Salt Attack Research Articles

Incorporation of Glass and Plastic Waste into Alkali-Activated Mill Residue Bricks

Recycling of glass and plastic waste has been increasingly attracting the attention of researchers worldwide. Relevant studies have been conducted to prove the feasibility of incorporating glass and plastic wastes into cement-based concrete and fired bricks. However, the high embedded energy and large carbon footprint of these materials have hindered the achievement of sustainable goals. Hence, this study attempts to diversify the recycling pathways for glass and plastic waste via a low carbon route. The brick clay mill residue has been used as a precursor to prepare alkali-activated bricks containing plastic and glass fines with a specific curing regime. The compressive strength, water absorption, linear shrinkage, and microstructure were investigated with varied content of glass and plastic content. The results showed that the maximum acceptable ratio of glass fines was around 55 wt.% for samples with the glass waste solely, achieving the compressive strength of 22 MPa. While foror samples incorporating plastic (PET) waste only, the maximum allowable ratio was only 2 wt.%, because excessive plastic resulted in the spalling of the sample surface. When both the glass and plastic waste were added to the samples, the maximum substitution ratio was 25 wt.% of glass and 2 wt.% of plastics. Scanning Electron Microscope images indicates that the plastic particles had more adverse effects on the microstructure of the alkali-activated samples than the glass particles. There was little or no bonding between plastic waste and alkali-activated mill residues. In contrast, the bonding between glass particles and alkali-activated mill residues was captured. The effect of the addition of glass and plastic samples on the durability of alkali-activated mill residue material needs to be further investigated, such as dimension stability, resistance to salt attack, freeze and thaw, and so on.

Assessing the interfacial corrosion mechanism of Inconel 617 in chloride molten salt corrosion using multi-modal advanced characterization techniques

The United States Department of Energy (DOE) has committed to expanding the domestic clean energy portfolio in response to the rising challenges of energy security in the wake of climate change. Accordingly, the construction of a series of Generation IV reactor technologies are being demonstrated, including sodium-cooled, small modular, and molten chloride fast reactors (MCFRs). To date, there are no fully qualified structural materials for constructing MCFRs. A number of commercial structural alloys have been considered for the construction of MCFRs, including alloys from the Inconel and Hastelloy series. Informed qualification of structural materials for the construction of MCFRs in the future can only be ensured by expanding the current fundamental knowledgebase of information pertaining to material performance under environmental stressors relevant to operation of the reactor, including corrosion susceptibility. The purpose of this investigation is to illustrate how a correlative multi-modal electron microscopy characterization approach, including the novel application of focused-ion beam 3D reconstruction capabilities, can elucidate the corrosion mechanism of a candidate structural material Inconel 617 for MCFR in NaCl-MgCl2 eutectic salt at 700°C for 1,000 h. Evidence of intergranular corrosion, Ni and Fe dealloying, and Cr-O enrichment along the grain boundary, which most likely corresponds to Cr2O3, is a phenomenon that has been documented in other Ni-based superalloys exposed to chloride molten salt systems. Additional corrosion products, including the formation of insoluble MgAl2O4, within the porous network produced by the salt attack is a novel observation. In addition, Mo3Si5 and τ2 precipitates are detected in the alloy bulk and are dissolved by the salt. Furthermore, the lack of detection of design γ′ precipitates in Inconel 617 after 1,000 h could indicate that the molten salt corrosion mechanism has indirectly induced a phase transformation of Al2TiNi (τ2) and Ni3(Al,Ti) (γ’) phase. This investigation provides a comprehensive understanding of molten salt corrosion mechanisms in a complex material system such as a commercial structural alloy for applications in MCFRs.

Thermal gradient mass transport corrosion in NaCl-MgCl2 and MgCl2-NaCl-KCl molten salts

A small scale natural circulation loop, or microloop , has been developed at TerraPower for the evaluation of material corrosion via thermal gradient mass transfer with molten chloride salts. Molten chloride salts are high temperature, low vapor pressure heat transfer fluids with applications in advanced nuclear, solar thermal power generation, and energy storage. As of now, forty nine loops have operated or are currently operating, accruing over nine flow–years of data with nine different commercially available alloys. Results indicate that only molybdenum is impervious to chloride salt attack, with extended circulations forming a molybdenum-rich corrosion microstructure in certain alloys. Out of the alloys tested, only three had corrosion results of less than 100 μ m yr −1 : alloy 600, alloy C-276, and alloy N. This report aims to discuss the design and operating characteristics of the microloop platform, while exploring thermal gradient mass transport corrosion results in NaCl-MgCl 2 and MgCl 2 -NaCl-KCl eutectics—two typical chloride salts of interest.

Mass transport properties of recycled aggregate concrete under coupling the action of chloride salt attack and uniaxial tensile loading

Water and chloride permeability are two important parameters for the evaluation of recycled aggregate concrete (RAC) durability. In service, the tensile loading plays an extremely important role in the generation and propagation of microcracks inside the RAC. Thus, aiming at understanding the mass transport properties of RAC under the coupled action of chloride salt attack and uniaxial sustained tensile loading, an improved experimental set-up was self-designed. And then a series of tests involving the effects of different uniaxial sustained tensile stress levels (10%, 30% and 50% of ultimate tensile stress, namely λt = 0.1, 0.3 and 0.5) and different replacement ratios of recycled coarse aggregate (RCA) (0, 30%, 50% and 100% mass replacement of normal coarse aggregate, namely R0, R30, R50 and R100) on the transport properties of RAC were conducted, and their coupling effects were further analyzed. Generally, the results indicate that both the sorptivity and chloride diffusion coefficient of RAC increase with the increase of RCA replacement ratio and tensile stress level. The synergistic effect of RCAs and tensile stress significantly accelerates the process of water and chloride invasion into concrete. The initial sorptivity of R100 specimens at λt = 0.5 was about 4.44 times that of R0 specimens without loading. Moreover, the chloride diffusion coefficient exhibits a linear relationship with the RCA content, while it has a quadratic relationship with the tensile stress level.

Diffusion resisting performance of concrete modified with sodium methyl silicate in saline soil area

• A new type of concrete mixed 2.4% sodium methyl silicate was prepared. • An instantaneous diffusion model of chloride ions in concrete was proposed. • The diffusion reducing performance of the new concrete were compared against ordinary concrete. • A useful means for the corrosion resistance of tunnel lining was proposed. Concrete of tunnel lining in saline soil area is subjected to compound salt attacks, which decrease the service life of tunnel. In this study, a new type of concrete mixed 2.4 % sodium methyl silicate was prepared to improve the compound salt damage resistance of concrete. The properties of the concrete, including chloride diffusion resisting performance, compressive strength, and water absorption, were investigated. The results showed that the chloride diffusion resisting performance of the concrete modified with methyl sodium silicate was notably better than that of normal concrete in compound salt solution. The maximum compressive strength had not changed significantly compared with normal concrete, while the occurrence of peak strength was delayed by about 30 days. The water absorption of the concrete modified with sodium methyl silicate was reduced by 21.09 % compared with the normal concrete. Moreover, chloride diffusion resisting mechanism of the concrete immersed in compound salt solution was elucidated. Furthermore, based on the Fick’s second law and experimental results, a time-varying diffusion model for predicting the chloride ion mass fraction of chloride in the concrete was proposed in this paper. The proposed approach is a useful means for the chloride diffusion resisting of concrete in some saline soil area of Western China.

Effect of halophilic bacteria on reducing chloride-ion concentration in mortars

• A new biological mortar was developed to enhance the salt damage resistance. • Halophilic bacteria were used for decomposing chloride compounds in concrete. • Halomonas venusta is favorable for reducing the chloride-ion concentration. • We confirmed that the activity of bacteria in the hardened cement matrix. • We verified the potential of the developed mortar as a biomimetic material. The present pioneering study examines the significance and limitations of biological mortars originally developed to enhance the salt damage resistance of concrete. Three strains of halophilic bacterium are isolated considering the decomposition mechanism of bacteria for chloride compounds in the cement matrix, thereby reducing the chloride ion concentration in the mortar. Test results showed that Halomonas venusta exhibited a good potential in reducing the chloride-ion concentration in mortars exposed to salt attacks, indicating a lower chloride-ion diffusion coefficient and lower amounts of Friedel’s salt by consuming the chloride ions as an energy source for its activity and growth.

Influence of chlorides and salt concentration on salt crystallization damage of cement-based materials

Durability of concrete exposed to physical salt attack (PSA) has primarily been studied on specimens partially submerged in sulfate solution. However, in sulfate-containing soils, chlorides are often present. The aim of this study is to investigate the influence of salt concentration and the presence of chlorides on the deterioration of cement-based materials caused by PSA. Cement mortars partially submerged in three different concentrations of sodium sulfate solutions (5%, 9% and 13%) and two mixed Na2SO4–NaCl solutions (5%–2% and 5%–5%) and exposed to cyclic drying-wetting were investigated. The crystallization behavior of salt solutions and the alteration in the macroscopic properties and microstructure of the specimens were observed to understand the differences in deterioration. The results showed that the presence of chloride ions significantly reduced the surface scaling above the solution level. Microstructural characterization suggested that thenardite tended to precipitate homogeneously in the specimens partially submerged in solutions containing chlorides. Consequently, crystallization pressure is less likely to develop in such a case. On the contrary, for the specimens partially submerged in pure sodium sulfate solutions, a higher concentration of salt solution facilitated more thenardite accumulation in a thin layer beneath the surfaces, which in turn accelerated the damage process. The findings may improve guidance on the evaluation of concrete resistance to PSA when chlorides are detected in sulfate-bearing environments.

Effect of Temperature on the Physical Salt Attack of Cement Mortars under Repeated Partial Immersion in Sodium Sulfate Solution.

Physical salt attack (PSA) is one of the dominant durability issues of cement-based materials, where salt crystallization pressure is the driving force inducing damage. However, research on the temperature-related deterioration behavior of cement-based materials is limited. In this study, salt-contaminated cement mortars were rewetted at different temperatures. The assessment criteria were based on the visual appearance, weight evolution and size distribution of scaled materials, and the alterations in the microstructure were investigated by microscopy, thermal and mineralogical analyses. The results indicated that more severe damage developed at 5 °C than that at 20 °C due to the greater crystallization pressure caused by the conversion from thenardite (Na2SO4) to mirabilite (Na2SO4·10H2O) at the lower temperature. No damage was observed at 35 °C, since the repeated dissolution and re-crystallization of thenardite were harmless for the specimens. In addition, two distinct damage patterns were observed for PSA performed at 5 °C and 20 °C, namely, granular disintegration and contour scaling.

Synergistic action of chloride and sulfate ions on the mechanical properties of cement-based materials by the experimental and molecular dynamics study

The effects of chloride content on the mechanical properties and erosion mechanism of sulfate eroded cement-based materials were studied by experiment and molecular simulation. The experimental results show that the compressive strength and flexural strength of cement-based materials first increase and then decrease with the increase of chloride salt concentration. Although the experiment generally indicated that salts affect the mechanical properties of cement-based materials, the reaction mechanism in nanoscopic is still unclarified. Here, we supplied a molecular insight into the reaction of salt attack gel products (CSH) through the reaction molecular dynamics simulation. Uniaxial tensile tests were carried out on CSH gel in Interchain, chain, and Inter-sheet chain directions, respectively. The simulation results show that the chloride salt concentration shows an interesting barrel effect on the three-direction uniaxial tensile results of the sulfate attack CSH. Moreover, chloride ions break the silicon chain, and then the silicon chain re-chain from another direction in process of stretching. The uniaxial tensile results of molecular simulation are consistent with the experimental results.

Salt weathering impact on Nero/Ramses II Temple at El-Ashmonein archaeological site (Hermopolis Magna), Egypt

Nero’s Temple at El-Ashmonein archaeological site, in Minia (middle of Egypt), is considered one of the most important of all temples of Nero. This temple dates back to 1520 BC–1075 BC in the New Kingdom and was reused in the era of Nero (the Fifth Emperor of Rome). The temple construction materials are severely decayed from surrounding environmental impacts, especially contaminated water sources. The main objective of this paper is to identify the construction materials of Nero’s Temple and their decay by-products. To achieve them, X-ray diffraction, micro X-ray fluorescence spectrometry, and portable Raman spectroscopy were utilized to identify the compositions and alteration by-products/degradation compounds (mainly saline efflorescence and crusts) from the construction materials, such as limestone walls, and structural mortars of the temple. In addition, a polarizing microscope was used to identify the minerals inside the construction materials and reveal the alteration of the minerals because of decay. Digital microscopy and scanning electron microscopy with EDS were used to detect decayed materials' morphological features. Finally, results showed that the main decay factor is salt attack (chlorides, sulfates, phosphates, nitrates, carbonates, and bicarbonates) for all architectural and structural elements of the temple, which have been carried to the construction materials from various sources of contaminated water (canal, sewage, and agricultural water).Graphical

Thermodynamic modeling of the phase evolution in alkali‐activated slag cements with sulfate salt exposure

AbstractThe phase evolutions in sodium hydroxide and sodium silicate–activated slag cements upon sulfate salt attack were investigated via thermodynamic modeling. The effects of different sulfate salts (i.e., Na2SO4 and MgSO4) and slag compositions were studied. In thermodynamic modeling, a solid solution model, that is, MgAl–SO4–LDH_ss, was proposed to describe the sulfate‐intercalated hydrotalcite. The modeling results were presented and discussed in comparison with experimental observations. Upon sulfate salt attack, ettringite, gypsum, sulfate‐intercalated hydrotalcite, magnesium silicate hydrate, and so on were predicted to form. By quantitatively evaluating the composition change of C–(N–)A–S–H gel, solid phase expansion, and alteration in pore solution chemistry, it was found that magnesium sulfate induced severer degradation of alkali‐activated slag cements compared to sodium sulfate. Upon sulfate salt attack with a fixed sulfate concentration, the ideal outcome shows that the slag with lower Al2O3 content not only gave a larger content of C–(N–)A–S–H gel but also caused the reduced decalcification and dealumination of C–(N–)A–S–H gel and solid phase expansion.

The role of nano-modified coverings against salt attack

The penetration of chloride and sulfate salts can cause detrimental damage in historic structures. Porous building materials that are usually engaged in such structures are susceptible to penetration of water that also permits the penetration of diluted salts. Coverings have been traditionally used as protective layers in such structures. In the present study, the performance of nano-modified, lime-based layers that can have a protective role against salt penetration, is evaluated. Lime pastes with nano-alumina (NA) and combination of NA and nano-calcium oxide (NC), as well as lime-pozzolan pastes with nano-silica (NS) and NA-NC combination were produced. The nano-modified materials were applied on ceramic bricks and the systems’ performance was evaluated by capillarity test, freeze-thaw cycles and resistance against salt penetration. NA improved the chloride absorbing ability of lime-based sacrificial layer and both NS and NA-NC combination improved the sulfate absorbing ability in lime-pozzolan based sacrificial layers. Additionally, the freeze-thaw cycles (from −10 °C to 40 °C) revealed that NA prevents expansion and spalling of the lime-based layers and that NA-NC combination offers durability and higher sulfate absorption ability to lime-pozzolan covering.

Reliability of the damage rating index to assess the condition of concrete affected by external sulfate attack

The damage rating index (DRI) has proven to be a quite reliable microscopic technique enabling the condition assessment of concrete affected by internal swelling reactions. Yet, very little research has been conducted on the use of the DRI to appraise induced deterioration caused by physical salt attack (PSA) and external sulfate attack (ESA). This study aims to assess the condition of concrete subjected to different salt solutions (i.e. sodium sulfate (Na2SO4), sodium chloride (NaCl), seawater and limewater), and exposure conditions (i.e. partially and fully immersed) through the DRI. Concrete specimens displaying two distinct water/cement ratios (i.e. 0.45 and 0.65) were manufactured and exposed to the above salt solutions for 12 months. Then, the samples were removed from the exposure conditions and prepared for microscopic analysis. The DRI was shown to be an effective technique to assess the condition of PSA- and ESA-affected concrete since different degrees of damage and features were captured for the various exposure conditions studied.

Acoustic emission signal processing for the assessment of corrosion behaviour in additively manufactured AlSi10Mg

Acoustic Emission (AE) technique is used for characterizing the corrosion behaviour of the AlSi10Mg specimens prepared from recycled feed-material using the Selective Laser Melting (SLM) Process. The corrosion behaviour is studied by exposing the specimens to a simulated salt attack for a period of 240 h. AE signals are recorded for the entire duration and are analysed in their time-frequency domain. Initially, noises are observed in the recorded AE signals. A methodology based on waveform entropy is developed to denoise the signals. The characteristics of the noise are studied to retain any useful information. The results show that some of the low amplitude signals could be misidentified as noise signals; it is rectified by studying the features of the noise such as peak frequency, frequency centroid and peak amplitude. The time-frequency characteristics of the AE signals are then studied along with the morphological features of the specimens exposed to different stages of corrosion. This provides a correlation between the corrosion behaviour such as pit formation, corrosion product formation and the corrosion crack formation and the time-frequency characteristics of AE signals. This information can identify the corrosion behaviour of the AlSi10Mg specimens intuitively.

Performance of repaired concrete piles partially embedded in Sulfate-Bearing soil

Physical salt attack (PSA) is a key damage mechanism of concrete in salt-bearing environments. Multiple case studies were reported throughout literature on PSA of concrete; yet, without any case on the performance of repaired concrete elements. The current paper presents a case study analyzing the condition of repaired concrete piles in 47-year-old administrative building in Winnipeg, MB, Canada, after 22 years from repair works. Deterioration of the concrete piles was visually observed above the ground level and repair zones, in the form of scaling, crumbling and reduction of cross section. In addition to fluid transport and pore structural features tests, mineralogical, thermal and microscopy analyses were performed on concrete chunks/cores extracted from the piles to elucidate the underlying mechanisms of damage. The repair concrete was capable of mitigating chemical and physical sulfate attacks; however, it could not stop the progress of PSA on the concrete above it, urging for careful design of repair strategies for elements subjected to PSA. Recommendations for future repair in this case are also presented.

Durability of Stainless-Steel Reinforced Grout against Salt Attack

Steel reinforced grout is one of the most effective mortar-based composites for the strengthening of masonry structures. Nonetheless, the deterioration of steel cords, especially when embedded in lime-based matrices, may compromise the long-term effectiveness of the strengthening systems. The use of stainless-steel may overcome this drawback, but it has received limited attention so far, since its higher cost makes it less competitive in the market. This work presents a laboratory investigation on the durability of stainless-steel reinforced grout against salt attack, which is the most severe aging condition. Tensile tests were carried out on bare textiles and composite specimens before and after aging in substitute ocean water for up to 5000 hours. Bent textiles, which are required by a number of structural applications, were aged and tested as well. Test outcomes indicate that this technology may be successfully used for the life-span strengthening of the built heritage.

Geopolymer Concrete: A Material for Sustainable Development in Indian Construction Industries

Geopolymer concrete (GPC) is a new material in the construction industry, with different chemical compositions and reactions involved in a binding material. The pozzolanic materials (industrial waste like fly ash, ground granulated blast furnace slag (GGBFS), and rice husk ash), which contain high silica and alumina, work as binding materials in the mix. Geopolymer concrete is economical, low energy consumption, thermally stable, easily workable, eco-friendly, cementless, and durable. GPC reduces carbon footprints by using industrial solid waste like slag, fly ash, and rice husk ash. Around one tonne of carbon dioxide emissions produced one tonne of cement that directly polluted the environment and increased the world’s temperature by increasing greenhouse gas production. For sustainable construction, GPC reduces the use of cement and finds the alternative of cement for the material’s binding property. So, the geopolymer concrete is an alternative to Portland cement concrete and it is a potential material having large commercial value and for sustainable development in Indian construction industries. The comprehensive survey of the literature shows that geopolymer concrete is a perfect alternative to Portland cement concrete because it has better physical, mechanical, and durable properties. Geopolymer concrete is highly resistant to acid, sulphate, and salt attack. Geopolymer concrete plays a vital role in the construction industry through its use in bridge construction, high-rise buildings, highways, tunnels, dams, and hydraulic structures, because of its high performance. It can be concluded from the review that sustainable development is achieved by employing geopolymers in Indian construction industries, because it results in lower CO2 emissions, optimum utilization of natural resources, utilization of waste materials, is more cost-effective in long life infrastructure construction, and, socially, in financial benefits and employment generation.

Modelling and Optimizing the Durability Performance of Self Consolidating Concrete Incorporating Crumb Rubber and Calcium Carbide Residue Using Response Surface Methodology

The world is now focusing on a sustainable environment and reducing the effects of global warming. One way to achieve such targets is to properly utilize waste and reduce greenhouse CO2 emissions. The cement industry is responsible for almost 10% of global CO2 emission due to the high demand for cement in the construction industry. One of the ways to minimize this effect is the partial replacement of cement by other materials in concrete. Therefore, in this study, calcium carbide residue (CCR), which is highly rich in calcium oxide, partially replaced cement for waste management. Waste tires were grinded to fine sizes in crumb rubber (CR) and partially replaced the fine aggregate. Therefore, this paper investigared the influence of CR and CCR on the durability properties and heat/temperature resistance of self-compacting concrete (SCC). The experiment was designed using response surface methodology to investigate the effects of CR and CCR on SCC properties, design models for properties of the SCC, and optimize the mixes to achieve the best results. The properties considered were the durability of acid attack resistance (H2SO4 attack), salt attack resistance (MgSO4 attack), and water absorption. The heat resistance considered was weight reduction and residual compressive strength after heating the samples at a 200 °C and 400 °C. The results findings showed that CR and CCR negatively affect the acid and salt resistance of the SCC. Furthermore, CR negatively affects the heat resistance of the SCC, while CCR slightly improved it at 200 °C. The models developed using RSM were significant with high degrees of correlation and predictability. The optimum properties achieved 2.9% CR as a fine aggregate replacement and 5.5% CCR as a cement replacement. The developed models can predict the durability performance of SCC mixes in terms of acid and salt attack resistance and the effects of elevated temperatures using CR, CCR, and fly ash as the variables. This will reduce the need for carrying out experimental work, thereby reducing cost and time.

Damage mechanism of pier concrete subjected to combined compressive stress, freeze-thaw, and salt attacks in saline soil

This study experimentally investigates the damage mechanism of pier concrete under the combined action of axial compressive stress (CS), freeze–thaw (FT) cycles, and salt attacks (SA). An indoor accelerated corrosion test of pier concrete under the combined action of CS, FT, and SA was conducted based on field investigations of concrete corrosion of piers in the saline soil of Xinjiang province in China. The experimental results of macro and micro analyses showed that the durability degradation of the pier concrete could be attributed to the damage to the cement slurry, aggregates, interface areas, and pore structure. A new delamination damage model was established to describe the mechanism of the combined damage, including the deterioration of the mortar layer, the generation of microcracks in the interface zone, the deposition of corrosion products, and crack development. The quantitative assessment of the durability degradation of the pier concrete was more accurate when the mass loss (ML) and relative dynamic elastic modulus (RDEM) were considered. These unique findings provide an important reference for the design and durability evaluation of pier concrete in saline soils.

Microstructure Study for Effect of Local Admixture in Concrete Durability

Concrete permeability plays the main role in concrete durability because of the entry of harmful substances such as chlorides, sulfates, carbon dioxide (CO2), oxygen (O2). Concrete permeability is affected by factors such as size and proportion of aggregate, type, and quantity of cement, water-cement ratio, type and dose of admixture used, which help concrete have a high life. This research aims to investigate the effect of local admixture prepared to improve concrete properties, especially reducing the permeability of concrete using its proven effectiveness in salt attack. This research studies the effect of this admixture on concrete microstructure for several concrete specimens. This chemical admixture, which contains calcium oxide (CaO), chloride (Cl), and others, helps obtain a good performance of concrete. Adding calcium oxide (CaO) plays an important role in improving the physicochemical properties of concrete. An increase in the compressive strength was observed for all specimens. Incorporating additives without CaO to concrete has been shown to decrease its strength. In the present study, concrete showed higher compressive strength than other concrete, which has not contain this admixture which may be explained by the larger quantity of CaO in the cement.