Landfill Liner Research Articles

Preheating and "snow-plow" composite application technique affect double bond conversion but not bond strength to dentine.

To measure degree of conversion (DC) of a flowable composite, microtensile bond strength (MTBS) to dentine in the snow-plow technique with/without preheating and temperature in the preheated composite. For DC, snow-plow specimens of Filtek Ultimate Flowable (Flow) and Filtek Bulk Fill (Bulk) (3M) were prepared by light-curing composites simultaneously in standardized molds while in control groups light-curing was separate. DC of Flow was measured using micro-Raman spectroscopy. For MTBS, specimens were prepared on dentine of human extracted molars by simultaneous (snow-plow) or separate (control) light-curing. MTBS was measured using a universal testing machine after 24 h and 6 months. Data were analyzed using ANOVA with Tukey's post hoc (α = 0.05). Increased curing time significantly increased DC in snow-plow from 13.4% ± 11.6% (10 s) to 31.8% ± 4.4% (40 s) albeit significantly lower than controls (p < 0.05). Preheated Bulk improved conversion in snow-plow (44.3% ± 1.7%) and control (50.5% ± 2.6%) (p < 0.05). No significant differences occurred in MTBS between groups (p > 0.05). MTBS values ranged between 66.7 ± 8.4 MPa (snow-plow group_21°C_baseline) and 54.1 ± 15.8 MPa (control_21°C_long-term). Temperature in the preheated Bulk dropped to ~38°C after 30 s. Snow-plow technique, irrespective of preheating, resulted in lower DC of Flow than separate light-curing of composite increments. Snow-plow, irrespective of preheating, resulted in similar initial and long-term MTBS to dentine. Clinicians with preference for flowable composite liners in Class II restorations should be aware that the snow-plow technique of simultaneous light-curing of flowable and bulk-fill composite increments affects monomer-to-polymer conversion, albeit no effect on immediate, and long-term bonding to dentine was detected. Preheating sculptable bulk-fill composite improves conversion of the flowable liner in the snow-plow technique but has no detectable effect on bond strength to dentine.

Research on the destroy characteristics of PTFE/Cu composite liner to explosive reactive armor

The jet generated through PTFE based inert material liner has the characteristics of low energy, low density, and large aspect ratio, which can effectively achieve the “penetration without explosion” of explosive reactive armor. PTFE/Cu composite material liner with various densities is prepared, to research the roles of preparation procedure and density in the destroy effect of jet on reactive armor. Through numerical simulation research, it was found that there was no reaction at all in the explosive layer penetrated by the jet generated by the sinter liner molded, while the explosive layer penetrated by the jet generated through the hot-pressing sintering and extrusion molding liner experienced local reactions on the jet impact channel, and the overall explosive layer did not undergo any reaction. Through experimental verification, it has been proven that all three types of jets have achieved “penetration without explosion” on explosive reactive armor.

Enhancing attapulgite and cement-modified loess for effective landfill lining: A study on seepage prevention and Cu/Pb ion adsorption

Abstract This study aims to use attapulgite (ATT) and cement to modify loess as the lining material of landfills in loess areas and to exert the adsorption property of modified loess to ensure seepage prevention. It provides a safe, efficient, low-cost anti-seepage material for constructing a landfill in a loess area. For ATT-modified loess, when the content of ATT is less than 10%, the decrease rate of permeability coefficient is obvious, and when the content is more than 10%, the decrease rate becomes slow. After adding 5% cement on this basis, the permeability coefficient of ATT cement-modified loess is 8 × 10−8 cm/s, which meets the standard requirements (≤10−7 cm/s). The results show that the adsorption of Cu and Pb ions on ATT cement-modified loess is higher than that on pure loess. Cu and Pb ions’ adsorption rates are 99.2 and 98.5% in a single solution. In the mixed solution, the adsorption rates of copper and lead ions were 97.5 and 98.2%, respectively. Therefore, the study obtained the ratio of modified loess (85% loess + 10% ATT + 5% cement) that can not only meet the seepage prevention requirements of the landfill but also can adsorb heavy metal ions in the leachate, providing security for the landfill.

A feasibility study of fly ash and bentonite composite mix for assessing its suitability as landfill liner material

A feasibility study of fly ash and bentonite composite mix for assessing its suitability as landfill liner material

Performance of Kenaf for Landfill Liner System Improvement

A landfill is a site to dispose of materials that threaten the environment, such as leachate, poisons, or greenhouse gases. Leachate is a liquid that can contribute to water pollution if there is a leakage of flow into groundwater sources from landfill waste or other outside water sources. Leachate is a liquid accumulated from landfill waste and other outside water sources. To prevent this leachate from mixing with water resources when it flows into the soil, the behavior of Kenaf (Hibiscus Cannabinus) as a landfill liner system is investigated and understood thoroughly on how permeability properties can increase with the soil. In addition, the herbaceous plants known as Kenaf have beneficial mechanical properties, and they do not pose any threat to the health of human beings. Kenaf has significant potential for commercial usage because of the ease with which it can be cultivated and the low prices at which it can be harvested. In addition, Kenaf can contribute to infrastructure and innovation for economic growth and development (SDG 9.0), where it can reduce the usage of clay linear and simultaneously, increase the Permeability of the soil properties to resist the flow of leaches into the soil. This admixture is gaining popularity as a result of the fact that it has a relatively low cost and is simple to apply. In this investigation, Kenaf was used because of its reputation as a good absorbent product that can hold up to six times its weight and has a leaching capability of less than one percent. The results of laboratory work are presented to demonstrate that this material is suitable for usage in landfills to solve the leachate problem.

3-year randomized clinical trial to evaluate the performance of posterior composite restorations lined with ion-releasing materials

To evaluate the impact of using ion-releasing liners on the 3-year clinical performance of posterior resin composite restorations after selective caries excavation with polymer burs. 20 patients were enrolled in this trial. Each patient had two deep carious lesions, one on each side of the mouth. After selective caries removal using polymer bur (PolyBur P1, Komet, Brasseler GmbH Co. KG, Lemgo, Germany), cavities were lined with bioactive ionic resin composite (Activa Bioactive Base/Liner, Pulpdent, Watertown, MA, USA) or resin-modified glass ionomer liner (Riva Light Cure, SDI, Bayswater, Victoria, Australia). All cavities were then restored with nanofilled resin composite (Filtek Z350XT, 3M Oral Care, St. Paul, MN, USA). All the tested materials were placed according to the manufacturers’ instructions. Clinical evaluation was accomplished using World Dental Federation (FDI) criteria at baseline and after 6 months, 1, 2, and 3 years. Data were analyzed using Mann–whitney U and Friedman tests (p < 0.05). The success rates were 100% for all resin composite restorations either lined with ion-releasing resin composite or resin-modified glass ionomer liner. Mann–whitney U test revealed that there were no statistically significant differences between both ion-releasing lining material groups for all criteria during the follow-up periods (p > 0.05). Resin composite restorations showed acceptable clinical performance over 3 years either lined with bioactive ionic or resin-modified glass ionomer liners after selective caries excavation preserving pulp vitality. After the 3-year follow-up period, Activa Bioactive and Riva Light Cure liners were clinically effective and they exhibited with the overlying composite restorations successful clinical performance.Trial registration number: NCT05470959. Date of registration: 22/7/2022. Retrospectively registered.

Enhanced gas and plasticizer barrier HTPB composite liner implanted with parallel orientation Fe3O4/RGO nanosheets by an ultrasound/magnet-coassisted method

It is of great significance to prepare liners with excellent inhibition of energetic plasticizer migration and gas barrier properties. Here, we have successfully prepared magnetic iron oxide decorated reduced-graphene-oxide nanosheets (MRGO) by using ultrasound-assisted method. The obtained MRGO nanosheet-fillers were filled into hydroxyl-terminated polybutadiene (HTPB) which was exposed to a magnetic field (200 mT) to achieve ordered orientation of MRGO in the HTPB matrix (Ordered MRGO/HTPB). The laser confocal microscopy demonstrates that MRGO exhibit ordered orientation structure in HTPB matrix with good dispersion, which renders the HTPB composite liners exhibiting high gas and plasticizer barrier capability, with a reduction of 18.9 % in water vapor permeability and a decrease of 14.1 % in dibutyl phthalate (DBP) migration equilibrium concentration as compared with those of random MRGO embedded HTPB composite liners (Random MRGO/HTPB). Moreover, a theoretical model accounting for such enhanced gas/plasticizer barrier performance of HTPB due to the implantation of order aligned MRGO was established, which shows that the effective diffusion pathways of plasticizer/gas for liner penetration would be significantly enhanced when the MRGO nanosheets are oriented within the HTPB matrix. This work provides an effective and facile strategy toward the design and development of composite liners with high plasticizer/gas barrier performance for industrial applications.

The influence of isotropic loading and unloading on anisotropic evolution of saturated hydraulic conductivity of bentonite-sand mixtures in a cube triaxial permeameter

Anisotropic permeability of bentonite mixtures governs water flow regime in buffer materials such as landfill cover systems, cutoff walls, and high-level waste repositories. Because of its widespread application, a series of 48 permeability tests were conducted in this study on specimens prepared from bentonite-sand mixtures with three bentonite contents. The tests were run along both isotropic loading and unloading paths to explore the evolution of anisotropic ratio from three distinct fabric anisotropy states. Accordingly, a new cubic sample-type, large-scale triaxial permeameter was introduced and employed. The results revealed an enhancement of as-compacted anisotropy ratio from 1 to almost 7 with bentonite contents. The anisotropy ratio was suppressed with isotropic loading for 40% and 70% bentonite while it was enhanced for 10% bentonite content. Unloading was revealed to reduce the anisotropy of higher bentonite contents due to the enhancement of fissures along horizontal and vertical directions. The practical implication in terms of the long-term performance of a landfill liner with medium to high bentonite contents is that despite a 10- to 30-fold reduction in permeability with loading, the leachate flow would be less anisotropic compared with the initial condition as supported by a reduction in the anisotropy ratio up to 3.5.

Randomized clinical trial of pulpotomy using a premixed injectable calcium silicate cement on mature permanent teeth with reversible pulpitis

The aim of this two-center randomized controlled trial was to assess the outcomes and relative factors associated with pulpotomies performed using a premixed injectable calcium silicate cement, as compared to mineral trioxide aggregate in mature permanent premolar and molar teeth with reversible pulpitis. Included teeth were randomly divided into two groups according to pulpotomy material (ProRoot MTA [PMTA] group, Endocem MTA Premixed [EPM] group). After pulp exposure, the superficial pulp was either removed to a depth of 2 mm (partial pulpotomy) or completely amputated to the level of the root canal orifice (full pulpotomy). A 3-mm layer of either material was randomly placed over the pulp wound, followed by the application of a thin layer of a light-cured glass ionomer composite liner. The restoration procedure was then carried out during the same visit. After one year of treatment, the pulpotomy success rate was 94.4% (67/71), with no significant difference between the PMTA and EPM groups. The success rate was 93.9% in the PMTA group and 97.1% in the EPM group. There were no significant factors related to the procedures. EPM is a viable alternative to PMTA for single-visit pulpotomies of permanent premolars and molars.

A review of lateritic soils and their use as landfill liners

A review of lateritic soils and their use as landfill liners

Preparation and characterization of high density polyethylene with TiO2 modified PEG 6000 filler as a landfill liner material

High-density polyethylene is an engineering polymer that is used in bottom liners of landfills. However, to be used in the environment application, it needs to have good mechanical and thermal qualities. Incorporation of inorganic fillers such as titanium dioxide into a polymer aimed at enhancing several features such as mechanical strength, thermal stability, and resistance to surface wear. In this study, HDPE preparation was carried out by adding TiO2 nanoparticles. TiO2 nanoparticles were synthesized using the precursor TiCL4 and then modified with the addition of PEG 6000. Furthermore, the resulting TiO2 was used as a filler in thermoplastic HDPE. Characterization of high-density polyethylene with TiO2 filler as a landfill liner material shows an increase in mechanical and thermal properties. The HDPE sample containing 8%wt filler had the highest tensile strength, measuring at 84.72 Mpa. In contrast, the use of 6wt% filler resulted in the lowest recorded tensile strength, measuring at 56.24 Mpa. The elastic modulus had its highest increase at 8 wt% TiO2, reaching a value of 729.33 MPa. However, the addition of 6 wt% TiO2 resulted in a notable decrease in elastic modulus, with a value of 522.79 MPa. Additionally, it was observed that the highest elongation at break was achieved with a 4% weight filler, resulting in a value of 49.37%. Similar to the reduction observed in the elastic modulus value, the elongation at break exhibited a substantial decrease of 39.22% upon the addition of 6wt% TiO2. DSC scan curves for both the fabricated nanocomposite systems clearly show that they are affected by the nanofiller and its percentage fraction. There was an increase in Tm1 in the composition of 8wt% TiO2, while an increase in Tm2 occurred in 2wt% TiO2. Therefore, HDPE which is given TiO2 filler has the potential to be used as landfill liner material.

Effect of collated fly ash, GGBS and silica fume on index and engineering properties of expansive clays as a sustainable landfill liner

The effect of supplementary cementitious materials (SCMs) such as fly ash (FA), GGBS and silica fume (SF) on the geotechnical index and engineering properties of expansive clays (EC) are studied in this research work. This manuscript aims to determine the workability (consistency limits (CL)), swellability (free swell index (FSI)), compaction properties, strength characteristics (UCS) and hydraulic conductivity (HC) of varied eighteen mix proportions of FA-EC (P-series), FA-GGBS-EC (Q-series) and FA-GGBS-SF-EC (R-series) are experimentally studied as a bottom liner in landfills. From the test results, CL and FSI significantly decreased in P, Q and R series, this is due to the effect of flocculation, a process that increases the average particle size of mix blends and also depletion of the double-diffusive layer thickness of EC by promoting the Ca2+ ions in the pore water from SCMs. The compaction parameters such as optimum moisture content decreased in all the series, due to the higher flocculation of mixes. However, maximum dry unit weight increased in Q and R and decreased in the P series. The UCS values increased with an increase in optimum SCMs quantities and with curing intervals tested at 0, 7, 14 and 28 days. The higher UCS value is attained at 40 %FA with EC (i.e. P2), 60 %FA-GGBS with EC (i.e. Q3) and 60 %FA-GGBS-SF with EC (i.e. R3) in R-series which confirmed to be optimum due to the loss of cementation action/reduced cohesion in the matrix. In the case of HC, P2, Q3 and R3 mixes are confirmed to be optimum and fall under the criterion standards of landfill liner as per USEPA recommendation. Overall, this work proves to be a novelty and shows the feasibility of various collated SCMs blended with EC as landfill liner material, furthermore, these mixes are optimized to combine with EC to create a sustainable landfill liner that fits with the United Nations sustainable goals of 2030

Multiscale insight to tribological mechanism of PTFE/aramid fiber composite liner containing PES/PMPS microcapsules under a high temperature environment

Polyaryl ether sulfone/polymethylphenlsiloxane (PES/PMPS) microcapsules were prepared and added to a polytetrafluoroethylene (PTFE)/aramid fiber composite liner for the first time to improve the tribological properties of self-lubricating fiber liners under high-temperature environments. Compared with the virgin liner, the friction coefficient and wear rate of the liner containing 9 wt% PES/PMPS microcapsules are reduced by 48.5% and 21.6%, respectively. At the microscopic and atomic scale, lubricant PMPS changes the interaction energy between PTFE and the Fe layer to weaken the adhesion of PTFE to the friction couple, further reducing the adhesive wear of the liner. Under the action of lubricating phases PMPS and PTFE, the tribological properties of the liner are significantly improved.

Investigations on the seepage characteristics of polymer grouting body for repairing HDPE geomembrane defects based on LF NMR

As high-density polyethylene (HDPE) geomembranes in landfill liner systems increasingly age and damage, seepage incidents frequently occur and severely threaten the surrounding ecological environment and groundwater safety. Targeted injection grouting with polymer materials can rapidly restore the barrier function by repairing defects in damaged geomembranes. To investigate the sealing mechanisms of polymer grouting bodies with various densities, this study used low-field nuclear magnetic resonance (LF NMR) techniques to monitor and visualize the permeation process within the grouting bodies. The results revealed two failure modes of the grouting bodies under water flows: 1) insufficient interfacial shear strength between the low-density polymer and geomembrane, leading to interfacial leakage; 2) gradual buildup of permeation pressure puncturing the foam cells of the polymer matrix and inducing permeation channels. Selecting polymers with suitable expansion ratios to produce appropriate expansive pressures is crucial to enhance interfacial shear strength while avoiding secondary damages to geomembranes. Increasing the density of the polymer grouting body can also enhance the compressive strength of foam cells and interfacial shear resistance. These are crucial for enabling grouting repair of defects in geomembranes and improving their barrier performance.

Equivalent analytical models for assessment of landfill composite liners

An equivalent analytical model based on time moments is proposed to estimate the properties of landfill composite liners. The service performance of landfill liners composed of a geomembrane layer (GMBL), a geosynthetic clay layer (GCL), and an attenuation layer (AL) and a GMBL, compacted clay layer (CCL), and AL were equivalently analyzed. The equivalent analysis and quantitative correlation of contaminants at the bottom of the GMBL/GCL/AL and GMBL/CCL/AL systems were considered according to the relative concentration (CN), instantaneous flux (JI) and accumulative flux (JA). The relative concentration (CN) was found to be the most conservative equivalent index. The thickness equivalent relation of the AL for the different composite liners was consequently obtained using the pure diffusion equivalent model and the advection–diffusion equivalent model. It was found that the pure diffusion thickness equivalent relationship was a simplified linear correlation and independent of time. The quadratic polynomial equivalent equations of AL thickness for different service times were obtained by the group method of data handling. The results showed that GCL-based composite liner had a better environmental protection performance than the CCL-based composite liner. When the thickness of the GMBL/CCL/AL composite liner was fixed, the corresponding equivalent thickness of AL in the GMBL/GCL/AL composite liner decreased with an increase in the leachate head and the wrinkle length for the same value of CN.

Conceptual Design and Selection of Natural Fibre Reinforced Composite Cyclist Helmet Liner Using an Integrated Approach

This paper describes the conceptual design phase in the product development of a natural fibre composites cyclist helmet liner, beginning with idea generation and ending with selecting the best design concept. The integrated Theory of Inventive Problem Solving (TRIZ), Biomimetic methods, and the Grey Relational Analysis (GRA) method are demonstrated in this paper. This work aims to produce nature-inspired design concepts and determine the best design concept for the composite cyclist helmet liner. Following that, four design concepts were generated using the TRIZ-Biomimetic method, and the variance of concepts was developed using a morphological chart. The GRA method was chosen as the multiple criteria decision-making tool to compare their cost and weight criteria. The design concept C1 was selected as the best design concept for the natural fibre composites of cyclist helmet liner conceptual design when the highest grey relational grade (GRG) value and rank with a value of 1.0000 satisfied the GRA method conditions. This paper demonstrates how the integrated method of TRIZ-Biomimetics-Morphological Chart and GRA helps researchers and engineers develop designs inspired by nature and select the best design concept during the conceptual design stage using a systematic strategy and justified solutions.

Desiccation and crack behavior of modified waste materials–clay mixture as landfill liner: a systematic review

Desiccation and crack behavior of modified waste materials–clay mixture as landfill liner: a systematic review

Self-healing capacity of GCLs under simulated field conditions

The self-healing capacities of a GCL with natural bentonite (NB) as core (NB-GCL) and a GCL with a polymerized bentonite (PB) as core (PB-GCL) were investigated under simulated field conditions, i.e. geomembrane-GCL-a clayey subsoil layer composite liner system with a damage hole on the geomembrane and the GCL. The clayey subsoils tested had initial water contents of 22.2% and 26.8%. The liquids used were deionized (DI) water and 0.3 M NaCl solution. The test results indicate that for both the PB-GCL and NB-GCL only hydrated on the subsoils for 1–3 months, a damage hole of 15 mm in diameter was almost not self-healed. For cases of applying a constant liquid head on the top of the geomembrane of 100 mm, the sizes of damage holes were self-healed in term of diameter is about half of the values reported in the literature for tests with plenty liquid supply to the damaged GCLs. Further, for the conditions tested and for the cases self-healed, DI water leaked into the subsoil was less than about 60 g, and 0.3 M NaCl solution leaked was less than 150 g.

Investigation of Enhanced Landfill Liners Using Kuttanad Clay

Landfill liners are layers of materials used to protect soil and groundwater from contaminants. A study aims to improve the performance and effectiveness of these liners by using bentonite and fly ash as amending materials. The research aims to contribute to the sustainable waste management practices by offering cost-effective and environmentally friendly alternatives for landfill liner construction. By using locally available materials, the proposed amended liners can reduce dependency on imported materials and minimize the environmental footprint associated with conventional liner systems. The study investigates the synergistic effect of bentonite and fly ash as amending materials for improving the mechanical and hydraulic characteristics of Kuttanad clayey soil. In economic view, to maximize the usage of fly ash, bentonite can be replaced up to 30%. This mix is found to be suitable amended soil liner with a coefficient of permeability value which satisfies the permeability criteria of landfill liner.

Bioclogging

Bioclogging or biological clogging refers to the blockage of pore space in soil by microbial biomass, including active cells and their byproducts such as extracellular polymeric substance (EPS). The microbial biomass obstructs pore spaces, creating an impermeable layer in the soil and significantly reducing water infiltration rates. Bioclogging occurs under continuous ponded infiltration at various field conditions such as artificial recharge ponds, percolation trenches, irrigation channels, sewage treatment systems, constructed wetlands, landfill liners and natural systems such as riverbeds and soils. It also affects groundwater flow in the aquifer, such as ground source heat pumps, permeable reactive barriers, and microbial enhanced oil recovery. Bioclogging is a significant problem where water infiltration is hampered and countermeasures such as regular drying of the system can reduce the levels of bioclogging. However, bioclogging can also serve beneficial purposes in specific conditions. For instance, bioclogging can be utilized to make an impermeable layer to minimize the rate of infiltration or to enhance soil mechanic properties.