Friedel's Salt Research Articles

Influence of chloride salt type on chloride ion diffusion performance of alkali-activated slag mortar

• Alkali-activated slag (AAS) mortar has better resistance to chloride ion corrosion. • Different cation types affect the D app of AAS mortar. • MIP and XRD was performed to show a decrease in porosity. • EIS was performed to show an inverse exponential relationship between R c,d and D app . This work focuses on evaluating the influence of four cationic chloride salts (NaCl, KCl, MgCl 2 and CaCl 2 ) on chloride ion diffusion characteristics of alkali-activated slag mortar. The chloride ion concentration profiles of alkali-activated slag mortar were tested in single cation and combined cation source solutions. The hydration products and mechanism of action were analyzed by XRD and MIP, and the chloride ion transmission characteristics of alkali-activated slag mortar were further analyzed in combination with EIS. The chloride ion apparent diffusion coefficient D app related to the chloride salt solutions with the four cation types decreases in the order of D app (KCl) > D app (NaCl) > D app (MgCl 2 ) > D app (CaCl 2 ). The combination of monovalent cations can promote the chloride ions diffusion of alkali-activated slag mortar, and the results of the combination of monovalent cations and divalent cations are different. The hydration products of slag are mainly C-S-H gels with low calcium to silicon ratio, which reacts with chloride salt to form Friedel's salt, which can fill the internal pores, optimize pore size distribution, and improve the resistance to chloride ion corrosion.

Investigation on the chloride ion erosion mechanism of cement mortar in coastal areas: From experiments to molecular dynamics simulation

• The influences of chloride ions on the phsysical and mechanical properties of cement mortar were analyzed. • The mechanism of bound and free chloride ions on the cement mortars properties were investigated in long-term erosion. • The effect of chloride ions in pores on C S H adsorption was investigated by molecular dynamics simulation. Chloride salts in groundwater are a serious threat to the durability of underground reinforced concrete structures in coastal areas. In order to effectively improve the durability performance of underground structural concrete in coastal areas, physical and mechanical properties such as compressive strength, water absorption rate and chloride ion permeability of cement mortar were studied. The influence laws of mineral additives such as fly ash, ground granulated blast-furnace slag and chloride ions on the relevant properties of cement mortar were analyzed. The effect of chloride ions on these physical and mechanical properties was investigated. The main hydration product categories of cement mortar were derived using microscopic analysis (XRD). The internal microstructure and the surface morphology of cement mortar were obtained by scanning electron microscopy (SEM). The effect of chloride ions in pores on C S H adsorption was studied by using molecular dynamics simulations. The results showed that chloride ion erosion increased the compressive strength of cement mortars doped with FA and GGBS at 28, 100, and 180 days by 2.76 %, 14.32 %, and 7.83 %, respectively. Chloride ion erosion moderately increased the compressive strength of cement mortar doped with FA and GGBS at all curing period. After chloride ion erosion, the electric fluxes of the four groups of specimens at 180 days decreased by 30.37 %, 31.64 %, 23.22 % and 17.41 %, respectively. After the addition of mineral additive, the bound chloride ions changed the influence law of water absorption rate of cement mortar, and reduced the electric flux of cement mortar. The molecular dynamics simulations revealed that the chloride ions in the pores weakened the physical adsorption of external chloride ions by C S H, resulting in the easier passage of external chloride ions through the pores. Microscopic analysis showed that the Friedel's salt generated by chloride ions attacking the cement-based materials filled communicating pores, which may be one of the reasons for the reduced electric flux of the cement mortar.

Chloride binding of early CO2-cured Portland cement-fly ash-GGBS ternary pastes

This paper compared the chloride binding of Portland cement pastes with and without early CO2 curing and examined the effects of FA and GGBS on the chloride binding of early CO2-cured cement paste. The results show that the chloride binding capacity of early CO2-cured Portland cement paste is much lower compared to the ones not subjected to early CO2 curing, and the former can be better described by Langmuir isotherm while Freundich isotherm is more suitable for the latter. The chloride binding of Portland cement-fly ash-GGBS pastes subjected to early CO2 curing mainly depend on the physical adsorption by C–S–H while the chemical binding related to the formation of Friedel's salt is extremely weak. The incorporation of FA and GGBS declines the chloride binding capacity of the Portland cement paste subjected to early CO2 curing due to lack of calcium hydroxide. However, the chloride binding of Portland cement-fly ash-GGBS pastes subjected to early CO2 curing are improved when CaCl2 solution is applied as soaking solution, which mainly comes from the enhancement of physical adsorption. The cation ions of chloride solution show little influence on the formation of Friedel's salt.

Effect of the prepared barium@hydrogel capsule on chloride ion binding of Portland cement paste

Utilization of sea sand in reinforced concrete is limited, due to the risk of steel corrosion caused by the introduced chloride. The chloride ions can be chemically bound by chloroaluminate salts (i.e., Friedel's salt and Kuzel's salt) in Portland cement, which would be an effective way to reduce the risk. However, SO42− from gypsum in Portland cement could form sulfoaluminate hydrates (e.g., monosulfate and ettringite), which would hinder the generation of chloroaluminates and weaken the chloride binding. In this study, an attempt was made to reduce this negative effect by introducing Ba2+ which had the effect of precipitating SO42−. A design of barium@hydrogel capsule with core-shell structure was proposed to control the release rate of Ba2+ to avoid the disturbance to the paste setting process. Results showed that the release process of Ba2+ from the capsule was controlled by the slow swelling behavior of hydrogel in the shell structure. Since most of Ba2+ was released from the capsule after 8 h, the negative influence of Ba2+ on the early setting process of cement paste was avoided. The released Ba2+ facilitated the transformation of sulfoaluminates to chloroaluminates, thus enhancing the chloride binding capacity of Portland cement system.

Development of a low-alkalinity seawater sea sand concrete for enhanced compatibility with BFRP bar in the marine environment

To enhance the durability performance of Basalt Fiber Reinforced Polymer (BFRP) bar reinforced Seawater Sea Sand Concrete (SWSSC) structure components in the marine environment, this paper investigated the feasibility of reducing SWSSC alkalinity to improve its compatibility with BFRP bars. The low-alkalinity ternary mixtures were designed with ordinary Portland cement (OPC), silica fume (SF) and fly ash (FA) through the simplex centroid design method. The evolutions of micro-morphology and hydration phase were characterized by isothermal calorimeter, Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD) and thermogravimetric analysis. The added SF and FA inhibit the formation of AFm phases and Friedel's salt, and consume the Portlandite content in seawater cement paste. Exposure in the marine environment can lead to magnesium and sulfur abundant zonation in the low-alkalinity SWSSC. The durability performances of BFRP bars reinforced SWSSC columns are evaluated through accelerated aging tests in a simulated marine environment at 55 °C. The tensile strength degradation of BFRP bars embedded in low-alkalinity SWSSC is significantly mitigated due to the less alkaline and less moist internal environment. After 180-day accelerated aging, the tensile strength retentions of BFRP bars wrapped by low-alkalinity and normal SWSSC are higher than 70% and less than 24%, respectively. After accelerated aging in seawater, the load-bearing capacity of BFRP bars reinforced low-alkalinity SWSSC column slightly improves and the ductility remains unaffected. Meanwhile, the ductility of BFRP bars reinforced normal SWSSC column is reduced by about 30% after conditioning. The research outcomes can serve as a solid base for the durability design of BFRP-SWSSC structures in the marine environment.

Deep insight into mechanical behavior and microstructure mechanism of quicklime-activated ground granulated blast-furnace slag pastes

Ground granulated blast-furnace slag (GGBS) could be used as a potential low-carbon binder when activated by a moderate activator. The use of seawater in producing construction materials has increasingly attracted attention in some coastal engineering with scarce freshwater. This study aims at studying the impact of quicklime proportions on the mechanical behavior and microstructure of the binder. The mechanical behaviors were investigated through unconfined compression tests. The hydration kinetics and microstructure characteristics were examined using XRD, TGA, FTIR, and SEM-EDX. The results indicated that the hydration heat and exothermic peaks enhanced with the quicklime proportion. The exothermic peaks were observed in the first few minutes and 4–18 h. The quicklime-GGBS pastes generated the highest UCS (>18 MPa) occurred at a quicklime proportion of 0.15. The platy-like portlandite, fibrous calcium silicate hydrate (CSH), needle-like ettringite (AFt), and Friedel's salt (Fs) were detected in XRD and SEM. The Cl− in seawater promoted the formation of Fs. The XRD peaks of CSH and AFt/Fs raised and then descended with the quicklime proportion, and reached the maximum at the quicklime content of 0.15. The mass percentage of CSH and AFt/Fs from TGA first increased and then became stable when the quicklime content was 0.1–0.15. The number of amorphous GGBS particles and pores decreased under the quicklime proportion of 0.05–0.15, while the portlandite increased as the quicklime content changed from 0.15 to 0.3. Overall, the quicklime-GGBS binder could provide a potential sustainable construction material in waste recycling and freshwater saving.

Synthesis and application of new core-shell structure via Pickering emulsion polymerization stabilized by graphene oxide

Pickering structures significantly improve the compatibility and stability of composite polymer emulsions by virtue of their unique nanoparticle interfaces. An innovative application of Pickering structures to the synthesis of core-shell emulsions is proposed in this paper, two Pickering emulsions containing polystyrene acrylate-polysiloxane core-shell structures stabilized by graphene oxide (GO) were designed. The synthesized Pickering emulsions have excellent dispersibility and physical stability, while its particle size distribution is uniform and below 120 nm. The Pickering structure improves the grafting proportion between the PSA and polysiloxane components to over 87.8%. The GO interface gives the core-shell structure a desirable molecular configuration and high crosslinking degree, facilitating the formation of complete shielding films and stable hydrophobic layer on the cement hydrates. With a contact angle of over 130° and surface energy of below 15 mJ/m2, the capillary water absorption of the concrete decreased by 98.3% with the Pickering emulsions. Meanwhile, the Pickering coatings have the high corrosion potentials under chloride and sulfate attack, weakening the formation of Friedel's salts, gypsum, and ettringite in the cement substrates. Furthermore, the Pickering coating films are resistant to attack by aggressive ions and free radicals under acid/alkaline corrosion and photo-oxidative aging, effectively inhibiting the degradation of polymer molecules and adhesion failure on the cementitious materials.

Coupled microwave hydrothermal dechlorination and geopolymer preparation for the solidification/stabilization of heavy metals and chlorine in municipal solid waste incineration fly ash

To improve the degradation efficiency of persistent organic pollutants (POPs) in municipal solid waste incineration fly ash (MSWIFA), as well as to overcome the difficulties of subsequent hydrothermal liquid and hydrothermal slag treatment, a two-step treatment strategy of microwave hydrothermal degradation coupled with geopolymer immobilization was proposed. Results showed that the optimal process parameters for microwave hydrothermal dechlorination were a temperature of 220 °C, a time of 1 h, and NaOH addition of 10 wt%. Microwaves accelerated the OH− mediated hydrolysis reactions and promoted the breaking of CCl bonds, leading to dechlorination. The compressive strength of the 20 % MSWIFA-based geopolymers reached 75.79 MPa, and the immobilization rate of the heavy metals (HMs) and Cl− surpassed 90 %. Alkaline environment provided by microwave hydrothermal promoted the formation of Ca(OH)2, which subsequently formed Friedel's salt (3CaO•Al2O3•CaCl2•10H2O) with Cl− in the geopolymer. The charge density difference and density of states (DOS) of Friedel's salt were analyzed by first-principles calculations, confirming that the existence of strong interactions between Ca-s, Al-p, O-p, and Cl-p states was the chemical mechanism of Cl− immobilization. The Friedel's salt and HMs were encapsulated by geopolymers with dense silica-alumina tetrahedral frameworks, achieving the solidification/stabilization (S/S) of HMs and Cl−. This work provided a new approach for the environmentally sound and resourceful treatment of MSWIFA.

Study on properties and degradation mechanism of calcium sulphoaluminate cement-ordinary Portland cement binary repair material under seawater erosion

For seeking repair materials suitable for Marine engineering, it is of great significance to study the seawater erosion resistance of calcium sulphoaluminate cement-ordinary Portland cement (CSA-OPC) blended system in tidal environment. In this study, the effects of OPC content on the compressive strength, mass loss, chloride ions of CSA-OPC blended system under the action of dry-wet cycle and artificial seawater erosion were investigated. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to analyze the erosion products and the morphology to reveal the degradation mechanism. The results showed that the compressive strength of CSA-OPC blended system was effectively improved by the addition of OPC at the artificial seawater environment. With the increasing OPC content, the compressive strength and combination rate of chloride ions increased first and then decreased. When the OPC content was 30 %, they reached the maximum. Additionally, the addition of OPC significantly increased the AFt content and led to a more dense matrix to prevent the erosion of ions. Moreover, the combination rate of chloride ions was enhanced by producing more Friedel's salts when OPC added. The above research results showed that CSA-OPC was a suitable repair material for Marine engineering under the appropriate OPC content.

Mineralogy optimization for immobilization of potentially toxic elements and halides in Co-disposed flue gas desulfurization brines and bituminous coal fly ash

• Co-disposal of flue gas desulfurization wastewater brine and bituminous coal fly ash. • Zero liquid discharge through solidification/stabilization. • Contaminants encapsulation through mineralogy optimization. • Aluminate addition enhances the formation of Friedel's salt. • Gypsum addition enhances the formation of ettringite. The flue gas desulfurization (FGD) wastewater and coal fly ash (CFA) are waste products containing potentially toxic elements (PTEs) and halides of environmental concerns. A novel co-disposal strategy for these two wastes is a zero-liquid-discharge (ZLD) method which treats the concentrated FGD brine via a solidification/stabilization (S/S) process using CFA and alkaline additives. The objective of this study was to improve PTE and halide immobilization of this ZLD method by optimizing the mineralogy of the S/S solids in co-disposed FGD brines and bituminous CFA. The formation of Friedel's salt, which is critical in binding oxyanions and halides, was specifically evaluated. Various mixtures of FGD brines, CFA, and alkaline additives were systematically tested and the formed S/S solids were evaluated by long-term leaching tests and quantitative X-ray diffraction (QXRD) analyses. Addition of reactive aluminate (2.5 % by weight) and lime (10% by weight) yielded S/S solids with enhanced formation of Friedel's salt by up to 23%, which were able to retain the majority of selenate (>90%), arsenate (>99%), chromate (>99%) and chloride (>50%) from the brine after nine weeks of leaching tests. Comparatively, addition of gypsum promoted the formation of ettringite, which only enhanced the immobilization of borate, but not selenate and chloride. The hydraulic conductivity of the S/S solids was another important factor for contaminant leaching, because it could affect the stability of Friedel's salt under the leaching conditions and governed the immobilization of halides since the halide concentration from the brine exceeded the binding capacity of formed Friedel's salt.

A novel strategy of polystyrene acrylate – Polysiloxane core-shell emulsion for surface protection of cementitious materials

Core-shell polymer coating is a significant means of improving the surface protection of cement-based materials. In this paper, a novel strategy for the paraffin-doped polystyrene acrylate-polysiloxane core-shell emulsions (CSP) are proposed by combining polyaddition and polycondensation reactions, integrating the superior corrosion-resistance of PSA emulsions with the high-hydrophobicity of siloxane emulsions. The CSP emulsions have excellent physical stability and rheological behavior, with a lower proportion of unsaturated bonds and lower content of chemically bound water. The core-shell structure promotes the formation of Si–O bonds between the polymer molecules and the cement matrix, and more conducive to the formation of new silicate crystals on the cement hydrate surface. Macroscopically, the surface energy of the cement samples treated with CSP coating is below 16.7 mJ/m2, while its superficial nanoscale papillae give a water contact angle of almost 140°. The capillary absorption coefficient of the Portland concrete treated with CSP coating can be decreased to only 2.09 g/(m2·h0.5). Meanwhile, the corrosion rate of Cl− and SO42− on the cementitious materials are significantly inhibited by the CSP membrane, reducing the levels of Friedel's salt, ettringite and gypsum generated by ionic corrosion, respectively. Furthermore, the CSP membranes have excellent molecular structural integrity and high cross-linkage under acid/alkaline corrosion and photo-thermal aging, maintaining superior adhesion and corrosion resistance with the cement substrate.

An experimental study on the influence of continuous ambient humidity conditions on relative humidity changes, chloride diffusion and microstructure in concrete

Most engineering structures are exposed to various harsh environments, such as temperature fluctuations and humidity cycles, simultaneously. Additionally, moisture transfer and corrosive ion transport in concrete are driven by humidity gradients. Therefore, studying Chloride transport in concrete under constant humidity conditions is a meaningful research project. In this work, a new experimental setup was designed, and the Chloride diffusion behavior of concrete under a continuous humidity environment and NaCl immersion was investigated. Meanwhile, to accurately evaluate the internal humidity of concrete, humidity sensors were applied to the concrete. Additionally, the impacts of the water-binder ratio (w/b) and ambient humidity on the humidity diffusion coefficient, free Chloride content and bound Chloride content in concrete were evaluated. The microstructure was characterized by scanning electron microscopy, X-ray diffraction and mercury intrusion porosimetry. The results show that the content of free Chloride increases with an increasing w/b ratio. The humidity diffusion coefficient of concrete during water absorption (continuous high humidity environment) is significantly higher than that during water loss (continuous dry environment). Furthermore, under the drying condition, the Chloride content and the humidity diffusion coefficient on the concrete surface gradually increased, while during the wetting procedure, the Chloride content inside the concrete increased, and the humidity diffusion coefficient gradually decreased. However, the bound Chloride content inside the concrete is not affected by the humidity level in the environment. In the wetting environment, the calcium hydroxide in the matrix is gradually consumed, and the Chloride diffuses to the matrix to form more Friedel's salt and calcium carbonate. Moreover, lowering the w/b ratio or increasing the ambient humidity can enhance the formation of more hydrated compounds (C–S–H gel), which can reduce the total porosity and can also improve the ability of concrete to resist Chloride diffusion. Overall, this study provides a better understanding of and insight into the design and maintenance of seaside RC infrastructures.

The interaction between monosulfoaluminate and calcium chloride aqueous solution

Scanning transmission X-ray microscopy (STXM) and calcium L2,3-edge near-edge X-ray absorption fine structure (Nexafs) spectra were used to investigate the morphology and chemical information of cement-based materials. The interaction between calcium chloride (CaCl2) and monosulfoaluminate (Ms) was investigated and the intermediate phases were identified. With an increase in the concentration of the calcium chloride solution, calcium Ms was converted into ettringite, Kuzel's salt (Ks) and Friedel's salt (Fs) to varying degrees, while SO42− ions in the ettringite and Ks were continuously replaced by Cl− ions in the solution, eventually forming Fs and gypsum. Based on the calcium L2,3-edge Nexafs absorption spectra, ettringite, Ms, Ks and Ms were greatly distinguished by the number and shape of the leading peaks in the spectra due to the difference in SO42− content among the interlayer structures of Ms, Ks and Fs. The present work is based on the references for the STXM study of the calcium (sulfo)aluminates, for demonstrating a more complete understanding of the phase evolution under chloride environments.

Removal of sulfate and chloride ions from reverse osmosis concentrate using a two-stage ultra-high lime with aluminum process

Reverse osmosis (RO) concentrate generated from RO desalination is necessary to be managed due to its discharge toxicity and mineral scaling. In this work, the removal of SO42− and Cl− from RO concentrate and further improvement of water quality were systematically investigated using the two-stage ultra-high lime with aluminum (UHLA) process and carbonation post-process, respectively. Firstly, batch results of the one-stage UHLA process proved the competitive inhibition effect of coexisting SO42− on Cl− removal. Thus, a two-stage UHLA process was designed to preferentially precipitate SO42− as ettringite (Ca6Al2(SO4)3(OH)12) in stage I and then dislodge partial Cl− as Friedel's salt (Ca4Al2Cl2(OH)12) in stage II. Results showed that almost all of SO42− and 77.8 % of Cl− could be removed at the optimal conditions. And the XRD and SEM analysis results showed formation of ettringite and Friedel's salt with good crystal morphology in stage I and stage II, respectively. This technology was further applied in the real RO concentrate treatment and achieved almost complete SO42− removal and high Cl− removal of 70.5 %, which confirmed the feasibility and effectiveness of the two-stage UHLA process. Finally, the carbonation post-process was applied to precipitate remaining Ca2+ as well as lower the pH and conductivity, so as to improve the treated water quality. This two-stage UHLA process is promising to be applied to saline wastewater containing high concentrations of SO42− and Cl−.

Effect of dosage of silica fume on the macro-performance and micro/nanostructure of seawater Portland cement pastes prepared with an ultra-low water-to-binder ratio

Seawater and sea-sand based ultra-high performance concrete (UHPC) is currently regarded as one of the most innovative and promising construction materials. To provide design guidance for the usage of silica fume (SF) during the production of seawater and sea-sand based UHPC, this work investigated the effect of SF on the later-age macro-performances and micro/nanostructure of seawater ordinary Portland cement (OPC) pastes prepared with a low water-to-binder (W/B) ratio. The results showed that the optimal SF dosage in seawater OPC-SF system was 10 wt% while that for the deionized (DI) water OPC-SF system was 20 wt%. This showed that the usage of SF could be reduced for the production of the seawater based UHPC system. It was found that the later-age compressive strength of seawater OPC-SF system was increasingly degraded with increasing SF dosage when compared with the corresponding DI water OPC-SF system. The difference in the distribution of unhydrated clinkers in the matrix as SF addition increased was the main cause. The seawater OPC-10%SF system exhibited the highest compressive strength and the lowest pore content among all the seawater-OPC systems. Additionally, with the usage of this ultra-low W/B ratio, Friedel's salt was only present in the seawater OPC pastes prepared without SF, but absent in the seawater OPC-SF pastes.

Utilization of APC residues from sewage sludge incineration process as activator of alkali-activated slag/glass powder material

In this paper, the soluble salts from the air pollution control (APC) residues of a sewage sludge incinerator and solid sodium silicate were used as a hybrid activator to prepare alkali-activated materials (AAMs) using slag and waste glass powder (GP) as the precursors. The effect of the hybrid activator on the mechanical properties and its reaction mechanism was discussed. The experimental results showed that the APC residues obviously decreased the early compressive strength of the AAMs due to its lower activity, but a steady growth of later compressive strength was achieved due to the dense microstructure. The alkali-activated slag and GP/slag suffered from severe drying shrinkage, but the drying shrinkage of the AAMs reduced by 30%–50% when the 20% APC residues were added. In addition, when the APC residues and GP was used, the insufficient aluminum and calcium contents restrained the formation of the C-(A)-S-H gels in the alkali-activated GP/slag, and the N-(C)-A-S-H gels were formed until the available Ca was exhausted. Some crystalline materials including the ettringite, hydrotalcite, albite and Friedel's salts were detected in the alkali-activated slag/GP after the incorporation of the APC residues in addition to the N–S–H gels.

Friedel's salt: Temperature dependence of thermoelastic properties

Friedel's salt is an AFm phase playing a major role in immobilizing chloride ions in cement-based materials. This phase exhibits a displacive phase transition between 30 and 40 °C. Data on the physical properties of Friedel's salt and their temperature dependence is lacking in the literature. Here, we perform molecular simulations to compute Friedel's salt's elastic constants, heat capacity, and thermal expansion. AFFF, a force field focusing on AF-phases in cement systems, is extended to account for phases with chloride. We capture the temperature transition with the simulations, provide the thermoelastic properties as a function of the temperature, and assess the dynamics of water and chloride in Friedel's salt. Such information can be readily used in multiscale modeling requiring data on Friedel's salt thermoelastic properties.

The role of CaO and MgO incorporation in chloride resistance of sodium carbonate-activated slag

Partial substitution of CaO or MgO for slag accelerates the reaction kinetics and strength gains of sodium carbonate (Na2CO3)-activated slags, yet their impact on the durability performance remains unknown. This study compares the effects of CaO and MgO substitution at various contents (2.5% and 5%) on the fresh properties, reaction kinetics, phase assemblage, pore structure, chloride binding capacity and chloride diffusion resistance of Na2CO3-activated slags. The results show that in addition to its higher effectiveness in boosting strength development, the substitution of CaO for slag results in superior enhancement in chloride binding and resistance of Na2CO3-activated slag compared to the system modified by MgO. Hydrotalcite is identified to have a comparable contribution to the chloride binding of CaO- and MgO-modified AAS, but the greater Friedel's salt formation is the main reason for the higher chloride immobilisation capacity of the CaO-modified AAS. The results demonstrate the technical promises of CaO and MgO as substitutes to control reaction kinetics of Na2CO3-activated slag while improving its chloride durability.

RETRACTED: Monitoring of chloride and Friedel’s salt, hydration components, and porosity in high-performance concrete

The innovative paper evaluated the water of the sea as a curing component and mixing constituent in high-performance concrete (HPC). This motivation would provide an understanding for the reader of how the water from the sea affects the HPC. This paper would provide information about the mechanism and the influence of prepared high-performance concrete mixed with either freshwater or seawater and made to cure in freshwater, seawater, or air. The mechanism and the influence were evaluated by XRD tests, SEM observations, and petrography analysis of HPCs at 3 days, 7 days, 28 days, and 90 days. The structure of the Friedel's salt increases tobermorite and ettringite (3CaO.Al 2 O 3 .3CaSO 4 32H 2 O) and retards portlandite (Ca(OH) 2 ) and calcium silicates (2CaO.SiO 2 and 3CaO.SiO 2 ) in HPC mixed with seawater for 3–90 days. Air curing reduces the formation of portlandite (Ca(OH) 2 ), tobermorite (3CaO.2SiO 2 .3H 2 O), ettringite (3CaO.Al 2 O 3 .3CaSO 4 32H 2 O), and calcium silicate (3CaO.SiO 2 ) in seawater HPC while increasing the formation of calcium silicate (2CaO.SiO 2 ). SEM analysis supports the mechanism and influence of mixing of seawater, curing in the water of the sea, and curing treatment in the air. According to data from petrographic analysis and porosity testing, the porosity was decreased by the seawater and curing treatment in the seawater in HPC mixes. In terms of hydration components, SEM observation, porosity, and petrographic analysis, the HPC-3 shows the best performance in the work.

Investigation on chloride binding capacity and stability of Friedel's salt in graphene oxide reinforced cement paste

Chloride binding capacity is one of the important factors affecting chloride induced rebar corrosion in reinforced concrete structures. Moreover, the stability of Friedel's salt will also affect the chloride binding capacity of cement-based materials. This study investigates the effect of graphene oxide (GO) on the chloride binding capacity of cement paste and stability of Friedel's salt under different pH conditions. Experiments of X-ray diffraction (XRD), Thermogravimetric analyzer (TGA), Scanning electron microscope (SEM) and Energy dispersive spectroscopy (EDS) were performed to analyze the phase assemblage, micro morphology, element ratio and the enhanced mechanisms. Results showed that the 0.2 wt% GO addition can significantly improve the chloride binding capacity of cement paste where the amount of bound chloride ions increased by approximately 46%. Meanwhile, the release of bound chloride ions at low pH conditions (from 12 to 9) can be suppressed by GO addition, which the chloride ion desorbing rates of cement-based materials dropped from 88% to 38% with 0.2 wt% GO addition. Microstructural and hydration analyses illustrated that GO addition promoted the formation of stable Friedel's salt by strong charge adsorption effect on calcium ions. Also, inhibiting the chloride ion desorbing and decomposition of Friedel's salt at low pH conditions.