High Fines Content Research Articles

1D Compressibility of High Moisture Content Clays Solidified with Small Cement Dosages

Soft soil is normally associated with high moisture content and fine content which result in high compressibility and low strength. However, a proper treatment such as solidification by means of hydraulic binders is required in order to be usable for beneficial purposes (e.i backfilling). This paper experiments the effects of cement treatment on the one-dimensional (1D) consolidation behavior of a high moisture content (MC) soil (twice liquid limit), based incremental loading test. The effects of Portland cement addition are evaluated for dosages ranging from 0 % to 15% by dry mass of soil. After curing, it was found that 10 % cement was required to make meaningful reduction in MC for kaolin while no major difference was noted between after mixing and after curing for DMS. In kaolin the moisture content decreased by 6.5 % for each 5 % increment of cement. Similarly, the MC of DMS reduced by 10 % for each 5 % increment. Thus, the reduction, immediately after mixing, in DMS was higher by 3.5 % compared to kaolin. The most evident effect of the treatment feasibility is the development of a cementation-induced yield stress after 7 days of curing: the bigger the cement dosage, the greater the yield stress and the greater the vertical effective stress that can be sustained at any void ratio. The maximum yield stress at 15 % cement content was found 30 kPa and 70 kPa for DMS and kaolin respectively. The highest void ratio values were found in the control specimens (3.77) in kaolin and DMS (5.66) whereas the lowest void ratio was corresponded to 15 % cement 3.35 and 4.65 for kaolin and DMS respectively. The control specimens decreased dramatically from 38.93 m2 / KN - 0.13 m2 / KN and 36.03 m2 / KN - 0.19 m2 / KN for kaolin and DMS specimens respectively. The results correspondingly provide a consistent depiction of the effects of cement treatment on MC, void ratio and coefficient of volume compressibility. The effectiveness of the treatment is obvious compared to the untreated soil.

Compressibility and the Effects of Structure of Tropical Clay in Incremental Loading Oedometer Tests

Several problems in geotechnical and geological engineering have been analysed based on the properties of soil obtained from compression tests and the behaviour in compression is a fundamental aspect of deformation in geomaterials. A detailed analysis has been made into the mechanics of compression of Nigeria tropical clay in incremental loading oedometer for the soils in the reconstituted and natural states, allowing for the effects of geological structure. In addition to classification and index tests, microstructure and geochemistry were studied using SEM equipped with EDS and mineralogical indices were investigated using XRD for the soils retrieved from different depths and two locations. The soils are heterogeneous and the spatial variability is low. The soils have low plasticity and clay minerals are dominated by kaolinites. The soils converged to unique intrinsic normal compression lines showing no transitional mode of behaviour. The intrinsic behaviour of the soils was consistent with fines content, plasticity and clay minerals. The finer and better-graded soil with higher fines content, plasticity and clay minerals content have higher compressibility. The effects of structure, which is the degree of enhanced resistance of the natural sample in compression, were positive and small to medium.

Research on Treatment of Oily Sludge from the Tank Bottom by Ball Milling Combined with Ozone-Catalyzed Oxidation.

Difficult separation of oil–solid phase and high fine content of the recovered oil were two problems in the treatment of oily sludge from the tank bottom by the hot water-based extraction process. To solve the problems, one technology with “ball milling + ozone-catalyzed oxidation” as the core was studied, and the process parameters of ball milling and ozone-catalyzed oxidation were respectively optimized. After ball milling treatment, the oil content of dry oily sludge decreased from 33.9 to 10.2%. Then, an ozone catalytic oxidation treatment technology with aluminum ore as the catalyst was developed to further treat this stubborn oily sludge. Under the optimal conditions, the oil content of oily sludge could be further reduced to 0.28%, which met the treatment and disposal requirements stipulated in GB4284-2018. For further research on the contribution of the catalyst to the ozone catalytic oxidation system, the reaction activation energy and reaction rates of ozone oxidation and ozone catalytic oxidation were compared from the perspective of kinetics. The results showed that, with the catalyst addition, the reaction rate constants increased about three times and the reaction activation energy reduced 82.26%, which showed the effectiveness of the catalyst on the kinetics quantitatively. The combined process with “ball milling + ozone-catalyzed oxidation” as the core can solve the two problems in the treatment of oily sludge from the tank bottom by hot water-based extraction and provides a reference for the harmless and resourceful treatment of oily sludge from the tank bottom.

Analyzing filtration flow rate change of woven geotextiles for fine grained slurries

Many studies have been performed in recent years to investigate the dewatering phenomena of slurry using geotextile tubes. The laboratory test methods primarily used the pressure filtration test (PFT) and falling head test (FHT) to evaluate the dewatering nature of geotextiles using slurries with different fines contents. The objective of this paper is to examine and analyze the published test data obtained from various testing conditions, and to develop a general equation that can predict the change of flow rate over time. For the PFT, a power law showed a good fit with test data at different fines content ranges. Furthermore, the change of filtration rate with time decreased with the fines content, indicating that slurry with high fines content resulted in a faster drop in filtration rate than slurry with low fines content. For the FHT, a two-term power law was found to fit all of the test data, indicating a two-stage filtration behavior.

Enhancing the eco-efficiency of concrete using engineered recycled mineral admixtures and recycled aggregates

Non-conventional densely packed concrete mixtures are proposed and evaluated in this paper using engineered recycled mineral admixtures and recycled aggregates obtained from steel slag, quartz mining tailings, and quartzite mining tailings. High fines content sand-concretes containing coarser- and finer-than-cement recycled powders were designed to obtain blends with broader particle-size ranges and improved packing density. As a result, compressive strength up to 99 MPa, cement intensity up to 2.33 kg/m³/MPa, and consumption of recycled material up to 95 vol% were obtained. Compressive strengths up to 66 MPa and cement intensity up to 2.34 kg/m³/MPa were also obtained with the addition of coarse aggregates to such sand-concrete mixtures, with consumption of recycled material up to 96.5%. The results launch new insights on the role of recycled admixtures and aggregates on the mixture design of cement-based composites regarding efficiency improvement and technological performance.

Comparing the behaviour of spherical beads and natural grains in bedload mixtures

AbstractIt is common to use idealised materials to study the dynamics of granular transport in fluid flows, but the impact of this choice upon sediment behaviour has not been extensively explored. To tackle this research gap, two experiments were undertaken to explore the influence of a finer grain input to a channelized coarser granular flow driven by a shallow fluid flow. The first set of runs was undertaken using spherical glass beads, and the second set with natural fluvial sediment. The transport system approximates a narrow slice through the bedload at the bottom of a river. In the runs with natural grains, the infiltration of fine sediment into the bed was similar to the spherical glass beads, but with reduced infiltration capacity. We ascribe this behaviour to irregular and variable pore shapes and sizes in the natural material. The behaviour of the bedload in the natural material runs matched that of the bead runs only when the feed contained a high content of fines. When the feed contained a low content of fines the transport of natural grains was more complex, including the emergence of migrating collections of grains. However, the overall changes in bed and water slope due to the finer grain input were comparable in both sets of experiments. We conclude that artificial, idealised materials qualitatively represent sedimentary phenomena, but that quantitative differences in the outcomes must be expected. © 2020 John Wiley & Sons, Ltd.

Cold Briquetting of DRI Fines for Use in Steel Making Process

DRI fines, generated during its manufacture and handling, generate high content of fines in the size fraction less than 2 mm. It has iron content above 80%. It is difficult to directly use such iron-rich material in the primary steel making process, without agglomeration. At JSW Steel Vijayanagar, around 50 to 70 tons per day of DRI fines with < 2 mm size fraction get generated. The fines are used in base sinter mix or it may be agglomerated suitably to use it as a coolant in the primary steel making process. Since the fines are extremely reactive, they are susceptible to oxidation if it is not agglomerated as soon as it is generated. The present study brings out the development of an agglomeration process for the DRI fines to a dense metallized briquette, for use as a coolant in basic oxygen furnace. Initially, the conditions for briquetting such as use of binder, hardener, lime, dust, moisture, briquetting and curing conditions were established in a 10 kg batch size. This was followed by industrial-scale processing, at 500 kg batch size. The physical and chemical characteristics of the fines and briquettes were assessed at different stages. The cold compressive strength of the cured briquette was found to be a function of moisture content. The handling parameters in the production condition, for long-term pile-up of briquettes against oxidation, were brought out. The successful use of the briquettes in basic oxygen process was demonstrated.

Mineralogy, Micro-fabric and the Behavior of the Completely Decomposed Granite Soils

The main objective of this study is to investigate the impact of the micro-fabric and soil mineralogy on the overall macro-behavior of the completely decomposed granite soil through a set of drained and undrained triaxial shearing and isotropic compression tests on a medium-coarse grading completely decomposed granite soil. The mineral composition of the soil was a substantial factor governing the compressive behavior. The soil compressibility increased significantly in the case of existence crushable and weak minerals within the soil minerals like fragile feldspar, as well as the high content of fines, especially the plastic fines. The scanning electron microscopic photos indicated that the micro-fabric of the soil had a paramount impact on the compressive behavior. The mechanism of the volumetric change depended on the stress levels, the soil mineral composition and the grain morphology. In the low consolidated stress levels, the soils’ grains rearrangement was the prevailing mechanism of the volumetric change, particularly with the absence of weak and crushable minerals. On the other hand, at the high consolidated stress levels, particles’ crushing was the prevailing mechanism in the volumetric change. Both the mechanisms of volume change could occur simultaneously at the low stress levels in the case of presence crushable minerals in addition to micro-cracks in the soil grains. The soil showed an isotropic response after 250 kPa, as this stress level erased the induced anisotropy from the moist tamping preparation method. Under the drained shearing conditions, the soil showed a contractive response, while during the undrained shearing conditions, the soil exhibited both the contractive and dilative responses with phase transformation points. The studied soil showed a unique critical state line, irrespective of the drainage conditions and initial states, the critical state line was parallel to the isotropic compression line in the void ratio effective stress space. In the deviator effective mean stresses space, the studied soil approached a unique CSL with a critical stress ratio equal 1.5, corresponding to critical friction angle of 36.8°.

Effects of water content on resilient modulus of a granular material with high fines content

The granular materials with high fines content are commonly adopted as the fill materials in the substructures of pavement and railway. The high-fraction fines may exist at the construction stage or accumulate gradually during the service life of transport infrastructures. Very few studies have been conducted on the resilient behaviour of granular materials with high fines content, especially when the changing water content is considered. In this study, three saturated cyclic triaxial tests with step-wisely increasing cyclic deviator stress were performed to determine the required reasonable cycle number for determining a stabilized resilient modulus. A new parameter, termed as “representative cycle number”, was newly defined to distinguish the unstable and stable periods of the deformation of the testing material under cyclic loading. The test data from this study and previous literature proved that the resilient modulus starts to level off when cycle number reaches “representative cycle number”. Furthermore, a series of cyclic triaxial tests with various water contents were conducted on a granular material with high fines content. The results indicated that the resilient modulus of the granular materials with high fines content would drop firstly with the increasing cyclic deviator stress and then turned to increase gradually. The level of cyclic deviator stress at which resilient modulus started to rise increases with the increase of water content of the specimen. Lastly, a modified prediction model is proposed, considering the effects of water content and stress paths, to capture the non-monotonic relationship between resilient modulus and stress state.

Minimum void ratio characteristic of soils containing non-plastic fines

The minimum void ratio is an index widely used to indicate the contraction characteristics and the densest state of soils. The minimum void ratio obtained by the traditional test method has been utilized to represent the density of soils irrespective of their fines content despite the restriction (FC ≤ 5%). By considering the effect of the blow count, pore water, and their primary properties, the applicability of the minimum void ratio to soils containing fines was examined with an automatic tapping machine. It was confirmed that the blow count of the traditional method is not sufficient for soils with a high fines content. Furthermore, the presence of pore water had a significant effect on the minimum void ratio of soils containing fines. The characteristics of the cyclic minimum void ratio, which indicates the minimum void ratio obtained throughout the repetition of liquefaction and drainage, were also examined.

Performance and design of reinforced slopes considering regional hydrological conditions

This study presents a series of numerical analyses investigating the impact of rainfall on the performance and design of geosynthetic-reinforced soil slopes (RSSs). The importance of considering regional hydrological conditions for designs of RSSs, particularly when marginal soil is used as backfill, is demonstrated and highlighted. RSSs with backfills containing five different fines contents subjected to various combinations of initial hydraulic conditions and major rainfall events were modeled. The input rainfall was determined from the rainfall intensity–duration–frequency (I–D–F) curves to realistically account for the impact of regional hydrological conditions. The hydraulic responses and stability of the RSSs including their porewater pressure development and factor of safety were then evaluated and compared. The results revealed that the applied rainfall scenarios had little influence on the performance of RSSs with high-quality backfills (i.e. backfill with low fines content), whereas those with prolonged rainfall duration substantially affected the performance of RSSs with high fines content backfills. Rainfall thresholds were established for the RSSs with various backfills and initial conditions and compared with the regional I–D–F curves to provide a simplified and robust method for facilitating backfill selection and assessing the failure risk of RSSs.

Study of the wall adhesive tensile contact of moist iron ore bulk solids

The adhesive tensile stress between moist bulk iron ore solids and wall surfaces are critical to control and avoid blockage in large throughput material handling plants. In this study, an experimental system was designed to investigate the adhesive tensile contact between a range of iron ore materials and wall lining specimens. The contact mechanism between the material specimen and the wall surface was initially characterised. The experimental results indicated that the adhesive tensile stress is dependent on both the moisture content and the applied major consolidation stress, with the former exhibiting more significant contribution to increasing the magnitude of stress. The surface roughness of the wall showed a negligible effect in determining the adhesive tensile stress. Additionally, the iron ore sample with a higher fines content was observed to be able to achieve a higher adhesive tensile stress compared to the coarse samples. Consequently, the insights resulting from the study demonstrated practical applicability through measures such as blending and/or beneficiation, which reduce the adhesive tensile stress and minimise blockages.

Formic acid pulping of crops residues available in Bangladesh

Bangladesh is a densely populated agricultural country. As the allocated forestland for pulpwood production is very limited and a substantial amount of crops residues are generated each year, the latter can substitute pulpwood. But it is hard to use crops residues as pulping raw materials in a conventional pulping process due to its high content of silica and fines. It was observed that formic acid (FA) pulping process can overcome these limitations. In this context, fourteen residues of crops produced in Bangladesh were evaluated by FA pulping with varying FA charge for 4 h at the boiling temperature followed by peroxyformic acid (PFA) treatment under constant conditions. It was observed that pulp yield and delignification degree decreased with FA charge. Also, PFA treatment further reduced the kappa number of pulps. Final pulp yields were 39–51% with the kappa number of 12–28 depending on crops residues. Holocellulose and α-cellulose content in crops residues were positively correlated (R2 = 0.95) with pulp yield at 0% level of significance. Pulps were bleached by alkaline peroxide bleaching and brightness reached to about 80% with acceptable papermaking properties.

모래의 입도분포와 세립분 함유량에 따른 액상화 저항특성 비교

The liquefaction phenomenon occurs when the groundwater is pumped up through the top of sediments as the pore pressure increases due to the earthquake. There have been many studies on the loose sandy soils and various samples through repeated triaxial compression tests and shaking table tests, but there have been few studies on the effects of particle size distributions and the fine contents of sand on the liquefaction of sand. In this study, the undrained repeated triaxial compression tests were performed on sands with different particle size distributions, confining pressures, relative densities, and deviatoric stresses. The results of analysis showed that, with increasing relative density, SW(Well-graded sand) samples had higher liquefaction strength than SP(Poor-graded sand) samples. This is due to the lower void ratio of sand in SW samples than in SP samples. It was also found that the liquefaction strength decreased with a high fine content due to he rapid destruction of the filling of fine particles between the soil particles, leading to lower liquefaction strength.

Relative soil water content as a factor for wind erodibility in soils with different texture and aggregation

Abstract The soil water content is one of the main factors influencing the beginning of soil particle movement by the wind. Although, some authors studied the effect of soil water content on threshold wind velocity and have defined a value to prevent wind erosion, the critical relative soil water content (HRc), most of them used disturbed and/or sieved soil samples. Under these conditions, the effect of aggregation, i.e. the natural state of the soil, cannot be evaluated. So, our objective was to determine HRc in soils with different textures in Semiarid Argentinian Pampas Region (SAPR) using uncrushed soil samples under variable wind velocities. Wind tunnel simulations were performed at three wind speeds (2.1, 8.0 and 10.5 m s−1) during 3 min in each case. Results indicated that the quantity of collected soil (Q) decreased with increasing relative soil water contents (HR) up to a HRc value at which it became negligible. HRc values were lower in fine textured soils than in coarse soils. All soils showed increasing HRc values as wind velocity increased from 2.1 to 10.5 m s−1, while the wind velocity effect is more important in coarse textured soils. HRc was negatively related to micro-aggregation in a linear way. For that reason, soils with high fine silt and clay content need lower HRc values to inhibit wind erosion. In conclusion, not only texture is important factor in defining the HRc value at a specific wind velocity but also the micro and macro-aggregation of the soils.

Estimation of the shear strength of a coarse soil with high fines content by parallel gradation method

The determination of the mechanical properties of soils containing particles larger than the allowable size of standard laboratory equipments is complex. It is indeed necessary to remove the coarsest fraction to carry out the tests. This scalping poses a problem of reliability of the results at the scale of the structure. Parallel gradation is the method commonly used for estimating the shear strength of heterogeneous granular soils from tests on their finer fraction. However, the effect of high fines content on the estimation of shear strength by this method is not well understood. The results of this study show that the parallel gradation method can predict the friction angle of the initial soil with high fines content when the modelled soil has a similar skeleton as the initial soil. However, the cohesion of the initial soil is overestimated.

Silicone bridged iron metallocene butadiene composite solid propellant binder: aspects of thermal decomposition kinetics, pyrolysis and propellant burning rate

ABSTRACTPropellant binders are essential components of composite solid propellants (CSP’s) used in launch vehicles and missiles. Binders act as a fuel and contribute directly to the combustion in conjunction with oxidizer particles and metallic fuel apart from imparting structural integrity to the solid propellant grain .The performance of CSP’s are directly related to the burn rate of the propellant. The burn rates of the ammonium perchlorate (AP) propellants are generally moderated using various types of transition metal oxide (TMO) catalysts. However, TMO’s are associated with inherently large dispersions in propellant burn rates and compromise on energetics. One of the most suitable methods for achieving lower dispersion in burn rate is using binders wherein a burn rate catalyst is grafted to the polymer matrix. In the present paper, the thermal decomposition of ferrocene bound hydroxyl terminated polybutadiene (FC-Si-HTPB) grafted to butadiene backbone via hydrosilylation was investigated The thermal degradation mechanism, stability and its effectiveness as burn rate catalyst are the most important aspects for use in CSP’s. The mechanism of decomposition of the neat resin and in combination with AP has been elucidated using pyrolysis gas chromatography–mass spectrometric technique (GC-MS). FC-Si-HTPB exhibits single stage decomposition in the temperature range of 263–491°C. The decomposition of FC-Si-HTPB with AP oxidizer follows a two stage mechanism in the 195–490°C.The char residue was characterized using FTIR, Raman spectroscopy and FE-SEM analysis, which enables to vindicate the mechanism of reaction. The activation energy for the decomposition of HTPB is 283.6 kJ/mol, FC-Si-HTPB is 251.5 kJ/mol and for Fc-Si-HTPB-AP system is 67.1 kJ/mol. The major pyrolysis products of neat FC-Si-HTPB are ferrocenyl derivatives, silylated ferrocenyl derivatives and precursors emanating from polybutadiene backbone. The propellants based on the new binder exhibited an increase in burn rate with iron content and higher fine content. A comparison of propellant burn rate with conventional micron sized ferric oxide exhibited an improvement of 34%.Based on the thermal analysis studies, the thermal endurance of the system was computed to be FC-HTPB> HTPB> FC-HTPB-AP.

Spatial and Temporal Variability in Emissions of Fluorinated Gases from a California Landfill.

Emissions of twelve (hydro)chlorofluorocarbons (F-gases) and methane were quantified using large-scale static chambers as a function of cover type (daily, intermediate, final) and seasonal variation (wet, dry) at a California landfill. The majority of the F-gas fluxes was positive and varied over 7 orders of magnitude across the cover types in a given season (wet: 10-8 to 10-1 g/m2-day; dry: 10-9 to 10-2 g/m2-day). The highest fluxes were from active filling areas with thin, coarse-grained daily covers, whereas the lowest fluxes were from the thick, fine-grained final cover. Historical F-gas replacement trends, waste age, and cover soil geotechnical properties affected flux with significantly lower F-gas fluxes than methane flux (10-4 to 10+1 g/m2-day). Both flux and variability of flux decreased with the order: daily to intermediate to final covers; coarser to finer cover materials; low to high fines content cover soils; high to low degree of saturation cover soils; and thin to thick covers. Cover-specific F-gas fluxes were approximately one order of magnitude higher in the wet than dry season, due to combined effects of comparatively high saturations, high void ratios, and low temperatures. Emissions were primarily controlled by type and relative areal extent of cover materials and secondarily by season.

Attrition in the kimberlite system

The sustained transportation of particles in a suspension commonly results in particle attrition leading to grain size reduction and shape modification. Particle attrition is a well-studied phenomenon that has mainly focussed on sediments produced in aeolian or fluvial environments. Here, we present analogue experiments designed to explore processes of attrition in the kimberlite system; we focus on olivine as it is the most abundant constituent of kimberlite. The attrition experiments on olivine use separate experimental set-ups to approximate two natural environments relevant to kimberlites. Tumbling mill experiments feature a low energy system supporting near continual particle-particle contact and are relevant to re-sedimentation and dispersal processes. Experiments performed in a fluidized particle bed constitute a substantially higher energy environment pertinent to kimberlite ascent and eruption. The run-products of each experiment are analysed for grain size reduction and shape modification and these data are used to elucidate the rates and extents of olivine attrition as a function of time and energy. Lastly, we model the two experimental datasets with an empirical rate equation that describes the production of daughter products (fines) with time. Both datasets approach a fines production limit, or plateau, at long particle residence times; the fluidized system is much more efficient producing a substantially higher fines content and reaches the plateau faster. Our experimental results and models provide a way to forensically examine a wide range of processes relevant to kimberlite on the basis of olivine size and shape properties.

Stabilisation of construction and demolition waste with a high fines content using alkali activated fly ash

This paper deals with the stabilisation of the fines portion of Construction and Demolition Waste (CDW) produced by a Portuguese recycling company. The recycled aggregate was analysed with and without the addition of a well-known precursor – fly ash (FA), considering different CDW/FA weight ratios. The resulting mixtures were activated with a solution based on sodium hydroxide and sodium silicate, and their microstructure and mechanical behaviour were extensively characterised, using XRD, FTIR, SEM, BSEM/EDX and uniaxial compression strength (UCS) tests. Results obtained showed that the presence of fly ash improves compression strength and elasticity module, reaching UCS values higher than 8 MPa, after 28 days of curing at ambient temperature and relative humidity. Such values are above any kind of threshold considered for geotechnical works such as road and railway foundations or infrastructure embankments, which are regarded as effective applications for recycled CDW. The products resulting from the alkali activation of the CDW/FA mixtures were characterised as a mixture of the gels NASH and CASH, which was attributed to the initial high content of amorphous Si, Al and Ca of these mixtures.