Chloride Binding Research Articles

Chloride ion permeability of concrete containing recycled composite powder from building demolition waste

Buildings in the marine environment are vulnerable to chloride ion erosion, which threatens the service life of concrete structures. To facilitate the application of concrete containing construction demolition waste in the marine environment, recycled composite powder concrete (RCPC) was prepared using recycled composite powder as cement substitute. The chloride ion permeability of RCPC was evaluated by chloride ion diffusion test and rapid chloride ion migration test (RCM). The chloride ion permeability of RCPC continued to enhance with growing content of recycled composite powder. During the immersion age, the surface chloride ion content of the samples containing recycled composite powder increased by an average of 18.3–65.3% over the control group, with a corresponding average increase in chloride ion diffusion coefficients ranging from 17.0% to 31.5%. The chloride ion migration coefficients in the RCM test raised by 9.5–24.7%. A series of microscopic tests such as nuclear magnetic resonance (NMR), X-ray diffraction (XRD) and scanning electron microscope-energy dispersive spectrometer (SEM-EDS) suggested that the total porosity increased by 11.9–29.5% with the addition of recycled composite powder. The chloride ion diffusion coefficients exhibited a linear increase with growing total porosity and porosity of capillary pores, whereas an exponential increase with the porosity of transitional pores. The poor reactivity of the recycled composite powder resulted in a looser microstructure and weakened chloride binding capacity, and these factors boosted chloride ion transport. A chloride ion diffusion model of RCPC considering the time dependence of chloride ion transport was developed, and the reliability of the model was verified by experimental data.

Chloride binding of barium-containing zeolite corrosion inhibitor in Portland cement mortar

The use of sea sand is limited in reinforced concrete due to the presence of corrosive free chloride ions. In this study, a barium-containing zeolite corrosion inhibitor was designed and added into mortar to improve the chloride binding ability by avoiding the interference of SO42− in forming chloroaluminate salts under the condition of ensuring the necessary setting time of the mortar. Ion dissolution tests showed that the amount of Ba2+ released by the corrosion inhibitor in the first 3 h was only 29.6 mg/L, which avoided the problem of rapid setting of the mortar. The ability of the mortar to bind free chloride ions was assessed by leaching titration, and the sample with 16 wt% corrosion inhibitors showed a 32% increase in the bound chloride ratio compared to the control sample at 28 d. The results of XRD, TG-DTG, 27Al MAS NMR and SEM-EDS tests indicated that the slow-release Ba2+ from the corrosion inhibitor promoted the formation of chloroaluminate by precipitating SO42− in the late hydration stage in the mortar. Electrochemical impedance spectroscopy results further confirmed the effectiveness of the corrosion inhibitor in inhibiting the rusting of the steel bars. This study provides guidance for the use of sea sand resources and the long-term corrosion prevention of reinforced concrete.

Factors affecting free chloride contents of hardened cement paste with a low water-to-binder ratio determined by rapid water extraction

This paper assesses the free chloride content in hardened cement paste with a low water to binder (w/b) ratio by a proposed water extraction method. Key parameters including extraction time, particle size of the sample, types and concentrations of chloride salts are thoroughly investigated to understand their effects on the extraction results. The findings reveal that the increase of extraction time from 1 to 20 min and the decrease of particle size from 0.315-1 mm to 0.045–0.08 mm exhibits limited influence on the hydration degree of cement paste with low w/b ratio during the extraction process. With the increase of extraction time, the extracted chloride content gradually increases. Beyond the 10-min mark, the extracted chloride content stabilizes gradually, indicating a stable status in the extraction process. The content of Friedel's salt remains relatively unchanged throughout the 10min water extraction, while physically bound chloride gradually releases into the extraction water. Almost all physically bound chloride in NaCl and CaCl2 mixed specimens is desorbed within the 10min of extraction time when the particle size is set at 0.045–0.08 mm. However, the physically bound chloride in MgCl2 blended specimens keeps relatively stable when the particle size varies, which is due to the improved chloride binding capacity by M-S-H. The rapid water extraction method is proved suitable for free chloride testing of hardened cement paste with low w/b ratio by controlling suitable parameters. Consequently, the particle size of 0.08–0.16 mm and extraction time of 10 min are recommended for conservative evaluation of free chloride content in hardened cement paste with low w/b ratio.

Effects of a novel carbon nanomaterial on hydration, mechanics, and chloride binding of cement composites

Nanomaterials have made significant progress in the field of cementitious materials, but suffer from primary problems of high cost and poor dispersity. Carbon dots (CDs) as a novel low-cost and high-dispersity nanomaterial preliminarily demonstrate their potential for cement. Nevertheless, it lacks systematic research on their effects on cement properties. For the first time, this work comprehensively investigates the effects of CDs on the hydration, mechanics, and chloride binding of cement composites. More importantly, the relevant mechanisms are revealed in depth. Specifically, cost-efficient ($0.013/g) and well-dispersed (dispersed in simulated concrete pore solution for 7 d) CDs are directly prepared by a facile microwave approach. The CDs dramatically retard the early hydration, improve later mechanical performance, and obviously enhance chloride binding. In detail, 0.2 wt% CDs reduce the second exothermic peak value by 75%, but improve the chloride binding capacity of paste by 51%. And 0.1 wt% CDs enhance the compressive/flexural strength of mortar by 17%/21%. Crucially, related influence mechanisms are uncovered. Namely, CDs create a protective barrier to retard hydration through the complexation of their abundant surface groups with Ca2+; While CDs exert the nucleation effect to boost the formation of C–S–H and Friedel's salt, thereby playing a positive impact on chloride binding; Meanwhile, CDs with suitable dosages carry out nucleation effect to counteract their air-entraining effect, thus improving later mechanical properties of cement composites. This study is expected to provide a novel low-cost and high-dispersity CDs nanomaterial to advance the development of high-performance cementitious materials.

Synthesis of CaLiAl-LDHs and its optimization on the properties and chloride binding capacity of eco-friendly marine cement-based repair materials

Chloride attack in the marine environment adversely affects the durability of ordinary Portland cement-sulfoaluminate cement-ground granulated blast furnace slag (OPC-SAC-GGBFS) repair materials, leading to the premature failures of repair engineering. In this research, CaLiAl-LDHs (CLA-LDHs) was synthesized by a modified co-precipitated method, and the characterisation and adsorption behaviour for chloride ions were investigated. In addition, the impact of the synthesized CLA-LDHs on the mechanical properties, chloride binding capacity and hydration process of OPC-SAC-GGBFS repair materials were systematically researched. The obtained results revealed that the adsorption capacity of CLA-LDHs for chloride ions was 41.47 mg/g, and the adsorption process conformed better to the quasi second-order model and Langmuir isotherm model. The chloride binding capacity of OPC-SAC-GGBFS was enhanced by adding CLA-LDHs, mainly due to the formation of more FS/LDHs-Cl. Furthermore, the addition of CLA-LDHs promoted the early hydration of OPC-SAC-GGBFS, shortened the setting time, improved the early mechanical properties, but slightly reduced the mechanical properties at 28 d. It is noteworthy that the mechanical properties of OPC-SAC-GGBFS at −10 °C was significantly enhanced by CLA-LDHs.

A novel ultrasonic method to exfoliate CLDH toward improving mechanical and chloride binding properties of cementitious composites

With the complexity of architectural structures increasing, traditional cement-based materials inevitably face challenges of mechanical performance and durability. Calcined layered double hydroxide (CLDH) attracts significant attention due to its potential for improving mechanical and chloride binding properties of cement-based composites, but suffers from poor dispersion, limiting its full potential. To tackle this issue, a novel method utilizing graphene quantum dots (GQDs) in conjunction with ultrasound has been developed to efficiently exfoliate CLDH, thereby enhancing the mechanical and chloride binding properties of cement composites. Most importantly, its related enhancement mechanisms were revealed by comprehensively analyzing hydration heat evolutions, phase compositions, and microstructures of relevant cement samples. Specifically, highly dispersed CLDH (G-CLDH) prepared by GQDs-assisted ultrasonication possessed a larger specific surface area (SBET), significantly increasing by 92.04 % compared with CLDH treated by pure ultrasonication (i.e., U-CLDH). After incorporating 0.8 wt.% (by weight of cement) G-CLDH, the cement composites demonstrated 22.29 % and 58.56 % improvement in compressive strength and chloride binding capacity respectively than blank group. The enhancement mechanism of compressive strength and chloride-binding capacity by G-CLDH was rationally proposed. As for the former, it was attributed to a significant reduction of porosity and a remarkable increase of hydrated calcium silicate (C-S-H) gels; Regarding the latter, that was a larger number of C-S-H gels and better dispersed G-CLDH led to more physically adsorbed chloride and more ion-exchanged-caused bound chloride respectively. The developed innovative approach could prepare high-dispersion CLDH to simultaneously enhance mechanical performance and chloride binding capacity of cementitious materials, promoting to the advancement of high-performance cement composites.

A Cationic Catechol Derivative Binds Anions in Competitive Aqueous Media.

A simple dihydroxy isoquinolinium molecule (3+) was prepared by a modification of a literature procedure. Interestingly, during optimisation of the synthesis a small amount of the natural product pseudopalmatine was isolated, and characterised for the first time by X-ray crystallography. Compound 3+ contains a catechol motif and positive charge on the same scaffold and was found to be a potent anion receptor, binding sulfate strongly in 8 : 2 d6-acetone:D2O and 7 : 3 d6-acetone:D2O (Ka>104 and 2,100 M-1, respectively). Unsurprisingly, chloride binding was much weaker, even in the less polar solvent mixture 9 : 1 d6-acetone:D2O. The sulfate binding is remarkably strong for such a simple molecule, however anion binding studies were complicated by the tendency of the molecule to react with BPh4 - or BF4 - species during anion metathesis reactions. This gave two unusual zwitterions containing tetrahedral boronate centres, which were both characterised by X-ray crystallography.

Effects of SCMs on chloride binding capacity of ultra-low water-to-binder ratio cement paste with internally introduced chloride

Chloride binding is a critical factor affecting the chloride-induced corrosion of concrete with embedded steel reinforcement. The supplementary cementitious materials (SCMs) play an important role in chloride binding including chemical binding and physical adsorption. However, limited knowledge is available on effects of SCMs and their chemical components on chloride binding of cement systems with ultra-low water-to-binder ratio (w/b). This study investigated the chloride binding mechanisms of cement paste with ultra-low w/b ratio incorporating three types of SCMs with different chemical compositions. The chloride was introduced internally through the mixing water. The free chloride content was measured using pore solution expression and titration. The characterization techniques, including XRD and TGA, Zeta potential, SEM/EDS, and FTIR were conducted to evaluate the physically and chemically bound chlorides. The results showed that the content of total bound chloride was a function of the content of chemical bound chloride and physical adsorbed chloride that were governed by CaO and Al2O3 in SCMs. The CaO had an instrumental effect on the physical chloride binding capacity, while Al2O3 was the main factor in the chemical chloride binding.

Tetra-azobenzene extended calix[4]pyrroles: influence of photo-isomerization on chloride binding and its transport through liposomal membranes

Photo-modulation in chloride binding affinity and transmembrane transport with tetra-azobenzene extended calix[4]pyrroles.

Medium transmission property of the interfacial transition zone between MK-GGBFS geopolymer mortar and aggregate

In this study, metakaolin (MK)–ground granulated blast furnace slag (GGBFS) was used to prepare geopolymer mortar, and concrete was prepared using prismatic-shaped basalt or aged cement mortar block as coarse aggregate. The pore structure characterization of the mortar, chloride binding capacity of the corresponding paste and the micro dimension of the interfacial transition zone (ITZ) in concrete were analysed by using a mercury intrusion porosimeter, the chloride adsorption equilibrium method and scanning electron microscopy-energy dispersive spectroscopy, respectively. The medium transmission properties of the concrete and corresponding mortar were analysed through a moisture diffusion test, chloride migration test, and chloride natural diffusion test. On this basis, the permeability resistance of the ITZ in geopolymer concrete was studied by manipulating the parameters for the basalt aggregate. The result shows that the geopolymer mortar exhibits higher porosity compared to cement mortar with similar strength, while the most probable pore size is significantly smaller, with more than 80% of the pores showing a pore size of less than 50 nm. The chloride binding mechanism for geopolymer paste primarily involves physical adsorption, and shows a greater binding capacity than cement paste at a chloride ion concentration greater than 1 mol/L. The medium transmission coefficient for geopolymer concrete is found to be 55.1–79.0% of that of cement concrete for the same parameters of the coarse aggregate. The impermeability of geopolymer concrete and its ITZ is found to be always better than that of cement concrete for varying parameters of the coarse aggregate.

An Ion-Pair Induced Intermediate Complex Captured in Class D Carbapenemase Reveals Chloride Ion as a Janus Effector Modulating Activity.

Antibiotic-resistant Enterobacterales that produce oxacillinase (OXA)-48-like Class D β-lactamases are often linked to increased clinical mortality. Though the catalytic mechanism of OXA-48 is known, the molecular origin of its biphasic kinetics has been elusive. We here identify selective chloride binding rather than decarbamylation of the carbamylated lysine as the source of biphasic kinetics, utilizing isothermal titration calorimetry (ITC) to monitor the complete reaction course with the OXA-48 variant having a chemically stable N-acetyl lysine. Further structural investigation enables us to capture an unprecedented inactive acyl intermediate wedged in place by a halide ion paired with a conserved active site arginine. Supported by mutagenesis and mathematical simulation, we identify chloride as a "Janus effector" that operates by allosteric activation of the burst phase and by inhibition of the steady state in kinetic assays of β-lactams. We show that chloride-induced biphasic kinetics directly affects antibiotic efficacy and facilitates the differentiation of clinical isolates encoding Class D from Class A and B carbapenemases. As chloride is present in laboratory and clinical procedures, our discovery greatly expands the roles of chloride in modulating enzyme catalysis and highlights its potential impact on the pharmacokinetics and efficacy of antibiotics during in vivo treatment.

Salt scaling resistance of pre-cracked ultra-high performance concrete with the coupling of salt freeze-thaw and wet-dry cycles

Wet-dry cycles and cracking are unavoidable problems of concrete structures and reduce durability by enhancing the penetration of harmful ions and water, which may have a synergistic adverse influence with severe surface damage caused by salt freeze-thaw cycles. This study aims to investigate the salt scaling resistance of ultra-high performance concrete (UHPC) under multiple harsh environments including wet-dry cycles and pre-cracking. The relationship between workability, absorption behavior, and scaling resistance with fiber content increases is assessed. Mass loss, chloride binding behavior, pore structure, and pore morphology are analyzed to describe the influences of pre-cracking and wet-dry cycles. The results reveal that the workability of fresh concrete and the distribution of steel fibers are the key factors in determining the salt scaling resistance of UHPC. Pre-cracking and wet-dry cycles inhibit the rapid scaling damage of UHPC by accelerating chloride accumulation, which reduces the icing pressure of pore liquid and refining the micropores (<200 nm) capable of remaining non-frozen at low temperatures through the chemical binding of chloride. However, the combined effect of pre-cracking and wet-dry cycles can lead to the corrosion of internal steel fibers and more scaling damage, and the crack width should not be greater than 0.1 mm.

Microstructure, Hydration, and Chloride Binding Behavior of Limestone Calcined Clay Cement Prepared Using Seawater

Microstructure, Hydration, and Chloride Binding Behavior of Limestone Calcined Clay Cement Prepared Using Seawater

Insights on the chloride adsorption stability in cement mortar under current field and sulfate attack: From experiments to molecular dynamics simulation

The destabilization together with boundary chloride ions releasing leads to the corrosion of steel bars, posing nonnegligible risks to the durability of structures. This work attempted to design the typical pore solution of underground constructions via methods of combining NaCl with Na2SO4 along with conducting a stray current continuously. The bound chloride stability of mortar under the action of electric current was systematically determined. The reaction mechanisms were tested by quantitative XRD, TG-DTG, FTIR, FESEM, and X-CT. Molecular dynamics was utilized to simulate the physical binding processes of C–S–H of Cl−/SO42- and their interaction under the actions of electric field by comparing the ions displacement trajectory, radial distribution function, and moving ability. The experimental results showed that the SO42- weakened the chemical chloride binding capacity with the Friedel's salt, portlandite, and calcium silicate decomposed to produce gypsum or ettringite. The electric field demonstrated less impact on the stabilities of chemical-bound Cl−, but promoted SO42- redistributions, causing substantial pore coarsening. The simulation revealed that the physical binding contained short-range ion Coulomb-interactions and long-range van der Waals interactions. The SO42- inhibited the binding of the C–S–H on Cl− by fact that the deposition large cluster of Na–SO4 blocked the nano-meter channels and competitive adsorption occurred at the SiOCa+ sites, while the introduction of electric field weakened the dominating effects of Coulomb-interactions and improved the ions desorption gradually. Hopefully, the transport and adsorption mechanisms of the Cl− in the cement-based materials can help guide the underground concrete with durability.

Chloride binding mechanism and free chloride reduction method of alkali-activated slag/fly ash mixed with seawater

The chloride binding mechanism of alkali-activated materials (AAM) under various granulated blast furnace slag (GBFS)/fly ash (FA) ratios is investigated in this work. Two types of layered double hydroxides (LDH), i.e., MgAl-LDH and CaAl-LDH, and active magnesium oxide (MgO) were added to reduce the concentration of free chloride in AAM. The results demonstrate that the ratio of GBFS to FA has non-negligible influence on the AAM’s ability to bind chloride. The content of bound chloride increased by 3.78%-17.42% as the FA content in seawater-based alkali-activated materials (SAAM) raised. The chloride binding forms of SAAM were mainly chemical binding by the hydrated calcium aluminate (AFm) phase and physical adsorption by calcium (alumino) silicate hydration (C-(A)-S-H) gels when the FA dosage is less than 20% in SAAM. When the FA mass ratio in SAAM was larger than 20%, the chloride binding form of SAAM was mainly the physical adsorption by calcium (sodium)alumino-silicatehydrate ((C,N)-A-S-H) gels. Among the three additive materials, CaAl-LDH was the most effective in reducing the free chlorine content by 11.34%. While for MgAl-LDH, the chloride binding capacity was compromised by the less strength loss. In this work, seawater was used as the mixing water to introduce chloride ions, the results of which could provide a reference for the application of seawater in future projects.

Coupling of augmented PAN membranes by surface immobilization of pincer ligands with an activated sludge to treat a real wastewater

In the present study, industrial estate wastewater was subjected to treat with a conventional activated sludge (CAS) bioreactor and then purified using a highly efficient surface-modified PAN ultrafiltration membrane. Response surface methodology (RSM) has been employed to analytically design, carry out, and optimize biological experiments using two independent operating variables, MLSS (6,000–14,000 mg/L) and HRT (5–15 h). This resulted in an effluent that was optimally stabilized before ultrafiltration due to the consequent responses of COD removal (90 %), effluent turbidity (1 NTU), and SVI (82 mL/g). To rationally tailor the antifouling PAN UF membranes for this intended purpose, novel hydrophilic pincer ligands were formed by covalent binding of cyanuric chloride (CC) activated membrane surfaces with various loadings of (1.0, 3.0, and 5.0 wt%) 5-amino-1, 3, 4-thiadiazol-2-thiol (AMT). In terms of hydrophilicity, surface roughness, antifouling characteristics, and permeate flux, the optimum membrane surface-modified with 3.0 wt% pincer ligand loading outperformed the others, leading to a low WCA of 42.75°, smoother surface (Sa = 14.77 nm), FRR of 97.1 %, and PWF of 56.07 kg/m2.h. The operated CAS followed by surface-modified Pincer/PAN membranes is therefore an appealing proposal for generating high-quality effluent from industrial wastewaters.

4-year monitoring of degradation mechanisms of seawater sea-sand concrete exposed to tidal conditions: development of chemical composition and micro-performance

In tidal zones, the transfer of conductive ions accelerates concrete deterioration due to dry-wet cycles, temperature, and humidity gradients over time. Thus, this study investigates the effects of ground granulated blast furnace slag (GGBS), silica fume (SF), and metakaolin (MK) on the deterioration rate of seawater Sea-sand concrete (SWSSC) exposed to tidal conditions for four years caused by carbonation, sulphate and chloride penetration. Results showed continuous exposure to MgSO4, reduced Fe content and converted AFm into AFt, contributing to an increase in total SWSSC porosity of 12.9% while reduced to 10.2%, 7.4% and 7.3% with the optimal addition of GGBS, SF and MK. In combined sulphate and chloride-rich conditions, enhanced gel phase physical properties were more influential than AFm phases in increasing chloride binding capacity. SF suppressed AFt expansion, formed dense C−S−H with optimal Ca/Si ratio and physically increased the chloride binding capacity of SWSSC. Similarly, despite its high alumina content, MK restricted chloride mobility mainly through C−S−H and, subsequently, AFm phases. Additionally, through its initial acceleration of calcium-hydroxide consumption, SF reduced alkalinity and minimized the formation of CaCO3, outperforming MK in mitigating carbonation. Higher CaO and MgO in GGBS-mixed samples led to dolomite formation in severely carbonated zones, causing long-term mechanical strength reduction. In summary, SF significantly enhanced SWSSC durability and served as an effective additive in tidal-exposed SWSSC.

Investigating the effects of testing protocol factors on chloride binding capacity in cementitious materials

This study investigates the influence of testing protocol factors, such as the degree of saturation (DoS), exposure solution composition, sample shape, and the solid-to-exposure solution mass ratio (SLR), on the measured chloride binding capacity of cementitious systems. Samples underwent varying degrees of saturation, including vacuum-saturated, partially saturated, and oven-dried conditions. The exposure solution composition included calcium, potassium, and sodium ions, in addition to pure sodium chloride. Different sample forms (powdered, crushed, and disk-shaped) were explored. Three SLRs of 1:3, 1:6, and 1:10 were also examined for their impact on chloride binding. The results indicated that DoS significantly influences chloride binding, with vacuum-saturated samples exhibiting higher binding capacity than partially saturated and oven dried samples. Additionally, the findings showed that samples in solutions containing additional ions had reduced binding capacities compared to pure chloride solutions. Increasing the sample surface area by crushing or powdering it led to an increase in chloride binding capacity compared to solid, disk-shaped specimens. Lastly, the results demonstrated that increasing the SLR can enhance the binding capacity of the system.

Corrosion of steel in chloride-contaminated calcium aluminate cement (CAC) mortar depending on its hydrations

The present study concerns the resistance of calcium aluminate cement (CAC) against steel corrosion. Corrosion behaviour of steel, chloride binding/buffering and chloride transport were evaluated to predict the risk of steel corrosion. The CAC mortar had no corrosion of steel, irrespective of the curing temperature and CAC types, while ordinary Portland cement (OPC) indicated a severe corrosion on the steel surface. The chloride binding capacity for CAC was lower than OPC, but the buffering to a pH decrease was highly ranked in CAC paste. Moreover, ingress of chlorides at all depths was reduced in CAC, imposing the mitigated corrosion risk.

Influence of nanosilica in the chloride binding capacity of sustainables ground blast furnace slag and metakaolin

This work investigates the chloride binding capacity combine of two sustainable pozzolanic additions such as granulated blast furnace slag (G) and metakaolin (M) used in cement to decrease its carbon footprint. They are also combined with two nanosilicas with different specific surface area (O and A). Blends of alone M or G and with nanosilica are mixed in water with Ca(OH)2 and chloride (C) to compare chloride binding capacity of both in presence or not of nanosilica. Blends are analysed by XRD, FTIR, DTA–TG and chloride binding capacity is determined too by potentriometric titration with AgNO3. The addition of chlorides to both pozzolanic M and G indicates that M shows higher chloride binding capacity than G although very similar Friedel's salt formation, indicating a higher physisorbed chlorides contain. Chlorides addition meaningfully replaces carbonates in carboaluminates phases to form Friedel's salt, being this exchange higher for samples with M than for G blends. The combination of experimental techniques used in this study have shown that the effect of nanosilica addition to samples with M and G show an opposite effect in Friedel's salt formation, increasing for samples with G and decreasing for samples that contain M.