Increase In Bentonite Content Research Articles

Evaluation of road performance and micro-mechanism analysis of bentonite plastic concrete subgrade

This study evaluated the performance of bentonite plasticized concrete with good deformation coordination as a road base material, to address the poor deformation coordination of rigid base layers in roads. Through tests such as slump, strength, permeability, and scanning electron microscopy (SEM) and x-ray diffraction (XRD), the study analyzed the variations in workability, mechanical properties, and durability of plastic concrete as a base material under different bentonite and cement contents, as well as the underlying micro-mechanisms. The results showed that plastic concrete exhibited good workability, which improved with increased bentonite and cement content. The 28-day mechanical properties of the plastic concrete met the design criteria for road base layers and had features of higher load-bearing capacity, good toughness, slow strength attenuation, and overall integrity. In durability, the increase of bentonite content enhanced the concrete’s permeability, but decreased abrasivenes and shrinkage. From economic, performance, and engineering perspectives, the optimal bentonite and cement contents for the plastic concrete base were in the ranges of 90 kg m−3 to 120 kg m−3 and 110 kg m−3 to 150 kg m−3, respectively.

Study on the hydraulic conductivity of plastic concrete vertical cutoff walls

With the rapid development of global economy and the accelerating process of urbanization, the prevention and control of groundwater pollution has received great challenges. In the remediation of contaminated sites, the traditional method is to use isolation barriers for in-situ remediation. However, due to the influence of various factors, the permeability of barriers will be changed to different degrees. This paper takes plastic concrete as the research object, through the permeability, water content and SEM test, discusses the water-binder ratio, no pollution and the presence of Ba2+ conditions on the permeability. The results show that in the case of no pollution, the decrease in the water-binder ratio and the increase of bentonite content will decrease the permeability, which decreases with the increase of age and satisfies the exponential relationship. Both Ba2+ and pH had adverse effects on the permeability. Ba2+ inhibits the formation of hydration products and the bonding between aggregate and bonding of cementitious materials, resulting in the decrease of compactness and the increase of porosity, which adversely affects the permeability. The addition of Ba2+ and the increase of pH will have adverse effects on the permeability, and these influencing factors need to be considered in the actual project.

Ageing Effect On Shear Strength Of Mixed Kaolinite-Bentonite And Sand Clay Minerals

Ageing Effect On Shear Strength Of Mixed Kaolinite-Bentonite And Sand Clay Minerals

A Preliminary Study on the Improvement of Gangue/Tailing Cemented Fill by Bentonite: Flow Properties, Mechanical Properties and Permeability.

Backfill mining has significant advantages in safe mining, solid waste utilization and ecological environmental protection, but solid waste materials (tailings, gangue and coal gasification slag, etc.), as derivative residues of the chemical and metallurgical industries, contain a large number of heavy metal elements, which is posing great challenges to the underground environment after backfill. In order to study the feasibility of bentonite for reducing the permeability of gangue/tailing sand cemented backfill body, relevant tests were carried out from the basic performance index, flow performance and mechanical properties of paste backfill materials. The test results show that bentonite has a significant effect on the water secretion rate of cemented fillers, and also promotes the improvement of slump and diffusion diameter of backfill slurry. The enhancement effect of mechanical properties in the early stage is not obvious, mainly concentrated in the middle and late stages of specimen curing. With the increase of bentonite content, the 28-day uniaxial compressive strength increased from 7.1 MPa and 7.9 MPa to 8.7 MPa and 9.0 MPa, respectively. Bentonite is filled between the pores of the cemented backfill with its fine particles and water swelling, which can reduce the porosity and permeability of the gangue and tailings cemented backfill. Therefore, on the premise of satisfying the flow and mechanical properties of paste backfill, bentonite can be used to improve the permeability of cemented backfill and reduce the leaching and migration of heavy metal ions.

Hydro-mechanical behavior and microstructure evolution of red clay-bentonite backfills

Soil-bentonite (SB) cutoff walls have been extensively used as vertical engineering barriers to control groundwater flow and subsurface contaminant migration. As the pollution containment capability of the SB backfills is intimately related to the hydro-mechanical behavior, consolidation tests and hydraulic conductivity tests were carried out to investigate the effects of bentonite content on the hydro-mechanical behavior of red clay-bentonite backfills, and the microstructure evolution of backfills under vertical loading was evaluated based on mercury intrusion porosimetry (MIP) tests and field emission scanning electron microscope (FESEM) observations. The results of microstructure analysis also evaluated the influence of bentonite on the clay fabric which changed the relationship between hydraulic conductivity and void ratio. The results indicated that the void ratio and hydraulic conductivity decreased linearly with the increase of the effective consolidation stresses, and the compression index decreased with the increase of bentonite content. Meanwhile, the pore size distribution (PSD) curve of the backfill specimen almost turned into unimodal characteristics with only micropores distributed after consolidation. Additionally, the flow paths became more tortuous under compression which decreased the hydraulic conductivity. The montmorillonite aggregates in red clay-bentonite backfill formed into tortuous network structure which bound the clay aggregates together and effectively increased the tortuosity of flow paths.

Engineering Characteristics and Microscopic Mechanism of Soil-Cement-Bentonite (SCB) Cut-Off Wall Backfills with a Fixed Fluidity.

Soil-cement-bentonite (SCB) backfill has been widely used in constructing cut-off walls to inhibit groundwater movement in contaminated sites. This study prepares SCB backfill with fixed fluidity. We conducted a series of experiments to investigate the engineering characteristics and microscopic mechanism of the backfill. The results indicate that the water content in the slurry was more sensitive to the bentonite content. The unconfined compression strength (UCS) value increased with an increase in the cement content, and the change with an increase in bentonite content was not noticeable. The permeability coefficient decreased distinctly with an increase in the cement and bentonite contents. The porosity of the SCB backfill increased with increasing bentonite content and decreased with increasing cement content. The UCS of SCB backfill was linearly and negatively correlated with the porosity; the permeability coefficient was not significantly related to the porosity. The percentage of micro- and small-pore throats in the backfill increased with increasing bentonite and cement contents. As cement and bentonite content increased by 6% in the backfill, the proportion of micro- and small-pore throats increased by 0.7% and 1.2%, respectively. The percentage of micro- and small-pore throats is deduced to be more suitable as a characterization parameter for the permeability of the SCB backfill. The overall results of this study show that the reasonably proportioned SCB backfill has potential as an eco-friendly and cost-effective material. Based on the requirements of strength and permeability coefficient (UCS > 100 kPa, 28 days permeability coefficient <1 × 10-7 cm/s), we suggested using a backfill with 12% bentonite and 9% cement as the cut-off wall mix ratio.

An ultra-high performance concrete incorporating viscosity-controlling agent: Fiber distribution and microstructure

In order to realize the stability of steel fiber inside ultra-high performance Concrete (UHPC) under vibration and improve the use efficiency of fiber, bentonite is used as auxiliary cementitious material in this study. The influence of bentonite dosage on the mechanical properties of UHPC matrix and the mechanical properties and microstructure of ultra-high Performance fiber Reinforced Concrete (UHPFRC) is explored. On this basis, the functional relationships between the distribution and orientation of steel fibers, the freshness of the matrix and the rheological parameters of UHPC are established, and the evaluation model of the service efficiency of steel fibers is established. The results show that with the gradual increase of bentonite incorporation, the use efficiency of UHPFRC steel fiber increases first and then decreases, and when the cement content of bentonite was 2.5%, 5.0%, 7.5% and 10.0%, the flexural strength of UHPFRC increased by 9.0%, 17.6%, 18.5% and 6.1%, respectively. In addition, the increase of bentonite content will lead to the continuous decrease of the fluidity of fresh UHPC slurry (from 261 mm to 100 mm). When the bentonite content is 10.0%, the UHPC slurry has almost no fluidity (100 mm), which leads to the appearance of pores in the UHPC matrix and the decrease of compressive strength.

Composite Aerogel Comprised of Sodium Alginate and Bentonite via Supercritical CO2 Drying: An Efficient Adsorbent for Lysozyme.

To meet the demand for the separation of specific substances, the construction of porous composite aerogels with a high specific surface area and a strong adsorption capacity is still a challenge. Herein, a sodium alginate/bentonite composite aerogel was efficiently prepared through supercritical fluid drying. The aerogel’s volume shrank less during supercritical drying, maintaining its original three-dimensional mesh structure. The resulting aerogel had a large specific surface area (445 m2/g), a low density (0.059 g/cm3), and a large pore volume (3.617 cm3/g). Due to the fixation and intercalation effects, bentonite was uniformly dispersed in the sodium alginate matrixes. The adsorption of lysozyme by the composite aerogel was evaluated, and the results showed that the optimal adsorption pH was 8 when the pH of the phosphoric acid buffer solution was between pH = 5 and 8.5. The time for adsorption to reach equilibrium was 8 h. The adsorption capacity increased with the increase in bentonite content, and when the initial concentration of lysozyme was from 0.2 to 1.2 g/L, the adsorption capacity first increased and then stabilized, and the maximum adsorption amount was 697 mg/g. The adsorption behavior was simulated in the isothermal region, and the linear correlation coefficient of Langmuir isothermal adsorption fitting was found to be 0.997. Thus, this composite aerogel with strong adsorption capacity can be used as a good alternative to enzymatic adsorbents or immobilized materials.

Effect of Bentonite Content and Hydration Time on Mechanical Properties of Sand–Bentonite Mixture

The bentonite is commonly used mixed with soils for groundwater retention and waste contaminant facilities. The incorporation of bentonite could significantly reduce hydraulic conductivity. In this study, the effects of bentonite content, hydration time and effective confining pressure on the static properties of a sand–bentonite mixture were studied using experimental and numerical methods. Firstly, a large number of drainage static triaxial tests on the sand–bentonite mixture with various bentonite contents were conducted. The test results show that the increase in bentonite content and hydration time leads to a slight decrease in shear strength and initial tangent modulus of the sand–bentonite mixture. The presence of bentonite reduces the shear shrinkage and dilatancy trend of the mixture. The cohesion of the mixture increases with the increase in bentonite content and hydration time, but the internal friction angle decreases correspondingly. The hydration of bentonite on the surface of sand particles changes the contact form between particles. The bentonite slurry between pores of the sand skeleton also affects the mechanical behavior of the sand–bentonite mixture. Then, a series of 3D discrete element models were established for numerical simulations of drainage static triaxial tests. The numerical model parameters were calibrated by experimental results. The meso-mechanism of bentonite content affecting the mechanical behavior was revealed according to the contact force distribution between particles. The research results are helpful to understand further the mechanism of bentonite on the mechanical properties of the sand–bentonite mixture.

Microwave shielding characteristics of thermoplastic/graphene composites with montmorillonite (bentonite) clay addition for improved thermal stability

ABSTRACT PMMA/graphene/Bentonite and PVC/graphene/Bentonite hybrid composites were prepared by solution casting method. Thermal stability, electrical conductivity and EMI shielding effectiveness in X-band were studied in detail. PVC composite with 5 wt.% Bentonite exhibited an enormous improvement in the thermal stability compared to the PVC/graphene counterpart. However, increase in Bentonite content in the hybrid composites reduced their electrical conductivity and resulted in lower overall shielding effectiveness in X band. The hybrid nanocomposites were found to have a significantly stronger influence of absorption in the overall shielding effectiveness when compared with respective polymer/graphene composites. The detailed microstructural/mechanical characterization elucidates the underlying mechanisms.

Prediction of compressibility and hydraulic conductivity of bentonitic mixtures

Compressibility and hydraulic conductivity are the key parameters to ensure the structural integrity of landfill liner. The compressibility and hydraulic conductivity of compacted pond ash–bentonite and sand–bentonite mixes were determined from conventional consolidation tests. The results showed that both the compression index and coefficient of volume change increase, whereas the coefficient of consolidation decreases with an increase of bentonite content in the mix. Empirical models are proposed to predict the compression index and hydraulic conductivity of bentonitic mixtures from the basic soil parameters (specific gravity, liquid limit, void ratio and shape parameter), which have been compared and validated with existing models and experimental data sets. The compressibility characteristics of sedimented slurry and compacted mixes do not follow similar trends; therefore, two distinct empirical models are proposed in this study. The observed compression index values of the compacted specimens fall in the range of ± 20% from the line of equality, whereas the deviation is within ± 15% for sedimented slurry. Similarly, the estimated hydraulic conductivity values fall within ± 20% of the values predicted by the proposed empirical equation. Thus, the proposed empirical models may be used to predict the compressibility and hydraulic conductivity of compacted bentonitic mixtures.

Evaluation of Bentonite Mixed Indigenous Clays for Development of Clay Liners

This study presents experimental investigation of indigenous clays mixed with Bentonite to assess their suitability in potential use as clay liners. Soil samples with 0, 4, 8, and 12% Bentonite content from three different sites in Peshawar region were tested for various geotechnical properties. Grain size distribution, specific gravity, Atterberg limits and free swell were found through laboratory tests using appropriate ASTM procedures. Maximum dry density and optimum moisture content were calculated using Atterberg limits in available relationships. Finally, one dimensional consolidation tests were conducted to find relevant parameters for calculating hydraulic conductivity. A decrease in specific gravity, increase in free swell, and in optimum moisture content, decline in maximum dry density and hydraulic conductivity was observed with increase in Bentonite content across all three soil samples. During free swell, the soil clusters become larger leading to formation of floccules resulting in the narrowing of inter-particle space and thus blocking of permeable paths. It is concluded that 8% Bentonite content by weight yields a suitable mixture for a clay liner that has hydraulic conductivity in the range of recommended limits.

Consolidation Characteristics of Artificially Structured Kaolin-Bentonite Mixtures with Different Pore Fluids

The consolidation characteristics of kaolin, bentonite, their mixtures, and natural clays have been widely evaluated. However, the effect of pore fluid on the consolidation characteristics of artificially structured kaolin-bentonite mixtures should be more investigated. In this study, the oedometer tests were carried out on mixtures of kaolin with 10%, 20%, and 30% bentonite reconstituted with distilled water and 1 M NaCl. The testing samples with an “artificial structure” were prepared using the preconsolidation procedure. The test results show that bentonite greatly affects the consolidation behavior of mixture samples, especially when the pore fluid is distilled water. In the case of distilled water, the addition of bentonite to kaolin clay significantly increased the compression index (Cc), swelling index (Cs), and coefficient of volume change (mv). In this case, themvof mixture samples increased significantly at low effective axial stress (σ′a) levels (less than the preconsolidation pressure) and then decreased as theσ′afurther increased. In the case of 1 M NaCl as the pore fluid, theCc,Cs, andmvslightly changed with the increase of bentonite content. The research results also confirmed that the effect of saline water on the compression index was noticeable when the liquid limit of soil with distilled water was higher than 110%, and the compression index of soil with distilled water was higher than 1. Regarding the coefficient of consolidation (Cv), theCvof kaolin sample increased as theσ′aincreased, and this trend was independent of the pore fluid chemistry. By contrast, theCv − σ′atrend of mixture samples depended not only on the pore fluids but also on the stress level.

Low cost and regenerable composites based on chitin/bentonite for the adsorption potential emerging pollutants

Composites based on bentonite and chitin were prepared and its application for trimethoprim (TMP) adsorption from aqueous solution was investigated. Composites were characterized by ATR-FTIR, XRD, DSC and TGA. Characterization data revealed the intercalation of the chitin macromolecules into the bentonite interlayer. Several important parameters of TMP adsorption were explored including the composition of composites, pH medium, isotherms, contact time, and reused in batch experiments. Batch adsorption studies showed that TMP adsorption on composites increased with increase in bentonite content on composites and in acid medium. Langmuir adsorption model showed the best agreement with the experimental data used to describe adsorption isotherms. Langmuir isotherm indicated that the maximum adsorption capacity of TMP was 67 mg/g. Sectioned composite had around 100% adsorption capacity after three regeneration cycles.

EFFECT OF CEMENT AND BENTONITE MIXTURE ON THE CONSOLIDATION BEHAVIOR OF SOFT ESTUARINE SOILS

In order to study the effect of mixed cementitious materials on the consolidation behavior of soft estuarine soils in South East Queensland, a series of oedometer tests were performed in the geotechnical laboratory. To fulfill the objectives, specimens were prepared with different additive content of stabilizing agents and were cured for 7 and 28 days, in which cement content remained at 10 % while the content of bentonite was varied from 2.5% to 7.5%. The testing results indicate that both cement-treated and cement-bentonite treated samples represented a significant decrease in compressibility compared with untreated samples, in which cement-bentonite mixture shows higher effect on soil stabilization than cement only. However, with the increase of bentonite content, the consolidation behavior of cement-bentonite treated samples did not change consistently which indicates that the effectiveness of cement-bentonite mixture has no linear relationship with the bentonite content and the optimum bentonite content is around 5%.

Determination of the soil–water characteristic curve of unsaturated bentonite–sand mixtures

To investigate the effect of the changes of the soil suction on volume changes, laboratory experiments were conducted on pure bentonite and bentonite mixed with sand of proportion: 30, 40 and 50% at different initial water contents and dry unit weights that were chosen from the compaction curves. In addition, large-scale model with dimensions (700 × 700 × 650) mm was used for testing soils prepared at the same initial water content and dry unit weight to show the effect of water content changes on different relations (swelling potential, swelling pressure and soil suction). The soil water characteristic curve (SWCC) was measured by the tensiometer at depths 200 and 500 mm from the surface footing. The SWCC was obtained experimentally from the tensiometer method. Different curves were obtained due to different initial water contents and different soils. It was concluded that the suction tends to decrease steeply with increase of the initial water content. The increase in bentonite content shifts the SWCC slightly. The residual water content increases as the bentonite content increases when the residual water content decreases from 44 to 32% when adding 30% sand to pure bentonite due to that the samples with higher bentonite content had a higher volumetric change potential on wetting than samples with low bentonite content. The air-entry value (AEV) increases with increase of initial water content and clay content, where AEV for B1 (pure bentonite) soil sample is 10 kPa, while AEV is 25 kPa for B2 (pure bentonite) soil sample due to increase of initial water content from 25 to 34%; however, AEV for BS1 (70:30, bentonite/sand) soil sample is 8 kPa, on the other hand, AEV reaches 6 kPa for BS3 (60:40, bentonite/sand) soil sample due to decrease of the clay content in this sample.

Effects of bentonite binder dosage on the properties of green limestone pellets

This paper presents the results of tests carried out to determine how the dosage of bentonite added as binder, affects the properties of green pellets made of the limestone fines that originate from Lithothamnium limestone processing. Bentonite was added to limestone in different mass fractions (1, 2.5, 5 and 10%), whereas all the other parameters of the pelletizing process remained constant. The aim of pelletizing was to consolidate limestone fines and form mechanically stable pellets, provided that all the other properties of limestone remain unchanged. The pellets formed in this way were analysed applying DTA/TG analysis and FTIR and SEM analyses. The results showed uniform distribution of bentonite in the pellets, demonstrated that the pellets are compact and there is no formation of new compounds. The pellets were tested for resistance to impact, compressive strength and abrasion resistance. Also disintegration tests were performed to determine the time required for the pellet to disintegrate completely in water. These mechanical properties are essential for transport, handling, storage and general use of pellets. The values of most of the parameters established for pellets with 5% bentonite, meet the standards required for use in agriculture for liming acid soils, however their application is limited because their impact resistance is unsatisfactory and the time required for their complete disintegration in water is extremely short. It should be noted that further increase of bentonite content (over 10%) will not improve the quality of green pellets. In view of the results obtained, it is necessary to introduce drying into the pelletizing process in order to bring the green pellets into solid state.

Cyclic and post-cyclic shear behavior of low-plasticity silt with varying clay content

This paper investigates the cyclic and post-cyclic shear behavior of low-plasticity silt and the impact of additional clay content. Bentonite clay was added to the low-plasticity Mississippi River Valley (MRV) silt (PI=6) to increase the clay content of the soil. A series of triaxial tests were conducted in the laboratory to examine the shear and pore pressure behavior during and after cyclic loading. As the bentonite content in the reconstituted specimens increased, the excess pore pressure developed at a slower rate and the total excess pore pressure decreased at the end of cyclic loading. In contrast to the MRV silt, the specimens modified with bentonite experienced cyclic softening rather than initial flow liquefaction. The cyclic shear strength increased with an increase in bentonite content. The post-cyclic reconsolidation behavior was a similar to a virgin compression process, and not recompression. Adding bentonite to the MRV silt results in changes in permeability, compressibility, undrained shear strength, and initial stiffness. Additionally, the cyclic loading had a marked effect on the shear behavior of low-plasticity soil with a PI<6, but not noticeable with a PI>6. This study suggests that the behavior of the Mississippi River Valley silt changes from contractive sand-like material to clay-like behavior at a PI≈6 due to the addition of clay.

Evaluation of the Permeability Behaviour of Sand-Bentonite Mixtures Through Laboratory Tests

In recent years, when suitable impervious soils are not available for containing the waste, barriers constructed using sand-bentonite mixtures are being frequently adopted to contain the waste. This paper presents the laboratory evaluation of permeability of sand-bentonite mixtures through falling head tests performed with rigid wall permeameter and oedometer on different categories of sand-bentonite mixtures. Five different categories of sand-bentonite mixtures were formulated by varying bentonite content in increments of 5 % from 5 to 25 % by dry weight. Atterberg limits and compaction characteristics of sand-bentonite mixtures were evaluated. With an increase in bentonite content, the unconfined compressive strength of the sand-bentonite mixture was found to increase linearly and a sharp decrease in permeability was registered up to a bentonite content of 15 % and beyond this the decrease in the permeability was marginal. Permeability tests were carried out with and without prior saturation of the samples. It was found that permeability behavior of sand-bentonite mixtures was affected by the initial saturation process and type of permeability testing method.

Effect of Bentonite Binder on Adsorption and Cation Exchange Properties of Granulated Nano NaY Zeolite

In order to investigate the effect of bentonite binder on adsorption and cation exchange properties of granulated nano NaY zeolite, the adsorption of Xe and N2 and removal of Sr2+ ion from aqueous solution was studied. The results showed that increase in bentonite content of granules from 20 to 40 weight percent caused increase in the rupture load of granules by 232%, decrease in BET surface area by 66% and lower the Sr2+ uptake percentage by 35%. The Henry’s law constant, heat of adsorption, effective crystal diffusivity as well as activation energy of diffusion of Xe over granulated nano NaY with 25% bentonite was also measured by pulse chromatography method. Obtained results were compared with similar results of binderless micron sized NaY material. Results indicated that although the adsorption of xenon on the binder of bentonite was negligible, the diffusion resistance created by this binder was significant such that the effective crystal diffusivity in the granules with 25% binder determined to be 4302 percent lower than the granules with no binder.