Friedel's Salt Formation Research Articles

Synergizing metakaolin and waste-glass for sustainable and functional UHPCC– a central composite design and ecological footprint assessment

Optimizing ultra-high-performance cementitious composites (UHPCC) with sustainable materials often compromises certain properties due to the chemical nature of alternative binders used to replace standard UHPCC components like Portland cement (OPC) and microsilica (MS). In the context of Waste-Glass-UHPCC, the reduction in early strength, attributed to the varied pozzolanic reactivity of MS and recycled glass powder as cementitious materials, may reduce its application that requires high early strength. This study addresses the early strength deficiency of Waste-Glass-UHPCC by incorporating metakaolin (MK) and also aims to assess the impact of MK on 28-day compressive strength, durability, and carbon footprint. Research investigating the effects of MK on UHPCC with reduced OPC and MS content is currently limited. Specifically, this investigation explores the influence of MK on UHPCC characterized by a cement content of 620 kg/m3. By utilizing advanced statistical methods [i.e., the Central Composite Design (CCD) and Response Surface Methodology (RSM)], this study investigates the substitution of MK for OPC in formulations of Waste-Glass-UHPCC. The experimental design comprises 18 encoded mixtures, allowing for the development of second-order regression models for critical responses [slump flow and compressive strength at different ages]. Besides, visualization through RSM-3D graphs facilitates a comprehensive examination of the effects of various factors. For a deeper analysis, two of the CCD's points, i.e., SP-12 (Waste-Glass-UHPCC without metakaolin), and SP-10 (Waste-Glass-UHPCC with 65.77 kg of metakaolin per cubic meter) were further investigated along with a control dosage that represents a typical UHPCC formulation. The responses studied encompassed 1, 7, and 28 d compressive strength, chloride ion penetration, and carbon footprint measured by a systematic life cycle analysis (following ISO 15804), assessing the environmental impact of the UHPCC's making materials from raw extraction to disposal. Despite encountering challenges in meeting self-compacting concrete criteria due to MK's tendency to accelerate hydration, the enhanced early strength properties (61 % higher than those of the Waste-Glass-UHPCC) make the MK-based mixture appropriate for various applications such as bridge engineering or pavement rehabilitation. Additionally, the addition of MK in UHPCC formulation demonstrated superior resistance to chloride ion permeability even compared to the control mixture, attributed to MK's ability to enhance the concrete's microstructure and capture chloride ions, attributed to Friedel's salt formation. Noteworthy findings include a significant (27 %) reduction in carbon footprint with the incorporation of MK in Waste-Glass-UHPCC compared to the control counterparts. The current study highlights the durability and environmental advantages of MK-based UHPCC blends while emphasizing the critical requirements of workability and strength development of sustainable UHPCC.

Fillers to improve the ductility and impermeability of crumb rubber concrete

Crumb rubber concrete (CRC), a type of eco-friendly concrete materials, has attracted pronounced interest in the field of infrastructure construction and waste management. However, special attention should be paid to its permeability since it is an important indicator to determine its service life for building structures, especially in coastal regions. Present study discusses the feasibility of pozzolanic fillers to improve the ductility and impermeability of CRC. By incorporating fly ash (FA), silica fume (SF), and ground granulated blast furnace slag (GGBFS), fresh properties, mechanical strength and chloride resistance of CRC were evaluated. Results show that the fillers adopted enhance the toughness of CRC in terms of ductility index considering splitting-tensile and compressive strength, among which SF has the most positive effect. Micro-aggregate effect of FA particles, high active silica content of SF and more Friedel's salt formation are the main reasons for the improved impermeability of CRC. Radar charts are plotted to analyze the overall performance of CRC with fillers. Relative area values indicate that SF exhibits the most significant improvement in CRC performance, followed by GGBFS and FA.

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.

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.

Study on influence of nitrite and phosphate based inhibiting admixtures on chloride interaction, rebar corrosion, and microstructure of concrete subjected to different chloride exposures

The study aims to assess the effect of nitrite and phosphate based inhibiting admixtures, i.e., sodium nitrite (NaNO2) and di-Sodium hydrogen phosphate (Na2HPO4) against corrosion of reinforcing steel in concrete exposed to chloride environment with different chloride salts through electrochemical measurements. Further, the influence of inhibiting admixtures on penetration of chloride ions, chloride binding, and changes in microstructure of concrete were investigated. Electrochemical measurements indicated that NaCl is more aggressive in depassivating the rebar early thereby reducing corrosion initiation period, and also increasing corrosion rate compared to CaCl2 followed by MgCl2. The addition of inhibiting admixtures enhanced resistance of concrete against corrosion. NaNO2 exhibited improved resistance against corrosion of rebar compared to Na2HPO4 even in presence of higher amount of chloride ions near rebar level. Corrosion current density in concrete containing NaNO2 was 1.50 times, 1.74 times and 1.89 times lower than Na2HPO4, in case of exposure to NaCl, MgCl2 and CaCl2 solutions respectively. The formation of denser microstructure in concrete made from Portland pozzolana cement was more dominant in minimizing the extent of corrosion over the effect of inhibiting admixtures compared to concrete made from ordinary Portland cement. Microstructure analysis indicated formation of more amount of Friedel's salt in concrete admixed with Na2HPO4 than NaNO2. However, Friedel's salt formation mostly decreased with increase in Na2HPO4 dosage whereas the reverse variation was observed in case of NaNO2.

Behavior of blends of CSA and Portland cements in high chloride environment

Calcium SulfoAluminate (CSA) cement has received increasing interest in recent years, mainly for its environmental aspects. However, few drawbacks such as its higher cost, compared to Ordinary Portland Cement (OPC), or the high carbonation rate, limits its application in reinforced concrete even when high early strengths are required.A technological solution could be combining CSA cement with non-corrosive reinforcements, widely used for structure exposed to marine environments. In order to evaluate the feasibility of this innovative solution even in high chlorides environments, blends of CSA clinker and limestone Portland cement were investigated in combination with seawater and varying the constituent proportions.The results show that sulfates play a key role in the equilibria between AFt/AFm influencing the Friedel's salt formation, thus the ability to bind chlorides. An optimal blend composition, able to improve the durability of concrete in marine environment, is suggested.

Sewage sludge ash recovery as valuable raw material for chemical stabilization of leachable heavy metals.

This paper proposes, for the first time, the use of sewage sludge ash (SSA), obtained by sludge combustion for the stabilization of fly ashes containing heavy metals as Pb and Zn. In particular, the proposed method aims to take advantage of valuable raw materials present in SSA, such as phosphate, silica, and alumina. The stabilization has been explained by the synergic phosphate, carbonation, and pozzolanic reactions together with the Friedel's salt formation. This method to sewage sludge management allows the complete recovery of valuable raw materials otherwise destinated for lanfill. This is virtuous example of the use of waste materials for de-pollution processes.

Effect of exposure temperature on chloride-binding capacity of cementing materials

Chloride-induced corrosion of reinforcement is one of the main causes of concrete deterioration in marine environments. The service life of reinforced concrete (RC) structures exposed to chloride ions is closely related to the rate of chloride ion diffusion through the concrete. Chloride binding has a remarkable influence on chloride penetration and hence on the time to corrosion initiation in RC structures. Determination of the apparent chloride diffusion coefficient of concrete takes into account the chloride-binding capacity but not the effect of temperature on the chloride-binding capacity. This paper examines the effect of temperature, from −4°C to 70°C, on the chloride-binding capacity of paste mixes containing supplementary cementitious materials (SCMs) as cement replacements. The results of the current study suggest that Friedel's salt formation is the major cause of the reaction between chloride ions and tricalcium aluminate (C3A) and hence the chloride-binding capacity decreases with increasing temperature; the order of chloride-binding capacity as a function of exposure temperature is 22°C > −4°C > 3°C > 35°C > 50°C > 70°C. Both the experimental and modelled results indicate a non-linear relationship between the exposure temperature and the chloride-binding capacity for cement paste containing SCMs as cement replacement.

Synthesis, characterization and formation mechanism of friedel’s salt (FS: 3CaO·Al2O3·CaCl2·10H2O) by the reaction of calcium chloride with sodium aluminate

The synthesis of Friedel's salt (FS: 3CaO center dot Al2O3 center dot CaCl2 center dot 10H(2)O) by the reaction of calcium chloride with sodium aluminate was investigated. Factors affecting the preparation of Friedel's salt, such as reaction temperature, initial concentration, titration speed, aging time and molar Ca/Al ratio were studied in detail. XRD, SEM images and particle size distribution show that the reaction temperature, aging time and molar Ca/Al ratio have significant effect on the composition, crystal morphology, and average particle size of the obtained samples. In addition, the initial CaCl2 concentration and NaAlO2 titration speed do not significantly influence the morphology and particle sue distribution of Friedel's salt. With the optimization of the operating conditions, the crystals can grow up to a average size of about 28 mu m, showing flat hexagonal (or pseudohexagonal) crystal morphology. Moreover, two potential mechanisms of Friedel's salt formation including adsorption mechanism and anion-exchange mechanism were discussed. In the 'adsorption mechanism, Frieders salt fonus due to the adsorption of the bulk Cl- ions present in the solution into the interlayers of the principal layers, [Ca2Al(OH-)(6)center dot 2H(2)O](+), in order to balance the charge. In the anion-exchange mechanism, the freechloride ions bind with the AFm (a family of hydrated compounds found in cement) hydrates to form Friedel's salt by anion-exchange with the ions present in the interlayers of the principal layer, [Ca2Al(OH-)(6)center dot 2H(2)O](+)-OH-.

Friedel's salt formation in sulfoaluminate cements: A combined XRD and 27Al MAS NMR study

Four different binders based on calcium sulfoaluminate cements have been submitted to accelerated chlorination through ionic exchange on hydrated pastes, in order to investigate their ability to chemically bind chloride ions that might reduce chloride penetration. The composition of hydrated cements before and after the treatment was evaluated by means of an X-Ray Diffraction–27Al Magic Angle Spinning Nuclear Magnetic Resonance Spectroscopy combined study, allowing to take into account even partially amorphous phases and to make quantitative assumption on the relative abundance of the different aluminium-containing phases. It was found that low SO3 Sulfoaluminate–Portland ternary systems are the most effective in binding chloride ions and the active role played by different members of the AFm family in chloride uptake was confirmed. Moreover, a peculiar behavior related to the formation of Friedel's salt in different pH conditions was also established for the different cements.

TEM and SAED Characterization of Metakaolin. Pozzolanic Activity

The present study deals with a characterization of metakaolin pozzolanic activity and its chemical character exhibited in the Ordinary Portland Cement (OPC) blends by means of Transmission Electron Microscopy (TEM) and Selected‐Area Electron Diffraction (SAED) techniques principally. Metakaolin sample was prepared by calcination of kaolin rock (Guadalajara, Spain) at 780°C. Two OPC of different chemical composition from the tricalcium aluminate content point of view were chosen and Portland cement blends series elaborated and then submitted to the pozzolanic activity test (EN 196‐5 or Frattini test). The main mineralogical components of the metakaolin are determined qualitatively: χ‐alumina and quartz. The chemical character of the metakaolin is described because of its final composition as well as due to its Al atoms possible coordination. The crystalline order of the material is found to be of both amorphous and polycrystalline, being an intimate amorphous mixture of alumina and silica. Finally, all the alumina capable of reacting chemically is denominated and classified as reactive alumina component, Al2O3r−, of pozzolans, as well as the aluminic chemical character of metakaolin in OPC blends is once again proved and exhibited by means of Friedel's salt formation studied already at 4 h‐age.

Modelling of isothermal coupled moisture–ion transport in cementitious materials

A numerical model has been developed to predict isothermal coupled moisture–ion transport in cementitious materials. Ionic transport is described by the extended Nernst–Planck equation, which accounts for advection of the liquid phase. Moisture transport includes Fickian water-vapour relative diffusion and Darcian liquid-phase movement. The ion effect on liquid/vapour water equilibrium is taken into account. The variations of the transport properties vs the degree of saturation are described by integral functions or analytical formulas. A Freundlich's type description along with instantaneous Friedel's salt formation is considered for chloride binding at equilibrium. A kinetic equation is added in the cases of non-instantaneous binding processes. The governing equations, as well as the methods of assessment of the material properties required as input data, are described in the paper. Moreover, examples of application of the model in lab conditions are provided, which highlight its capability of predicting moisture/ionic concentration profiles even in complex configurations.

Stabilization/Solidification of Petroleum Drill Cuttings: Thermal and Microstructural Studies of Binder Hydration Products

A typical organic waste, petroleum drill cuttings containing hydrocarbons, heavy metals, and chlorides, was treated by stabilization/solidification (S/S) using cement and high carbon fly ash. Analytical techniques, including differential scanning calorimetry, Fourier transform infrared spectrometry/microspectroscopy, and scanning electron microscopy with energy dispersive X-ray microanalysis, were used to investigate the effect of drill cuttings on binder hydration products, the interaction between binders and drill cuttings, and the type of immobilization mechanism occurring. Results show that both high carbon fly ash and drill cuttings addition decreased the amounts of binder hydration products. Hydrocarbons were discovered to be physically trapped by micro- and macroencapsulation in the matrix formed by binder hydration. Chemical interaction was observed between binders and chlorides leading to Friedel's salt formation. Differential scanning calorimetry and Fourier transform infrared analysis of residues from leaching test indicated that exposure of S/S products to leaching conditions could compromise their integrity. This work demonstrates use of these techniques to investigate the interactions between a waste and binder during S/S, thus aiding the development of an effective S/S system.

Impedance spectroscopy study of saturated mortar samples

Mortar samples saturated with different solutions (deionised water, 0.5 M NaCl and 1 M NaCl) are studied to quantify microstructural changes induced by weathering of concrete in near-neutral solutions containing chlorides. The study is based on physical and electrochemical techniques. Mercury intrusion porosimetry is employed to quantify porosity and pore size distribution, and impedance spectroscopy as a non-destructive technique able to give information on structural changes. SEM imaging, XRD, and EDX characterisation allow elucidating the causes of the observed structural changes. Portlandite leaching tends to increase porosity. Nevertheless, the leaching process towards near-neutral solutions makes resistivity to increase. The presence of chlorides induces Friedel's salt formation, a slow process associated to the development of small size pores (around 10 nm). Impedance spectroscopy in the frequency range 10 −2 to 10 2 MHz is successfully employed to follow Friedel's salt formation and pore network development in mortars.

Slurry Consistency and In Situ Synchrotron X‐Ray Diffraction During the Early Hydration of Portland Cements With Calcium Chloride

Class A and H oil well cements are compared at 25° and 50°C with 0%, 1%, 2%, and 4% CaCl2. Up to 4% CaCl2 accelerated Class A thickening, but 4% led to slower thickening than 2% for Class H. C3S hydration in the two cements responded differently to CaCl2. CaCl2 always accelerated aluminate hydration. For Class A, CaCl2 accelerated early Ca(OH)2 precipitation, but sometimes reduced the amount at longer times. This may be coupled to C–S–H gel composition changes. For Class H, Ca(OH)2 precipitation changes nonlinearly with CaCl2 concentration. Ettringite to monosulfate conversion and Friedel's salt formation were sometimes seen.

Residual Strength and Durability of Volcanic Ash Concrete Exposed to High Temperature

The strength and durability performance of concretes incorporating 0 to 40% of volcanic ash (VA) as cement replacement (by mass) subjected to high temperatures up to 800 °C (1472 °F) is described. The strength properties were assessed by unstressed residual compressive strength, while durability was investigated by rapid chloride permeability test (RCPT), mercury intrusion polosimetry (MIP), differential scanning calorimetry (DSC) and crack pattern observations. Volcanic ash concrete (VAC) showed good performance showing higher residual strength, higher chloride resistance and higher resistance against deterioration particularly at temperatures below 600 °C (1112 °F) compared with the control ordinary portland cement (OPC) concrete. The improved performance of VAC can be attributed to the refinement of pore structure, lowering the presence of free chloride due to Friedel salt formation and pozzolanic action due to the presence of VA. The deterioration of both strength and durability of VAC increased with the increase of temperature up to 800 °C (1472 °F) due to substantial reduction in residual strength and an increase in pore volume and pore diameter. The serviceability assessment of VAC after a fire should therefore, be based on both strength and durability considerations.

Studies using 27Al MAS NMR of AF m and AF t phases and the formation of Friedel's salt

This paper describes the application of the magic angle spinning (MAS) NMR spectroscopy to study the chemical environment of 27Al-bearing phases in Portland cement-based concrete. A specific methodology is described that allows reliable spectra to be determined for combinations of different types of cements and fillers (in this case, Portland cement, fly ash, slag, silica fume, metakaolin and limestone filler). As well as the study of ‘molecular structure’ of cement matrix, the paper reviews the mechanism of Friedel's salt formation in cement systems. Mechanisms based on ion exchange of chloride for hydroxide in hydroxy-AF m and on chloride absorption on formation are discussed. Finally, the nature of the chloride/hydrate binding phenomena are described to provide a reasonable robust and fundamental picture of the role different cements can play in the provision of overall concrete durability to chloride ingress from a chemical perspective.

Mechanism of Friedel's salt formation in cements rich in tri-calcium aluminate

In the present investigation, based on pore solution analyses, the mechanisms of Friedel's salt formation and the related chemical processes taking place in mortar due to chloride binding are dealt with. Pore solutions from mortars containing NaCl and CaCl 2 added during mixing were analyzed. Based on the results it is proposed that in the presence of NaCl the Friedel's salt forms by two separate mechanisms; an adsorption mechanism, and an anion-exchange mechanism. In the adsorption mechanism, Friedel's salt forms due to the adsorption of the bulk Cl − ions present in the pore solution into the interlayers of the principal layers, [Ca 2Al(OH −) 6.2H 2O] +, of the AFm (Aluminate Ferrite mono) structure to balance the charge. In the anion-exchange mechanism, a fraction of the free-chloride ions bind with the AFm hydrates (C 4AH 13 and its derivatives) to form Friedel's salt by an anion-exchange with the OH − ions present in the interlayers of the principal layer, [Ca 2Al(OH −) 6.nH 2O] +. As a result of Friedel's salt formation by the adsorption mechanism, an amount of Na + ions equivalent to the adsorbed chloride ions (in moles) are removed from the pore solution to maintain the ionic charge neutrality. The Na + ions thus removed from the pore solution, bind with the calcium silicate hydrate (C-S-H) gel lattice to balance the charge arising due to the replacement of Si 4+ ions by Al 3+ and Fe 3+ ions. In contrast, the Friedel's salt formation by the anion-exchange mechanism involves the release of OH − ions from the AFm hydrates into the pore solution, thereby increasing the pH of the pore solution. The above mechanisms are also valid for CaCl 2 salt introduced in a similar way. Although the addition of CaCl 2 salt to the mortar lowers the net pH of the pore solution, the total bound chlorides were significantly higher in comparison with the equivalent Cl − added as NaCl salt. The higher chloride binding with equivalent CaCl 2 addition is explained by the lower degree of competition offered by the OH − ions during the bulk free-chloride adsorption into the interlayers of the principal layers.