Saturated Calcium Hydroxide Solution Research Articles

Effect of Cation Types on the Steel Corrosion Inhibition Behavior of Calcined Layered Double Hydroxides in Saturated Calcium Hydroxide Solution

Effect of Cation Types on the Steel Corrosion Inhibition Behavior of Calcined Layered Double Hydroxides in Saturated Calcium Hydroxide Solution

The dispersion and influence of graphene-oxide-modified polycarboxylate superplasticiser in alkaline cement solution

The aggregation of graphene oxide (GO) in alkaline solutions is a critical factor that limits its potential applications in cement-based materials. In this study, a polycarboxylate superplasticiser (PCE) was employed as a dispersant and a GO–PCE water-reducing agent was synthesised through the method of dropwise addition. This synthesis approach not only preserved the water-reducing capabilities of PCE but also enhanced the dispersibility of GO in alkaline cement solutions. Furthermore, the synthesis method is straightforward. The results showed that that GO–PCE had excellent dispersion in a saturated calcium hydroxide (CH) solution. Furthermore, it was found that the GO–PCE enhanced the workability of cement, accelerated cement hydration, reduced the crystallite size of the CH and increased the compressive strength of the cement mortar.

Calcined schist as promising ordinary Portland cement substitution: C3

AbstractAn effective method to make cement and concrete more sustainable is to blend them with the proper supplementary cementitious materials (SCMs). This study evaluates a pair of schist‐type materials with slightly different phase compositions, as a partial replacement for ordinary Portland cement (OPC). Materials received from several mines in ground powder form were studied by X‐ray diffraction, thermogravimetric analysis (TGA), and scanning electron microscopy. According to the TGA results, the activation procedures for the candidate SCMs were determined. The as‐received powders were heat treated in three different decomposition regimes (30%, 50%, and 80% of the total weight losses during thermal decomposition). These regimes corresponded to the activation level of the potential SCMs due to the de‐hydroxylation of the clay‐type minerals within them. Pozzolanic reactivity (pozzolanicity) of untreated as well as treated powders were estimated via electrical conductivity measurements in saturated calcium hydroxide solution. Blended cement pastes with 30 wt.% of OPC substituted with calcined clay‐type materials have developed mechanical properties equal to those of pure cement (100 wt.% OPC) paste after 28 days of hydration time. Two blended cement pastes prepared with candidate SCMs were compared to 100% OPC and OPC composite paste with metakaolin, which is regarded in the literature as a standard.

Increasing the Hydration Activity of Tricalcium Silicate by Adding Microdispersed Ettringite as a Nucleating Agent.

Tricalcium silicate (C3S) as a binder material has a decisive influence on the processes of hardening and strength gain of cements and concretes. One of the promising directions is the introduction of dispersed additives into cement mixtures, which allow micro-level control of the composition of hydration products and change the dynamics of the structure formation of cement stone. In this paper, the effect of a microdisperse ettringite additive on the kinetics of the hydration and hardening process of tricalcium silicate was studied. It was shown that ettringite crystals selectively adsorb Ca2+ and OH- ions from a saturated solution of calcium hydroxide, which contributes to the formation of hydrosilicate nuclei on their surface during cement hydration. Hydration of C3S in the presence of ettringite proceeds more intensively; the addition of ettringite contributes to an increase in the content of calcium hydrosilicates in hydration products at the initial stage of the process. Addition of 10 wt.% ettringite to C3S reduces the induction period of the beginning of the main phase of heat release by around two times and increases the amount of heat released on the 1st day of hydration by 15% compared to the control sample. According to electron microscopy data, it was found that during the first hours of hydration of modified C3S, a significant number of nuclei of fibrous particles of calcium hydrosilicates with sizes of 0.2-2 microns were formed on the surface of ettringite crystals. According to the results of kinetic modeling of the setting process of cement pastes using the Avrami-Erofeyev model, it was shown that in the presence of the addition of microcrystals of ettringite, the setting rate is characterized by a slowdown in nucleation, whereas for a sample without an additive, this process proceeds with an acceleration of the formation of solid-phase nuclei. Based on the comparison of kinetic results and mechanical measurements, it is concluded that needle crystals of ettringite during C3S hydration and cement stone hardening are preformed centers for the growth of hydrosilicate nuclei, and they also act as a reinforcing filler, increasing the bending strength of modified samples. The results of the work can be used in practice in the development of methods for controlling the processes of hydration and hardening of cements, as well as for controllable structure formation of cement stone which is important in particular for 3D printing of building products and constructions.

Effective corrosion inhibitor of mild steel in marine environments: Synthesis and application of hydrazides

A new corrosion inhibitor of long chain fatty hydrazides (HH) were synthesized from hydrazine hydrate and natural grease. The current research aimed to examine the effectiveness of HH as a mild steel corrosion inhibitor in maritime applications. The corrosion inhibition experiments were conducted in a saturated calcium hydroxide solution containing 3.0% NaCl. Measurements of weight loss, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) methods were used to assess corrosion inhibition. The molecular structure of HH was analyzed through FTIR and NMR, providing a description. Furthermore, the examination included the effects of concentration, temperature, and time on inhibition. The weightlessness results show that the corrosion inhibition rate of HH-1 is about 70% at low concentration of 10 mg·L−1, further corrosion inhibition rate reaches to about 80% at 20 mg·L−1, and inhibiting rate reaches higher than 90% at 50 mg·L−1 in 3.0% NaCl-containing saturated Ca(OH)2. Polarization test results demonstrated that HH-1 was a cathode-based corrosion inhibitor, slowing down the dissolution of steel by blocking the active site on metal surface. What's more, the adsorption on the mild steel followed Langmuir adsorption isotherm model, 3D scanning, AFM and XPS characterization demonstrated the formation of a protective layer on the steel surface as a result of adsorption of functionalized HH molecules. This layer effectively shielded the steel from aggressive 3.0% NaCl attack following a 48-h immersion in the solution. Quantum chemical calculations and molecular dynamics simulations provided insights into the molecular/atomic-level inhibition mechanism. Ultimately, our research findings validate the effectiveness of a novel environmentally friendly and efficient corrosion inhibitor in safeguarding steel bars against corrosion in marine environments.

Contribution to the Concrete Structure Project Executed with Rolled Pebbles in the City of Manaus – Usual Procedures and Recommended Standards

Initially, the aggregates used in concrete construction available in the building materials market in the city of Manaus were assessed. Samples were collected from the North, South, East, and West zones to determine their quality indices and physical properties, with the aim of producing concrete mix designs using regional materials. Subsequently, prototypes of slabs and beams were constructed to obtain concrete cores for evaluating their compressive strengths. These elements were exposed to outdoor environmental conditions, including rain, sunlight, and wind. One group was also subjected to wetting and drying cycles at the beginning and end of each day. Additionally, cylindrical specimens were cast for axial compression tests. During the concrete curing phase, these specimens were identified and divided into two groups exposed to different conditions: immersion in a saturated calcium hydroxide solution, outdoor exposure, outdoor exposure in a covered environment, and outdoor exposure subjected to wetting and drying cycles. The experiments were conducted over the course of a year to assess the influence of environmental conditions, including relative humidity and temperature, on concrete strength. The results revealed that environmental conditions, during the period from July to November, in conjunction with the standard curing method adopted in the city of Manaus (wetting the surfaces at the beginning and end of each day), affect the concrete’s strength gain, resulting in a final value lower than expected. This not only reduces the load-bearing capacity of the structure but also increases concrete porosity and reduces its modulus of elasticity. Therefore, when designing and constructing concrete structures in Manaus, the region’s specific characteristics must be considered. These considerations should encompass aggregate types, environmental conditions, and the local curing practices.

Long-term deformation and mechanical properties evolution of cement paste with ultra-low water-to-cement ratio driven by water migration

Degradation of cement-based materials with ultra-low water-to-cement ratio may occur under water and drying conditions. However, the mechanisms remain unclear. In this study, we compared the mechanical properties, deformation, and mass change of cement pastes with a water-to-cement ratio of 0.17, which had been cured in saturated calcium hydroxide solution, sealed, and drying conditions for one year. The results show that the compressive strength of the cement pastes enhances and afterwards degrades under the three curing conditions. In both self-desiccating and drying conditions, the non-uniform shrinkage induced by water consumption dominates the evolution of the mechanical properties. Hydration affected by water adsorption/desorption has a stronger influence on compressive strength development compared to the weakening effect induced by water adsorption/desorption itself. When there is enough additional space in cement paste, extra hydration products formed with the external water supply can repair defects and fill pores, increasing compressive strength. In contrast, in dense structures, further hydration can cause swelling, cracking, and reduction in compressive strength. This study also confirms the contribution of the swelling of the calcium-silicate-hydrates gel on the expansion of cement paste in saturated conditions.

The cytotoxic effect of cysteamine and its combinations with various endodontic intracanal medications on fibroblast cells: in vitro study

BackgroundThis study was established to assess cysteamine’s cytotoxic effect alone and in combination with various intracanal medications on fibroblast cells, because the biocompatibility of intracanal medication is considered one of the main factors that affect the selection of specific medication for usage near vital periodontal tissues.MethodsAll tested medications were prepared in a solution form. Cysteamine preparation was prepared at 200 mg/ml concentration in distilled water. The chlorhexidine–cysteamine combination was prepared by dissolving 10 mg/ml of cysteamine in chlorhexidine. Calcium hydroxide–cysteamine combination was prepared by dissolving 10 mg/mL of cysteamine in a saturated solution of calcium hydroxide (CaOH). Triple antibiotic paste (TAP)–cysteamine combination was prepared by dissolving 10 mg/mL of cysteamine in triple antibiotic paste (TAP). BHK cells were seeded in well-microtiter plates. The testing materials were filtrated using a 0.22 μm syringe filter. BHK-21 cells precultured well plates were treated with descending 12-fold serially diluted medications at 37 °C for 24 h. Residual living cells were treated with 25 μl of MTT dye. MTT was discarded, and then, dimethyl sulfoxide was added as 50 μl/well. The absorbance was conducted at 570 nm. The mean optical density and 50% cell growth inhibition (IC50) were calculated. Cell viability data showed parametric distribution, so they were analyzed using one-way ANOVA followed by Tukey’s post hoc test for intergroup comparisons and repeated measures ANOVA followed by Bonferroni’s post hoc test for intragroup comparisons. The significance level was set at p ≤ 0.05.ResultsViability % and IC50 results showed that triple antibiotic paste (TAP)–cysteamine combination had the lowest cytotoxicity level compared to other intracanal combinations followed by cysteamine and the highest cytotoxicity was with chlorhexidine–cysteamine combination.ConclusionsTriple antibiotic paste (TAP)–cysteamine combination was the safest drug compared to other drug combinations with cysteamine, so it needs more research to detect its acceptance with stem cells and its effect on defense mechanisms during healing.

Efficacy of an organic–inorganic hybrid phosphorus compound in corrosion mitigation of reinforcement steel in concrete. I. Gravimetric and electrochemical analysis

Bis(hexamethylene)triamine-pentakis(methylphosphonic acid) (BTPMP) was investigated for its inhibiting action on corrosion of Fe500D reinforcement steel. Results of gravimetric studies inferred that 10 mM of BTPMP is effective in corrosion control of the steel in saturated calcium hydroxide solution tainted by chloride ions. According to the electrochemical studies, the interface of the metal/solution exhibits higher charger transfer resistance and lower constant phase element values in the presence of BTPMP. The open circuit potential (OCP) measurements indicate that the presence of BTPMP shifts OCP values of steel in concrete in positive direction. The nature of the film is protective as observed from prolonged time taken for failure of BTPMP-protected rebar compared with unprotected rebar during accelerated corrosion tests. Furthermore, it is observed that the bond strength between concrete and steel is unaffected by the inhibitor film.

Effect of types of curing environments on the self-healing capacity of mortars incorporating crystalline admixture

The presence of microcracks can lead to a reduction in the durability of concrete structures. In recent years, crystalline admixture has been used to repair microcracks in concrete. In this study, the effect of different amounts of crystalline admixture on the performance of mortar was firstly determined. In order to reveal the purpose of this study, a mortar with 4% crystalline admixture has been healed under three types curing environments (standard curing, water immersion, and saturated calcium hydroxide solution). The self-healing effect of the specimens was characterized macroscopically by water absorption tests and visualized crack images after repair. The type of crack filler was determined by microscopic analysis experiments XRD and SEM-EDX. The experimental results show that, firstly, the self-healing effect of mortar with crystalline admixture is limited by standard curing environments. Secondly, water immersion environment plays a weak role in promoting crack healing of mortars without crystalline admixture, and the addition of crystalline admixture leads to self-healing of the mortar due to a large amount of production of hydrated calcium silicate. Finally, the saturated calcium hydroxide solution has a beneficial effect on the self-healing of cracks in mortars without crystalline admixture due to the precipitation of calcium hydroxide from the healing solution. After the addition of crystalline admixture to the mortar, calcium ions and water promote the generation of calcium silicate hydrate, and the precipitation of calcium hydroxide acts together to fill the crack, resulting in the crack being completely healed.

Localized corrosion of steel in alkaline solution with low-level chloride and elevated sulfate concentrations

Localized corrosion developed on post-tensioned steel strand in deficient grout, relating to elevated concentrations of sulfate ions. The deficient grout can also have low-level chloride ion concentrations below threshold values originating from the base materials. Open-circuit potential, linear polarization resistance (LPR), and electrochemical noise (EN) measurements were made on steel specimens exposed in saturated calcium hydroxide solution with 0.012 M Cl−, 0.04 M SO42−, or combined. Results showed that the combined presence of sulfates in low-level chloride alkaline solutions elevated the corrosion rate and the extent of corrosion pitting. The EN technique was shown to provide corrosion rate estimates consistent with LPR and was able to identify pitting characteristics. The outcomes of the research provides supporting evidence that analysis of deficient grout for chlorides alone may not capture the risk for corrosion and that corrosion associated with elevated sulfate concentrations can be exacerbated in presence of low-level chlorides.

Coupling effect of cementitious capillary crystalline waterproof material and exposure environments on self-healing properties of engineered cementitious composites (ECC)

Due to the healing mechanism of self-healing technologies, there are some limitations and challenges for application in concrete structures. Based on the characteristics of cementitious capillary crystalline waterproof material (CCCW) in powder and active materials moving along cracks, this work presents CCCW as a direct internally mixed self-healing material, and quantitatively explored the coupling effect of CCCW and exposure environments on the self-healing properties of engineered cementitious composites (ECC). Four types of ECC mixtures with CCCW doping of 0%, 1.5%, 3% and 4.5% were prepared. Exposure environments contained water, air and saturated calcium hydroxide solution. The self-healing behavior of ECC was evaluated by the recovery of mechanical properties, water impermeability and closure behavior of crack. Microscopic analysis of healing products was performed by scanning electron microscope (SEM), thermogravimetric analysis (TG) and X-ray diffraction (XRD). The test results showed that the recovery of mechanical properties and water impermeability of ECC was improved by directly adding CCCW. The percentage of re-opened healed cracks number in specimen EC45 with 4.5% CCCW content was 83.33% lower than that in specimen EC0 without CCCW. The normalized closure rate of crack area was raised by 167.98% by mixing 4.5% of CCCW in saturated calcium hydroxide solution, compared with that without CCCW. While it was enhanced by 132.44% in water. There was a superimposed enhancement of CCCW and calcium hydroxide solution. Microscopic analysis of healing products showed that CCCW facilitated the production of healing products, especially in saturated calcium hydroxide solution. Finally, the additive effect coefficient Ki was introduced to quantitatively characterize the coupling effect of environments and CCCW on the self-healing properties of ECC.

High temperatures and CO2 dissolution can cause nitrogen losses from urine stabilized with base

Human urine is rich in valuable nitrogen which can easily be lost due to biological urea hydrolysis and subsequent ammonia volatilization. While this enzymatic reaction can be prevented by alkalizing the urine, recent studies suggest that chemical urea hydrolysis can result in substantial nitrogen losses when drying alkalinized urine at high temperatures. Furthermore, it was previously suggested that CO2 dissolution from the air used to evaporate water from alkalinized urine could result in a pH decrease to values which allows for biological urea hydrolysis and subsequent ammonia losses. This study aimed to determine the kinetics of chemical urea hydrolysis in alkalinized human urine and confirm the effect of CO2 dissolution with controlled laboratory experiments. We measured the change in urea concentration at different temperatures and pH values for real human urine and determined the corresponding rate constants for chemical urea hydrolysis. We showed that the rate constant increases as a function of temperature and that pH has a negligible effect on the rate of chemical urea hydrolysis in the high pH range of alkalized urine (>11). The rate constants for chemical urea hydrolysis in a saturated calcium hydroxide solution were found to be 0.00147 d−1, 0.00595 d−1, 0.0204 d−1 and 0.0848 d−1 for temperatures of 25°C, 40°C, 55°C and 70°C, respectively. The effect of CO2 dissolution on urea hydrolysis was determined by aerating human urine alkalinized with calcium hydroxide (Ca(OH)2). In order to represent biological urea hydrolysis, urease was added to the solution. The computer simulations of the experimental results showed that CO2 dissolution and the subsequent dissociation of carbonic acid to carbonate ions, bicarbonate ions and protons is the main cause of the pH decrease, but CaCO3 precipitation, and NH3 volatilization foster the pH decrease. However, biological urea hydrolysis prevents the pH from decreasing below 9. Residual undissolved Ca(OH)2 was shown to substantially delay the pH decrease. Overall, this work provides valuable insights into the mechanisms of urea hydrolysis in alkalinized urine during dehydration, which can be used to design more efficient decentralized sanitation systems and minimize nitrogen losses.

Electrochemical Assessment of Galvanized Steel Corrosion in Alkaline Sulfate Solution

Corrosion of steel prestressing strand in bonded post-tensioned bridge tendons have been associated with elevated concentrations of sulfate ions in deficient grout that can develop due to grout segregation [1]. Previous research indicated that the early presence of elevated sulfate ion concentration in the deficient grout in contact with the embedded steel can impair steel passivity. Metastable pitting was observed for steel in saturated calcium hydroxide solutions with sulfate ion concentrations greater than 1,300 ppm and pitting was observed in solutions above 20,000 ppm [2-4]. In addition to steel strand corrosion, galvanized steel ducts in direct contact with the deficient grout with elevated sulfate ion concentrations were also observed to have severe localized corrosion [1]. Galvanized steel in alkaline solutions, such as in cement pore water, have been characterized to have greater resistance to chloride-induced corrosion with chloride threshold concentrations as much as 2.5 times greater than carbon steel [5]. Information relating to sulfate concentrations is less available. Electrochemical testing including the electrochemical noise (EN) technique was conducted to identify the role of early sulfate ion presence on corrosion of galvanized steel.EN provides a test method to assess the corrosion modality without the influence of an external excitation that can affect the electrode surface and electrolyte chemistry (such as metal oxidation and oxygen reduction) [6-7]. The testing aims to identify the corrosion mitigation characteristics of the galvanized steel such as zinc activity and protective barrier surface oxide layers in presence of sulfate ions as well as combined cases with chloride ion contamination below reported threshold concentrations for galvanized steel. In the testing here, steel specimen were exposed to alkaline solutions simulating pore solutions with pH 12.6 with varying sodium sulfate levels and sodium chloride. Supplemental electrochemical experiments included the steady-state condition (open circuit potential, linear polarization test, and electrochemical impedance spectroscopy). References K. Lau, and I. Lasa. "Corrosion of prestress and post-tension reinforced-concrete bridges." Corrosion of steel in concrete structures. Woodhead Publishing, 2016. 37-57. DOI: https://doi.org/10.1016/B978-1-78242-381-2.00003-1.S. Permeh, K. K . Krishna Vigneshwaran, K.Lau., and I.Lasa. “Corrosion of Post-Tensioned Tendons with Deficient Grout. Part 3: Segregated Grout with Elevated Sulfate and Vestigial Chloride Content.” Corrosion 75 (2019) pp.848-864.S. Permeh, K. Lau, M. Duncan, and R. Simmons. “Initiation of localized steel corrosion in alkaline sulfate solution.” Materials and Structures, 54 (2021), pp.1-17.S. Permeh, K. Lau, M. Duncan, and R. Simmons. “Identification of steel corrosion in alkaline sulfate solution by electrochemical noise.” Materials and Corrosion, 72(2021), pp.1456-1467.S. Yeomans. Galvanized steel reinforcement in concrete. Elsevier, 2004.S. Permeh, and K. Lau. "Electrochemical Behavior of Steel in Alkaline Sulfate Solutions with Low Level Chloride Concentrations." ECS Meeting s. No. 10. IOP Publishing, 2021.K. Lau, S. Permeh. “Assessment of durability and zinc activity of zinc-rich primer coatings by electrochemical noise technique.” Progress in Organic Coatings, 167(2022): 106840.

Corrosion of aluminium in ordinary Portland cement paste: Influence of matrix porosity and the presence of LiNO3 corrosion inhibitor

AbstractThe Belgian reactor 1 fuel cladding is made of aluminium. If disposed of in a geological disposal repository, aluminium could come into contact with ordinary Portland cement and is going to corrode to form hydrogen gas and aluminium hydroxide. In this study, the long‐term corrosion was evaluated by electrochemical impedance spectroscopy on metal embedded in cement paste immersed in saturated calcium hydroxide solution under anaerobic conditions. Mass transfer effects were investigated by embedding aluminium in cement paste with two different porosities. LiNO3 was also added to the systems to study its corrosion inhibiting effect. After high initial values, the corrosion rate rapidly declined to reach a steady state after a few days. After ~100 days, the corrosion rate was the lowest when cement paste possessing a low porosity with the addition of LiNO3 was used and the highest when cement paste with high porosity without LiNO3 was used. Finally, scanning electron microscopy–energy X‐ray dispersive spectroscopy revealed that the corrosion product layer was thicker than expected by electrochemical impedance spectroscopy measurements, while it is only composed of aluminium and oxygen. Aluminium was found to diffuse into the cement paste close to this corrosion product layer.

Influence of a Show Case Polish Coating on Corrosion Resistance of Mild Steel in Simulated Concrete Pore Solution

Mild steel is relatively less expensive. So in reinforced concrete, mild steel can be used. Mild steel in concrete structures may experience corrosion. To avert corrosion of mild steel, a number of inhibitors are used along with concrete admixtures. In this category of research, saturated calcium hydroxide solution is considered as simulated concrete pore solution (SCPS). Numerous corrosion inhibitors have been utilized in this field along with organic coatings. In the present investigation show case polish coated mild steel has been used in concrete. The corrosion resistance has been calculated by electrochemical studies such as polarization study and AC impedance spectra. When show case polish coated mild steel is immersed in SCPS, the corrosion resistance of mild steel increases. This is long-established by the facts that in presence of show case polish coating , the linear polarization resistance value increases, corrosion current value decreases, charge transfer resistance increases, double layer capacitance decreases, impedance increases, and phase angle increases. The protecting layer functions as anodic inhibitor and controls the anodic reaction primarily. The protective coating offers 99.99% inhibition efficiency. It implies that the show case polish coated mild steel can be used in concrete technology. This will increase the lifetime of the rebars.

The immediate and short-term degradation of the wood surface in a cement environment measured by AFM

This study aims to measure the pit torus and border to monitor the immediate and short-term degradation of wood surfaces after the concrete is cast and the cement hydration releases heat. The surface morphology and adhesion force curves were measured by atomic force microscopy during the treatments in saturated calcium hydroxide solutions ranging from 1 h to 27 days. The results showed that the pit torus and pit border showed different degradation processes. The adhesion force was sensitive to the type of the surface chemical components exposed during the degradation, while the surface modulus, deformation and jump-off force ratio were sensitive to the surface structural strength. The surface modulus of the pit torus degraded to 0.61–0.66 of the untreated original (95% CI) after 7-h treatments, and degraded almost completely after 48-h treatments. The surface modulus of the pit border degraded to 0.83–0.95 of the untreated original (CI) after 10 days and to 0.20–0.23 of the untreated original (95% CI) after 27 days of treatments. The treatment temperature 50 °C caused a 10-times faster degradation in the torus modulus compared to the temperature 20 °C.

Effect of a Fast Potential Change on the Early Stage of Zinc Passivation in a Saturated Calcium Hydroxide Solution

The fast and sharp corrosion potential change from the active state to the passive state, that pure zinc plates immersed in calcium hydroxide saturated solutions with and without chlorides spontaneously exhibit at the early stage of passivation, was studied. The corrosion behavior was investigated by corrosion potential monitoring, anodic polarization curves and electrochemical impedance spectroscopy. The zinc surface was characterized by scanning electron microscopy and X-ray energy dispersive spectroscopy. Experimental results show that the presence of chlorides increases the rate of change of potential by 10-fold in the early stage of passivation, producing a porous passivating film of corrosion products mainly made of calcium hydroxy-zincate Ca(Zn(OH)3)2· 2 H2O, with a less protective barrier effect than the non-porous film formed without chlorides. On the other hand, a modeling approach was achieved by solving the transient 2D Nernst–Planck equations and considering 12 chemical species. Numerical results confirm that the composition of the chemical products generated on the Zn surface certainly depends on the concentration of Cl¯ ions: Simonkolleite and hidroxides become unstable in the presence of high Cl¯ concentrations, whereas calcium hydroxyl-zincate is the main chemical compound generated on the Zn surface. However, the presence of the latter compound is much more important in electrolytes with very low concentration of Cl¯ ions.

The Effects of Graphene Oxide-Silica Nano-Hybrid Materials on the Rheological Properties, Mechanical Properties, and Microstructure of Cement-Based Materials.

Despite their excellent performance, two-dimension nanomaterials have certain limitations in improving the performance of cement-based materials due to their poor dispersity in the alkaline environment. This paper has synthesized a new two-dimension stacked GO-SiO2 (GOS) hybrid through the sol-gel method. Nano-SiO2 is coated on the surface of GO with wrinkling characteristics, and the atomic ratio of C, O, and Si in GOS is 1:1.69:0.57. The paper discusses the impacts on the spreading, Marsh cone flow time, rheological properties, mechanical properties, and microstructure of cement-based materials for the GOS at different mixing quantities. Furthermore, with the same mixing quantity of 0.01%, the influences on the dispersity, flow properties, rheological parameters, and mechanical properties of GOS and graphene oxide (GO) are compared. Lastly, fuzzy matrix analysis has been adopted to analyze the comprehensive performance of cement-based materials containing GOS. The research results indicate that, compared with the reference sample, the spreading for the GOS cement mortar with 0.01% mixing quantity was reduced by 4.76%, the yield shear stress increased by 37.43%, and the equivalent plastic viscosity was elevated by 2.62%. In terms of the 28 d cement pastes, the compressive and flexural strength were boosted by 27.17% and 42.86%, respectively. According to the optical observation, GOS shows better dispersion stability in the saturated calcium hydroxide solution and simulated pore solution than GO. Compared with the cement-based materials with the same mixing quantity (0.01%), GOS has higher spreading, lower shear yield stress, and higher compressive and flexural strength than GO. Finally, according to the results of fuzzy matrix analysis, when the concentration of GOS is 0.01%, it presents a more excellent comprehensive performance with the highest score. Among the performance indicators, the most significant improvement was in the flexural properties of cement-based materials, which increased from 8.6 MPa to 12.3 MPa on the 28 d.

Effect of macropores at the steel-concrete interface on localized corrosion behaviour of steel reinforcement

The steel-concrete interface determines the steel corrosion and the durability of concrete structures. In this paper, the relationship between macropores and localized corrosion is quantified, based on the natural deterioration of 5 wt% Cr steel reinforced mortar and laboratory tests of 5 wt% Cr steel in the saturated calcium hydroxide solution. The results show that, considering environmental factors with the same chloride content and water saturation, large interfacial macropores are always the weakest zones at which both corrosion initiation and propagation preferentially take place. The localized rate of steel corrosion (mm/year) increases linearly with the logarithm of the macropore volume (μL), and the slopes are in the range of 0.05–0.11 depending on the chloride level. The weakened pH buffering effect of solid Ca(OH)2 at interfacial macropores is not the only reason for this phenomenon; the impacts of macropores and their volume on the electrochemical corrosion process are also significant. In small macropores, both cathodic and anodic polarizations are strengthened, and the thermodynamic driving force of the iron dissolution reaction is reduced.