Aggressive Substances Research Articles

Investigation of the Effect of Volumetric Hydrophobization on the Kinetics of Mass Transfer Processes Occurring in Cement Concretes during Corrosion.

The entry of aggressive substances into the pore structure of concrete causes the development of corrosion processes and leads to the destruction of the cement stone structure. Hydrophobic additives provide high density and low permeability and are an effective barrier to the penetration of aggressive substances into the structure of cement stone. To assess the contribution of hydrophobization to the durability of the structure, it is necessary to know how much the processes of corrosive mass transfer slow down. To study the properties, structure and composition of the materials studied in the work (solid and liquid phases) before and after exposure to liquid-aggressive media, experimental studies were carried out using chemical and physicochemical analysis methods: determination of density, water absorption, porosity, water absorption and strength of cement stone; differential thermal analysis; quantitative analysis of calcium cations in liquid medium by complexometric titration. The article presents the results of studies of the effect on the operational characteristics of the introduction of a hydrophobic additive of calcium stearate into the cement mixture at the stage of concrete production. The effectiveness of volumetric hydrophobization was evaluated to prevent the penetration of an aggressive chloride-containing medium into the pore structure of concrete destruction and the leaching of calcium-containing components of cement stone. It was found that the introduction of calcium stearate in an amount of 0.8-1.3% by weight of cement increases the service life of a concrete product during corrosion in liquid chloride-containing media with a high degree of aggressiveness by four times.

Citric Acid as an Alternative to Sulfuric Acid for Hard Anodizing in Aluminum Alloys Used in the Aeronautical Industry

In the aircraft industry, Al-Cu alloys are widely used as a structural material in the manufacture of commercial aircraft due to their high mechanical properties and low density. Al-Cu alloy have low resistance to corrosion in aggressive substances; as a result, these alloys are surface treated to increase their resistance to corrosion. Anodizing was done hard in aluminum alloy AA 2024 in a solution composed of citric and sulfuric acid for 60 minutes with constant agitation using current densities of 3 and 4.5 A/dm2. Afterwards, a sealing procedure was performed for 60 minutes in water at 95 °C. Scanning electron microscopy (SEM) was used to characterize the microstructure and Vickers microhardness (HV) as a mechanical test of the material. The electrochemical evaluation was carried out using cyclic potentiodynamic polarization curves (CPP). The results indicate that the corrosion resistance in citric acid solutions with a current density of 4.5 A/dm2 was the best, with corrosion current densities of 2 x 10-8 and 2 x 10-9 A/cm2.

New Materials and Technologies for Durability and Conservation of Building Heritage.

The increase in concrete structures' durability is a milestone to improve the sustainability of buildings and infrastructures. In order to ensure a prolonged service life, it is necessary to detect the deterioration of materials by means of monitoring systems aimed at evaluating not only the penetration of aggressive substances into concrete but also the corrosion of carbon-steel reinforcement. Therefore, proper data collection makes it possible to plan suitable restoration works which can be carried out with traditional or innovative techniques and materials. This work focuses on building heritage and it highlights the most recent findings for the conservation and restoration of reinforced concrete structures and masonry buildings.

Increasing the Biostability of Concrete by the Introduction Of Additives

To increase the resistance to fungal corrosion and improve the performance of concrete cement stone, it is proposed to introduce calcium stearate and active metal nitrates in an amount of 0.5% by weight of cement into the cement mixture at the manufacturing stage. To determine the degree of corrosion damage of cement stone by fungal microorganisms Aspergillus niger, porosity, density, water absorption and strength were determined. It has been found that the introduction of a hydrophobic additive of calcium stearate into the cement mixture during the manufacture of concrete reduces water absorption, reduces porosity and increases strength. Additives of nitrates of active metals do not affect the characteristics of the cement stone of concrete. As a result of 6 months of fungal corrosion, the water absorption, porosity and density of cement stone containing calcium stearate did not change, and the strength decreased by 4%. Metal nitrates do not prevent damage to the cement stone by microorganisms, but slow down the flow of aggressive substances to the surface of the reinforcement in concrete. The combined introduction of calcium stearate and nitrates into the cement mixture will improve the characteristics of concrete, increase its corrosion resistance and ensure the safety of reinforcement in concrete.

Self-healing concrete techniques and performance, A review

Modern society faces the duality of rapidly expanding structure, making concrete one of the world's most traded materials. However, cement manufacturing can pollute the environment by releasing approximately one tonne of CO2 for every tonne of cement produced. Concrete cracks can provide superior access for aggressive substances such as chlorides and sulfates, resulting in structural deterioration. So, to fix concrete cracks, different traditional methods were used, which use cement and some chemical agents that are hazardous to the environment. Because of the environmental issues and sustainability challenges associated with cement and concrete, it is preferable to reduce the amount of cement used by developing promising and unique solutions to enable quick crack healing in concrete and extend the structure's lifetime. Therefore, incorporating self-healing mechanisms into construction materials has been proposed to improve their performance and durability while reducing the need for maintenance and repair. This review assesses the performance and causes of autogenous and autonomous self-healing techniques. The autogenous technique occurs naturally due to inherent material properties, while the autonomous technique uses various healing agents, such as chemical or biological substances. Both techniques rely on forming calcium carbonate (CaCO3) crystals as the principal agent for concrete healing. Previous findings showed that the autogenous technique has limited efficacy in repairing larger cracks with a width exceeding 0.3mm. In contrast, autonomous techniques have shown successful repai of cracks exceeding 2mm in width. The application of an autonomous methodology in the field of concrete has resulted in significant results, such as effectively repairing large cracks, enhancing structural integrity, and substantially decreasing permeability levels from high to exceedingly low levels

Simulation of micro cracks introduced by environmental stress in amorphous plastics

Environmental stress crack resistance (ESCR) is a major problem especially for amorphous polymers. The interaction between aggressive substances and both mechanical external and residual stresses can lead to a fracture of the plastic part. In a previous study, a method was developed to measure the ESCR. The specimens are bent over a circular jig to introduce external stresses and a softener is applied as aggressive substance. After a certain time, the samples fracture giving a measure for the ESCR. In this study, this method is under further investigation using the example of acrylonitrile butadiene styrene. Before the sample fractures, there are several micro cracks visible on the surface. The growth of these micro cracks was measured by dye penetrant testing and the shape of the cracks was determined with computer tomographic measurements. From these measurements, artificial samples were constructed for a simulation. Through the simulation, the stresses in the samples were determined to get an insight into the failure mechanism of the samples. It has been shown that the number of the micro cracks in a sample is constant at all times even though there is a great variation in the number of cracks in the different samples. The cracks grow almost linearly with time. This means that all cracks initiate in one specimen at the same time and in the following phase these cracks grow while no more new cracks initiate. This can be explained by the simulation showing that the stress accumulates at the tips of the cracks and the tensile stress at the surface of the specimens decreases. These results were compared with the results from a stress relaxation test which also showed a decrease in the tensile stress at the surface with time, hence verifying the simulative results.

Autogenous self-healing of cracked concrete exposed to the marine tidal zone

The autogenous self-healing of cracks can reduce the risk of ingress of aggressive substances into concrete. Although autogenous self-healing mechanisms of concrete have been studied by simplified simulation experiments in the laboratory, few investigations have been carried out in the actual environment. This paper presents the autogenous self-healing mechanism of cracked concrete exposed to the marine tidal zone. The phases shown in the self-healing products were quantified by X-ray diffraction (XRD) and thermogravimetry-differential thermogravimetry (TG-DTG). The micromorphology of the self-healing products and elemental distribution in cracks were studied by SEM. The results show that the self-healing efficiency and composition of self-healing products are highly dependent on the crack width. For 50 and 100 μm cracks, the crack closure rate is 84% and 73%, respectively. Regarding 200 μm cracks, the average crack width is reduced, but partial self-healing of the crack is not observed. Cracks wider than 350 μm are increasingly enlarged due to spalling caused by the physical attack of ocean currents. Carbonization and rehydration are the main self-healing mechanisms of cracks more minor than 200 μm. Brucite is the main self-healing product in cracks larger than 350 μm. The micromorphology observation and quantitative analysis illustrate that seawater impurities are attached to the crack surface, which may hinder the crack self-healing.

Corrosion Resistance of Aluminum Alloy AA2024 with Hard Anodizing in Sulfuric Acid-Free Solution.

In the aeronautical industry, Al-Cu alloys are used as a structural material in the manufacturing of commercial aircraft due to their high mechanical properties and low density. One of the main issues with these Al-Cu alloy systems is their low corrosion resistance in aggressive substances; as a result, Al-Cu alloys are electrochemically treated by anodizing processes to increase their corrosion resistance. Hard anodizing realized on AA2024 was performed in citric and sulfuric acid solutions for 60 min with constant stirring using current densities 3 and 4.5 A/dm2. After anodizing, a 60 min sealing procedure in water at 95 °C was performed. Scanning electron microscopy (SEM) and Vickers microhardness (HV) measurements were used to characterize the microstructure and mechanical properties of the hard anodizing material. Electrochemical corrosion was carried out using cyclic potentiodynamic polarization curves (CPP) and electrochemical impedance spectroscopy (EIS) in a 3.5 wt. % NaCl solution. The results indicate that the corrosion resistance of Al-Cu alloys in citric acid solutions with a current density 4.5 A/dm2 was the best, with corrosion current densities of 2 × 10−8 and 2 × 10−9 A/cm2. Citric acid-anodized samples had a higher corrosion resistance than un-anodized materials, making citric acid a viable alternative for fabricating hard-anodized Al-Cu alloys.

Study of Effect of Reference Time of Chloride Diffusion Coefficient in Numerical Modelling of Durability of Concrete

The results of numerical calculations on the resistance of the reinforced concrete bridge deck to chlorides are compared with a different approach to the diffusion coefficient of the input parameter, and presented. The aim is to point out the necessity of a correct model adjustment in the case of using diffusion parameters obtained differently at different measurement times. The diffusion parameter, as a typical concrete material constant, was derived from electrical resistivity measurements and using the least-squares method from a direct chloride test. Due to the different times of obtaining the concrete parameters, a control calculation was performed, which showed that the numerical model for calculating the initiation of reinforcement corrosion in chloride-exposed reinforced concrete requires the application of not only a suitable diffusion parameter but also an adequate reference time. The article points out the need to use an adequate reference time introduced in the numerical calculation of the durability of reinforced concrete with respect to aggressive substances. The results show that the most appropriate reference time value is derived from the average measurement time related to the lifetime of the concrete.

Improvement of the durability of cement-based material through surface modification with nano-engineered releasing agents

• Modified releasing agent with NS/NT to make nano-engineered releasing agent. • NS and NT increased the contact angle of releasing agent and help their adhesion on mold. • Reduction of the surface porosity (within 2 mm thick). • Nano-engineered releasing agent can achieve durable concrete surface. Aggressive substances can gain access to the inner structure of cement-based materials through the surface, resulting in deterioration of the structure. This work developed an effective way of improving the quality of cement-based materials surface by applying nanoSiO 2 -/nanoTiO 2 -engineered releasing agents (nSRa/nTRa) on the formwork surface. Continued with our previous work, the positive effects of nSRa/nTRa on cement hydration were used to improve the surface quality of the cement-based samples through its spraying on the mold surface. This work firstly characterized the adhesive properties of these agents on mold surface (contact angle and viscosity measurement), and then their effects on the surface microstructure and the durability of cement-based materials such as 1) sulfate resistance, 2) chloride resistance, and 3) freeze–thaw resistance were determined. Results showed that nanoparticle addition increased the contact angle of releasing agents and helped their adhesion to mold. Applying nSRa/nTRa on cement-based samples benefited the reduction of surface porosity (within 2 mm thick) by 14.2 %, 19.4 %, 8.6 %, and 18.9 % in the nS2Ra-, nS4Ra-, nT4Ra- and nT16Ra-engineered samples. After 120 days of sulfate attack, mortar samples cast in Ra-, nS4Ra-, and nT16Ra-coated molds showed reductions in compressive strength loss of 1.57 %, 0.73 %, and 0.23 %. Noticeable reductions in the chloride migration coefficient of 23.9 % and 26.6 % were found in the nS4Ra-/nT16Ra-modified mortar sample, while their relative dynamic modulus elasticity was 6.72 % and 12 % higher than Ra-sample after 200 freeze–thaw cycles. This work proved that nano-engineered releasing agents can effectively improve the durability of the concrete structure.

The verification of the possibility of alkalis penetration from the surrounding environment into the concrete pavement slabs

The short material service life of concrete is currently a frequently discussed topic, especially for newly constructed roadways with cement concrete pavement. This early degradation of cement concrete pavement slabs is a major problem that threatens the service life of sub-sections or the entire road. As some partial results demonstrate, a possible cause of this degradation can be seen in the surrounding road environment, namely the possibility of transferring aggressive substances to the concrete pavement slab. This paper is concerned with the verification of the possibility of the penetration of alkalis penetration from the surrounding environment into the concrete pavement slab by simulating the effect of different external conditions and environments.

Autogenous self‐healing of concrete: Experimental design and test methodsA review

AbstractCracks in concrete structures can serve as pathways for aggressive chemical substances that can lead to a progressive deterioration of the cement stone as well as of the reinforcement, affecting the load capacity, service life and useability of concrete structures. However, concrete and reinforced concrete exhibit an intrinsic ability to heal cracks, defined as autogenous self‐healing. This effect includes the precipitation of calcium carbonate in the presence of water and CO2 and is accompanied by continued hydration, swelling, and mechanical blocking of the crack pathway. Experiments led to the inclusion of crack sealing by autogenous self‐healing in Eurocode 1992–3 for water retaining concrete structures. However, despite code restrictions, autogenous self‐healing of concrete shows limited effectiveness in practice. This indicates the need for further research to provide engineers with reliable design rules. Therefore, this study aims for giving a broad literature review on the state‐of‐the‐art knowledge on autogenous self‐healing, the boundary conditions, consensus, and controversy of processes and factors influencing the efficiency of autogenous self‐healing. Regarding the transferability of laboratory results to real concrete constructions, materials, crack initiation techniques, experimental concepts, and methods for assessing the effectiveness of autogenous self‐healing are discussed and recommendations for future experiments are set.

Cucumber (Cucumis sativus L.) Leaf Extract as a Green Corrosion Inhibitor for Carbon Steel in Acidic Solution: Electrochemical, Functional and Molecular Analysis.

An extract of cucumber leaves (ECSL) was prepared as a green corrosion inhibitor for carbon steel. Its carbon steel corrosion inhibition performance against 0.5 mol L−1 H2SO4 was investigated using electrochemical methods and scanning electron microscopy (SEM). Its composition was analyzed by gas chromatography and mass spectroscopy (GC−MS). Quantum chemical calculations and molecular dynamics simulations (MDS) were conducted to elucidate the adsorption mechanism of the inhibitor molecules on the carbon steel surface. The results indicated that the inhibition efficiency increases with its increasing concentration. The extract acted as a mixed type corrosion inhibitor, and its inhibition properties were ascribed to the geometric coverage effect induced by its adsorption on the metal surface in accordance with Langmuir’s law. The active components in the extract were identified as mainly organic compounds with functional groups such as aromatic moieties and heteroatoms. The inhibition activities of ECSL are delivered through the ability of the active components to adsorb on the metal surface through their functional groups to form a protective layer which hinders the contact of aggressive substances with carbon steel and thus suppresses its corrosion. This research provides an important reference for the design of green corrosion inhibitors based on plant waste materials.

Transport properties of 3D printed cementitious materials with prolonged time gap between successive layers

3D concrete printing is a promising additive manufacturing technique, integrated in construction industry to improve the geometrical complexity without expensive formworks. Due to the layered extrusion of the material, the porosity increases. This makes the component more prone to shrinkage and crack formation and increases the preferential ingress paths for aggressive substances. This can affect the durability and microstructure of the printed elements in a negative way. To assess the durability of 3D printed materials, three deterioration mechanisms (i.e. chloride ingress, carbonation and freeze/thaw) are investigated, considering different time gaps (i.e. 0 and 30 min) in between the layers and a comparison with traditional cast specimens was made. It was found that the resistance of 3D printed specimens against the penetration of chemical substances decreases with an increasing time gap. Compared with cast specimens, a higher saturated mass after frost attack could be observed in case of printed specimens.

Relationship of Time-Dependent Parameters from Destructive and Non-Destructive Tests of Structural Concrete

Reinforced concrete structures are typically exposed to a combination of aggressive substances and mechanical stresses, which contribute to fast degradation. The present research was conducted to evaluate five time-dependent parameters from several different tests, namely compressive strength, static modulus, dynamic modulus, surface, and bulk electrical resistance. Some parameters were obtained using destructive testing (DT) and some using non-destructive testing (NDT). Due to the correlation and calculation of regression curves, it was possible to compare the correlation of parameters important for estimating the durability of reinforced concrete structures in relation to degradation and corrosion. Concrete of C40/50 grade was examined in several time periods, and the parameter relationships were analysed. At the same time, a statistical evaluation was carried out, and therefore the study contains the average values and standard deviations of all measured parameters. The results show that the compressive strength and the electrical resistivity of the surface and bulk have a high correlation. In contrast, the dynamic modulus and electrical resistivity have low linear correlation, but it was possible to apply a quadratic curve with a high degree of fit. For the comparison of static elastic modulus and electrical resistance, the quality of the quadratic regression model was low but sufficient. The results show that, for structural concrete, the presented NDT methods can be used to estimate other parameters obtained from the DT methods.

Formation and Evolution of the Corrosion Scales on Super 13Cr Stainless Steel in a Formate Completion Fluid With Aggressive Substances

The formation and evolution of the corrosion scales on the super 13Cr stainless steel (SS) surface after exposure in a formate completion fluid with the presence of various aggressive substances was investigated. The results indicate that the formation of Fe3O4 covered the surface of super 13Cr SS as the inner layer accompanied with outer scattered FeS. The corrosion rate was below 0.07 mm/year after 120 h of exposure in the formate fluid at 180°C under N2 environments; the presence of aggressive substances such as sulfide and CO2 in the formate fluid promoted the proceeding of anodic dissolution in the early period, and the ingress of CO2 progressively increased the general corrosion rate to 1.7 mm/year. For CO2-containing conditions, the formation of FeCr2O4 and Cr(OH)3 was detected in the inner corrosion product layers, and the precipitation of “sheet”-shaped iron carbonate (FeCO3) was detected as the outer layer. The accumulation rate of corrosion products increases by two orders of magnitude with the ingress of CO2, corresponding to thicker corrosion products, but the dissolution rate is still three orders of magnitude higher than when CO2 was absent.

Sustainable ZTA composites produced by an advanced centrifugal slip casting method

The centrifugal slip casting method presented in the paper is used to form ceramic sleeves with a good shape representation, eliminating material losses in machining or other forms of mechanical treatment that could be necessary when other moulding methods with a poorer shape representation are used. Sleeves developed this way can be used as system components to transport aggressive substances under elevated pressure and temperature conditions. To confirm the functionality of the sleeves prepared with the method, Al2O3, ZrO2, and composite components of ZTA were characterised for acid-base behavior, phase composition, microstructure, and mechanical strength. The tests confirmed the formation of expected gradient structures for ZTA composites. It results in the generation of components with improved flexural and torsional strength compared to non-gradient ZTA composites with the same Al2O3 to ZrO2 ratio. Applying a smaller quantity of ZrO2 should bring a positive economic effect, considering its high price. The analysis of accompanying environmental impacts was carried out for developed materials along with the lifecycle analysis. The paper describes a reduced waste generation method for making components for aggressive substance transportation systems. The present paper presents characteristics of materials for their resistance to factors under working conditions, demonstrating their durability and potential to reduce waste related to the operation of such system types.

Идентификация тринитротолуола (TNT) в дальней ИК-области с помощью параметрического лазера

Computational and experimental studies of the amplitude-time and spectroscopic characteristics of an IR parametric laser based on mercury thiogallate with frequency tuning in the range from 5 to 9 mi-crons, an output energy of 10 MJ and a spectral emission width of ≤ 0,7 cm-1 have been carried out. A multifunctional IR parametric laser complex for remote detection and identification of atmospheric gases, including explosive and chemically aggressive substances in the range of electromagnetic wave-lengths from 1,41–9,07 microns, by differential absorption and dispersing has been developed, created and tested. The paper presents the results of computational and experimental studies on remote determination of spectroscopic characteristics of the most famous explosives TNT, RDX, PETN. It shows the possibility of highly sensitive determination of the concentration (~1 ppm) of explosives using a multifunctional optical system based on an IR parametric laser.

Processes and technologies of cold gas dynamic spraying of products agricultural equipment

Modern equipment of processing industry, animal husbandry, bioenergy complexes is used for processing, storage or transportation of aggressive substances. Functional coatings made of inert materials do not enter into any chemical reactions with food, processed products, livestock waste, acids and other aggressive media. There is a question of protection of the equipment of the processing industry, animal husbandry, bioenergy complexes from aggressive environments by application of processes of a cold gas-dynamic spraying. This is an urgent problem for the development of protective technologies and appropriate equipment for the implementation of the process of creating functional coatings

ZTA Pipes with a Gradient Structure-Effect of the Rheological the Behavior of Ceramic Suspensions on the Gradient Structure and Characterized of the Obtained Products.

This paper focuses on the verifying the possibility of producing Al2O3-ZrO2 composite pipes with a gradient structure using centrifugal slip casting method. The aim of the research is to define the correlation between the rheological properties of aqueous suspensions of ceramic powders with different solid loading and obtaining the ZrO2 phase gradient in the Al2O3 matrix. Such products, due to their unique properties, can be utilized in the transport of aggressive substances, even in extreme temperature or corrosive conditions. The suspensions and the sintered samples were characterized by: broad rheological analysis, scanning electron microscopy, X-ray diffraction, stereological analysis and Vickers hardness tests. The study reports on a series of samples produced of ceramic suspensions (70 vol.% Al2O3–30 vol.% ZrO2) differing in the total solid loading in the range of 30–55 vol.%. The results clearly indicate that obtaining the gradient structure of ceramic-ceramic composite pipes is closely related to the rheological properties of the suspensions from which the samples are cast. The phase gradient is obtainable from suspensions 30–40 vol.%, in which the possibility of moving ZrO2 particles relative to the Al2O3 is quite high—these suspensions are characterized by low viscosity and the dominance of viscous over elastic properties (G′ > G″).