid material predicting deformations and stresses occurring within the clay structure. Experiments have then been carried out to validate the finite element modelling. In this experimental approach, the clay pastes were transformed with water content respecting the Atterberg limits which determine the plasticity of clays. The samples compaction has been carried out under variable loadings in order to determine the suitable low energy consumption loading.

Features of chemical-mineralogical composition and processing properties for medium-ferrous bauxites

The features of chemical-mineralogical composition and processing properties of bauxites from Iksinsk and Severoonezhsk deposits are investigated in the paper. It is found that the studied bauxites are coarsely dispersed and low-dispersive, high-alumina clay raw materials with a high content of colouring oxides. According to their mineralogical composition, Iksinsk and Severoonezhsk bauxites are boehmite-hydrargillite-kaolinite clay bauxites. Moreover, Iksinsk bauxite samples are characterized by the total absence of quartz impurities. The samples of plastic molding based on Iksinsk bauxites are fully sintered at 1500 °C with the formation of strong structures with a compressive strength of 70-120 MPa (depending on the variety of bauxites). The samples based on Severoonezhsk bauxites are fully sintered at 1450 °C, and they are characterized by a compressive strength to 70 MPa in the sintered state.

The impact of modifications of the smectite-bearing raw materials on their thermal expansion ability

The effects of modifications of the clay rocks containing smectite on their thermal expansion have been studied at the example of the claystones from Dylągowka (Dynow Foothills, south-eastern Poland). Hot-stage microscopy was employed combining a dedicated procedure of digital image analysis. The chemical modification of three rock types from the Dylągowka deposit included the treating with an addition of Na2CO3, activation with a H2SO4 solution, and firing at 560 °C. X-ray diffraction and thermal analyses (DTA, TG) helped determine the impact of the modification processes on the structural changes in smectite, the major component of the rocks in question. The investigations into thermal expansion have shown that the clay rock varieties poor in CaO can be acid-activated with a significant improvement their expansion in comparison with such an ability of natural rock equivalents. It is a result of introducing silica into the melt that forms on heating the natural clay rock at high temperatures due to its presence of alkalis (Na2O and K2O). The silica, in turn, comes from the protonated silica gel generated due to the acid treatment of smectite-bearing rocks. The liquid phase (the melt) with a high viscosity may form a cover on the surface of granules of the product being fired and prevents the expulsion of gases into the ambience. An addition of Na2CO3 is favourable as it considerably lowers the firing temperature of the expanded product, both in the case of clay raw materials poor and rich in CaO. The acid activation of the latter variety (CaO-rich) is less effective because of the reaction of acid (H2SO4 used by the authors) with calcite; the mineral is decomposed, and at least part of the acid does not activate a clay material.

Factor space differentiation of brick clays according to mineral content: Prediction of final brick product quality

Chemical composition and XRD qualitative analysis were used to calculate mineral contents of 139 brick clay raw materials using LPNORM. The second order polynomial models (SOP) for all the samples, which express the relation between mineral contents and the characteristics of fired laboratory products, did not fit to experimental data satisfactorily, due to low coefficients of determination (r2). In order to improve the models, the samples are divided into four groups in factor space (four quadrants), according to their mineral content similarity, using principal component analysis (PCA). Predictive models of compressive strength (CS), water absorption (WA), firing shrinkage (FS), weight loss during firing (WLF) and volume mass of cubes (VMC) are obtained for each of the groups. Second order polynomial (SOP) models are developed, and the influence of certain minerals to brick clay bricks quality within the groups is discussed. Developed models were able to predict the final quality of products in a wide range of mineral content and temperature treatment data, showing coefficient of determination (r2) in range between 0.704–0.995. In order to estimate the adequacy of these models, the results were applied to the experimental data and compared according to additional statistical tests, so the next values are determined: coefficients of determination, reduced chi-square (χ2), mean bias error (MBE), mean percent error (MPE) and root mean square error (RMSE).

Practical use of variographics to identify losses and evaluate investment profitability in industrial processes

Author Summary: This work illustrates variographic analysis applied to industrial production processes to identify and reduce adverse production deviations (over-specification, loss) and evaluate profitability. A first example concerns production of light-weight expanded clay aggregates (Exclay), produced in cement-like rotary kilns. Clay raw material is heated to 1150 °C to be expanded. An adverse periodicity was observed in a specific plant cooler manifested as fluctuations in the material volume (height level) causing a periodic variance in the production output from the kiln. This problem must be resolved by instigating a more stable cooler, which could in fact be engineered by a very small investment of about 5,000 Euro. A variogram characterization was carried out to evaluate the amplitude of the periodicity, and the quantities involved (losses), which information was used to calculate the investment pay-back time. From the variogram it was observed that the reduced kiln output volume was at least 0.7%. During one year with improved cooler level control, this translates into savings of about 100,000 Euro, i.e. a pay-back time will be less than one month. A second example is from a LRM-project (Loss and Reduction Model) at a plant producing bagged pre-mixed mortars, in which the variance of the weight of the produced bags was found to be consistently too large. A pilot variographic analysis was applied with an aim to identify the root causes of this problem (three filling stations at the same line were investigated, all with identical filling systems and scales): Two stations were found to have a total material loss of 1.2%, while the third was running perfectly well (low V(0) and low sill), but with a too high set point. The technical resolution shows that it is possible to reduce material loss with existing equipment by improved monitoring/recording routines but no need to acquire new expensive belt scales a.o. For two of the stations V(0) (MPE) was in fact at a level almost identical to the sill making it structurally impossible to keep bag weight within specifications. Recurrent monitoring of V(0) and moving average smoothing should be evaluated at the very many similar production lines in the multinational corporation involved to gain improved process control to reduce overfilling. While relatively small on the basis of an individual filling line, the potential accumulated corporate savings take on a quite different economic significance. Variographic analysis is a powerful tool for industrial technicians and process engineers to improve processes —and in the present cases for industrial managers as well for evaluating ultimate investment profitability in industrial processes.

Potentiality of clay raw materials from Gram area (Northern Tunisia) in the ceramic industry

The geological study of Miocene clays from Gram area, North West of Tunisia shows an important series of clay materials to use them in the faience ceramic. Selected samples were studied with the objective of analyzing their chemical and mineralogical composition, morphology, particle size, plasticity, thermal analysis and their ceramic aptitude to be used in the faience ceramic. Raw materials are mainly composed of illite and kaolinite are the dominant clay minerals with minor quartz and dolomite.The plasticity indexes are lower than 15.40%, suggesting that these clays are not plastic. Technical characterization was carried out on one representative mixture of Miocene clay samples. The firing characteristics (shrinkage and water absorption) were measured. The optimum firing temperature of clay mixture (M) has been established. These clays could be used in the manufacture of ceramic pieces.

Swelling pressure of natural and modified smectite-bearing clay raw materials

Smectite clays, due to their barrier properties and swelling ability, are often applied for waterproofing purposes. A proper value of swelling pressure is one of the parameters, which must be met by the fillers used in hybrid waterproofing materials. The authors determined the swelling pressure of selected clay raw materials in their natural state and after chemical modification. This parameter was measured by the Komine method, as this procedure is more accurate than the standard edometric method. The authors introduced some changes in the method. The samples represent Krakowiec clays (Miocene) and a Triassic clay, collected in active pits of building clays, which are widely exploited in south Poland. The content of the smectite group minerals, determined from the sorption of methylene blue and copper(II) triethylenetetramine, ranges between 15 and 35%. Further characteristics of the clays were obtained with X-ray diffraction, chemical analyses (calcium carbonate content including) and pH measurements. It has been found that the activation of smectite clays with sodium lowers their swelling pressure as water penetrates easier the interlayer spaces of the smectites modified. This is important from the viewpoint of assessing the quality of bentonite fillers.

Compressed Bricks Made of Makabaye and Pitoaré Clay: Implementation and Production

In a strong commitment to economic valorisation that began a decade and relevant contribution to the problems of housing and creation of small jobs response, the Cameroonian government has invested heavily in promoting use of local materials through the creation of MIPROMALO (Mission for Promotion of local Materials) in 1991 (economic crisis), and through the signing of government circular from the Prime Minister, thus placing its development policies in prior to any development strategy more distant prospect. It was then that housing through development of local building materials becomes one of major policy priorities of Cameroonian’s government. However, there is a low valuation thereof despite availability of local materials and political will expressed in Circular No. 002/CAB/PM of 12 March 2007 on the use of local materials in construction of public buildings. In this study, we analyse the contribution that can play promotion of local materials in construction in the Sahel zone which for a harmonious sustainable development. Specifically, it’s to highlight the added value of using local materials, propose strategies for implementation and production of compressed bricks. This scientific work has therefore a double interest, scientific and technological industrial view and contributes to the development, promotion of local materials and the development of soil and/or basement areas. We arrived after analysis of our data to the conclusion that valuation of clay materials from Maroua’s town was a factor for economic growth and sustainable development. This inventory allows us to implement and produce prototypes suitable compressed bricks, shapes of housing in Sahel zone. However, physical and geotechnical tests on materials clay (raw materials for production of bricks), allow us to better assess characteristics of clay before production of bricks. Well after we submit our bricks to various mechanical and technological tests to assess their ability to withstand loads in extreme temperature conditions of Sahel zone.

Identification and Ceramic Application of Some Tunisian Clays

Mineralogy, chemistry, and plasticity of the raw clay materials, outcropping in different Tunisian domains were studied. These clays constitute the only mineral resource of the ceramic industries in Tunisia, and are exploitable at eight quarries. Powder X-ray diffraction analysis revealed that illite and kaolinite are the major mineral phases. However, other clay minerals, such as illite/ smectite mixed-layer, and chlorite are also present. The associated minerals detected in powdered materials are: quartz, calcite, feldspar and, dolomite. These raw materials are marly clays with 6% - 14% CaO, represented essentially by calcite; they show the greatest relative amount of Na2O K2O (~3.5%) and iron-oxide (~6%). The plasticity index and liquid limit of crude samples do not exceed 22% and 42%, respectively. This indicates that these clays belong to the zone of illitic clays, classified in the low to moderate plastic domain. The analysis will be used to find appropriate applications for traditional ceramic. In addition, this paper shows that the ceramic defects observed in the pieces manufactured from these Tunisian clays are lamination, cracks, and lower mechanical and bending strength. Some solutions are assured to avoid these ceramic defects.

Influence of Stony Rocks Additives on Strengthening of Aluminosilicate Ceramics from Fusible Clays

The paper presents the results of the research, connected with the granulometric and mineralogical compositions of fusible clay raw materials of Krasnoyarsk region - argillic and loose clay varieties. The influence of granitoid and diabase rocks stony additives on the sinterability and strength characteristics of the ceramic materials based on fusible clays is evaluated. It is found that the introduction of sintering additives into the loose fusible clay leads to the significant increase of samples strength – 50-100MPa, while the introduction of the similar additives in the argillic clay does not influence positively on samples strength.

Regulation of the structure formation of ceramic masses of the system multimineral clay– kaolin-feldspar raw materials

Polymineral clay raw materials with absent sintering interval was selected as the main raw material for the synthesis of ceramic masses, production of ceramic clinker for various purposes using the plastic extrusion method.Kaolin and pegmatite from the Khmelivskyi deposit that may act as fluxing agents were selected as kaolinite-feldspar raw materials.Methods of directed structure formation regulation of ceramic masses based on polymineral clay raw materials using kaolinite-natural feldspar raw materials were investigated.Using mathematical planning, mathematical models of interaction and influence of various technological factors on the properties of experimental masses were developed. Using the correlation analysis method, the relationships in the system polymineral clay-kaolinite-natural feldspar raw materials were examined.Based on the ceramic mass 9 and 11 of the system polymineral clay-montmorillonite-substandard kaolin-pegmatite of the Khmelivskyi deposit, possibility to produce ceramic clinker by optimizing the chemical-mineralogical composition, and masses with a wide sintering interval was shown.

Influence of characteristics of alumina-silicate raw materials on the formation process of clinker

The traditional alumina-silicate raw materials, for example, clays, in the precalcining technique of cement production, have been replaced by low grade and high silica content sandstones, shales, and industrial waste residues, including fly ashes, slag, and others. The results are the change of compositions and characteristics of raw materials applied and a great effect on cement calcination process and clinker formation. In this work, the cement clinker formation process of different alumina-silicate raw materials to replace clay raw material was studied by chemical analysis, X-ray diffraction, differential thermal analysis, and high temperature microscope based on the characteristics of the alumina-silicate raw materials. The formation heat of the clinker was determined by the acid dissolution method. Influence of different alumina-silicate raw materials on the clinker burnability and formation process was studied. The results show that the changing of alumina-silicate raw materials, especially using industrial waste residues, can reduce the formation temperature of high temperature liquid phases, improve the burnability of raw materials, reduce the formation temperature and formation heat of clinker. And this study also observed the formation temperature and transformation of high temperature liquid phases in the heating process of raw materials by high temperature microscope.

Potential use of clay from Burkina Faso as filler in rubber production

raw clay materials deposit in Burkina Faso have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and chemical analysis to evaluate their potentialities to be used in rubber compounds production as filler. The samples are composed principally by aolinite, illite and quartz. The rubber compounds have been done in open two-roll mill at room temperature and tested for cure characteristic (ts5, tc90), ineralogical composition by XRD, microstructure by SEM and mechanical properties (Elongation at break, Tear strength, tensile strength, hardness shore A and modulus). The cure characteristics of the rubber compounds formulated with the sample are feeble than those made with commercial kaolin (control). The mechanical properties are in general, except the longation at break, for the sample lowest than those of control. However the different values obtained with the sample are not far to those obtained with commercial kaolin. The different samples can then be used as filler in rubber production after a pre-treatment to reduce the impurities.Keywords: Raw clay materials, rubber, rheology.

Нетрадиционное глинистое сырье как компонент неорганических дисперсных систем

Нетрадиционное глинистое сырье как компонент неорганических дисперсных систем