This study investigated the adsorption of CO₂ on three cation-exchanged montmorillonites (Li-Mt, Na-Mt, K-Mt) using density functional theory (DFT). CO₂ adsorption primarily occurred through electrostatic attraction with the surface cation, decreasing in strength: Li-Mt > Na-Mt > K-Mt. Li-Mt showed the strongest adsorption capacity. Significant charge transfer occurred between the CO₂ molecule and the montmorillonite surface, facilitated by orbital hybridization between CO₂ and surface cations. These interactions formed ionic bonds, stabilizing the adsorbed CO₂. The addition of a water molecule affected the adsorption configurations, bond lengths, and the occupancy of CO₂ on cation-substituted montmorillonite. This computational analysis provided insights into CO₂ capture mechanisms by montmorillonite, highlighting the influence of different surface cations on adsorption efficiency. These findings could inform the design of more effective clay-based materials for carbon capture applications.

As waste production increases and resources become limited, sewage sludge presents a valuable resource with potential beyond traditional land use and incineration. This review emphasizes exploring innovative non-fertilizer applications of sewage sludges and advocates for viewing wastewater treatment plants as sources of valuable feedstock and carbon sequestration. Innovative uses include integrating sewage sludge into construction materials such as asphalt pavements, geopolymer, cementitious composites, and masonry blocks. These methods not only immobilize heavy metals and mitigate environmental hazards but also support carbon sequestration, contrasting with incineration and land application methods that release carbon into the atmosphere. The review also addresses emerging technologies like bio-adhesives, bio-binders for asphalt, hydrogels, bioplastics, and corrosion inhibitors. It highlights the recovery of valuable materials from sewage sludge, including phosphorus, oils, metals, cellulose, and polyhydroxyalkanoates as well as enzyme production. By focusing on these non-fertilizer applications, this review presents a compelling case for re-envisioning wastewater treatment plants as sources of valuable feedstock and carbon sequestration, supporting global efforts to manage waste effectively and enhance sustainability.

This work investigates the potential inhibition efficiency of sulfur-containing and aromatic amino acids such as cysteine (Cys), methionine (Met), phenylalanine (Phe), tyrosine (Tyr) and tryptophan (Trp) for magnesium in Hank’s solution. Theoretical methods including Density Functional Theory (DFT) and Monte Carlo (MC) simulations were applied in order to gain an in-depth understanding of their interaction with the metal surface. The study covers frontier molecular orbitals (HOMO and LUMO), Fukui function, Mulliken electron density distribution analysis and global reactivity descriptors. The adsorption energies were calculated and determined the most stable low energy configurations for the adsorption of selected amino acids on Mg (001) surface. Based on the calculated adsorption energies, our study indicates that Met and Tyr exhibit the highest potential for corrosion inhibition efficiency among the studied amino acids. Compared to Met, Tyr exhibits stronger adsorption on magnesium surface by forming shorter Mg-O bonds with a more negative adsorption energy, which accounts for the better inhibitive performance of Tyr. The findings of these studies can serve as a theoretical basis for the search of green and sustainable corrosion inhibitors that can effectively protect magnesium and its alloys from corrosion damage.

Mild steel is essential in modern industry due to its favorable mechanical properties and economic availability. However, its high susceptibility to corrosion, especially in acidic environments, poses a significant challenge, reducing service life, increasing operating costs, and raising the risk of failures. This study investigates the corrosion inhibition mechanism of mild steel St1 in a 2 M H₂SO₄ solution at various temperatures using the broad-spectrum antibiotic azithromycin (AZM). Experimental results indicate that AZM presence increases the polarization resistance of mild steel in the acidic solution. AZM acts as a mixed-type inhibitor, influencing the kinetics of both cathodic and anodic processes. The introduction of 200 mM AZM leads to an increase in the polarization resistance of the steel electrode in 2 M H₂SO₄ by up to 2.4 times. The inhibition mechanism involves forming a protective layer of protonated AZM forms on the negatively charged Fe surface. These protonated forms can also adsorb on cathodic areas, competing with hydronium ions (H₃O⁺) and thereby inhibiting hydrogen evolution processes. The protective effect of AZM diminishes with increasing temperature of the corrosive environment, as confirmed by Monte Carlo simulations showing decreased adsorption energies for AZM and its protonated forms at higher temperatures. An assessment of the protective effect of 200 mM AZM showed that an increase in the temperature of the corrosive environment from 293 to 333 K leads to a decrease in the protective effect by almost 5.6 times. Quantum chemical calculations determined the reactivity of AZM and its protonated forms, identifying the molecular groups involved in the adsorption mechanism.

The imperative to mitigate carbon emissions and seek sustainable alternatives to cementitious materials has driven the advancement of geopolymer binders, which are inorganic binders of aluminosilicate industrial-waste materials activated by alkaline agents. The use of geopolymers carries the potential for significant reductions in greenhouse gas emission. Furthermore, the incorporation of plastic waste as aggregates addresses not only resource conservation but also environmental sustainability. This study conducted a comprehensive life-cycle assessment of the use of geopolymers from fly ash as a precursor with polyethylene terephthalate (PET) waste as a substitute for natural aggregates. It was observed that when replacing natural aggregates with PET waste to the maximum extent, the global warming potential (GWP) in the category of emissions related to aggregate preparation increased by 16.7 %. This increase was attributed to significant emissions generated during PET processing, including activities such as washing and grinding. The total GWP to produce one cubic meter of geopolymer mixture was 643.55 kgCO2-e without PET aggregates and 667.86 kgCO2-e with maximum use of PET aggregates. The optimization of energy-intensive PET preparation processes led to a remarkable reduction of 19.63 % for production of geopolymer mixture with maximum use of PET aggregates. These findings show the potential for improved sustainability in the production of geopolymer mixtures and emphasize the critical role of optimizing the production processes in mitigating their environmental impact.

During the manufacturing of foam concrete, conventional chemical and physical foaming methods are still inadequate for regulating and stabilizing the bubble properties. In this work, a one-pot method, denoted as in-situ mechanical frothing, was proposed preparing foam concrete by vigorously stirring the mixture of water, cement, sandy soil, and foaming agent. Sandy soil (SS) was used in the content range of 25–75 % as cement replacement to decrease the binder consumption and reduce costs. The influence of in-situ mechanical frothing technology and SS dosage on the properties of paste rheology, pore structure, compressive strength, and thermal properties was investigated. The results showed that the average pore size of foam concrete prepared by this method is between 45.73 and 74.58 μm. The compressive strength of the formed foam concrete at dry density of 600–1000 kg/cm³ was 2.78–16.37 MPa, which was 85%–231 % higher than that the standard values. The incorporation of SS resulted in smaller and homogeneous pore structure in foam concrete. Moreover, foam concrete with 25–75 % SS dosage showed 7–40 % decrease in thermal conductivity. The overall analysis showed that the 25–50 % SS-incorporated foam concrete enabled achieving higher standard properties through in-situ mechanical frothing.

In recent years, researchers have expressed growing concern regarding the environmental impact of traditional binders such as lime and cement. This has led to an increased focus on finding alternative materials that not only meet the demands of modern construction but also align with international initiatives for eco-friendly building practices. In response to this need, alkali-activated materials have emerged as a promising substitute for conventional binders. However, the current production processes for alkali-activated materials involve substantial energy consumption and carbon emissions, presenting a global challenge in the quest for sustainable construction practices. This paper aims to present a novel proposition: utilizing construction and demolition waste as a potential precursor for manufacturing alkali-activated materials. Drawing upon a comprehensive survey and analysis of pertinent literature from diverse sources, this paper synthesizes a wealth of knowledge. The extensive review encompasses a thorough analysis of existing research findings, allowing for a nuanced exploration of the utilization of construction and demolition waste as a viable precursor in the manufacturing process of alkali-activated materials. Construction and demolition waste typically contains significant amounts of silica and alumina, making it an attractive and sustainable alternative for alkali-activated materials production. Moreover, this approach offers the additional benefit of mitigating the environmental repercussions associated with waste disposal. By providing an extensive overview of existing literature on the use of construction and demolition waste as a precursor for alkali-activated materials production, this paper also identifies crucial areas that warrant further research in this field.

Galvanic deposition of copper, tin and their alloys is widely used in microelectronics, printed circuit boards, anticorrosive and decorative finishing of products for various purposes. One of the main factors determining the structural and morphological characteristics of the deposited coatings is the value of cathodic polarization during the deposition, which depends on the presence of complexing ions and surfactants. Complexation is one of the most effective and widespread ways to increase the cathodic polarization, as well as the convergence of deposition potentials of copper and tin. In this work we studied the combined effect of thiourea and N-octylpyridinium bromide additives on the kinetics of Cu, Sn, and Cu-Sn electrocrystallization from sulfuric acid electrolytes. The combined presence of these additives allows obtaining homogeneous and fine-grained Cu-Sn coatings. The results of theoretical studies agree well with experimental data and show that the introduction of thiourea and N-octylpyridinium bromide leads to the inhibition of cathodic reduction of hydrated copper(II) and tin(II) ions.

Bound water on the surface of clay minerals determines the nature of a wide class of phenomena, from the diffusion of interlayer cations to synthesizing prebiotic macromolecules during the early Earth. However, the nature of forming the bound water layer’s spatial structure and properties has yet to be fully investigated. Many factors, including peculiarities of structural charge distribution, surface adsorption centers, and OH-groups of the octahedral sheet of the clay minerals, can affect it in natural clays. In this work the role of hydroxyl ligands and isomorphic substitutions of the octahedral sheet in trans- and cis- vacant sites in the formation of the bound water layer structure on the basal surface of montmorillonite was studied by the Density Functional Theory. It was found out that in the case of single isomorphic substitution in the octahedral sheet OH-groups in the cis-vacant sites provide higher adsorption energy of water molecules on the basal surface as compared to OH-groups in the trans-vacant sites. The double isomorphic substitution in the octahedral sheet creates a mutual enhancement effect due to the difference in the structural arrangement of the OH-groups. This leads to an increase in the interaction with adsorbed water molecules. The maximum increase in adsorption energy is observed for the case with isomorphic substitutions of Mg-cis and Fe-trans in the octahedral sheet. The results of the theoretical study contribute to explaining the experimental data available in the literature.

A comparative study on water sorption by different components of the binder phase formed in geopolymerization was performed using the Grand Canonical Monte Carlo (GCMC) simulation method. Water sorption isotherms for crystalline, defective and amorphous model structures with Na+ exchangeable cations at temperatures of 298 K were obtained. The isosteric heats of adsorption of water in each structure were calculated. In addition, the distribution pattern of H2O molecules in the researched frameworks and the preferred sorption sites were also investigated. The GCMC results showed that the structural changes in the host framework significantly affect water sorption properties, leading to changes in water sorption capacity and nature of interactions with guest water molecules. The GCMC simulation results have provided useful information on the behavior of water confined in geopolymeric binder phase, which is difficult to observe experimentally, contributing to a better understanding of the mechanism of water adsorption in geopolymer-zeolite hybrid materials.

This work investigates the recycling potential of polyethylene terephthalate (PET) bottle wastes as natural sand substitute in geopolymer (GP) mixtures to reduce plastic pollution and transition to a circular economy. Fresh and hardened properties of coal fly ash-based GP mortars with replacement of quartz sand by grinded fine PET particles of 0.315–1.25 mm in size (20%, 40%, 60%, 80% and 100%) were evaluated. It was found out that an increase in plastic aggregate content leads to a decrease in compressive strength and flexural strength of geopolymer mortars. In turn, the splitting tensile strength increased slightly when up to 40% of the sand volume was replaced by plastic aggregate. At this replacement level, the fresh geopolymer mixes had workability close to that of conventional mortar. The flake-like PET particles contributed to the reduction of cracking of the specimens and more ductile failure modes. Furthermore, GP mortars containing recycled PET bottle wastes at the full replacement level of natural aggregate showed advantages in lightweight (up to 15%), water absorption (up to 26%) and thermal insulation properties (up to 59%), enabling production of sustainable construction materials with environmental and economic benefits.

The interaction of amino acids with clay minerals plays an essential role in many natural processes. Understanding the mechanisms of their adsorption on natural clays opens the way to a wide range of nanobiotechnological applications and helps to clarify the origin of life on Earth. In this work, the adsorption mechanisms and behavior of aliphatic amino acids (glycine, alanine, valine, leucine, and isoleucine) on kaolinite surfaces have been studied by the Density Functional Theory (DFT) method. The role of functional groups of aliphatic amino acids (AA) and their orientational behavior during the formation of hydrogen bonds with siloxane and hydroxyl surfaces of kaolinite have been systematically scrutinized. It has been found that the carboxyl group plays a crucial role in the mechanism of interaction between AA and kaolinite surfaces. The strongest hydrogen bonds are formed between the H-atom of the carboxyl group of AA and the O-atom of the hydroxyl surface of kaolinite. An additional hydrogen bond can be formed between the N-atom of the amino group and the surface –OH groups of kaolinite. The adsorption energy of AA on a hydroxyl surface is ~3 times higher than that on the siloxane surface. The obtained theoretical results comply with and help to explain the experimental data available in the scientific literature.

This paper analyzes the current development of additive manufacturing (AM) technologies exploiting geopolymers (GPs) as promising green and sustainable 3D printable aluminosilicate inorganic materials. Material design and processing strategies to achieve or enhance three-dimensional printability of various geopolymer systems are summarized. The main methods of GPs additive manufacturing based on material extrusion and powder-based printing processes are considered. Their features, advantages, and limitations are scrutinized. There is presented a brief description and a principle of operation of the varieties of 3D printers, with whose help these fabrication approaches are implemented. Fresh and hardened state properties of 3D printed GPs are discussed in detail from the point of view of chemical reactions and structural transformations occurring in the material. The areas and specific examples of the application of advanced printable geopolymer materials and products are surveyed. The main current challenges, perspectives and directions of future work required to improve this technology have been delineated.

This research investigated the influence of shape and size of plastic waste on the fresh-state and hardened-state properties of geopolymer (GP) mortars. Geopolymer composites were prepared using fly ash and waste plastic bottle composed of polyethylene terephthalate (PET). PET was introduced in form of shredded flakes, strips, and grinded particles of different sizes. The flowability and mechanical properties of PET/geopolymer mortars improved with decreasing size of the plastic aggregates. PET grinded particles were found to be the most effective form of aggregate. Although the geopolymer composites containing PET particles had workability and flexural strength close to those of the control mixture, their compressive strength and splitting tensile strength were noticeably lower due to poor interaction between PET particles and the matrix. The latter issue could potentially be addressed by enhancing the adhesion at the interface of PET particles and geopolymer mortars.

In this work, nanocellulose/geopolymer composites were successfully fabricated through mixing an ultrasonically dispersed suspension of cellulose nanofibrils (CNF) with a metakaolin-based geopolymer (GP) binder. Fresh and hardened state properties of geopolymer composites containing 0.025, 0.05, 0.1, and 0.25 wt% CNF were investigated. The results showed that cellulose nanofibrils can be effectively used as a reinforcing phase of geopolymers, providing a significant increase in the tensile strength. With an increase in the content of cellulose nanofibrils, the consistency of the mixture changes dramatically, becoming viscous, impairing its workability and limiting the incorporation of larger CNF dosages. Therefore, in order to realize the full cellulose nanofibrils reinforcing potential, it is necessary to provide further optimization of the composition of CNF/GP composites, in particular through the addition of plasticizers and/or regulation of water-to-solids ratios.

Existing waste tire management strategies such as landfill, warehousing, incineration, and pyrolysis are associated with significant emissions of hazardous compounds including gases, heavy metals, and oils. A sustainable rubber waste disposal strategy is immobilizing them in a crushed form in eco-friendly geopolymer (GP) matrices. However, the implementation of this approach is constrained by the strength degradation of rubberized geopolymer composites. In order to solve this problem, this article includes a comparative investigation of the effect of various physical and chemical pre-treatments of tire crumb rubber (CR) with NaOH, H2SO4, (CH3)2CO and KMnO₄ solutions, as well as ultraviolet radiation, on the mechanical performances and microstructure of rubberized fly ash-based GP composites. It has been established that the best effects are demonstrated by treatment with an aqueous solution of potassium permanganate; oxidative reactions with the solution lead to the formation of surface-active functional groups on the rubber. As a result, there is more than a twofold increase in the hydrophilicity of CR particles, estimated from the mass of adsorbed water vapor (from 1.5 to 3.3 wt%). This provides a strong adhesive contact of the filler with the geopolymer matrix, which favorably affects the change in the mechanical properties of the composites. The compressive strength in this case has been increased from 12.8 MPa (GP/untreated CR composite) to 15.5 MPa at addition of 10.0 wt% KMnO4 treated CR. Further optimization of the composition and of the curing mode of the geopolymer binder can potentially provide an additional positive effect in this aspect.

The use of mine tailings (MTs) as aggregates or precursors of alkali-activated materials and geopolymers (GPs) seems to be a promising approach for their sustainable utilization since it allows not only reducing the dynamics of MTs accumulation in the environment and the environmental damage they cause but also it combines the advantages geopolymer technology that is associated with reducing the carbon footprint, the ability to utilize other technogenic aluminosilicate waste, the versatility of the properties of GPs as a general construction binder. Taking into account the complex material composition of mine tailings, and relatively little knowledge of the features of the geopolymerization of tailings and the influence of various factors on the properties of MTs-based geopolymers, there is now a need to generalize these aspects and assess the prospects for possible applications. This article is a generalization and a detailed analysis of the relationship between structural, mechanical, and thermal properties, durability, leaching behavior, and other important characteristics of MTs-based geopolymers. Here, in addition to the key fundamental aspects of the formation of properties of MTs based geopolymers, well-known examples of their applications in binder pastes, mortars, and concretes, as well as bricks, backfill materials, adsorbents, porous materials, and other promising applications are considered in detail. In addition, economic and production aspects are also discussed.

This review aims to provide a general view on anti-corrosion coatings for the protection of steel railway structures exposed to atmospheric environments. The article describes the specific features of the operation of railway structures with steel elements, including culverts and bridge structures (bridges, viaducts, flyovers, overpasses), track and catenary. The structural, metallurgical and environmental factors influencing the nature and corrosion rate of these structures are summarized and discussed. The mechanisms of electrochemical processes of atmospheric corrosion of steels, corrosion products and layers are analyzed. The types of the most widely used anti-corrosion coatings for steel railway structures, their main components, and characteristics are depicted. The protective mechanisms of such coatings, as well as the processes leading to their degradation and destruction, are investigated. In conclusion, the article highlights key bottlenecks and areas for further research in this area in the context of increasing environmental compliance requirements, lower operating costs, and improved performance of anti-corrosion coatings for steel railway structures.

Using the computational methods of Density Functional Theory (DFT) and Monte Carlo (MC), we investigated the potential and mechanism of corrosion inhibition of iron, copper and aluminum by small peptides of aliphatic amino acids (AAs), such as L-alanine (Ala) dipeptide and tripeptide. The article provides an assessment of the local and global descriptors of the reactivity of Ala in neutral and protonated forms and its changes when combining Ala into di- and tripeptides. There was established a boost in the inhibitory effect of di- and tripeptides, due to an increase in the number of reaction centers of the molecular structure. The authors calculated the adsorption energies, and determined the most stable low energy configurations for the adsorption of alanine amino acids and small peptides on Fe (110), Cu (111), and Al (111) surfaces. It has been established that Ala and Ala-derived peptides can be absorbed on these substrates by chemisorption, predominantly located on epitaxial grooves. The absolute values of the adsorption energy between these inhibitors on the studied metal surfaces rise with an increase in the number of amino acid residues. The stronger adsorption of small peptides is also indicated by a decrease in the shortest bond lengths between the layer of on-surface Fe, Cu and Al atoms and the nearest inhibitor atoms that are characterized by the following sequence: Ala > Ala-Ala > Ala-Ala-Ala. The peptides have the best adsorption ability to the iron surface, which characterizes their highest inhibitory efficiency from a theoretical point of view. The results of the studies performed have demonstrated promising prospects for the use of small peptides as effective “green” corrosion inhibitors.

Normative documents in many countries that regulate the construction of highways and railways subgrade, in order to reduce the costs, allow the use of soils from nearby excavations and quarries. Large length of roads leads to noticeable variations in the properties of soils along the construction line, which is reflected in design decisions. For example, the results of laboratory studies performed in this work demonstrate a scatter in the optimum moisture content of cohesive soils up to 40 %, and a spread in the soil densities after compaction, up to 20 %. In such conditions, the task of achieving the required quality of construction is partially transferred to the input control of materials, allowing determining its compliance with the requirements of the project. Since the use of input control technologies can increase the construction time, they must rapid. In this study, to accelerate the routines for comparing soil properties, a method for determining the mineral composition based on the use of infrared spectroscopy technologies is developed. The use of this method allows determining the mineral composition of soil building materials by the IR spectroscopy with an accuracy of 10–15 %.

The mining industry produces a large amount of mine waste rock and tailings, which pose a severe threat to the environment. The most common way for the disposal of these industrial wastes is dumping at sites, which contributes to soil degradation and water pollution, and also covers the useful land. Recycling of mine tailings (MTs) in raw material — intensive applications presents a good alternative to manage the waste generated from mining and mineral processing industries. The geopolymer technology provides a green solution to the utilization of MTs, avoiding its negative environmental impacts. This paper is the first part of the review which summarizes the physicochemical and environmental aspects of different types of MTs, as well as the technological aspects of the preparation of geopolymers (GPs) based on them. The work scrutinizes potential environmental and socio-economic risks of the mining industry associated with the accumulation of tailings. The issues of MTs toxicity that should be taken into account when developing methods for disposal of tailings in geopolymers are touched upon. The features of the chemical and mineral composition of tailings used in geopolymers, as well as their physical properties, are systematized and scrutinized. Methods of utilizing MTs as precursors of GPs or aggregates described in the scientific literature, as well as general patterns of the geopolymerization process are discussed. Finally, the key issues in this area that require additional research are highlighted.

Corrosion significantly limits the operational capabilities of metals and alloys reducing their service life. Finding environmentally friendly and economically justified alternatives to commercially used corrosion inhibitors is an important problem. Amino acids are promising compounds from a wide class of organic inhibitors. In this work, using the example of aliphatic amino acids glycine (Gly) and alanine (Ala) and their dipeptides, a quantum-chemical and Monte Carlo evaluation of their inhibitory effect is given and the conditions for the increase in their inhibitory effect in comparison with individual amino acids are studied. The role of the peptide bond in increasing the inhibitory effect of compounds based on aliphatic amino acids and expansion of their application to media with different pH is studied. The impact of the amino acid sequence when synthesizing dipeptides on their inhibitory effect has been revealed. The peptide molecular group participates in donor-accepting processes interacting with the metal surface. It is an additional adsorption center that can boost adsorption interaction with the metal surface which enhances the inhibitory effect. Aliphatic dipeptides based on Ala and Gly show an improved inhibitory effect compared to amino acids in an acidic medium according to Monte Carlo simulations. The theoretical results are in agreement with the experimental data. The results obtained can be of interest as a starting point for studying large peptide chains which require significant computational resources.

The widening of the railway roadbed for additional tracks is one of the effective ways to increase the carrying capacity of railway lines. However, the experience in using such railway sections shows that differences in the properties of soils and the degree of their compaction, as well as the effects of external force and climatic factors, greatly complicate the possibility of ensuring stable long-term joint operation of a new and old parts of the subgrade. This problem is especially acute with an increase in axle train loads associated with the transition from conventional to heavy traffic. In this work, we use the finite element method to perform a comparative analysis of the effectiveness of reinforcement of a widened railway embankment for heavy traffic by various structural countermeasures, including geosynthetics reinforcement, soil nailing techniques, and piled constructions. The purpose of the work is to establish the relationships between the reinforcement scheme, train load intensity, and the nature of embankments deformation, and to identify rational areas of their application. The regularities in the changes in the deformability of soils during reinforcement, as well as the changes in the stress gradient and the safety factor under axle loads from heavy trains are revealed. The mechanism of destruction of the slopes of the widened part of the embankment is investigated. Rational application domains of reinforcing structures for a widened railway embankment in terms of increasing the stability of its slopes and minimizing the deformability of the subgrade are determined.

In this work we studied the effect of pre-treatment of low-grade flax product (flax tows, FTs) by cleaning it mechanically from shives and weeds, followed by mercerization with a 5% aqueous NaOH solution and ultrasonic (US) treatment (22 kHz, 500 W) in alkaline medium, on the mechanical properties and microstructure of fly ash-based geopolymer (GP) composites. A series of three-point bending flexural tests was conducted on several types of GP/FTs composites while ATR-FTIR spectroscopy, scanning electron microscopy, and confocal laser scanning microscopy were applied to evaluate morphological and chemical characteristics of FTs and their interface strength with GP matrix. It is shown that combined treatment with alkali and high-intensity ultrasound is an effective way to process and modify the surface of FTs fibers for reinforcing “green” geopolymer composites, providing the best technical and economic effects.

In this study, we report on preparation, mechanical properties, and a microstructure of novel fly ash-based geopolymer (GP) composites that have been randomly reinforced with 0.25–1.0 wt% short-cut flax tows (FTs). It is established that if the amount of FTs in geopolymer has been increased, the flexural strength at a bend has also grown up to ~22%: from 4.0 MPa (unreinforced GP) to 4.9 MPa at addition of 1.0 wt% FTs. Unlike brittle GP matrices, GP/FTs composites show a plastic character of destruction and possess higher residual bearing capacity, preserving integrity without destruction after maximum mechanical influences. At the same time, FTs addition leads to deterioration of compressive and split tensile strengths. However, these drawbacks can be minimized by FTs pretreatment and surface modification for the purpose of removal of non-cellulosic components (waxes, hemicellulose, pectin, and lignin) and increase in interfacial adhesion of a matrix to flax fibers, and also by optimization of rheological properties of geopolymer paste.

The roadbed is the most deformable and most heterogeneous component of the railway track infrastructure, which state is the main factor determining the efficiency of the road, and the main cause of premature degradation of the path and the failure of its components, increasing the cost of current maintenance. In the face of the increasing dynamic impact of trains on the railway infrastructure resulting from intensive development of heavy haul transportation, this problem becomes particularly important. In this paper, an analysis is made of the problem of degradation and providing the stability of the track foundation with an increased axial load on the track, with a special emphasis on analysis of the excitation mechanisms of cyclic impacts and the process of their damping by the soil environment. The main types of deformations and defects are described; the mechanisms and reasons for their occurrence are analyzed. Much attention is paid to the analysis of soil degradation processes of the roadbed under the dynamic impact of heavy trains. Various elements of the roadbed are considered, which require reinforcement for operation under heavy haul traffic and large axial loads. The modern methods and structures of reinforcing the roadbed are described, the use of which allows to increase the efficiency of the heavy haul transportation. In conclusion, the authors identified areas of additional research to address the problem of ensuring the stability of the roadbed in the organization of heavy haul traffic.

To understand the nature of the bonding mechanism between poly(lactic acid) (PLA) and halloysite nanotubes (HNT), a first-principles DFT study was performed on the adsorption behavior of the PLA monomer, lactic acid (LA), on the outer, inner, and edge surfaces of the HNT. The role of LA functional groups, and its orientation behavior in the formation of bonds with HNT are systematically studied. Analysis of the adsorption energy, total and partial electron density of states (DOS), electric charge transfer between LA atoms and HNT mineral surfaces shows that van der Waals attraction governs their interaction. The calculations of the most stable adsorption configurations of LA show that the predominant number of hydrogen bonds is determined by the activity of the carboxyl functional group of LA on the hydroxylated surfaces of HNT. The important role of the –OH surface groups in the mechanism of lactic acid binding has been established; their absence on the external siloxane surface significantly reduces the LA affinity for HNT. The binding energy of lactic acid on the hydroxylated internal and edge surfaces of the HNT is much higher (by about 275%) than on the external siloxane surface. Mulliken population analysis showed that the formation of a hydrogen bond with the LA atomic groups leads to a more significant redistribution of charge on the inner and edge surfaces of the HNT in comparison with its outer surface. Van der Waals attraction between the LA and HNTs, as well as hydrogen bonds, is responsible for the formation of the bonding mechanism in halloysite nanotubes-PLA nanocomposite. Our results are in accord with available literature.

The samples of organic-modified clays based on a Wyoming SWy-2 sodium montmorillonite (Na+-Mt) with the cationic surfactant hydroxyethylalkyl imidazoline (HEAI) and the amphoteric surfactant oleylamidopropyl betaine (OAPB) were synthesized via a cation exchange process. The obtained materials were characterized using XRD analysis, ATR-FTIR spectroscopy, SEM, BET and Water contact angle measurements. The potential sites of binding of OAPB and HEAI to the mineral surface were determined by the DFT calculations. For the variants of the structure of the complex, DFT calculations is performed and the interaction energy of the surfactant and clay mineral is estimated.