Chloride Binding Capacity Research Articles

Chloride penetration resistance and chloride binding capacity under different application environments of ferroaluminate cement

Free chloride is a crucial factor that threatens the long-term performance of marine concrete structures. The resistance of cement to chloride penetration and its capacity to bind chloride are important parameters for assessing the ability of cement-based materials to resist chloride invasion. Ferroaluminate cement (FAC) has considerable application potential in concrete used for marine structures; however, its resistance to chloride invasion and mechanism of chloride binding have not yet been revealed. In this study, the chloride diffusion coefficient and chloride binding capacity of FAC, for both internal and external chloride ions, are experimentally investigated and compared with that of ordinary Portland cement (OPC). The results show that the chloride diffusion coefficient of FAC mortar is approximately 2.5 times lower than that of OPC mortar. FAC exhibits finer overall pore distribution and the number of pores with sizes within 10–100 nm is reduced, which is responsible for its notably lower chloride diffusion coefficient. The chloride binding capacity of FAC to internal chloride ions is slightly lower than that of OPC, and a portion of the chloride ions are chemically bound by reacting with ye'elimite during hydration. The chlorides bound by physical adsorption constitute a dominant portion of the entire bound chloride content. In the case of external chloride ions, the bound chloride content of FAC is lower than that of OPC. The chemical chloride binding capacity of FAC is comparable to that of OPC and the lower physical adsorption capacity for chloride in FAC leads to a weaker chloride binding capacity compared to that of OPC.

Chloride resistance and improvement of fully recycled cementitious materials with both recycled aggregate and recycled powder

Reusing recycled aggregate (RA) and recycled powder (RP) for fully recycled mortar can effectively reduce the amount of construction and demolition waste. This work studied the chloride transport and resistance improvement of fully recycled mortar incorporating both RA and RP. The results showed that RP had certain nucleation and filler effects. . The addition of RA or RP had an increase in chloride diffusion of mortar. Including RA improved the chloride binding capacity, but mixing RP reduced the chloride binding capacity. At equal waste powder content, recycled paste powder blended mortar owned superior chloride binding capacity to recycled mortar/concrete powder blended mortar. The chloride diffusion of fully recycled mortar with both RA and RP were much higher than that of plain mortar. Mixing various RPs could reduce chloride diffusion of fully recycled mortar, and a significant decrease in chloride diffusion occurred as silica fume or metakaolin was incorporated.

The role of hydrotalcite in the chloride binding of hydrated C3A pastes containing dolomite

To better understand the limitations of the hydrotalcite formation and the capacity of hydrotalcite to bind chloride in dolomite-containing Portland cement-based materials, the reaction of dolomite in C3A pastes and the corresponding chloride binding behavior were investigated in this study. The phase assemblages, the chloride binding capacity, and the pH value were determined. The results indicate that hydrotalcite can only form in a limited range of (active magnesium)/(available aluminum) ratios. The dissolution of dolomite, which provides the magnesium activity, rather than the dedolomitization reaction, appears to be what drives the dolomite reaction with C3A and is primarily dependent on dolomite content. The hydrotalcite formation is not affected by Ca(OH)2. Hydrotalcite seems to possess a greater capacity to bind chloride than monocarboaluminate in hydrated C3A pastes, especially at high chloride concentrations. Chemical chloride binding contributes approximately 10% to the total chloride binding capacity of hydrotalcite. The remaining dolomite reduces chloride binding by increasing carbonate ion activity, and Ca(OH)2 reacts with dolomite to decrease carbonate ion activity and thereby promote chloride binding.

Improved chloride transport resistance of cement mortar using quartz sands modified with MgAl-LDH

The chloride transport into concrete is responsible for the durability deterioration of concrete under chloride-laden conditions. This paper aims to restrict the chloride transport into mortar by the partial replacement of fine aggregates with the quartz sands modified by MgAl-LDH, which were prepared by the co-precipitation method. The microstructures of modified sands and mortars were characterized. Besides, the chloride transport properties in mortar were evaluated by the rapid chloride migration test and long-term chloride diffusion test. The results indicate that quartz sands with in-situ-growth MgAl-LDH have improved specific surface area and chloride binding capacity. With the replacement ratio of modified sands increasing, the resistance of mortar against chloride penetration is significantly improved. The reason for the improved chloride transport resistance may be due in part to the improvement of the microstructure of ITZ, but more importantly, to the chloride ions immobilization of the modified quartz sand.

Durability of concrete incorporating organic light-emitting diode (OLED) display waste as cement binder replacement.

The use of supplementary cementitious materials is customary in contemporary concretes. Different industrial by-products and waste materials have been investigated earlier for such applications. In this paper, the use of organic light-emitting diode glass (OLED) display waste as a partial replacement of cement binder in concretes has been explored. Concretes with 10%, 20%, and 30% substitution (by weight) of ordinary Portland cement (OPC) by OLED powder were developed, and the resulting mechanical properties and durability characteristics were evaluated. The results showed that OLED addition leads to strength improvement of up to 8% after 28-day age. Also, the resistance to chloride-ion penetration and sulfate attack improved considerably. The chloride binding capacity for the developed concretes was also investigated. It was demonstrated that the OLED powder incorporation is beneficial in improving the corrosion resistance of the modified concrete. The enhanced mechanical and durability properties of modified concrete point toward the excellent performance of OLED-incorporated concrete for improved service life. Incorporating OLED display waste in concrete as a partial cement replacement can also reduce environmental burden and concrete cost.

Effect of slag on strength, microstructure and rebar corrosion of chloride-rich geopolymer concrete

The effects of slag substitution (0, 30 and 60%) and chloride concentration (1.5 and 3.5% sodium chloride) on microstructural changes during strength development between 28 and 360 days, rebar corrosion up to 600 days and chloride binding capacity (CBC) in chloride-rich geopolymer concrete (GC) were investigated. The microstructural changes of the GC were evaluated through field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction and Fourier transform infrared spectroscopy analyses. The strength enhancement was higher for the GC mixes based on fly ash (FA) (F-GC mixes) than for the GC mixes based on FA and slag (F/S-GC mixes). The presence of chloride in the GC mixes caused a strength reduction at all ages, but the F/S-GC mixes with the higher slag content mostly showed a smaller strength reduction than the other mixes. Furthermore, the F/S-GC mixes made with the higher slag content exhibited less negative corrosion potential and lower corrosion current density than the other mixes, indicating better resistance against rebar corrosion. The CBC was mostly higher for the GC mixes with a higher slag content. A greater amount of calcium-bearing gels and a higher atomic calcium/silicon ratio in the F/S-GC mixes were responsible for reducing the influence of chloride on strength reduction and rebar corrosion, when compared with the F-GC mixes. Shifting of the Si–O–Si(Al) bond to a lower wavenumber indicated the formation of more binding gel, and thereby a denser microstructure, in the F/S-GC mixes.

Carbon nanofibers and polyvinyl-alcohol fiber hybrid-reinforced high-performance concrete: Mechanical property, chloride penetration resistance, and material characterization

The hybridization of nanomaterials and macroscopic fibers is currently a popular topic. The aim of this study was to explore the application potential of incorporating carbon nanofibers (CNFs) into concrete and to analyze the effect of CNFs dispersant on concrete slump and early strength. Polyvinyl alcohol (PVA) fibers and CNFs were used to prepare composite fiber-reinforced (CNFs-PVA) concrete to improve the continuity of concrete properties at the micron/nanometer scale. The engineering properties such as compressive strength, flexural strength and resistance to chloride ion erosion performance of the concrete were investigated, and the microstructure of concrete was characterized using X-ray diffraction (XRD), scanning-electron microscopy (SEM), and X-ray computed tomography (X-CT). The results showed that CNFs could improve the early strength. The combined use of CNFs and PVA increased the 28-day compressive and flexural strength by 23.38% and 28.73%, respectively, compared to the control group. Correspondingly, the electric flux and Migration rate of chloride ions (DRCM) were minimized. From the SEM and XRD test results, it is clear that CNFs and PVA fibers can: (i) bridge low-density C-S-H to form higher-density C-S-H gels, (ii) form longer chain-like fibers with enhanced load transfer and chloride binding capacity, (iii) act as internal curing agents to enhance hydration at the interface, (iv) promote the formation of the aluminum phase hydration products and calcium carbonate phase, and (v) CNFs and PVA refine the pore size by increasing the gel pores and reducing the percentage of microcracks. The combined results indicate that the improved performance of CNFs-PVA is due to the combined effect of bridging and nucleation of hydration products by CNFs, adsorption of hydration products by CNFs-PVA, and promotion of pore filling by the generated hydrides such as calcium carbonate and ettringite. These findings provide new insights for the design of high-performance concrete materials.

The Durability of High-Volume Fly Ash-Based Cement Composites with Synthetic Fibers in a Corrosive Environment: A Long-Term Study

The utilization of class F fly ash (F-FA) is limited to 15–30% as a substitution for cement. The study intends to tap into the potential of high-volume F-FA as a pozzolan and micro filler by eliminating aggregates. The article presents the long-term behavior of a novel cement composite called no-aggregate concrete (NAC), incorporating 20% ordinary Portland cement (OPC) and 80% F-FA, with polypropylene (PP) fibers in 0.6, 0.8, and 1.0% volume fractions, in a corrosive environment. The bulk diffusion of preconditioned 100 mm cubes reveals that all mixtures’ chloride-binding capacity increases significantly with prolonged exposure. The total chloride content for mixtures M1, M2, and M3 is within acceptable limits as per EN 206. M4 with 1.0% PP fibers shows a higher total chloride content at 2 cm depth. The average chloride content for all mixtures is within 0.4%. The compressive strength of mixtures cured in water is about 90 MPa at 730 days, and is severely affected in the absence of fibers in a corrosive environment. The microstructure of mixtures at 730 days displays a cohesive, compact, continuous matrix, and the presence of unreacted F-FA.

Reusing thermoactivated construction waste spoil as sustainable binder for durable concrete: Microstructure and chloride transport

Construction and demolition waste is predominantly comprised of construction spoil. However, the proper recycling of this construction spoil in a manner that maximizes its value has historically received insufficient attention. Therefore, the objective of this study investigated the micro-structure and chloride transport of cement concrete including thermoactivated construction spoil powder (CSP) as a substitute for cement. The results highlights that the un-treated CSP consisted of massive inert components, and active metakaolin and amorphous components were generated in thermoactivated CSP after 800–1200 ℃ activation treatment. Mixing un-treated CSP negatively impacted the micro-structure and strength development of concrete, but the thermoactivated CSP blended paste had improved micro-structure and better strength than the un-treated CSP blended paste. Incorporating un-treated CSP raised the chloride transport in concrete. At the constant replacement ratio of CSP, the thermoactivated CSP blended concrete had lower chloride transport than the un-treated CSP blended concrete, and decreasing the particle size of thermoactivated CSP could further decline the chloride transport in thermoactivated CSP blended concrete. The concrete with 1200 ℃-activated CSP even had lower chloride transport than the reference concrete. The mix of un-treated CSP up to 30% reduced the chloride binding capacity of concrete, but the thermoactivated CSP blended concrete had superior chloride binding capacity to the un-treated CSP blended concrete. Particularly, the concrete with 20% thermoactivated CSP and 10% active metakaolin/silica fume had similar strength and lower chloride transport than reference concrete. By optimizing the thermoactivation temperature, replacement ratio, and particle size of CSP, it was possible to prepare a durable concrete with low chloride transport.

Effect of calcium leaching on the characteristics of chloride physical adsorption and chemical binding of cement-based materials

Chloride corrosion is an important reason for the degradation of bearing capacity of reinforced concrete structures. When chloride ions transport from external environment into concrete, a part of ions will be bound by the cement matrix through the behaviors of chemical binding and physical adsorption. In this paper, the cement paste samples (R0, R5 and R15) with different degrees of calcium leaching are prepared to investigate the chloride binding capacity, by performing the experiment of chloride isothermal adsorption and desorption. In the experiment, the R0, R5 and R15 are immersed into NaCl-CH composite solutions with different chloride concentrations (Cf-Cl). The change of total binding chloride ion (TBCI), physically adsorbed chloride ion (PACI) and chemically bound chloride ion (CBCI) concentrations in the samples with Cf-Cl is obtained. Then, the linear and nonlinear adsorption laws are adopt to fit the experimental data of chloride concentrations, and the most appropriate adsorption laws are determined separately for the behaviors of TBCI, PACI and CBCI. Finally, the equations for chloride binding capacity of R0, R5 and R15 are obtained, which can be used to analyze the capacity of TBCI, PACI and CBCI of cement-based materials subjected to calcium leaching.

Chloride binding behavior of calcium silicate hydrates and Friedel's salt of pastes

Understanding the chloride binding capacity of cement pastes is crucial to investigating the concrete durability. To characterize the chloride binding behavior of calcium silicate hydrates (C–S–H) and Friedel's salt (Fs), this study investigates the chloride binding capacity of four types of cement paste using chloride binding isotherms, analyzes the correlation between phase composition and chloride binding capacity, and discusses the evolution law of the chloride binding capacity of Fs and C–S–H. The results indicate that the influence of mineral admixtures on the chloride binding capacity of C–S–H is basically the same as that of pastes. Slag (SL) has a significant positive effect, while silica fume (SF) generally plays a negative role, and the effect of fly ash (FA) depends on the concentration of NaCl solution. As to the influence of chloride concentration, the chloride combined by per unit mass of C–S–H and Fs presents different evolution trends, and a concentration break-even point exists between C–S–H and Fs combined chloride. Notably, this point provides the insight into which substance occupies the majority of the total bounded chloride. Moreover, the impact of chloride concentration on the chloride binding capacity of pastes cannot be solely determined by the content of C–S–H and Fs, and the chloride combined by per unit mass of C–S–H and Fs at different chloride concentrations offers more relevance.

Using recycled aggregate and powder from high-strength mortar waste for durable cement-based materials: Microstructure and chloride transport

The large-scale application of high-strength mortar in engineering will inevitably generate a significant amount of high-strength mortar waste in future, but there has been relatively limited research to date on the reuse of high-strength mortar waste as recycled building materials. Therefore, this paper studied the microstructure and chloride transport in cement-based materials using recycled fine aggregate (HCRA) and recycled powder (HCRP) derived from high-strength mortar waste or from high-strength mortar waste separated from high-strength concrete waste recycling. HCRA had much better physical and mechanical properties than ordinary recycled aggregate. HCRP contained some active components, and mixing appropriate HCRP refined paste pore structure; besides, reducing HCRP particle size could further refine the pore diameter of HCRP doped mortar. The strength of mortar first raised and then declined with the increment of HCRA replacement, but the strength decreased as HCRP was incorporated. Incorporating HCRA slightly reduced the chloride migration in mortar, and the mortar with HCRA had better chloride resistance than the mortar with recycled fine aggregate crushed from ordinary mortar waste. Mixing appropriate HCRP could reduce the chloride diffusion coefficient and chloride concentration. Reducing HCRP particle size further declined the chloride transport in HCRP blended mortar, and the mortar with HCRP had superior chloride resistance to the mortar with ordinary recycled powder. Mixing HCRA and HCRP both raise the chloride binding capacity. Particularly, fully recycled mortar with 100% HCRA and 30% HCRP exhibited even better chloride resistance than reference mortar. Incorporating appropriate HCRA and HCRP could prepare durable cement-based materials with good chloride resistance.

Physics-informed deep neural network for modeling the chloride diffusion in concrete

Chloride diffusion in concrete is a complex chemo-physical process and it is of pivotal importance to forecast the initiation time of corrosion. But limited equations are accessible to simulate the chloride diffusion considering the nonlinear chloride binding capacity of concrete. This study proposes a physics-informed deep neural network to simulate the chloride diffusion mechanism and forecast the distribution of chloride concentrations in concrete. Physical laws are formulated as a loss term to guide the training process and to mitigate the data required for model training. The physical constraint loss (based on the governing equation and boundary conditions) and the training loss (based on the neural network) are then fused to produce the loss function. Different experimental cases are first employed to validate the proposed model and then the model is compared to numerical applications and purely data-driven approaches. Results revealed that the proposed model could effectively simulate the chloride transport behavior and forecast the diffusion coefficient of concrete with high precision over other states of art methods. The application of this method to the temporal and spatial domains of the chloride concentration within the concrete samples showed its potential as a powerful tool for investigating concrete properties.

Identification of chloride diffusion coefficient in concrete using physics-informed neural networks

The corrosion of steel caused by chloride is one of the important causes of the deterioration of reinforced concrete structures. In order to describe the transport behavior of chlorides in concrete and to make quantitative durability designs based on it, it is necessary to determine the chloride diffusion coefficient correctly. However, the commonly used analytical method is not suitable for the free chloride diffusion coefficient considering the nonlinear chloride binding capacity of concrete. In this study, by comparing the results of solving forward problems involving chloride transport equations using finite element method (FEM) and solving corresponding inverse problems using physics-informed neural networks (PINNs), it is verified that PINNs can be applied to identify the chloride diffusion coefficient in non-steady-state immersion tests and accelerated chloride migration tests considering no chloride binding, Langmuir binding, or Freundlich binding. The robustness of PINNs is verified by training with 5% and 10% noise data as observed data. The results of interpolation and extrapolation using PINNs trained successfully show its excellent generalization performance.

Effect of curing temperatures and additional activators on chloride ingress and its induced mineralogical alteration of ground granulated blast furnace slag activated by Ca(OH)2

The impact of additional activators (sodium sulfate, sodium nitrite, and calcium nitrite) and curing temperature (20 and 35 °C) on chloride binding and ingress resistance of ground granulated blast furnace slag activated by Ca(OH)2 was studied using X-ray diffraction, scanning electron microscopy, thermogravimetric and thermodynamic modeling. The outcomes of the study indicated that the difference in the chloride binding capacity at low chloride concentrations was primarily affected by the types of the AFm phase. The solid solution formed between Friedel's salt and various types of AFm phases resulted in a decrease in the chloride binding capacity. At a curing temperature of 35 °C, the chloride binding capacity reduced due to the leaching of calcium ions and carbonation induced by the coarse pore structure. It was found that the chloride ingress resistance was significantly related to the leaching of calcium and carbonation, and the denser calcite layer formed at the exposure layer had a positive impact on the chloride ingress resistance.

Evaluation on effect of carbonation on chloride binding capacity and stability of cement hydration products with multiple testing methods

Carbonation leads to decrease in chloride (Cl-) binding capacity of hardened cement paste, and subsequently endangers safety of reinforced concrete structures. During the research process, the results obtained by different standards and methods used to quantify the deterioration differ greatly and are unsuitable for comparison. To solve this issue, multiple standards, appointed with various conditioning regimes, for testing acid- and water-soluble Cl- contents in hardened cement paste were followed to evaluate binding capacity and stability of monosulfoaluminate (AFm) and tricalcium aluminate (C3AH6) on premixed Cl- exposed to external CO2. Results show that the methods used in three standards can completely dissolve the acid-soluble Cl-; the different conditioning temperatures lead to different water-soluble Cl- content measured, resulting in significance difference in the AFm chloride binding results, while the difference can be slight and negligible in the C3AH6. Cl- binding products of AFm was relatively stable within room temperature to 70 °C, and the stability decreased once higher than 70 °C; the products of C3AH6 showed relatively good stability between 20 and 100 °C. The Cl- binding capacity and stability of both AFm and C3AH6 were greatly reduced after a carbonation of 3 d. Detailed results for evaluating changes in the binding capacity of AFm before and after carbonation were related to the standards selected, while that for the C3AH6 was quite close.

A novel approach for chloride control in sea sand cement composites utilizing graphene oxide

The scarcity of river sand has resulted in the inappropriate use of sea sand in numerous countries, particularly in coastal regions. Without effective desalination techniques and sufficient monitoring, the presence of chloride ions in sea sand leads to rapid reinforcement corrosion and frequent structural failures every year. In this paper, a novel pre-treatment method utilizing graphene oxide (GO) coating on amino-functionalized sea sand (GO-CAFSS), and the effects of GO-CAFSS on suppressing internal chloride leaching and performance of sea sand cement-based composites were investigated. Due to strong covalent bonds between GO and amino-functionalized sea sand, agglomeration of GO in the cement matrix is restrained, which leads to enhanced cement hydration and densified ITZs proved by combined microstructure tests. The chloride leaching test shows that the mass percentage of chloride ions leached from the surface of GO-CAFSS are effectively inhibited, from 0.082% (untreated sea sand) to 0.042%. The chloride binding experiment reveals that the treatment of sea sand cement-based composites with GO-CAFSS can enhance their chloride binding capacity by up to 39.5% after 14 days of exposure to NaCl solution. XRD/TGA test results indicate that GO can enhance the chloride binding capacity by promoting calcium silicate hydrate (C-S-H) and Friedel’s salts (FS) formation, further increasing the physical adsorption and chemical substitution of remaining free chloride ions in the pore solution. It is also found that GO can contribute to the conversion of Ettringite (AFt) into FS with Cl− substituting SO42− to a certain extent, especially with additional intermixed SO42− brought by sea sand. Overall, GO-CAFSS is investigated to be a promising way for making high performance sea sand cement composites with harmful chloride ions effectively controlled.

Chloride binding and diffusion of slag blended concrete mixtures

Ground granulated blast furnace slags (GGBFS/slag) can have a range of chemical compositions, especially in alumina content that could potentially affect several concrete properties including chloride binding capacity and chloride penetration. Chloride binding capacity and diffusivity of several cement-slag combinations were assessed using two slags of 8% and 17% alumina contents and four cements, ASTM C150 Type I, ASTM C150 Type I (high alkali), ASTM C150 Type II(MH) and ASTM C595 Type IL(14) at a cement replacement level of 60%. The findings indicate slag addition improved chloride binding and lowered chloride diffusivity. Between the two slags, chloride binding capacity was higher in high alumina slag. Type I cement mixtures had the highest binding capacity while it was the lowest in Type IL cement mixtures due to lower C3A, C3S and clinker factor. Chloride diffusivity experiments showed that plain Type IL mixture had the highest chloride ion penetration while it was the lowest when blended with high alumina slag due to carboaluminate formation. Therefore, chemical, mineralogical, and physical characteristics of cement-slag combination should be considered in service life analysis of slag blended concrete mixtures.

Chloride penetration and binding behavior in unsaturated alkali-activated slag mortars

A comprehensive study from detailed microstructure analyses to mass transport investigations was implemented to explore chloride penetration of unsaturated alkali-activated slag (AAS) mortars accounting for chloride binding behaviors. Unsaturated chloride penetrations reflected from diffusion cases of instantaneous plane source and sorption cases of wetting-drying exposure were elaborated in relation to solid hydrates and pore structure features. It is found that the specimen with lower saturation has a slower chloride diffusion but a larger chloride penetration under wetting-drying cycles. Slag mortars with sodium hydroxide activation exhibit higher chloride binding capacity owing to more hydrotalcite-like phases and higher Ca/Si ratio of C-(N-)A-S-H gels in the outer product zones as compared to sodium silicate activated slag mortars, regardless of the saturation. Accelerations of the chloride penetration under the wetting-drying exposure are limited in saturated AAS specimens while for unsaturated AAS specimens more wetting-drying cycles result in the inner layers to be gradually diffusion-controlled. The chloride binding capacity of AAS specimens follows Langmuir's isotherm and clearly decreases with a lower saturation. It is advised to consider the electrical double layer effect within narrow pores when applying rapid chloride migration tests for AAS systems.

Experimental and theoretical analyses of chloride transport in recycled concrete subjected to a cyclic drying-wetting environment

Chloride diffusion within concrete is proved to reveal an impact on the service life of reinforced concrete structures, however, its penetration within recycled concrete has not been fully comprehended. To clarify this process, the chloride transport in recycled concrete over time was investigated through experimental and theoretical work, and the outcomes were further interpreted by microstructural analyses. The results indicate that unlike normal concrete, different chloride transport behaviors were seen in recycled concrete, which resulted from the high porosity of recycled aggregates. Meanwhile, the high porosity of recycled aggregates resulted in a quicker rise in the maximum chloride concentration over time in the drying-wetting environment, but a slower rate of decrease in the chloride diffusion coefficient. In addition, the relationship between several parameters related to chloride diffusion within recycled concrete (e.g., the chloride diffusion coefficient and the chloride binding capacity) was established. Finally, a more sophisticated model that could well describe the chloride diffusion within recycled concrete was proposed, which considered a number of key indexes.