High Fines Content Research Articles

Effect of waste sandstone microfines on mechanical strength, abrasion resistance, and permeability properties of concrete

River sand is a non-renewable resource. The erosion of rocks obtains it, taking thousands of years. The mining of river sand is increasing exponentially due to rapid economic growth and urbanization. Due to a shortage of river sand, low-quality river sand is being used in construction. Concrete can be made more resource-efficient and sustainable by using waste and recyclable materials for sand. Nowadays, manufactured sand (M-sand) is being utilized in construction to lessen the natural sand demand. Higher fines content, angular shape of particles, increased surface area, and rough texture are the key characteristics of M-Sand. The prime focus of this research article is to evaluate the potential of sand made from quarry waste of sandstone to be used as a 100 per cent replacement of river sand in concrete. Waste sandstone microfines were also used and replaced with fine aggregate from 5 to 25%, by weight with an increment of 5%. The generation of microfines is an unavoidable part of the sand manufacturing process. Microfines are particles of size less than 75 µm. These microfines are discarded through sieving or washing, resulting in a waste of our valuable and non-renewable natural resources. The effect of the w/c ratio and sandstone microfine content on the workability, mechanical strength, abrasion resistance, permeability, and ultrasonic pulse velocity of concrete is demonstrated in this paper. The tests revealed that M-sand and microfine content significantly influence concrete's fresh and hardened properties. The strong interlocking of M-sand particles and the filler effect caused by microfines improved concrete's mechanical strength and durability parameters. However, this positive impact of microfines in concrete is lowered by the higher entrapped air at a low w/c ratio. This study establishes that using moderate amounts of sandstone microfines in M-sand can be a sustainable approach to solve the problem of natural sand shortage and reduce the loads from landfills.

Coal Moisture Variations in Response to Rainfall Event in Mines and Coal-Fired Power Plant Stockpiles—Part 1: Runoff, Infiltration, and Drainage

Excessive coal moisture leads to a lower heating value and power plant efficiency, and increased transportation costs. Therefore, coal stockpile management and moisture control are particularly important in regions with heavy precipitation. This paper and Part 2 address factors influencing moisture retention and migration in coal stockpiles. Part 1 of this paper series simulates phenomena of runoff, infiltration, and drainage in a stockpile after a rainfall event. Part 2 reports the effect of coal particle size and climate conditions on the rate and depth of moisture evaporation process within a coal stockpile. To perform this study, two coal samples were collected from the Witbank mine in South Africa. The results of the present study showed that smaller interparticulate void spaces because of the compaction or fines particles (−0.5 mm fraction) inhibited infiltration, leading to increased runoff volume. An increase stockpile slope increased the amount of runoff due to coal–water contact time reduction. The ability of heavy rainfall to destroy near-surface structures (erosion) happened more readily at stockpiles with high slopes and high fine content. The fine content significantly influenced the dewatering efficiency of drainage. Coals with higher ash contents had stronger moisture retention ability than that of other coals even though coals with low ash contents had a high fine content. This was ascribed to the contribution of the clay minerals, such as kaolinite, in the high ash coal. The results of this paper can be used for the effective management of coal stockpiles to prevent excessive moisture in stockpiles for the best possible utilisation of coal in power plants.

Evaluation of the Effectiveness of a Soil Treatment Using Calcium Carbonate Precipitation from Cultivated and Lyophilized Bacteria in Soil’s Compaction Water

Microbial-induced carbonate precipitation (MICP) is a bio-inspired solution where bacteria metabolize urea to precipitate. This carbonate acts as a bio-cement that bonds soil particles. The existing framework has focused mainly on applying MICP through infiltration of liquid bacterial solutions in existing soil deposits. However, this technique is inefficient in soils with high fines content and low hydraulic conductivity, and thus few studies have focused on the use of MICP in fine soils. The main objective of this study was to evaluate the effect of MICP applied to compaction water in soils containing expansive clays and sandy silts. This approach searches for a better distribution of bacteria, nutrients, and calcium sources and is easy to apply if associated with a compaction process. In soils with expansive minerals, the effect of MICP in swelling potential was explored at laboratory and field scales. In sandy silts, the evolution of the stiffness and strength were studied at the laboratory scale. The treatment at the laboratory scale reduced the swelling potential; nevertheless, no significant effect of MICP was found in the field test. In sandy silts, the strength and stiffness increased under unsaturated conditions; however, subsequent saturation dissolved the cementation and the improvement vanished.

Injection Treatment for Tunneling Excavation in Sandy Soils with High Fines Content

Instability and high permeability are two of the problems facing tunnelling excavations in soils with high fines content. Among the different techniques used to improve these soils, the injection of cement grouts stands out. In this work, a grouting treatment is designed to ensure the stability of the ground during the construction of two tunnels linking two municipalities in the north of Spain in Biscay, and to reduce the inflow of water from the aquifer located in the vicinity of these tunnels. First of all, the rock mass is analysed and the material to be injected is selected on the basis of the authors’ experience as well as setting time and compressive strength. Subsequently, with a test device designed by the DinRock research group of the University of Oviedo, two types of laboratory tests are carried out in order to analyse the effect of fines migration and washing on the water flows and the effect of re-injections of grouts with different densities on the permeability value. The results show that, in sandy materials, obtaining high degrees of waterproofing together with large stable zones can only be achieved by a combination of treatments and stages with different materials and densities. In addition, maximum values for both injection pressure and flow rate must be established depending on the type of grout and the permeability of the soil. Once the problem has been analysed, the injection treatment is designed and executed. The treatment consists of one pre-injection in four stages with 30 boreholes drilled in the top heading, 19–20 boreholes drilled in the bench, and one post-injection with boreholes drilled around the perimeter of the tunnel in those areas where the pre-injection does not achieve the desired degree of waterproofing.

Acid sulfite pulping of Acacia mangium and Eucalyptus pellita as a pretreatment method for multiproduct biorefineries

AbstractConversion of biomass into saleable biochemicals and fuels requires the use of a pretreatment to enable subsequent processing. Acid sulfite pulping is one of the most cost‐effective strategies, because the chemicals are inexpensive and the technology is available on an industrial scale. It also allows the simultaneous production of cellulosic fibers and lignosulfonate. However, too little is known about the feasibility of acid sulfite pulping of tropical hardwoods. The objective of this research was to gain a better understanding of the response of Acacia mangium and Eucalyptus pellita in acid sulfite pulping. The plantation‐grown hardwood chip samples were obtained from Sabah, Malaysia. The sulfite cooking experiments were carried out in autoclaves with temperatures of 130°C and 140°C and varied chemical charges. The results revealed that a cooking temperature of 140°C was needed to reach kappa numbers below 30, but this also resulted in much reduced fiber length and higher fines content than 130°C, probably due to the intensified acid hydrolysis. To reach kappa numbers below 20, more severe cooking conditions are needed. These results demonstrate that using A. mangium and E. pellita as feedstocks allows feasible production of chemical pulp and sulfonated lignin, which are intermediate products for biorefineries.

Chemical-free production of lignocellulosic micro- and nanofibers from high-yield pulps: Synergies, performance, and feasibility

Far from being devoid of improvement, mechanical fibrillation benefits from high-yield pulping and refining to produce lignocellulosic micro- and nanofibers (LCMNFs). Spruce thermomechanical pulp was pretreated in a PFI mill to 10,000–30,000 revolutions and then passed, from 3 to 12 times and at 300–900 bar, through a high-pressure homogenizer. Mainly depending on those variables, the yield of nanofibrillation (in weight) ranged from 3% to 23%. The successive passes in the homogenizer significantly increased the specific surface area of the LCMNFs, hereby determined by Congo Red (from 115 to 164 m2/g) and poly(diallyldimethylammonium chloride) (from 54 to 89 m2/g) adsorption and contributed to higher cationic demands and water retention values, reaching values up to 229 μeq/g and 2.53 g/g, respectively. The performance of LCMNFs as a strengthening additive in papermaking was assessed, addressing the feasibility of the process. For instance, LCMNFs that had undergone 20,000 PFI revolutions and 6 passes through the homogenizer produced a 73% relative increase in breaking length of a virgin pulp, with an energy input of 19.2 kWh/kg (implying ~1.3 $/kg). Considering the synergic effects between mechanical treatments, a high fines content and the presence of lignin and hemicellulose, this can be a step towards waste minimization and reduction of hazardous chemicals, including sulfur and chlorine compounds.

Assessment of Geologic Controls of Flooding in Parts of OBIO/AKPOR L.G.A., Rivers State, Nigeria

Flooding of Municipal areas is a frequent environmental occurrence in Rivers State that occurs when rainfall runoff meets land surfaces with low water absorbing capacity or when it overwhelms drainage channels. In order to assess the flood situation in the study area, an integrated method which involves Field-measurement, Geographic information system (GIS), Laboratory analysis of soil samples and topographic studies were employed. Digital Elevation Model of the study area reveals that the flooded areas are situated in areas with elevations lower than its surrounding, thereby acting as a natural basin to retain flood waters after rainfall. Four holes were drilled to depth of 3m to obtain soil samples at 1 m sampling interval, from which laboratory analysis was carried out to determine some geotechnical parameters such as soil’s particle size, specific gravity, bulk density, porosity, moisture content, permeability and hydraulic conductivity. Results from the analysis show that permeability, hydraulic conductivity and porosity diminishes with respect to depth. The soil in the flooded areas have high fines content (silt and clay), high bulk density which increase with depth and a specific gravity that is typical of organic rich soils that contain sand mixed with a considerable amount of fines. At Nkpolu, mean permeability rates of 0.003cm/sec, 0.009cm/sec and 0.033cm/sec were obtained at 1, 2 and 3m respectively. At Eneka, mean permeability rates of 0.011cm/sec, 0.018cm/sec and 0.014cm/sec were obtained at 1, 2 and 3m respectively, while at Rukpokwu, mean Permeability rates of 0.021cm/sec was obtained at 1m, while 0.006cm/sec was obtained at 2 and 3m respectively. The Mean hydraulic conductivity for the locations under study is of the order of 10-4ft/day. This study has shown that the flooded areas are located in low lying urban areas which act as basins, therefore, the top soil is crusted with highly compacted soil horizons beneath. With high and frequent rainfall in the region which generates a lot of runoff, in addition to poor drainage system, flooding of the study area occurs frequently. Therefore, construction and maintenance of efficient drainage channels for an effective solution to urban pluvial flooding in the study area are thereby recommended.

Wet route pellets production using primary sludge from kraft pulp mill

Abstract The substantial expansion of the Brazilian pulp and paper industry in the last years resulted in a significant increase in the solid waste generation. This paper investigates the production of pellets using primary sludge from the effluent treatment plant of a kraft pulp mill, as a fuel for producing energy, using a novel wet route process. The pellet samples were produced in a laboratory pelletizing press, which has a horizontal circular matrix. The samples were characterized by moisture content, high heating value, ash content, dimensions (diameter and length), mechanical durability and fines content. The net heating value and energetic density were also measured. The pellets manufactured with primary sludge were compared to the European standard for non-woody pellets. Pelletization caused a reduction of the moisture content by 37.8 %, and increased the net heating value by 41 % and bulk density by approximately 39 %, which resulted in a 263 % increase in the material´s energetic density. Pellet production using a wet route process was appropriate for the primary sludge, and produced pellets with a high mechanical durability (99.3 %) and low fines content (0.062 %), indicating the potential of thermal valorization for incineration in the biomass boiler to produce high-quality steam.

Influence of fines content on liquefaction from a critical state framework: the Christchurch earthquake case study

In earthquake engineering practice, the liquefaction potential of soils is commonly evaluated through simplified procedures. These approaches are suitable for sands with very low to no fines content, which have been traditionally thought to be the only liquefiable materials. However, field observations and experimental research have extensively demonstrated that low plasticity silty sands can also be highly liquefiable. Thus, this paper investigates the effect of nonplastic fines contents on the liquefaction potential of soils, taking the 2010–2011 Canterbury Earthquake Sequence as a case study. The validity of standard simplified procedures for high fines content soils is critically evaluated and compared with a finite element model based on a full solid–fluid coupled formulation. The model includes a state parameter-based constitutive law within the generalised plasticity theory, which allows the fines content to be taken into account explicitly. The standard simplified procedures are shown to be less effective in the evaluation of liquefaction potential in soils with high fines content but are still indispensable tools for evaluating the performance of soils over large urban areas. As the main conclusion, it is recommended that empirical models are complemented with an advanced numerical analysis in those cases where silty sands with high fines content are identified, as its outcomes can more realistically represent the soil behaviour during a seismic event.

The hematite ore liberation and separation properties in different comminution way

ABSTRACT In order to improve grinding efficiency and weaken over-grinding in the whole grinding process, the new process of “ultra-crushing in HPGR – classified separation” was proposed with an Anshan style hematite ore. The new process was discussed from the aspects of particle size distribution, liberation characteristics, and separation properties. Compared with the conventional impact crusher, there was no significant difference in coarse particles in HPGR. The “Particle Bed Breakage” characteristics of HPGR products are mainly concentrated in the fine particles (−0.18 mm), which is characterized by higher fines content (a yield of 38.43%), higher specific surface area and higher quartz liberation, etc. It’s worth mentioning that, fine-disseminated iron minerals are detached from the quartz mineral under large compressive-stress in HPGR, which is more conductive to the downstream separation. Magnetic separation tests showed the HPGR (−0.18 mm) tailings have the lowest grade of 7.29%, approximately one percentage point less than coarse grinding products. Based on the above analysis, the new process with a 0.18 mm prescreen size for an Anshan style hematite ore is feasible.

Models for compressive strength estimation through non-destructive testing of highly self-compacting concrete containing recycled concrete aggregate and slag-based binder

Indirect estimation of compressive strength through non-destructive testing is key to monitoring the strength of structural concretes used in construction and rehabilitation works. However, no models are available to perform this estimation in highly Self-Compacting Concrete (SCC) with Recycled Concrete Aggregate (RCA). To fill this gap, two indirect measures were tested in this paper, the hammer rebound index and Ultrasonic Pulse Velocity (UPV), to predict the compressive strength of highly SCC. To do so, 24 SCC mixes were developed with different aggregate powders, binders, such as Ground Granulated Blast Furnace Slag (GGBFS), and contents of fine RCA. Compressive strength, and both indirect measures of all mixtures were determined at 1, 7, 28, and 90 days. The development of specific models for highly SCC responded to the inappropriateness of conventional models that are not adapted to its high fines content. Modelling as a function of either UPV or the hammer rebound index yielded accurate predictions, although the UPV model proved more sensitive to compositional changes and presented higher uncertainty. The best predictions were modelled by combining both indirect measures. The models provided safe and accurate indirect estimations of the compressive strength of high flowability SCC in real structures.

Fresh and hardened properties of high-strength concrete incorporating byproduct fine crushed aggregate as partial replacement of natural sand

This paper presents the fresh and hardened properties of high-strength concrete comprising byproduct fine crushed aggregates (FCAs) sourced from the crushing of three different types of rocks, namely granophyre, basalt, and granite. The lowest void contents of the combined fine aggregates were observed when 40% to 60% of natural sand is replaced by the FCAs. By the replacement of 40% FCAs, the slump and bleeding of concrete with a water-to-cement ratio of 0.45 decreased by approximately 15% and 50%, respectively, owing to the relatively high fines content of the FCAs. The 28 d compressive strength of concrete was 50 MPa when 40% FCAs were used. The slight decrease in tensile strength from the FCAs is attributed to the flakiness of the particles. The correlations between the splitting tensile and compressive strengths of normal concrete provided in the AS 3600 and ACI 318 design standards are applicable for concrete using the FCAs as partial replacement of sand. The maximum 56 d drying shrinkage is 520 microstrains, which is significantly less than the recommended limit of 1000 microstrains by AS 3600 for concrete. Therefore, the use of these byproduct FCAs can be considered as a sustainable alternative option for the production of high-strength green concrete.

An incident of water and soil gushing in a metro tunnel due to high water pressure in sandy silt

A connecting passage of the Metro Line 18 in Shanghai was under construction in a sand layer featuring high fine content and a high level of confined water head. During the tunnel construction, an incident of water and soil gushing through the freezing holes resulted in large settlement and damage to the tunnel linings. The remedial measures were then carried out to prevent the incident and to strengthen the damaged tunnel linings. This paper analyzes the reasons for the water and soil gushing, the damage to the tunnels, and the effect of the remedial measures. The main reason for the incident was water and sand penetration through the gap between the freezing pipes and the borehole orifice pipes due to the high water pressure outside the tunnels. The monitoring results indicate that the grouting and the lining reinforcement with reinforced steel ring effectively improved the stability of the tunnel structures. This case study provides practical experience and guidance for similar tunnelling projects in the future to mitigate the risk of water and soil gushing.

Energy-based model for predicting liquefaction potential of sandy soils using evolutionary polynomial regression method

This study presents a comprehensive, energy-based model for the evaluation of the liquefaction potential of all types of sandy soils, including clean, silty, and clayey sands. Unlike previous energy-based capacity models, this study considers the effect of Plasticity Index (PI) and loading Frequency (Frq) in the proposed model. Introducing an innovative method, the model was developed in two steps. At first, a small-scale model was developed using Evolutionary Polynomial Regression method (EPR), considering PI, Frq, Fine Content (FC), mean grain size (D50), and uniformity coefficient (Cu). For this aim, 63 laminar shaking table tests were performed on different fine-grained soils mixed with sand, with a wide range of PI (from 0 to 26) to provide a comprehensive data bank for EPR modeling. Then, by introducing an appropriate scaling factor, the model was scaled up to the field condition considering effective stress (σv′) and relative density (Dr). The model was successfully verified using a number of 100 case-histories worldwide with various soil properties. The results showed that the present model is considerably superior to previous energy-based models. Parametric analysis demonstrated that the liquefaction capacity energy of sandy soils with high fine content is mainly influenced by FC and PI, respectively.

Valorization of Fine Recycled Aggregates Contaminated with Gypsum Residues: Characterization and Evaluation of the Risk for Secondary Ettringite Formation.

Fine recycled aggregates (FRA) (0/4 mm) are up to now not valorized on a high enough level because of characteristics like an elevated water absorption, higher fines content, and the presence of contaminations. Leftover gypsum residues from the construction site can cause internal sulfate attack when FRA are incorporated into new structures. Concern about this deteriorating reaction plays an important role in the rejection of FRA. In this study, samples of FRA from different recycling centers were characterized and incorporated into mortars. They were then subjected to swelling tests in order to evaluate the development of sulfate attack. Reference materials with different amounts of sulfates were used as a comparison. Results showed a variable sulfate content in industrial FRA, depending heavily on the source of the materials. In all but one case, the total amounts surpassed the acceptable sulfate contents specified in the European standard EN 206, meaning the FRA would be rejected for reuse in concrete. Nevertheless, swelling tests demonstrated that these contamination levels did not pose a risk for sulfate attack. These results indicated that the incorporation of FRA leads to acceptable mechanical performances and that the sulfate limit could be reviewed to be less strict.

Agglomeration of fine-sized copper ore in heap leaching through geopolymerization process

Low-grade copper ore with high fines content is required for agglomeration because of the low permeability of the ore bed during acid heap leaching. However, few binders are effective in keeping agglomerates stable in acidic solution. In this study, the effect of geopolymerization on the particle size, compressive strength, acid resistance, and microstructure of fine-sized copper ore-based agglomerates formed by drum agglomeration was examined. In addition, the performances of the feed, agglomerates, and coarse-grained ore in the column leaching process were examined. The results showed that the agglomerates had a larger particle size after the agglomeration process. Further, the agglomerates had high strength and acid resistance because of the formation of geopolymer gel by the geopolymerization process. Column leaching experiments revealed that the agglomerates had good stability, a looser bed, and better permeability in the column, whereas leaching of the feed in the column was difficult because of the low permeability of the feed. Moreover, the leaching rate of agglomerates formed by geopolymerization was significantly higher than that of the coarse-grained ore. The proposed method for the production of fine-sized copper ore-based agglomerates by geopolymerization has potential application in heap leaching.

Evaluation of grain size and content of nonplastic fines on undrained behavior of sandy soils

Marine sandy soils may liquefy under wave loading and/or seismic loading. Current research shows that the presence of fines can significantly affect the liquefaction potential of sandy soils. Thus, a quantitative evaluation of the effect of fines on the undrained behavior of sandy soils can provide useful information on soil liquefaction that can advance the design of foundations of coastal structures. However, little is known about how the grain size of nonplastic fines affects the mechanical behavior of sandy soils. In this study, a series of strain-controlled monotonic undrained triaxial compression tests and critical-state constitutive modeling are carried out on a medium dense saturated sandy soil for various fines contents (FCs), mean grain sizes ( s) of nonplastic fines, and initial effective confining pressures. The results show that the peak deviatoric stress decreases significantly with decreasing especially for high FCs. The equivalent granular state parameter (ψ*) at the phase transformation can be used to characterize the effect of fines on the dilatancy of sandy soils in constitutive modeling. Additionally, the initial value of ψ*() serves as physical index for characterizing the influence of fines on the undrained instability state of sandy soils.

Numerical evaluation of the performance of back-to-back MSE walls with hybrid select-marginal fill zones

Back-to-Back Mechanically Stabilized Earth (MSE) walls have become an integral part of the transportation infrastructures, especially as ramps, bridge approaches, etc. The permeability, strength and constructability attributes of well-graded granular soils have rendered them as the most suitable fill material for MSE walls. However, the scarcity of such good materials compels the usage of locally available soil with high fine content (marginal fill) having low permeability and high plasticity characteristics, which can cause excessive wall deformation or even failure, if not adequately designed and constructed. This study focused on the assessment of overall performance of back-to-back MSE walls with a trapezoidal marginal fill zone surrounded by a near-optimal amount of select fill (i.e., hybrid-fill) as an alternative to the wall with select fill only. The behaviour of hybrid-fill wall at the end of construction and during heavy rainfall infiltration were investigated through finite element modelling and compared with fully select fill and fully marginal fill walls. The study revealed that the overall performance (i.e., horizontal and vertical deformations, reinforcement tension, and factor of safety) of the hybrid-fill wall with 31–47% select fill is much better than that of fully marginal fill wall, especially during the extreme rainfall infiltration scenario. The response of this hybrid configuration is even comparable with that of fully select fill wall, suggesting the proposed hybrid-fill wall as a stable as well as cost-efficient alternative system in locations where sufficient quantity of well-graded soil is not readily available.

Debris Flow Behavioral Characteristic Based on Rheological Properties: A Case Study on Mt. Hwangnyeong and Mt. Umyeon

Debris flow, one of the major natural disasters in Korea, usually occurs because of heavy rainfall during the rainy season. Recently in Korea, rainfall, as well as the frequency of debris flow, has continually increased as a result of climate change. Therefore, it is necessary to study the characteristics of the debris flow behavior for hazard mitigation and damage assessment. In this study, vane-type rheometer tests were conducted to estimate the rheological properties (viscosity, yield stress) of two soil samples collected from Mt. Hwangnyeong and Mt. Umyeon Several series of small-scale flume experiments were also performed to evaluate the characteristics of the debris flow behaviors (flow velocity, runout distance, and deposition volume) of these two sites. The results of the experiments show that front velocity, runout distance, and deposition volume of the debris flow gradually decrease with increase in viscosity and yield stress. Especially in the case of the Mt. Hwangnyeong sample, which has a high fine content, experimental results showed that the rate of increase in front velocity, runout distance, and deposition volume tended to high as viscosity and yield stress decreased compared to Mt. Umyeon.

Estimation of the shear strength of coarse-grained soils with fine particles

The determination of the shear strength of coarse-grained soils in standard shear devices is a challenging task due to the presence of large grains. Three approaches could be used to reduce the grain size of the tested specimen. This study aimed to determine whether the shear strength of a coarse-grained soil with fines (particles smaller than 0.08 mm) can be estimated by the parallel gradation approach. Direct shear tests were conducted on parallel graded specimens of two soil types with different low plastic fines content. Two criteria can be used to select the dry density of the reconstituted specimen: the same dry density or the same relative density as the initial soil. The results showed that when the specimens had a low fines content, both criteria resulted in a similar dry density of the reconstituted soil, and the shear strength of the initial soil was correctly estimated. However, for the specimens with a high fines content, the friction angle of the initial soil was correctly estimated, and its cohesion was overestimated when the reconstituted soil was tested at the same dry density as the initial soil. A cohesion-fines content relationship was proposed to predict the initial soil cohesion.