Salt Attack Research Articles

Automated estimation of cementitious sorptivity via computer vision.

Monitoring water uptake in cementitious systems is crucial to assess their durability against corrosion, salt attack, and freeze-thaw damage. However, gauging absorption currently relies on labor-intensive and infrequent weight measurements, as outlined in ASTM C1585. To address this issue, we introduce a custom computer vision model trained on 6234 images, consisting of 4000 real and 2234 synthetic, that automatically detects the water level in prismatic samples absorbing water. This model provides accurate and frequent estimations of water penetration values every minute. After training the model on 1440 unique data points, including 15 paste mixtures with varying water-to-cement ratios from 0.4 to 0.8 and curing periods of 1 to 7 days, we can now predict initial and secondary sorptivities in real time with high confidence, achieving R² > 0.9. Finally, we demonstrate its application on mortar and concrete systems, opening a pathway toward low-cost and automated durability assessment of construction materials.

Ceramic matrix composites for corrosion-resistant next-generation nuclear reactor systems: A conceptual review of enhancements in durability against molten salt attack

Ceramic matrix composites (CMCs) are emerging as a key material class for enhancing corrosion resistance in next-generation nuclear reactor systems, particularly in high-temperature molten salt environments. These environments, critical for advanced nuclear reactors such as molten salt reactors (MSRs), present severe challenges, including aggressive chemical attacks that degrade traditional structural materials over time. This conceptual review explores the development and application of CMCs to improve the durability and corrosion resistance of nuclear reactors exposed to molten salt attacks. CMCs, which consist of ceramic fibers embedded in a ceramic matrix, offer significant advantages, such as high thermal stability, mechanical strength, and improved corrosion resistance compared to conventional materials. This review examines how CMCs can be tailored to withstand harsh operational conditions, with a focus on the selection of ceramic phases, fiber-matrix interactions, and innovative fabrication techniques that enhance their protective capabilities. Key challenges addressed include the optimization of composite design to resist molten salt corrosion, the effects of temperature on the material properties, and the long-term stability of CMCs under extreme conditions. Advances in surface treatments, coatings, and the development of hybrid CMC systems are also discussed, highlighting their potential to further enhance durability. The review outlines the use of advanced characterization techniques, such as high-temperature corrosion testing and in situ microscopy, to evaluate CMC performance in molten salt environments. Additionally, it identifies knowledge gaps in current research, emphasizing the need for long-term studies on CMC behavior under realistic reactor conditions. This review concludes by proposing future research directions and technological advancements required to integrate CMCs into next-generation nuclear reactor designs, aiming to improve system reliability and operational safety.

Tensile Performance and Aging Increase Factor Constitutive Model of High-Strength Engineered Cementitious Composites under Sulfate Salt Attack

This study investigates the uniaxial tensile behavior of high-strength engineered cementitious composites (HS-ECCs) in sulfate erosion environments. Five different sulfate erosion ages were established (0 days, 30 days, 60 days, 90 days, and 120 days), and the development of the macro-mechanical properties of HS-ECCs was revealed from a microscopic perspective using scanning electron microscopy (SEM). The results indicate that, under the influence of sulfate erosion, the strength of HS-ECCs exhibits a trend of initial increase followed by a decrease, while ductility shows a continuous decline. This phenomenon is primarily attributed to changes in the microstructure and reaction products. Based on the test results, an aging growth factor was introduced to fit the stress–strain curve, demonstrating that the model can effectively predict the tensile performance of HS-ECCs with greater accuracy compared to traditional models. This study not only provides data references for the engineering application of HS-ECCs in sulfate environments but also offers a novel approach for constructing predictive models in other environmental contexts.

Time-Variant Chloride Ingress Models for Probabilistic Assessment of Concrete Bridge Decks with De-Icing Salt Attack

This study is to propose time-variant probabilistic models of surface chloride and diffusion coefficient based on the survey data of 16 concrete bridge decks with the attack of de-icing salts. These models are developed, because there is no study that simultaneously considers both time-variance and probabilistic descriptors in the model for concrete bridge decks. From the study, it can be found that long-term surface chloride and its time-variant development are fitted with Log-normal and Weibull distributions, respectively. In addition, the 28-day diffusion coefficient and age factor are fitted with Log-logistic and Triangular distributions, respectively. Considering only the mean value in the models, the corrosion-free residual life of concrete bridge decks is equal to 18.3 years based on the target value of critical chloride of 1.2 kg/m3, whereas their cracking-free residual life is equal to 29.5 years based on the target value of critical chloride of 2.0 kg/m3. In comparison with the probabilistic analysis, it was nevertheless found that at year 18.3, there are 38% and 20% probabilities to have rebar corrosion and concrete cracking, respectively. However, at year 29.5, there are 63% and 42% probabilities to have rebar corrosion and concrete. Specifically, there are 6 and almost 7 out of 16 bridge locations having rebar corrosion in the year 18.3 and concrete cracking in the year 29.5, respectively.

The effect of pH and carbonation on the partially immersed mortar exposed to physical salt attack

In saline-alkali or salt-lake areas, the influence of pH value of underground aqueous solution and carbonation on the deterioration of cement-based materials remains an open question. This study utilizes various techniques to investigate the physical properties and degradation mechanism of partially immersed mortar incorporated with different dosages of fly ash exposed to combined action of salt solutions (10 wt% Na2SO4, 3.5 wt% NaCl + 10 wt% Na2SO4, and tap water) at different pH values (pH 5, 7, and 9) and carbonation (accelerated carbonation: 20 vol% CO2 and natural carbonation: 0.035 vol% CO2). The results indicate that the degree of deterioration of mortar increases with dosage of fly ash and pH value of salt solution, with the maximum mass loss exceeding 25 %. Physical sulfate attack (PSA) is responsible for the partially immersed mortar exposed to combined action of salt attack at various pH values and natural carbonation. However, when carbonation is accelerated, a more severe deterioration occurs, with the durability time of mortar reduced by nearly 60 %. PSA and decomposition of C-S-H are mainly responsible for the deterioration of mortar, while the formation of thaumasite and natrite is partially responsible for the deterioration of mortar. The presence of NaCl in mixed salt solution inhibits the precipitation of Na2SO4 crystals; the precipitation of NaCl clogs the pore network of mortar, which impedes the progressive penetration of CO2. The presence of NaCl in mixed salt solution is beneficial to salt resistance and carbonation resistance of mortar.

An Electrochemical Phase Field Model Applied to Molten Salt Dealloying Corrosion of Ni-Alloys

Metal alloys in contact with molten salts are known to corrode via a dealloying process, wherein the less-noble alloy elements (e.g. Cr) are selectively oxidized and dissolved, leaving behind a corroded structure that is enriched in the more-noble elements (e.g. Ni). In some cases, this can lead to molten salt infiltration into the alloy through discrete channels along specific microstructural features (e.g. grain boundaries). However, in other cases the dealloying process promotes a more full-scale attack of the alloy, generating a fine-scale ligament structure. This process can severely degrade the alloy’s structural integrity, which limits the practicality of these material systems in otherwise promising applications (e.g. molten salt-cooled power reactors).The thermokinetic conditions for dealloying corrosion depend on the salt chemistry and the metal microstructure, which together inform the reaction process occurring at their interface. The salt chemistry and oxidant content set the electrochemical potential for selective oxidation of the less-noble elements. The associated oxidation rate is expected to depend on the presence of an interfacial structure (e.g. double layer) and also on the transport rates of reactants towards the interface (e.g. species diffusion in the metal and oxidizer transport in the salt) and reaction products away from the interface (cation transport in the salt). The corrosion rate and morphology will also depend strongly on the rate of transport laterally along the metal-salt interface, since the reorganization of the more-noble species (Ni) towards ligament formation facilitates the attack of the alloy by the corrosive agent. It has been hypothesized that molten salts enhance this rate of solute diffusion along the metal interface.In this work, we propose an electrochemical phase field model to predict the microstructural evolution of model Ni-alloys undergoing dealloying corrosion in molten fluoride salts. The model incorporates metal oxidation and dissolution via experimentally determined redox potentials and activity coefficients for metal species in the molten salt. We show that the corrosion rate and development of pores is strongly dependent on solute transport rates within the metal and also along their solid-liquid interface. In particular, we reveal a mechanism in which grain boundaries couple with the solid-liquid corrosion front to promote rapid dealloying and molten salt attack. Oxidant content in the salt and double-layer formation at the interface are discussed for their roles in setting the electrochemical potential and reaction rate at the metal-salt interface. Finally, we discuss how the model leverages insights from atomistic modeling and highlight key knowledge gaps in the mesoscale modeling of electrochemical molten salt corrosion.

Mechanical and microstructural properties of biogenic CaCO3 deposition (MICP) on a specific volcanic sediment (unwelded Tuffs) by Bacillus pasteurii and Bacillus subtilis

Microbially induced calcite precipitation has garnered significant attention in recent years as a promising and environmentally friendly process for addressing sand stabilization and soil consolidation. While its potential to stabilize sand dunes and mitigate soil liquefaction is well-documented, the applicability of MICP in the consolidation of stone materials has not been thoroughly investigated. Tuffs, which are silicate-laden pyroclasts, have historical significance as hybrid materials for cement, emphasizing their importance in cultural heritage. In previous MICP applications, there has been a lack of exploration regarding the incorporation of urease-producing bacteria (UPB) into Tuffs. Consequently, the potential of MICP in substrates such as Tuffs has been largely overlooked. The primary objective of this study is to assess the feasibility of incorporating UPB into Tuffs as a consolidating agent to facilitate calcium carbonate precipitation. We aim to investigate the microstructure of the resulting polymorphs and the previously unknown mechanism of increased resistance to W-D cycles in the treated samples at the nanoscale. In this study, we compared the cementation response of Tuff when subjected to two different UPBs by evaluating changes in key parameters, including capillary water absorption (CWA), cyclic tests such as wet-dry and salt attack, and uniaxial compressive strength. Furthermore, the characteristics of crust formation were examined using FESEM, and an in-depth analysis of the microstructure of the deposited bacterial CaCO3 was conducted. The mechanism of increased W-D resistance in Tuffs reinforced by MICP has not been previously addressed by researchers. Our study demonstrated that the increase in resistance to W-D cycles was more pronounced in samples treated with Bacillus pasteurii. Further FESEM analysis showed the presence of Bacillus pasteurii spores in the nanopores of the (W-D) exposed samples. N2 adsorption analysis revealed that nanopore alteration occurred only in samples treated with Bacillus pasteurii. Additionally, Tuffs are prone to disjoining pressure, which occurs in nanopores. Based on these observations, we postulate that the increased resistance to W-D cycles in the samples treated with Bacillus pasteurii was caused by a decrease in disjoining pressure due to the recrystallization of amorphous calcium carbonate (ACC) in the nanopores of the studied Tuff.

Influence of temperature on hot corrosion behavior of GH4169 superalloy subjected to Na2SO4–NaCl salts attack

This work studies the hot corrosion behavior of GH4169 Ni-based superalloy, deposited with a mixture of salts comprising 95 wt% Na2SO4 and 5 wt% NaCl, across three distinct temperatures (i.e., 650 °C, 800 °C and 950 °C). Corrosion and non-corrosive exposure experiments were compared, yielding data on mass loss and gain, respectively. Material characterization results revealed that the corrosion layer was mainly comprised of Cr2O3, Fe2O3, NiO, Al2O3, TiO2, NbS2 and MoS2. Notably, as the temperature ascended from 650 °C to over 800 °C, the corrosion mechanisms underwent a transition from pitting to uniform corrosion, corresponding to low-temperature hot corrosion and high-temperature hot corrosion, respectively. At 650 °C, a large number of semi-ellipsoidal corrosion pits manifested on the surface. Conversely, at 800 °C and 950 °C, the corrosion layer on the surface exhibited nearly uniform spallation. The pit growth model and spallation dynamics model were, respectively, developed based on the observed microstructure features. The models serve as tools for quantitative examination of the hot corrosion process of the superalloy at different temperatures.

Bond Strength Evaluation of FRP–Concrete Interfaces Affected by Hygrothermal and Salt Attack Using Improved Meta-Learning Neural Network

Fiber-reinforced polymer (FRP) laminates are popular in the strengthening of concrete structures, but the durability of the strengthened structures is of great concern. Due to the susceptibility of the epoxy resin used for bonding and the deterioration of materials, the bond performance of the FRP–concrete interface could be degraded due to environmental exposure. This paper aimed to establish a data-driven method for bond strength prediction using existing test results. Therefore, a method composed of a Back Prorogation Net (BPNN) and Meta-learning Net was proposed, which can be used to solve the implicit regression problems in few-shot learning and can obtain the deteriorated bond strength and the impact weight of each parameter. First, the pretraining database Meta1, a database of material strength degradation, was established from the existing results and used in the meta-learning network. Then, the database Meta2 was built and used in the meta-learning network for model fine-tuning. Finally, combining all prior knowledge, not only the degradation of the FRP–concrete bond’s strength was predicted, but the respective weights of the environment parameters were also obtained. This method can accurately predict the degradation of the bond performance of FRP–concrete interfaces in complex environments, thus facilitating the further assessment of the remaining service life of FRP-reinforced structures.

Modeling carbonation depth of recycled aggregate concrete containing chlorinated salts

The durability of recycled concrete is susceptible to degradation from both chloride salt attack and carbonation when exposed in service environment. The depth of carbonation in recycled concrete subject to chloride salt attack was studied here. This investigation assessed the effects of mineral admixture, replacement rate of recycled coarse aggregate, and quality of recycled coarse aggregate on the carbonation depth. The carbonation depth Recycled concrete was studied through accelerated simulated carbonation in the laboratory for 7d, 14d and 28d. Based on the results, the correlation analysis was conducted to investigate the relationship between depth of carbonation, mineral admixture, recycled coarse aggregate replacement rate, recycled coarse aggregate quality and the presence of chloride ions. The objective of this study was mainly to investigate the effect of internal chloride ions on the depth of carbonation of recycled concrete subjected to chloride salt attack. The study referred to previous academic research on carbonation in recycled concrete that had not been affected by chloride salts, and conducted a comparative analysis to identify the carbonation depth pattern in recycled concrete influenced by chloride salt exposure. The study discovered a negative correlation between the replacement rate of mineral admixture and recycled coarse aggregate and the carbonation resistance of concrete. Moreover, enhancing the quality of recycled coarse aggregate positively impacted the carbonation resistance of concrete. An improved model was developed that considers the effect of internal chloride salts on the carbonation depth of recycled concrete, in reference to the empirical prediction model presently available. The model demonstrated a high level of agreement with experimental outcomes, displaying an error range of between −4.32% and 8.27%. It enables an in-depth comprehension of the carbonation behavior of recycled aggregate concrete in an environment exposed to chloride salt attack. Based on the model, the service life of recycled concrete structures can be more accurately forecasted, which can provide a theoretical direction for enhancing the durability of engineering structure.

Novel oxide based anti-corrosion composite coating for gas turbines

In the present study glass-ceramic−8YSZ based multilayered functionally graded corrosion resistant coating was developed for gas turbine applications. Corrosion resistance property of developed coating was evaluated by exposing coating to molten mixture of 80 wt% Na2SO4 + 20 wt% NaCl in air at 1000 °C up to 100 h. It was found that coating morphology was gradually changed with respect to time at 1000 °C. No thermally grown oxide (TGO) layer was observed within different layers of TBC. However, thin reaction film was developed at substrate-coating interface, which helped to increase adherence of coating with substrate. Tetragonal zirconia to monoclinic zirconia phase transformation was not occurred in top coat even after long corrosive salt attack that strengthened TBC system. Developed coating showed good potential to be used as corrosion resistant coating for actual superalloy based gas turbine engine components.

Development of Self-Passivating, High Strength Ferritic Alloys for CSP and TES Application

The addition of aluminum to ferritic stainless steels can result in self-passivation by the formation of a compact Al2O3 top layer, which exhibits significantly higher corrosion resistance to solar salt compared to a Cr2O3 surface layer. The development and qualification of realistic experimental methods for fatigue testing under superimposed salt corrosion attack will enable safe component design. Salt corrosion experiments were carried out at 600 °C with and without mechanical fatigue loading at a novel, self-passivating trial steel, using “solar salt” (60 wt.% NaNO3 and 40 wt.% KNO3). Cyclic salt corrosion tests at 600 °C under flowing synthetic air (without mechanical loading) showed that self-passivation to molten salt attack and mechanical strengthening by precipitation of fine Laves phase particles is possible in novel ferritic HiperFerSCR (Salt Corrosion Resistant) steel. A compact, continuous Al2O3 layer was formed on the surface of the model alloys with Al contents of 5 wt.% and higher. A distribution of fine, strengthening Laves phase precipitates was achieved in the metal matrix.

Effectiveness of Biological Mortars with Bacterial Glycocalyx on Service Life of Concrete Structures Exposed to Salt Attack

This study investigated the effectiveness and limitations of newly developed biological mortars regarding chloride ion diffusion resistance. Through several tests on the glycocalyx production capacity and growth potentials of bacteria cells under marine environments, Bacillus licheniformis was isolated and immobilized in the expanded vermiculites together with a bacterial culture medium for producing biological mortars. The chloride ion diffusion coefficient of the mortars up to 91 days was determined through natural diffusion cell tests. Subsequently, the service life of RC structure repaired with biological mortars under chloride attack was evaluated considering multilayer theory and time-dependent diffusion. The addition of expanded vermiculites immobilizing Bacillus licheniformis significantly reduced the chloride ion diffusion coefficient. When its addition increased from 10 to 30%, the chloride ion diffusion coefficient decreased by 50–90% compared to that of mortars without bacteria. The service life of reinforced concrete structures repaired with biological mortars containing 30% expanded vermiculite concentration and thickness of 50 mm was evaluated to be six times longer than that of repaired with conventional mortar. Overall, this novel approach holds significant potential in addressing the salt-induced deterioration challenges faced by RC structures.

Effect of Polymer/Nano-Clay Coatings on the Performance of Concrete with High-Content Supplementary Cementitious Materials under Harsh Exposures.

In recent concrete research, a novel category of coatings has emerged: polymers/nanoparticles blends. The efficacy of such coatings warrants extensive examination across various concrete mixtures, particularly those incorporating high-volume supplementary cementitious materials (SCMs) to mitigate carbon footprints, an industry imperative. This study used three vulnerable concrete mixtures to assess the effectiveness of ethyl silicate and high-molecular-weight methyl methacrylate blended with 2.5% and 5% halloysite and montmorillonite nano-clay. Findings from physical, thermal, and microstructural analyses confirmed vulnerabilities in concretes with a high water-to-binder ratio (0.6) under severe exposure conditions, notably with high SCM content (40% and 60% fly ash and slag, respectively). Neat ethyl silicate or high-molecular-weight methyl methacrylate coatings inadequately protected those concretes against physical salt attacks and salt-frost scaling exposures. However, the incorporation of halloysite nano-clay or montmorillonite nano-clay in these polymers yielded moderate-to-superior concrete protection compared to neat coatings. Ethyl silicate-based nanocomposites provided full protection, achieving up to 100% improvement (no or limited surface scaling) against both exposures, particularly when incorporating halloysite-based nano-clay at a 2.5% dosage by mass. In contrast, high-molecular-weight methyl methacrylate-based nano-clay composites effectively mitigated physical salt attacks but exhibited insufficient protection throughout the entire salt-frost scaling exposure, peeling off at 15 cycles.

A robust superhydrophobic coating of siloxane resin and hydrophobic calcium carbonate nanoparticles for limestone protection

Hydrophobic calcium carbonate (CaCO3) nanoparticles (NPs), modified with dodecanoic acid (DA), are produced and dispersed in solutions of KSE 100, which is a silicic acid ester base product used for the conservation and maintenance of heritage and modern buildings. The dispersions are sprayed on limestone and marble specimens. By adjusting the relative concentrations of DA and NPs, the treated stones obtain superhydrophobic properties. Focusing on limestone it is reported that the treatment has negligible effects on the colour and vapour permeability of the original stone and offers protection against water capillary rise. Several studies are performed to test the durability of the composite (KSE + CaCO3-DA NPs) coating against rain impact, freezing and thawing, salt attack and UV radiation. Moreover, the mechanical, chemical and thermal durability of the coating is studied according to the tape peeling test, contact angles of drops which correspond to a vast range of pH, and heat treatment. The results of the aforementioned tests reveal the very good stability of the composite coating. In sum, it is reported that the wetting properties of the KSE 100 stone strengthener, which is used in building conservation, can be highly improved by adding a small amount of modified CaCO3 NPs. The latter are chemically compatible with calcareous stones.

Influence of chloride salt erosion on the adhesion of asphalt-aggregate interfaces considering mineral anisotropy: insights from molecular dynamics.

Asphalt, a polymer mixture composed of various hydrocarbons, is extensively utilized due to its excellent performance. To evaluate the sensitivity of asphalt concrete to chloride salt damage at the nanoscale, considering the anisotropy of aggregate mineral crystal orientation, molecular dynamic simulations were employed to model the interface interactions between asphalt and aggregate mineral components (silica and calcite) under chloride salt exposure. The wetting processes of water droplets and chloride salt droplets on different crystal surfaces of silica and calcite were analyzed. Furthermore, the adhesive energy, decohesion energy, degradation ratio, and energy ratio of the interaction model between asphalt and aggregate mineral interfaces were analyzed to reveal the variations in the interfaces between the two components. The results demonstrated that the anisotropy of the minerals significantly affects the adhesion energy of asphalt and aggregate. Moreover, the surface hydrophilicity of calcite was larger than that of silica. The interfacial adhesion energy of asphalt-calcite was larger than that of asphalt-silica under dry condition and chloride salt attack, and the interfacial adhesion energy of both asphalt and mineral decreased with the increase of chloride salt concentration. The degradation ratio and energy ratio values of asphalt and calcite were larger than those of asphalt and silica, and the anisotropy of the mineral surface affected the degradation ratio and energy ratio values. This study provides a new method and theoretical basis for further research on the damage mechanism and strengthening measures of asphalt-aggregate under chloride salt attack. To investigate the interaction between asphalt and mineral aggregates under chloride salt erosion, models of asphalt, aggregate, and asphalt/aggregate composite systems were constructed using the Amorphous Cell module in Materials Studio 2020 software. Molecular dynamic simulations of the asphalt/aggregate composite system were then conducted using the Forcite module, employing the COMPASS II force field to describe atomic and molecular interactions. Initially, considering the crystal orientation and surface configuration of the aggregate minerals, the impact of mineral anisotropy on the asphalt-aggregate interface model was analyzed. Subsequently, by simulating the contact states of nano water droplets and chloride salt droplets with different mineral surfaces, the wetting characteristics of nano water droplets on silica and calcite surfaces were determined. Lastly, considering the corrosion effect of chloride solution at different concentrations, the adhesion energy, debonding energy, degradation ratio, and energy ratio of the asphalt-aggregate interface interaction model were analyzed.

Durability of micro-cracked UHPC subjected to coupled freeze-thaw and chloride salt attacks

The durability of ultra-high performance concrete (UHPC) with initial micro-cracking subjected to coupled freeze-thaw and chloride salt (FT-CS) attacks was investigated. The initial micro-cracking was introduced under controlled condition in the laboratory by pre-tensioning the dog-bone specimens and unloading them at a target strain of 1500 με. The micro-cracked UHPC specimens were then submerged in a sodium chloride solution with the concentration of 4 wt% and subjected to freeze-thaw (F-T) cycles. The micro-cracked UHPCs exhibited excellent chloride penetration resistance as evidenced by the consistently low chloride ion concentration (generally less than 0.5%) and the limited penetration depth (not exceeding 6 mm) even after undergoing 300 cycles of the coupled FT-CS attacks. The tensile strength and compressive strength of the micro-cracked UHPC were improved by 28.0% and 18.3% at 200 F-T cycles, respectively. The improvement in the mechanical properties can be attributed to the self-healing effect which densified the fiber-matrix interface and the matrix. Secondary hydration and carbonation were confirmed quantitatively by thermogravimetric test and qualitatively by scanning electron microscopy test. However, the detrimental effects stemming from the coupled FT-CS attacks outweighed the beneficial effect of self-healing at 300 F-T cycles, resulting in a decline in mechanical performance.

Double percolation phenomenon of carbon nanotube/cement composites as piezoresistivity sensing elements with exposure to salt environment

It has been known that the carbon nanotube (CNT)/cement composites can be used to reflect the external loading information and detect premature damage; however, the agreement on whether the piezoresistivity as a function of external loading is positive or negative has yet to be achieved, and the innate electrically conductive mechanism remains unclear. In this study, to minimize the application cost, small-size CNT/cement composites were embedded into the surface of the concrete as sensing elements, and the piezoresistivity of the CNT/cement composites under external loading along with/without salt attacks was tested. The results indicate that the piezoresistivity significantly depends on the percolation backbone density and the critical exponent of the CNT networks near the percolation threshold. Without salt environments, an “M” shape was observed in the curve of the fractional electrical resistivity (FCR) as a function of cyclic loading applied on the concrete samples. However, when the concrete samples were exposed to a salt environment, the “M” shape in the FCR curve disappeared. In addition, based on the percolation theory, the electrical resistivity changes as a function of strain fits well with an exponential function. The microstructure analysis demonstrates that the pore structure of the CNT/cement composites can be divided into spherical pores and cracks with layered structures. This study not only provides a new insight into the electrical conduction mechanism in CNT/cement composites systems but also sheds light on how to accurately monitor and analyze concrete structures with external loads, especially along with salt environment.

Mechanical and environmental performances of an epoxy-resin-based recycled artificial stone containing hazardous sediment

Solidifying and stabilizing hazardous sediment from petrochemical activities are not only expensive but make also high-volume waste to landfills. Parallel, finding alternative aggregates with lower costs can reduce the capital cost of artificial stone. For the first time, a combination of hazardous sediments and stone waste was used as aggregates to produce the recycled artificial stones. Furthermore, the target of this study is to evaluate the behavior of these recycled artificial stones under external forces and weathering, as well as in the acid environment. In order to evaluate the properties of the stones containing hazardous sediment, the compressive strength, the brightness variation, and water absorption under UV radiation, 60 cycles of salt attack, 60 cycles of freezing and thawing, and 60 cycles of thermal shock cycles were evaluated. In order to assess the leaching of heavy metals, according to the US toxicity characteristic leaching procedure (TCLP) and DIN38414-S4, two leaching tests were used to evaluate the leaching of the heavy metals under rainfall and acid environment, like soil. In order to conduct leaching tests, three spices from the crushed zone of the stone under compressive test were used. The results show that the stones have suitable performance in comparison to the performance of the artificial stone containing nonhazardous sand, travertine stone, and treated travertine stone using epoxy resin and nanocomposite. Based on the results, P90HSa10Eb25T25, with 39.3 MPa compressive strength, 3.02 color variation under 60 cycles of salt attack, and 1.59 color variation under UV radiation, has the best performance among the recycled artificial stones.

Improvement of the performance characteristics, fire resistance, anti-bacterial activity, and aggressive attack of polymer‐impregnated fired clay bricks-fly ash-composite cements

The research addressed the creation of various composite cement mixes by replacing 40 % of OPC with industrial solid wastes, Fly ash (FA), and/or Fired clay bricks (FCB) at different water/powder (w/p) ratios. The composite cement pastes were subjected to polymer-impregnation process, using methyl-methacrylate (MMA) monomer and benzoyl peroxide as an initiator. The physico-mechanical and chemical characteristics of the polymer-impregnated specimens, such as compressive strength, bulk density, total porosity, and polymer load, were examined. The findings showed that, as compared to neat pastes (PF1, PF2, and PF3), the compressive strength (CS) of mixes (PFH1, PFH2, and PFH3) rose considerably after 3 months of hydration by 10.53 %, 12.82 %, and 28.85 %, respectively. Additionally, mix PFH1 with a water/powder (w/p) ratio of 0.35 exhibited the greatest bulk density value (2.215 g/cm3) and the lowest total porosity percentage (12.72 %). Data demonstrated that polymer-impregnation is efficacious to strengthen constructions subjected to high temperatures and aggressive salt attacks. The study additionally revealed that, when thermally treated at 200, 400, and 600 °C, respectively, the CS of PFH1 paste increased by 1.44 %, 1.78 %, and 1.48 % after 14 days of curing, but increased by 10.85 %, 5.20 %, and 7.89 % at curing time of 28 days. Likewise, when CS was compared to that before to polymer-impregnation up to three months, it grew by 48.53 % following immersion in 5%-MgSO4 solutions but increased by 13.49 % after immersion in 5%-MgCl2 solutions.Moreover, the composite with a water/powder ratio of 0.45 demonstrated remarkable anti-bacterial activity against both Gram-negative and Gram-positive bacteria. In conclusion, the study shows that the compressive strength, antibacterial activity, fire resistance, and resistance to aggressive attacks of the composites are all improved by MMA polymer impregnation.