Increasing Fines Content Research Articles

Investigating the compaction and the mechanical behaviors of coal gangue as subgrade filler and constructing highway subgrade in practice

Using coal gangue as subgrade filler (CGSF) can address the accumulated issues of coal mine waste, but also save the constructing costs, which has the important ecological and engineering practical value. The well-graded limit of CGSF was captured based on the fractal model grading equation (FMGE). The large-scale vibration compaction test (LCT) shows that particle grading has a remarkable influence on the compaction of CGSF, with the increase of fine particle content, the dry density of sample first increases and then decreases. On this basis, the optimal range of particle grading was obtained. A series of large-scale triaxial tests (LTT) were conducted to investigate the mechanical behaviors of CGSF. The results shown that (1) the peak deviatoric stress shows a well-quadratic correlation with the fractal dimension. The optimal grading range of CGSF captured by LTT and LCT is basically the same, hence the suggestion of acquiring the optimal grading through LCT was given. (2) Increasing the compaction degree (DC) can significantly improve the strength of CGSF if DC is smaller, while when DC is greater, the strength improved by increasing DC will not be significant. (3) The grading and DC have a significant impact on the cohesive force of CGSF, while have little effect on internal friction angle. In addition, the research results provide good guidance for the constructing of a highway subgrade in practice.

Improving thermal insulation and thermal resistance properties of laterite‐based geopolymer foams by direct foaming

AbstractThis work aims to synthesize new foaming laterite geopolymer foam using laterite, sodium silicate solution, sand, and aluminium powder. The porosity rapidly increased with the addition of the foaming agent. The foam matrix had thermal conductivity values of 0.10 W/m K with 0.7% of Al powder and 0.64 W/m K with 0% of Al powder. For fire resistance, samples exposed to high temperatures (200°C and 500°C) showed increased flexural strength, linear shrinkage at 500°C, and a decrease at 900°C due to structural weakening under high thermal pressure and the appearance of new phases such as nepheline and akermanite in X‐ray diffraction analysis. The results also showed that a 30% increase in fine aggregate content increased the strength of the foam matrix, with flexural strength ranging from 5 to 9.1 MPa after 28 days of ambient curing. These laterite geopolymer foams have shown promising thermal insulation and mechanical qualities that are appropriate for building applications.

Stress-dilatancy behavior of marine coral sand incorporating non-plastic fines

The existed understanding of stress-dilatancy behavior is predominantly based on experiments conducted with clean quartz sand, with limited research focusing on coral sand. Particularly, impacts of fines and density state on stress-dilatancy response of marine coral sand is of significant concern. This work presents a systematic investigation into these issues through meticulously controlled geotechnical tests, coupled with corresponding discussion and interpretation. Results show that at a high stress level, both pure coral sand and its mixtures consistently undergo shear contraction regardless of fines proportion and density state. However, mixtures with minimal fines experience shear contraction initially, followed by dilatancy under a medium-low stress level. Friction angle at peak state (φps) and critical state (φcs), excess friction angle (φex), and maximum dilatancy angle (ψmax) decrease powerfully as increasing fines content. Besides, the lower and upper limits of variation for φps, φcs, φex concerning ψmax were presented. Correlation between φex and ψmax highlights that Bolton's stress-dilatancy equation, developed for pure sand, remains applicable provided that fines content remains below the threshold value. Additionally, gray correlation result suggests that fines post the dominant influence on above behaviors, followed by density state and stress level. Finally, potential mechanism behinds the influences of fines and density state was explored from the view of particle column buckling.

Influence of fines and gravel particles on strength-dilatancy of river sand: Effect of depositional conditions

Understanding the effects of low plastic fines and gravel contents on the mechanical behavior of sandy soils in terms of the strength-dilatancy relationship is crucial for various geotechnical applications. To gain deeper insights, an extensive series of direct shear tests were performed on two distinct types of mixtures: sand-fines mixtures and sand-gravel mixtures. The study systematically varied Fc/Gc content from 0% to 30%, using dry and wet methods, at a medium density (Dr = 50%) and a range of normal stresses (σn = 100–300 kPa). The experimental findings provide remarkable trends. For dry pluviated specimens, an increase in fines content led to a decrease in the shear strength of the mixtures. Conversely, the wet deposited specimens exhibited an opposite tendency, where higher fines content induced larger shear strength. Notably, the incorporation of gravel substantially improved the mechanical performance of the sand mixtures, regardless of the preparation method employed. Dry pluviated specimens generally exhibited higher shear strength than that of the wet deposited ones for the same Fc/Gc. A developed set of equations has been suggested to predict the strength-dilatancy relationships for all-tested materials. These equations take into account the impacts of fines and gravel contents and both specimen preparation methods.

Effect of Fine Particle Content on Solution Flow and Mass Transfer of Ion-Adsorption-Type Rare Earth Ores

Fine particle content significantly affects the in situ leaching of ion-adsorption-type rare earth ores. This study investigated the effect of fine particle content on solution flow and mass transfer in leaching. The results showed that with the increase in fine particle content, the peak concentration and peak time of rare earth increased. When the fine particle content exceeded 20%, all ion-exchangeable-phase rare earth ions could be replaced with a low dosage of the leaching solution. The leachate flow rate exhibited multi-stage variation, influenced by solution permeation, ion exchange, and fluctuations in accumulated liquid height. A mass transfer analysis showed that a higher fine particle content corresponded to a smaller plate height and a larger plate number of theoretical plates. As fine particle content increased, the final rising height of capillary water decreased, with rising rates varying across different stages for the samples. Moreover, an increase in fine particle content from 5% to 20% resulted in a 94% decrease in the samples’ permeability coefficients. A mechanism analysis showed that when the fine particle content was higher, the fine particles were embedded in the gaps between coarse particles, and the ore particles in the sample were arranged continuously, resulting in a lower permeability coefficient. Then, the leaching solution could penetrate uniformly, which was beneficial for reducing leaching blind spots and improving leaching efficiency. However, excessive fine particle content might have detrimental effects. Based on these results and considering actual mining conditions, the optimal fine particle content for rare earth leaching is 20%.

Effects of low clay content on the anisotropic behavior of sand-clay mixtures: laboratory investigation using TSHCA

Undrained behavior of sandy soil with fines content is a challenge in geotechnical research. In this article, the effect of low clay content (plastic Kaolin) on the anisotropic behavior of sand is studied. In the technical literature, there are different data about the effect of fine particles (generally high percentage), but there are not enough studies on low fines content (especially plastic fines) and anisotropic conditions. For this purpose, 30 undrained tests are performed using a torsional shear hollow cylindrical apparatus (TSHCA) with constant (αo) and (b) values on Firoozkuh sand. The specimens had Kaolin contents of 0, 3, 5, 7 and 10%, and the inclination angle (αo) is varied from 15o to 60o. The specimens are prepared by dry deposition method and are consolidated under P'c= 100 and 200 kPa. The results of the experiments show that increasing the (αo) leads to more contractive behavior in sand. By adding clay particles to the host sand up to 3%, the peak strength of the specimen is increased (7% and 6% for α=15°and 30°, respectively), and then with the increase of clay content up to 10%, the strength of the specimen is decreased (33% and 22% for α=15°and 30°, respectively). But at α = 60o, with the addition of 5% clay, decrease in the peak strength is observed (about 15%) and with a further increase in the clay content, unlike the angles of 15o and 30o, increase in the peak strength of the specimen is observed, so that at 10% clay, the strength of the specimen is higher than the host sand (about 7%), which can be attributed to the cohesion nature of the clay particles. With the increase of clay content, anisotropy degree is decreased. In other words, with the increase of fines content, the anisotropic behavior is decreased.

Study on Slump and Compressive Strength of Gangue Based on Aggregate Size Gradation

In order to solve the ecological environment pollution caused by a large amount of coal gangue accumulation and the problems of poor conveying performance and low support strength of paste filling materials. Based on the standard slump test and uniaxial compressive strength test, the slump and compressive strength (post-coagulation) of gangue paste under different aggregate size aggregations were obtained through orthogonal experiments in this study. The results show that the slump of the gangue filling paste with four types of aggregate size gradations is negatively correlated with the mass fraction, and the slump of the filling paste with a coarser aggregate content is more obviously affected by the mass fraction The increase of fine aggregate content has a significant impact on the compressive strength of the filling paste, which shows a trend of first increasing and then decreasing. When the mixing ratio of coarse aggregate and fine aggregate is 5:5, the compressive strength of the paste reaches the best. In addition, different proportions of aggregate mixing cause the filling paste to form different skeleton structures, including the skeleton void structure at 7:3 or 6:4, the skeleton dense structure at 5:5, and the skeleton suspension structure at 4:6, which are decisive for the final performance of the paste. By analyzing the experimental results of the compressive strength and slump of the gangue filling paste, it was found that the relationship between the compressive strength and slump of the gangue filling paste is a power index function. Through data fitting, it was found that the regression coefficient of the fitting function is no less than 0.97, and the fitting effect is good for evaluating the strength of the filling paste under the aggregate size grading.

Experimental Study on Tailings Deposition Distribution Pattern and Sedimentation Characteristics.

Tailings pond accidents frequently occur during an extended period, resulting in loss of life and property, wastage of resources, and environmental pollution. Relying on tailings pond engineering, this paper carried out sample particle fragmentation experiments and settling column experiments to explore the deposition distribution pattern of tailings in both horizontal and vertical directions as well as the impact of particle size distribution on the sedimentation stratification effect. The results show that the median particle size on the dry beach surface in the horizontal direction slowly decreased with the increase in the distance from the subdam. The particle size of tailings showed great fluctuations in the vertical direction, which gradually became finer with the increase in the depth overall. At the same time, saturated sedimentation experiments suggested the inconsistent variation rule with the field test, namely, coarse on the bottom and fine at the top, and the change in particle size greatly affected the tailing sedimentation stratification effect. With the increase in fine particle content in tailings, the appearance time of the water-sand interface was shortened to within 30 min, but the sedimentation and consolidation completion times were delayed to about 1400 min. The settling column results indicate that the increase in fine particle content gradually weakened the sedimentation stratification effect, and the sedimentation pattern transformed from independent sedimentation to floc-type average sedimentation, which led to the enhanced water-retaining property of the settled layer. This may lead to an increase in the saturation line and a decrease in the length of the dry beach, seriously affecting the safe operation of the tailings pond. The research results provide some theoretical guidance and basic data for analyzing the consolidation efficiency of tailings and the stability of the tailings pond.

Waste management in a tissue paper mill: a practical approach

The principles of sustainability, together with the Sustainable Development Goals (SDGs) defined by the United Nations (UN), are essential tools for achieving and maintaining quality of life for the coming years. The sector can make use of these objectives, and the process can become more efficient, with less water consumption and reduced waste. Using virgin cellulose fiber derived from eucalyptus or even recyclable white paper as raw material, this production method is responsible for producing paper with characteristics such as softness, low grammage and good liquid absorption, with products such as toilet paper, napkin, among others. Within the manufacturing process, several procedures can be responsible for the appearance of lint and paper dust, being a type of waste in this industry. Among these, we can mention the increase in fines content, resulting from the fiber refining process, initial mechanical treatment of the paper raw material, which provides the product with resistance. The paper crepe formation procedure is responsible for making the tissue sheet acquire characteristics such as softness and volume, but which can lead to the creation of waste. Through a simple approach related to the balance of process materials, with the analysis of process inputs and outputs, the aim of this work is to estimate the amount of material lost in a tissue paper machine. It is a fundamental preliminary assessment for making decisions regarding waste management.

A new procedure for characterizing the critical intergranular contact state of non-plastic sand – fines mixed materials

A key and urgent scientific issue is how to characterize the complex intergranular contact state and mechanical behavior evolution of sand–fines mixed materials and then show how this state contributes to the static and dynamic properties of such materials. Both theoretical analyses and experimental data suggest that the mixes have different intergranular contact states as the fines content (FC) increases, and the mixed materials can be classified as sand-like, in-transition, or fines-like. The capability of the Rahman semi-empirical formula to predict the threshold fines content FCth—which distinguishes the regime of “fines in sand” (sand-dominated behavior) from that of “sand in fines” (fines-dominated behavior)—is verified using the basic material and mechanical properties of mixed materials from the literature. Developed from the method for determining the theoretical minimum void ratio, a new method that allows unified characterization of the critical intergranular contact state parameters FCin-min and FCin-max for in-transition soils is established based on the binary packing model, and FCin-min and FCin-max can be determined simply through explicit expressions that use some material physical indices of pure-sand and pure-fines materials. The proposed procedure offers significant advantages for evaluating the critical intergranular contact state and mechanical properties of sand–fines mixed materials in geotechnical engineering practice.

Effect of compaction and moisture content on the deformation characteristics of unsaturated sandy soils varying fines content

ABSTRACT This research explores how the dynamic behaviour under cyclic compression loading affects compaction characteristics. Three types of sand, varying in fines content, are compacted under different saturation ( S r ) and compaction ( D c ) levels. Suction-controlled drained cyclic loading tests are conducted to predict axial strain accumulation, with initial suction measured for each compacted state. The study seeks to understand the correlation between axial strain accumulation and initial suction across soil types. Findings indicate that initial soil suction, influenced by saturation, significantly impacts axial strain under cyclic loading. Lower saturation enhances particle bonding, increasing initial suction and reducing strain accumulation. Moreover, an increase in fines content results in greater strain accumulation. Despite that, sands with elevated fines (18.8%) can achieve similar soil performance through effective compaction with precise saturation control. This underscores the role of saturation in moisture regulation during compaction, particularly for sands with higher non-plastic fines content, in achieving effective compaction.

Evaluating The Influence of Fines on the Characteristics of Pervious Concrete

Pervious concrete, also known as no-fines, gap-graded or porous concrete has an interconnected pore structure that freely allows the passage of water to flow through, thereby draining all or most of the water falling on its surface. This concrete can be used as paving material to reduce the storm water runoff to the drainage system and minimize water logging problems. In general, the porosity is achieved by omitting fine aggregate completely. But this results in a low strength concrete which cannot be used for most pavement applications. In this study, pervious concrete mixes have been formulated with a limited quantity of fines (10% and 20%) and the strength and permeability properties have been investigated for various types of fines (quarry dust, river sand and M-sand). While the strength of pervious concrete is increased considerably by adding fines to them, the permeability of the samples remains within the required range of 0.5 to 40mm/s. It has been observed that the addition of different types of fines had great influence in strength and permeability. The compressive strength increases with increase in fine content. Also, it is found that the compressive strength of cube with Quarry dust gives more strength compared to other fines.

Bacteria Pseudomonas taiwanensis as a decomposing agent of peat fiber

Efforts are needed to accelerate the decomposition of peat fiber to reduce the fiber content through bioaugmentation using Pseudomonas taiwanensis bacteria so that it can reduce the high-water content of peat fiber. The research aimed to determine the effect of adding Pseudomonas taiwanensis bacteria on the decomposition of peat fiber. This research is a laboratory experimental research. The research sampling location was in Bereng Bengkel Village, Palangkaraya. The parameters observed included fiber content, fiber size distribution, and peat fiber decomposition speed following the Peat Testing Manual. The research instrument was an observation sheet for fiber content, size distribution, and peat fiber decomposition speed. Research data was analyzed using descriptive statistical analysis. The results showed that adding 15% Pseudomonas taiwanensis bacteria with a curing period of 28 days in fibrous peat resulted in the highest reduction in fiber content, from the initial condition of 61.14% to 12.33%. This variation also shows a decrease in coarse and medium fiber content and a significant increase in fine fiber content. The decomposition rate for this variation shows good consistency. The conclusion was that adding 15% Pseudomonas taiwanensis bacteria with a curing period of 28 days showed optimal results in accelerating the decomposition of peat fiber through the bioaugmentation method.

An extended hypoplastic model for sands with additions of highly plastic fines formulated under the ISA framework

In the present work, the hypoplastic model for sands by Wolffersdorff, (1996) coupled with Intergranular Strain Anisotropy (ISA) by Fuentes et al., (2020) is extended to account for the influence of fines content on the undrained cyclic response and liquefaction resistance of the material. A set of undrained cyclic triaxial tests on clean Ottawa C778 sand and on the same sand with additions of bentonite or laponite were simulated to evaluate the model’s capabilities. The comparison between experiments and element test simulation results suggest that the proposed extended model is able to accurately describe the behavior of clean Ottawa C778 sand and the significant influence of plastic fines in the response of the mixtures, such as the reduction in the accumulation rates of strains and pore water pressure under cyclic loading, and therefore, the improvement in the liquefaction resistance with increasing fines content.

Compressive strength of fly ash based geopolymer utilizing waste completely decomposed granite

An attempt to recycle construction waste soils in southern cities of China was presented in this study, where completely decomposed granite (CDG) was utilized to replace fly ash in the production of environment-friendly low-carbon geopolymers. Five crucial parameters were identified and incorporated into the experimental design using the Taguchi method, including fine and gravel particle content of CDG, fly ash content, water-binder ratio, and curing temperature. Test results demonstrate that the newly formulated geopolymer can achieve a compressive strength of up to 14 MPa with a relatively high usage of CDG. The strength initially increases and then stabilizes with an increase in fine particle content. However, no significant relationship is observed between the compressive strength and gravel particle content. Higher curing temperatures and greater fly ash content lead to increased strength, while the strength initially decreases and then slightly increases with changes in the water-binder ratio. To examine the significance of these factors, Analysis of variance (ANOVA) were conducted and a correlation heatmap was drawn, revealing the following order of significance: curing temperature > fly ash content > water-binder ratio > fine particle content > gravel particle content. Furthermore, a robust strength prediction model was modified through multiple regression analysis. Another two additional groups of tests were performed to validate the proposed model, demonstrating the model's strong performance, particularly for curing ages beyond 14 days.

Структурно-морфологические свойства вторичного волокна из влагопрочного сырья при мягком размоле. Часть 2. Характеристика волокнистой мелочи

The process of recycled pulp refining is usually associated with a significant change in the morphological characteristics of the secondary fiber and the formation of additional amounts of fines. It is well known that fines have a great impact on the pulp properties, the papermaking process and the quality of the resulting paper. At the same time, the effect of fines both on the paper properties and on the papermaking process depends on the morphological characteristics of the fines. The aim of the study was to evaluate the changes in the morphological characteristics of the fines during gentle low-consistency refining of the recycled pulp. The recycled pulp was obtained from commercial wet-strength tissue paper, consisting of 100 % bleached softwood kraft pulp (BSKP) made from pine (Pinus sylvestris L.). The repulping of wet-strength paper was performed at 60 °C in three ways, namely, repulping with sodium hydroxide (indicated as RP (NaOH)), repulping with sodium hydroxide and sodium persulfate (RP (NaOH + Na2S2O8)), and finally repulping with sodium hydroxide and potassium monopersulfate (RP (NaOH + KHSO5)). Using an optical fiber analyzer, L&W Fiber Tester, it was found that accelerated persulfate and monopersulfate repulping of the wet-strength paper led to an increase in fines content after pulp refining by 0.20…0.28 % on length and by 0.9…1.5 % on number of particles. In addition, some fines were not detected due to the limited resolution of the measuring device. The morphological characteristics of the recycled pulps showed that the studied fines were relatively straight particles (Sl = 93.5...94.0 %) with low length polydispersity ((Ll/Ln) = 1.08...1.09). Fines had a mean slenderness ratio (L/W)l and (L/W)w of about 7, which in some length classes reached 8...9. Taking into account the experimental data on fines length (Ll = 132…134 µm) and fiber width (Wl = 29.7…30.0 µm), as well as SEM images of recycled paper, we can conclude that these particles can form fines-assisted bridges between several close deposited fibers in the fiber network, thus strengthening the paper web. For citation: Penkin A.A., Kazakov Y.V. Changes in the Morphological Characteristics of Secondary Fiber Obtained from Wet-Strength Paper During Gentle Refining of the Recycled Pulp. Part 2. Fines Characteristics. Lesnoy Zhurnal = Russian Forestry Journal, 2023, no. 4, pp. 169–179. (In Russ.). https://doi.org/10.37482/0536-1036-2023-4-169-179

Experimental Study on the Effect of Fines Content on the Frost Swelling Characteristics of Coarse-Grained Soil in Canal Base Under Open System

Abstract Engineering usually considers coarse-grained soils as non-frost swelling soils, but serious frost swelling still occurs in coarse-grained canal bases, which is directly related to the recharge conditions and the fine particle content in the soil. Little attention is currently paid to the effect of different fine particle contents on coarse-grained soil frost swelling, especially after the fine particle admixture content exceeds 16%. This paper considers the characteristics of coarse-grained soils in water conservancy projects with fines content between 0% and 50%. The coarse-grained soils with 5%, 15%, 25%, 35%, and 45% fines content were designed for freezing and swelling tests. The evolution of temperature and moisture fields and the amount of freezing and swelling of coarse-grained soils during the freezing process were studied by using servo-type freezing and swelling and thawing tester. The experimental results show that the cooling process of soil samples can be divided into a rapid cooling stage, a slow cooling stage, and a freezing stabilization stage. The cooling rate and the frost heave amount with increasing fines content showed a trend of first increasing and then decreasing.

Evaluation of the sieve analysis effect on the efficiency of PVC waste as sand replacement in concrete mixtures

Recycling materials has become an immerging tendency as a way for preserving natural resources. The waste disposal of polymeric materials has a significant impact on the environment and public health through their practical application in civil engineering constructions. The current experimental study aims to investigate the possibility of using polyvinyl chloride (PVC) waste in concrete and also to evaluate the PVC concrete properties in comparison with ordinary concrete (OC). This investigation research involves reusing the left-over PVC tube wastes and their incorporation in concrete. Three different replacement ratios (5%, 10% and 15%) of natural sand by polyvinyl chloride were considered, taking into account two different sizes (fine and fiber) of polymeric wastes. The effects of each incorporated PVC waste on the compressive strength, and tensile strength were studied. The fresh properties of concrete were investigated by conducting a slump test. The results revealed a decrease in the workability of the fresh PVC concrete compared to ordinary concrete. It was observed that the concrete made with fiber PVC shows a lower workability (decrease of 54%) in comparison with the first one which contains fine PVC aggregates. The concrete made with fiber PVC aggregates improves the compressive strength up to 23.5%. This latter increased simultaneously with increasing the replacement ratio of PVC waste. However, the increase of fine PVC waste content caused a decrease in compressive strength till 21%. The test results also revealed that the concrete mixes with high fiber and moderate fine PVC ratios enhanced the concrete mechanical performance.

Mechanical behavior of iron ore tailings under standard compression and extension triaxial stress paths

The disposal of mining tailings has increasingly focused on the use of dry stacks. These structures offer more security since they use filtered and compacted material. Because of the construction method and the heights achieved, the material that compounds the structure can be subjected to different stress paths along the failure plane. The theoretical framework considered in the design of these structures generally is the critical state soil mechanics (CSSM). However, the data in the literature concerning the uniqueness of critical state line (CSL) is still controversial as the soil is subjected to different stress paths. With respect to tailings, this question is even more restricted. This paper studies two tailings with different gradings due to the beneficial processes over extension and compression paths. A series of drained and undrained triaxial tests was conducted over a range of initial densities and stress levels. In the q-p' plane, different critical stress ratio (M) values were obtained for compression and extension stress paths. However, the critical state friction angle is very similar with a slightly higher critical state friction angle for extension tests. Curved stress path dependent CSLs were obtained in the ν-lnp' plane with the extension tests below the CSL defined in compression. Regarding the fines content, the studied tailings presented very similar M and critical state friction angle values. However, the fines content affects the volumetric behavior of the studied tailings and the CSLs on the ν-ln p' plane shift downwards with the increasing fines content for compression and extension tests. In relation to dilatancy analysis, the fines content did not present an evident influence on the dilatancy of the materials. However, different values of mean stress ratio N were obtained between compression and extension tests and can corroborate the existence of non-unique CSLs for these materials.

Morphology and fines type effect on packing of binary soils

Three sands with different particle shapes were mixed with non-plastic fines and plastic fines (clay), respectively, in an entire fines content from 0 % to 100 %. Test results on determining the maximum and minimum void ratios show that both the particle shape of host material and the plasticity of fines can delay the onset of the threshold fines content. For a given fines type in binary soils, the threshold fines content decreases linearly with increasing overall regularity of host material, which proves the feasibility of overall shape parameter in describing soil properties. Meanwhile, the linear equation considering two parameters was derived from test data to evaluate the variation of the maximum and minimum void ratios with increasing fines content by volume for sand-fines mixtures, and the effects of shape of sand and plasticity of fines on the two parameters were investigated. Moreover, non-linear or higher degree equations considering two boundary conditions may have a better performance on describing the variation, but some limitations still exist.