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To determine the optimum concentration of ammonium chloride solution within the range of 0.2-6.0 mol/L, accelerated leaching experiments were carried out on cement paste, and evolution laws of the leaching depth, cumulative relative leached calcium ion and porosity were studied. The microscopic mechanism was then analyzed by the X-ray diffraction analysis. The results show that the calcium leaching increases with the concentration of ammonium chloride solution. When the Fick's law of diffusion is represented by leaching depth and cumulative relative leached calcium ion, respectively, the obtained proportion coefficient increases linearly and then decreases in the former and exhibits a negative exponential growth trend in the latter. At the same depth of leached specimens, the diffraction peak of calcium carbonate decreases first and then increases. If the concentration of ammonium chloride solution is unreasonably high, it will make the calcium dissolution-diffusion process of cement-based materials significantly deviate from that of the actual mechanism in the natural environment, and the most appropriate concentration of ammonium chloride solution is 3 mol/L. [ABSTRACT FROM AUTHOR]

Low-heat Portland cement and ground granulated blast furnace slag are widely used for the preparation of hydraulic concrete. Nevertheless, the effect and mechanism of corrosion on low-heat Portland cement paste mixed with ground granulated blast furnace slag need to be further explored. This paper investigated the impact of ground granulated blast furnace slag on the calcium leaching of low-heat Portland cement paste by evaluating its mass loss, porosity, leaching depth, compressive strength, and Vickers hardness, and comparing it with the leaching performance of ordinary Portland cement paste. Furthermore, the phase composition and morphology of low-heat Portland cement paste containing ground granulated blast furnace slag were analyzed by X-ray diffraction, mercury intrusion porosimetry, and scanning electron microscopy. The results indicate that, after 180 days of soaking in ammonium chloride solution, the mass loss rate, growth rate of porosity, leaching depth, and compressive strength loss rate of low-heat Portland cement paste were 8.0%, 43.6%, 9.1 mm, and 27.7%, respectively, while those of ordinary Portland cement paste were 7.4%, 37.8%, 8.4 mm, and 30.1%, indicating that low-heat Portland cement paste is slightly more damaging than ordinary Portland cement. The addition of ground granulated blast furnace slag could significantly improve the leaching resistance of low-heat Portland cement. For instance, after adding 20% ground granulated blast furnace slag, the above test values were 2.4%, 28.5%, 5.6 mm, and 20.8%, respectively. The reason for this is that ground granulated blast furnace slag has the potential to reduce the porosity of low-heat Portland cement paste, and it can also undergo the secondary hydration reaction with its hydration product Ca(OH)2 to enhance the paste structure. Considering the cost performance, the suitable dosage of low-heat Portland cement paste for satisfactory leaching resistance is about 20%. [ABSTRACT FROM AUTHOR]

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This work investigated the effect of layered double hydroxides (LDHs) on the calcium leaching of cement pastes. The mass loss, porosity, leaching depth, compressive strength, and Vickers hardness were applied to evaluate the resistance to calcium leaching. Electrochemical impedance spectroscopy, X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, and mercury intrusion porosimetry were conducted to investigate changes of cement hydrates and microstructure in cement pastes. The results demonstrate that the resistance to calcium leaching improves with increasing the content of LDHs and calcined LDHs (C-LDHs), and C-LDHs perform better resistance than LDHs. It is due to the filling effect of LDHs and C-LDHs in cement pastes. Additionally, they promote cement hydration, increasing the content of cement hydrates. As a result, LDHs and C-LDHs decrease the porosity and refine the pore structure, increasing the resistance to calcium leaching. [ABSTRACT FROM AUTHOR]

The leaching of calcium in cement hydrates, particularly in harsh environments, significantly affects the durability of cement-based materials. Understanding the solid–liquid equilibrium of calcium is essential to elucidate the leaching mechanism and leachability for developing accurate degradation models of cementitious materials under chloride exposure. In this study, the effects of different types and proportions of supplementary cementitious materials (SCMs) on the calcium leaching process were investigated. This was achieved by simulating pore solutions at various leaching degrees. Key parameters of the equilibrium curves were extracted and analyzed at different leaching stages. Additionally, a functional relationship between these parameters and the proportions of various SCMs was established. The leachability was assessed by comparing the saturated concentration of calcium ions, the total concentration of solid-phase calcium, and the relative content of calcium hydroxide (CH) and calcium silicate hydrate (C–S–H). It was found that composite binder pastes containing 50% slag demonstrated the best performance in terms of calcium leaching resistance. This research provides valuable insights for the design of anti-leaching cementitious materials and contributes to the development of precise deterioration models for concrete exposed to aggressive environments. [ABSTRACT FROM AUTHOR]

This paper investigated the calcium leaching from plain and fly ash/limestone blended cement mortars under an electric field. The Ca2+ leaching degree and reduced CaO content were measured to assess the extent of calcium leaching, and the compressive strength loss was used as an indicator to evaluate the degradation of the mortars due to leaching. Additionally, the changes in mineralogical composition, micrograph, Ca/Si ratio of C–S–H gel, and pore structure of leached samples were analyzed through X-ray diffraction (XRD), scanning electron microscopy (SEM/EDS), and mercury intrusion porosimetry (MIP). The findings indicated a notable acceleration in the leaching of Ca2+ due to the application of an electric field. Consequently, the calcium leaching degree of mortars continuously increased with time. The accelerated calcium leaching resulted in the loose microstructure and increased porosity mainly for the cathode part as well as the reduction in compressive strength of mortars. The addition of fly ash was beneficial in reducing the calcium leaching and strength loss of mortars after 90 days of exposure to the electric field, contrary to the effects observed with the incorporation of limestone powders. Attention should be paid to the durability issues of cement-based materials induced by the electric field.

Low-heat Portland cement and ground granulated blast furnace slag are widely used for the preparation of hydraulic concrete. Nevertheless, the effect and mechanism of corrosion on low-heat Portland cement paste mixed with ground granulated blast furnace slag need to be further explored. This paper investigated the impact of ground granulated blast furnace slag on the calcium leaching of low-heat Portland cement paste by evaluating its mass loss, porosity, leaching depth, compressive strength, and Vickers hardness, and comparing it with the leaching performance of ordinary Portland cement paste. Furthermore, the phase composition and morphology of low-heat Portland cement paste containing ground granulated blast furnace slag were analyzed by X-ray diffraction, mercury intrusion porosimetry, and scanning electron microscopy. The results indicate that, after 180 days of soaking in ammonium chloride solution, the mass loss rate, growth rate of porosity, leaching depth, and compressive strength loss rate of low-heat Portland cement paste were 8.0%, 43.6%, 9.1 mm, and 27.7%, respectively, while those of ordinary Portland cement paste were 7.4%, 37.8%, 8.4 mm, and 30.1%, indicating that low-heat Portland cement paste is slightly more damaging than ordinary Portland cement. The addition of ground granulated blast furnace slag could significantly improve the leaching resistance of low-heat Portland cement. For instance, after adding 20% ground granulated blast furnace slag, the above test values were 2.4%, 28.5%, 5.6 mm, and 20.8%, respectively. The reason for this is that ground granulated blast furnace slag has the potential to reduce the porosity of low-heat Portland cement paste, and it can also undergo the secondary hydration reaction with its hydration product Ca(OH)2 to enhance the paste structure. Considering the cost performance, the suitable dosage of low-heat Portland cement paste for satisfactory leaching resistance is about 20%.

Understanding the degradation of 3D-printed cement paste (3DPC) is essential to evaluate changes in the long-term durability of concrete structures subjected to aggressive water. However, the degradation mechanism of 3DPC has yet to be reported, as the microstructure and pore characteristics of 3DPC are very different from those of its cast counterparts. This work studies the performance anisotropy of 3DPC due to calcium leaching to investigate the degradation mechanism. Samples with aggregate micro fines (AMF) and fly ash (FA) were prepared. A 6 mol/L NH4Cl solution was used in the accelerated experiment. At specific leaching durations, performances were tested on the samples in different leaching directions. The performance anisotropy of 3DPC exposed to aggressive water was investigated by comparing the changes in bulk density, water absorption, leaching depths, and compressive strength in different leaching directions. X-ray diffraction (XRD), differential thermal gravity-thermogravimetric (DTG−TG), and mercury intrusion porosimetry (MIP) were used to characterize the changes in hydration products and pore structure in different leaching directions. The results show that the performances of 3DPC in aggressive water have a significant anisotropic behavior. The evolution of pore defects and hydration products mainly governs the performance anisotropy of degraded 3DPC. The remaining hydration products of the surface of 3DPC leached in the Z direction are fewer than the other two directions because calcium ions leached in the Z direction are difficult to compensate through weak interfaces between layers. The test results clearly show that the calcium leaching mechanism of 3DPC in aggressive water is directly influenced by the hydration products, such as portlandite (CH) and C-S-H, and the pores. The current study may help us understand the degradation mechanism of 3DPC to assess its durability performance anisotropy. [ABSTRACT FROM AUTHOR]

Calcium leaching from cement hydrates has been shown to decrease the durability and shorten the service life of the concrete. Earlier studies have focused on investigating the leaching progress in deionized water or ammonium nitrate solutions, neglecting the effects of aggressive ion concentrations, types, and temperatures. In addition, the current equilibrium curve of calcium leaching is based on experimental data in deionized water, and its applicability to calcium leaching in actual marine environments is controversial. In this study, a dissolution experiment was carried out to study the effects of chloride ion concentrations and environmental temperatures. The functional relationship of critical parameters (x1 , x2 , and Csatu) of the equilibrium curves with the chloride ion concentrations and temperatures was established. Furthermore, considering the influence of calcium leaching on porosity and the diffusion coefficient of cementitious materials, the calcium leaching model was established within a time and space framework. The results showed that calcium leaching was accelerated by the increased concentration of chloride ions and the decrease in environmental temperature. In the authors' view, this study lays a theoretical foundation for a transport-reaction-mechanical deterioration model of concrete. [ABSTRACT FROM AUTHOR]

Cellulose ethers (CE) are generally used as viscosity modifying admixtures in cement-based materials. However, previous investigations scarcely focus on the effect of CE on the calcium leaching behaviors of host materials. This work studied the calcium leaching behaviors in CE-containing cement pastes. The resistance to the calcium leaching was evaluated by the leaching depth, pH values and compressive strength. Electrochemical impedance spectroscopy, X-ray diffraction analysis, thermogravimetric analysis, Fourier transform infrared spectroscopy, scanning electron microscopy and mercury intrusion porosimetry were implemented to reveal changes in the cement hydrates and microstructural properties to disclose the underlying mechanisms. Results indicate that CE decrease the amounts of CH and C-S-H because of the retardation effect on cement hydration. CE-containing samples exhibit CH crystals with eroded edges and a smaller size, and C-S-H phases with a disordered morphology and smaller dimension, thus increasing the rate of decomposition of CH and C-S-H. CE increases the total porosity by inducing capillary pores and large pores, which results in the decreasing pore connectivity and increasing tortuosity in cement pastes. The degradation of cement pastes during calcium leaching is prominently decided by the content of CH and C-S-H, instead of the initial pore structure. Consequently, CE increase the leaching degree of cement pastes with increasing the CE contents. Additionally, a non-destructive method is proposed to determine the leaching depth for CE-added cement pastes through establishing relationships between the leaching depth and damage factor. [ABSTRACT FROM AUTHOR]

Solid–liquid equilibrium curve of calcium (Ca) is important for analyzing the process of calcium leaching and its kinetics model. In this paper, the Ca solid–liquid equilibrium was experimentally investigated by hardened cement paste powder exposed to an accelerated leaching environment of 1 mol/L (1 M), 3 M and 6 M ammonium chloride (NH4Cl) solutions. The equilibrium curves of Ca, magnesium (Mg), sulfur (S), aluminum (Al) and iron (Fe) were obtained by EDTA titration and scanning electron microscope-electronic diffraction spectroscopy. Results show that, the obtained equilibrium curve in NH4Cl solution has a similar three-stage form to that in deionized water. It indicates that, the Ca leaching mechanism of cement based materials in ammonium solution is similar to that in water. In addition, the Ca leaching in NH4Cl solution is accompanied by the leaching of S and Mg, and they are also leached in three stages, but Al and Fe are not leachable. Based on the experimental data, the equations of Ca solid–liquid equilibrium curve under 1 M, 3 M and 6 M NH4Cl solutions were established. [ABSTRACT FROM AUTHOR]

This work investigates the influence of calcium leaching on mechanical and physical properties of limestone powder (LS)–cement pastes cured under different temperatures. In order to achieve this goal, three different mass percentages of LS (10%, 30%, and 50%) were selected to replace cement, and the LS–cement pastes were cured under three different temperatures (5°C, 20°C, and 50°C). The LS–cement pastes were soaked in NH4Cl solution to accelerate the calcium leaching and simulate the leaching influence from water. The mechanical and physical properties including the compressive strength, flexural strength, Vickers hardness (VH), leaching depth, and electrochemical impendence spectroscopy (EIS) were conducted. The prediction model of VH and the relationship between equivalent VH and mechanical strength were built. The microstructure of LS–cement pastes is characterized by X-ray diffraction (XRD), thermogravimetric (TG), scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP) tests. Experimental results demonstrate that with the increase of LS, the decrease degree of mechanical and physical properties of LS–cement pastes increases gradually; Furthermore, the leaching damage degree of LS–cement pastes is the largest under curing temperature of 5°C, followed by 50°C and 20°C. The microstructure results reveal that the Ca(OH)2 in the leached zone of LS–cement pastes is completely dissolved, and the calcium leaching makes the LS–cement pastes cured under 5°C obtain the loosest structure and the most serious leaching damage, followed by 50°C and 20°C. [ABSTRACT FROM AUTHOR]

Deterioration process of high belite cement (HBC) paste with and without 30 wt.% fly ash, when exposed to sulfate attack, calcium leaching and the dual actions, was investigated by mass loss, expansion rate, porosity, corrosion depth, compressive strength and Vickers hardness, so did the contrastive ordinary Portland cement. Moreover, XRD, TGA, 29Si NMR, SEM and EDS linear scanning measurements were also conducted to assess the chemical attack mechanisms under corresponding aggressive conditions. Results showed that, the degradation of HBC pastes varied between different exposure conditions, and the most severely corroded samples were that exposed to (NH4)2SO4 solution with coupling sulfate attack and calcium leaching, which interacted with each other and accelerated the transfer process of sulfate ions to the cement matrix and calcium ions to external solution. Compared with ordinary Portland cement, high belite cement had a better corrosion resistance against the dual actions of sulfate attack and calcium leaching, and it could be further promoted by the moderate substitute of fly ash.

Tunnel constructions built in karst areas are liable to calcium leaching, which can lead to CaCO3 deposits in tunnel drainage pipes and water gutters, resulting in the blockage of tunnel drainage systems. This research aimed to analyze the influence of liquid accelerators on shotcrete in karst area tunnels. To achieve this, the present study investigated the influence of accelerator type and the karst water environment on the degradation behaviors of shotcrete. More specifically, the calcium leaching processes of hardened cement pastes incorporated with various liquid accelerators were analyzed, and the tunnel drainage system blockage mechanism was expounded in terms of shotcrete lining. The results showed that the compressive strength of shotcrete decreased most significantly in a karst water environment, while the mass of shotcrete decreased most significantly in a flowing water environment. The shotcrete combined with an aluminum sulfate-based alkali-free liquid accelerator performed best in the attack test, and its maximum compressive strength decreased by only 0.33%. The accelerator can change the composition and microstructure of cement hydration, thus altering the deterioration resistance of shotcrete. In terms of shotcrete lining, calcium leaching can increase the pH value and calcium ion concentration of groundwater, resulting in the formation and crystallization of CaCO3.

A novel numerical model is proposed for characterizing the nonuniform corrosion of steel bars. The proposed model corrects the anodic Tafel slope through the concentration of chloride and accounts for the adsorption-binding impact of chloride. The viability of the presented model is confirmed with regard to chloride diffusion and the distribution of steel corrosion products. The rebar-concrete interface's non-uniform distribution of oxygen and chloride concentrations along the circumferential direction influences the corrosion current density. Calcium leaching influences the migration of oxygen and chloride, and speeds up the electrochemical corrosion of the rebar. • An non-uniform corrosion model considering the coupling of calcium leaching and chloride diffusion is presented. • The adsorption and desorption of chloride in concrete during corrosion is realized. • The effect of chloride concentration on the corrosion current density of steel reinforcement is considered. • The mechanism of calcium leaching affects the electrochemical corrosion process of steel reinforcement is studied. [ABSTRACT FROM AUTHOR]

The calcium leaching effect leads to a decrease in the impermeability of the impervious curtain. The inverse analysis strategy was introduced in this study because the calcium leaching parameters of the curtain are not easy to determine. An orthogonal design and the finite element method were used in the strategy. The time-series data of hydraulic head and leakage volume were applied to construct the objective function. The extreme learning machine (ELM) was proposed to build the reflection sets. Genetic algorithm (GA), simulated annealing (SA), sparrow search algorithm (SSA), and particle swarm optimization (PSO) were employed to accelerate the iterative search for the target parameters. The target parameters of the calcium leaching model were used for finite element verification by comparing the monitored and simulated values. The simulated values of hydraulic head and leakage by PSO show good agreement with measurements. The evolution of the curtain permeability coefficient in 100 years was analyzed. The results demonstrate the strategy's feasibility in determining the curtain's calcium leaching parameters and permeability coefficients. [ABSTRACT FROM AUTHOR]

This study examined the influence of graphene oxide (GO) dosage on the properties and microstructure of cement pastes against hydrochloric acid (HCl) attack. The mass loss (and sectional area loss) in 0 and 0.09 wt% GO-modified cement specimens after HCl attack were 6.1% and 4.2% (and 8% and 4.7%), respectively. These specimen losses decreased with an increasing GO dosage. The GO inclusion up to 0.09 wt% in cement paste significantly absorbs the free water and increased the viscosity to 13.7 folds, in comparison to control mix (i.e. without any GO). However, such GO inclusion densified the cement microstructure and further inhibited the decalcification-induced shrinkage cracks propagating because of the HCl attack. The cement zone in all samples altered by the HCl attack was found to be occupied with alumina-silica hydrogel. Overall, this study recommends the potential use of GO in the manufacturing of concrete storage structures operating in acidic environments. [ABSTRACT FROM AUTHOR]

Lime and gypsum application is one strategy for correcting soil acidity and improving soil fertility. However, soil compaction in no-till systems can influence these dynamics. This study aimed to assess the effect of lime and gypsum application under different soil compaction levels on soybean yield and soil chemical attributes. The application of lime and gypsum under artificial compaction levels and the movement of exchangeable calcium (Ca2+), magnesium (Mg2+), potassium (K+), and soil pH were monitored in the 0–0.05, 0.05–0.10, 0.10–0.20, and 0.20–0.40 m soil layer depths. Soybean grain yield was not influenced by the gypsum and lime applications and artificial compaction levels. In the 0.05–0.1, 0.1–0.2, and 0.2–0.4 m soil layers, the exclusive surface application of lime was effective in increasing the soil pH. Ca2+ and Mg2+ carbonates had low solubility and mobility in the soil; however, a rapid reaction to the surface over a relatively short period was observed. K+ concentration in the 0–0.05 m soil layer did not vary after the gypsum and lime applications. Therefore, the superficial application of lime is effective in acidity correction in no-till systems when the soil is not compacted. [ABSTRACT FROM AUTHOR]

In order to study the effect of the action of sulfuric acid on the dissolution rate of cement mortar, the immersion test of cement mortar specimens with a water-binder ratio of 0.4 in a sulfuric acid solution with pH=4.0 was carried out. Three control conditions were determined for the surface cleaning, and the curve of the acid consumption of the test piece with the immersion time was obtained in the experiment. Numerical simulation was carried out on the basis of the experiment. Based on the partial differential equation of calcium dissolution, an unconditionally stable implicit difference scheme was constructed, and the concentration profile correction method was introduced to simulate the cleaning process in the experiment, and the cement mortar specimens under different conditions were simulated. During the dissolution process, the simulated acid consumption curve of the test piece was obtained and compared with the measured value. The results show that the simulation value is basically the same as the test value, which verifies the reliability of the calcium dissolution model; the test control conditions will affect the rate of acid consumption of the test piece. The test conditions will increase the acid consumption of the test piece by 33% and 45%, respectively. [ABSTRACT FROM AUTHOR]

As a hidden engineering structure, tunnels are inevitably affected by the long-term erosion of groundwater, resulting in the phenomenon of calcium leaching in shotcrete. The effective components of the initial tunnel support are dissolved by groundwater, with a portion remaining in the tunnel drainage system and the rest discharged from the tunnel. This phenomenon can further accelerate the deterioration of the lining and cause blockages in the drainage system, posing new challenges to environmental protection and structural safety. To mitigate the problem of calcium leaching in tunnel shotcrete, new building materials, termed Calcium Stabilizing Agents (CSAs), were fabricated using industrial solid wasters such as silica fume, mineral powder, silicone zirconium, and metakaolin. An orthogonal experiment was implemented to investigate the influence of CSAs on the calcium ion (Ca2+) leaching concentration; the sensitivity analysis was conducted to identify the impact of each ingredient of CSAs on the calcium ion leaching concentration; and microscopic methods such as XRD, SEM, and TG were used to analyze the mechanism of the CSAs on anti-calcium leaching ability of mortar. The results showed that the addition of the CSAs can effectively improve the anti-calcium leaching ability of mortar. For the optimal dosage of the CSAs mortar, the calcium ion concentration of the 28-day CSAs mortar was reduced by 31.55 %, and the compressive strength and flexural strength were enhanced 31.09 % and 37.27 %, respectively. From the sensitivity analysis of calcium ion concentration, compressive strength, and flexural strength of CSAs mortar at 1 day, 7 days, and 28 days, silica fume and zirconium silicone show the greatest influence on the performance of mortar. Consequently, they are deemed as the core components of CSAs. The microscopic analysis showed that the internal cementitious structure of the cement stone grew denser after CSA was added. It also contained long-chain crystalline structures that effectively fill capillary pores to resist erosion. Finally, the CSAs product was applied to a tunnel under construction on site, and the results showed that the shotcrete mixed with CSAs had a good anti-calcium leaching effect and significantly improved compressive strength. The findings of this study can provide a new avenue for preventing and controling the tunnel crystallization diseases. [ABSTRACT FROM AUTHOR]

Porous cement stabilized macadam has a good drainage property, but the loss of strength due to calcium leaching can significantly reduce its road performance. The effect of the dosage of fly ash, silica fume, and slag powder on the calcium leaching resistance of porous cement stabilized macadam base material was investigated using the accelerated leaching method with 4 mol/L ammonium chloride. The results show that calcium leaching occurs simultaneously at multiple contact points between the internal cement paste and the leaching solution, and the leaching depth has exceeded the average thickness of the layered cemented paste within 3d. The dissolution of CH crystals and the decalcification of C-S-H gel increase the porosity of cement and reduce the strength of the base material. Volcanic ash reaction of silica fume and fly ash as well as slag powder by alkali excitation and sulfate excitation will consume CH and generate low alkalinity C-S-H gel with better dissolution resistance, which can reduce calcium leaching and delay the loss of strength. The optimum dosages of fly ash, silica fume, and slag powder are 20%, 15%, and 30%, respectively, and their optimum dosages can be estimated on the assumption that the mineral admixtures completely consume CH. [Display omitted] • The calcium leaching mechanism of porous cement stabilized macadam was studied systematically. • The effects of fly ash, silica fume, and slag powder on calcium leaching properties were studied. • Fly ash, silica fume and slag powder can effectively inhibit calcium leaching, with silica fume being the most effective. • Provides a basically consistent optimal dosage of mineral admixtures from both test results and estimation. [ABSTRACT FROM AUTHOR]

Extrusion-based 3D printed cementitious materials (3DPC) require specific parameters to be met that will substantially impact printed part durability, particularly when exposed to aggressive external conditions. Due to the specificity of the spatial distribution of the pores, 3DPC are reported to exhibit performance anisotropy compared to cast materials. A fundamental understanding of the discrepancy in the pore evolution between the printing direction, lateral direction, and top direction is essential for calcium leaching from 3DPC in aggressive water. This research investigates pore structure evolution in 3DPC with the three directions in a 6 mol/L ammonium chloride solution. The leaching depths of the samples in the three directions were tested and compared. In addition, their porosity, maximum, median, and average pore diameters, pore size distribution, and pore morphology are investigated using optical microscope (OM) and mercury intrusion porosimetry (MIP) analysis. Significant differences were found between the leaching depths in the different directions of the 3DPC. Samples leached in the top direction show less leaching depth than in the other two directions, indicating the anisotropic nature of 3DPC. This was attributed to the different pore structures of the sample in the top direction compared to the other directions, as confirmed by OM and MIP analysis. Furthermore, the pore morphology is more irregular and elongated in the printing and lateral directions than in the top direction. In turn, the calcium leaching increases the porosity and coarsens the pore structure of 3DPC. The results of this study can be used as a reference for the application of 3DPC in aggressive water environments. • 3DPC in ammonium chloride solution shows anisotropic calcium leaching behavior • Pore structure in X, Y, and Z directions in 3DPC is significantly different • Pore structure significantly affects the calcium leaching behavior of 3DPC • Pore morphology in 3DPC induces the calcium leaching front [ABSTRACT FROM AUTHOR]

The calcium leaching effect leads to a decrease in the impermeability of the impervious curtain. The inverse analysis strategy was introduced in this study because the calcium leaching parameters of the curtain are not easy to determine. An orthogonal design and the finite element method were used in the strategy. The time-series data of hydraulic head and leakage volume were applied to construct the objective function. The extreme learning machine (ELM) was proposed to build the reflection sets. Genetic algorithm (GA), simulated annealing (SA), sparrow search algorithm (SSA), and particle swarm optimization (PSO) were employed to accelerate the iterative search for the target parameters. The target parameters of the calcium leaching model were used for finite element verification by comparing the monitored and simulated values. The simulated values of hydraulic head and leakage by PSO show good agreement with measurements. The evolution of the curtain permeability coefficient in 100 years was analyzed. The results demonstrate the strategy’s feasibility in determining the curtain’s calcium leaching parameters and permeability coefficients.

The calcium leaching effect inevitably increases the grout curtain hydraulic conductivity. It is diffucult to sample and obtain the leaching-related calculation parameters for deep-buried grout curtains. This study introduced the inversion method into the calcium leaching analysis to get proper leaching-related calculation parameters and accurate results. An inverse analysis model was proposed using the genetic algorithm (GA) and finite element analysis technology to solve the calcium leaching problems. The objective function is constructed using the hydraulic head and leakage quantity time-series measurements, which improves the uniqueness and reliability of the inverse results. The proposed method was applied to the inverse analysis of the hydraulic conductivity evolution of the grout curtain in a concrete dam foundation. The predicted water heads and leakage quantity are consistent with the monitored data, indicating the rationality of this simulation. The grout curtain hydraulic conductivity prediction in 100 years is also presented. The results illustrate the feasibility of the proposed method for determining leaching-related parameters and the hydraulic conductivity prediction in the leaching process.

Sulfate attack is one of the crucial causes for the structural performance degradation of reinforced concrete infrastructures. Herein, a comprehensive multiphase mesoscopic numerical model is proposed to systematically study the chemical reaction-diffusion-mechanical mechanism of concrete under sulfate attack. Unlike existing models, the leaching of solid-phase calcium and the dissolution of solid-phase aluminate are modeled simultaneously in the developed model by introducing dissolution equilibrium equations. Additionally, a calibrated time-dependent model of sulfate concentration is suggested as the boundary condition. The reliability of the proposed model is verified by the third-party experiments from multiple perspectives. Further investigations reveal that the sulfate attack ability is underestimated if the solid-phase calcium leaching is ignored, and the concrete expansion rate is overestimated if the dissolution of solid-phase aluminate is not modeled in the simulation. More importantly, the sulfate attack ability and the concrete expansion rate is overestimated if the time-dependent boundary of sulfate concentration is not taken into consideration. Besides, the sulfate ion diffusion trajectories validate the promoting effect of interface transition zone on the sulfate ion diffusion. The research of this paper provides a theoretical support for the durability design of concrete under sulfate attack.

Hydropower dams are subjected to soft water penetration during their service lives. Concrete deterioration due to calcium leaching will decrease the durability of concrete and affect dam safety. The long-term performance of concrete dams due to calcium leaching should be evaluated and predicted accurately to complete reinforcement work in a timely manner. In this paper, a methodology that combined microscopic tests and numerical analysis to evaluate the long-term performance of dam concrete due to calcium leaching is proposed. The current state of concrete is evaluated by analyzing the components of sediments and seepage water through microscopic and spectroscopic tests, such as X-ray photoelectron spectroscopy, scanning electron microscopy, and inductively coupled plasma mass spectrometry. The long-term degradation of concrete was predicted by utilizing a multi-scale model of calcium leaching, which considered the micro-pore structure of cement hydrates flux with time. The simulated results using this calcium leaching model showed a good agreement with other experiments. Finally, a real case study including field inspection was performed and the long-term durability of dam concrete was predicted through microscopic tests and finite element analysis method. It implies that the proposed method could provide calculation and theoretical basis for the durability analysis of concrete dams due to calcium leaching.

The durability of dam concrete is considerably affected by environmental effects. Although great progress was achieved on environment-induced deterioration mechanism of concrete, there still seems that a gap exists between researches of the concrete durability in natural and standardised laboratory conditions. This article is concerned with carbonisation and calcium leaching-induced deterioration of concrete in dams in service. Field inspections and analyses of dozens of investigated dams in China are presented. The results show that the carbonation speed is closely related to the age of construction and its location. The carbonisation depth of the upstream surface is generally smaller than that of the downstream surface for the same dam. The calcium leaching degree of dam concrete is affected by several factors, such as reservoir water chemistry, type, height, construction age and quality of the dam. Calcium leaching of dam concrete is common in China because the reservoir water is usually soft and has medium soluble corrosivity. These deteriorating processes and characteristics are consistent with the previous laboratory results. A masonry gravity dam due to 17 years of exposure to natural environment was taken as a case study on concrete alteration mechanisms. Concrete cylinders drilled out at four vertically different locations on the upstream concrete-faced slab were analysed by compressive strength test and mercury intrusion porosimetry test. The deterioration process controlling the concrete near the waterline varies according to its location, resulting in the variation of micropore structures at various depths from the upstream surface. Long-term exposure to natural environment has led to chemical and mineralogical zonation of the concrete. The results of this study can be used to compare the similar results from the short-term laboratory investigations. [ABSTRACT FROM AUTHOR]

• Experiments coupling slow calcium leaching with dry/wet cycles were designed. • The coupling effect exists between dry/wet cycles and calcium leaching. • A quantitative prediction model for mechanical properties was established. The durability of marine concrete is significantly influenced by the coupled effect of calcium leaching (CL) and dry/wet cycles (DW). This study investigates their combined impact on the Vickers hardness and pore structure of hardened cement paste. The experimental setup includes two groups: Group A (CL followed by DW) and Group B (DW followed by CL), which superimpose the single-factor effects of each factor. Calcium leaching levels were set at 5 %, 10 %, and 15 % loss of sample mass, and dry/wet cycles were varied at 4, 8, and 12 times. A 4 mol/L ammonium nitrate solution was used to accelerate calcium leaching. The results demonstrate that the coupled effect of CL and DW reduces the Vickers hardness by increasing the porosity of the cement paste. Specifically, CL primarily increases the porosity of pores above 200 nm by dissolving calcium hydroxide, and it augments the porosity of 7 ∼ 50 nm pores by removing calcium from C-S-H gels. However, the combined effect of CL and DW on Vickers hardness is less pronounced than the total individual effects. Moreover, Group A exhibits a more substantial impact on the deterioration of mechanical properties in hardened cement paste compared to Group B. In addition, a model is applied for quantitatively predicting mechanical performance based on nominal porosity. [ABSTRACT FROM AUTHOR]

• An approach for quantifying calcium leaching effect on service performance of concrete impermeable structures was developed. • The effectiveness of the proposed method was verified by a laboratory calcium leaching test. • Numerically investigated the seepage and dissolution evolution of the concrete cutoff wall during long-term service. • The safe service life of concrete cutoff walls considering the calcium leaching effect was evaluated. Calcium leaching is one of the essential diseases of concrete impermeable structures; therefore, an effective numerical approach to quantifying the effect of calcium leaching on concrete impermeable structures is critical for evaluating the long-term service performance of the structure. To this end, a seepage and dissolution coupling model for simulating the degradation of hydraulic concrete properties is proposed in this paper by introducing performance parameter evolutionary models based on saturated–unsaturated seepage and calcium dissolution and migration theories. The model is developed in COMSOL with a staggered solution scheme, and a detailed numerical implementation method is presented. The effectiveness of the proposed method is examined by laboratory calcium leaching tests. On this basis, the model was applied to evaluate the effect of calcium leaching on the service performance of a concrete cutoff wall (CCW) of an embankment dam in Shaanxi Province, China. The results demonstrate that the proposed method can effectively reproduce the calcium leaching process of concrete, and the variation of leaching depth based on model simulations is highly consistent with the experimental results. Calcium leaching primarily occurs at the CCW's upstream waterfront surface, bypass seepage area and the partition of adjacent soil layers where the permeability varies greatly. Under seepage dissolution, the amount of leached calcium, average porosity, diffusion coefficient and hydraulic conductivity of the CCW increased exponentially with service duration, and solid-phase calcium leaching was the underlying cause of structural performance degradation. The length of the seepage path in the CCW decreases as the service duration increases, and the hydraulic gradient within it gradually increases. Based on the allowable hydraulic gradient of CCW, the safe service life of the CCW considering the calcium leaching effect was determined to be approximately 52a. [ABSTRACT FROM AUTHOR]

To contribute towards sustainability and cleaner production, we experimentally investigated the basic physicomechanical properties of a new porous mortar containing Japanese cedar woodchips and evaluated its durability by one-year immersion tests in ion-exchanged water and sodium chloride solution. The lightweight woodchip-containing porous mortar has high water and gas absorptivity, in addition to high skid resistance and high durability against calcium leaching. Calcium-leaching-induced strength reduction was not significant because it was compensated by strength increases from additional cement hydration in water during immersion tests. [ABSTRACT FROM AUTHOR]

• The leaching kinetics and related changes in mechanical behavior and microstructure of CA mortar were studied. • Three distinct zones in term of local calcium content in the direction of radius of the specimen were found. • Compressive behavior was modelled by the combination of compression damage model degradation damage model. Calcium leaching is an important durability problem for cement asphalt (CA) mortar used in ballastless slab track. In this paper, calcium leaching in CA mortar was accelerated by immersing in 6 mol/L ammonium nitrate solution. The leaching kinetics and related changes in mechanical behavior and microstructure of CA mortar were studied. Results showed that calcium leaching followed the Fick's law. The calcium leaching led to the formation of three distinct zones in term of local calcium content in the direction of radius of the specimen. Due to the leaching of calcium hydroxide and the progressive decalcification of C S H, the three zones had different chemical compositions. The compressive mechanical behavior was modeled by a compression damage model derived from Weibull distribution. The degradation damage model was established on the distribution of local elastic modulus. The combination of these two models can well predict the compressive behavior of partially leached CA mortar. [ABSTRACT FROM AUTHOR]

Abstract Influence of colloidal silica sol (SS) consisting of mono-dispersed nano-silica on properties and microstructure of the hardened cement-based materials was investigated as compared to the nano-silica (NS) powder with agglomerates in micron-scale through detecting the mechanical and durable properties of the hardened mortar and by using SEM observation, nano-indentation test and MIP analysis. The results showed that the strength enhancement of the mortar with SS addition revealed an overall more improvement but a higher discreteness than that with NS addition. After the calcium leaching test, it was found that the strength of the mortar with SS addition showed a clearly higher loss than that with NS addition, though the neutralization depth revealed a more reduction while incorporating SS and the residue strength still tends to increase with increasing the nano-silica addition. All these observations are resulted from the fact that the nano-particles in SS coagulate immediately once cement is mixed into water containing SS, forming loose flocs with a more open microstructure and a higher free water retention capacity than the agglomerates in NS, thus leading to a lower free water cement ratio in fresh cement paste and an overall more compact microstructure in hardened cement paste while incorporating SS. However, pozzolanic C-S-H gels from the gelled nanosilica can be observed to show a loose compaction, with nanopores and even micropores inside and also an abnormal growth of the larger CH crystals in the pozzolanic C-S-H gels but without nucleated growth of the C-S-H gels from cement hydration. The dissolution of the larger CH crystals in the coagulated gel network in the paste may leave large pores in the hardened cement mortar to cause a higher strength loss after the calcium leaching test. The MIP testing results indicated that the threshold pore size showed few differences for the HCP with and without 1.0% nano-silica addition, illustrating the permeability of the hardened cement paste may have nothing to do with the threshold pore size, but the total porosity and the micropores in the range of 100–10000 nm. [ABSTRACT FROM AUTHOR]

Highlights • Graphene oxide (GO) effectively inhibited calcium leaching of cement pastes. • Combined advanced techniques of ICP–MS, XRD, TGA, MIP, and SEM were applied. • Mass loss of calcium hydroxide decreased from 4.91% to 3.91% with GO addition. • Increment of total porosity decreased from 25.6% to 3.8% with GO addition. • Increment of pores (1–5 μm) mainly contributed to the increment of total porosity. Abstract In this study, inhibited effect of graphene oxide (GO) on calcium leaching of cement pastes exposed to deionized water for 14 and 28 days was investigated using combined advanced techniques of ICP–MS, XRD, TGA, MIP, and SEM. After leaching for 28 days, mass loss of calcium hydroxide decreased from 4.91% to 3.90% due to GO addition, while increment of total porosity mainly deriving from the increment of pores (1–5 μm) reduced from 25.6% to 3.8%. Overall, GO addition can reduce calcium dissolution and refine the pore structure of leached pastes, therefore effectively mitigating calcium leaching of cement pastes. [ABSTRACT FROM AUTHOR]

Highlights • Crude biodiesel was applied as a cosolvent in the sunflower oil methanolysis over CaO. • Under the optimum reaction conditions, the obtained methyl esters content was 99.8%. • CaO was reused with no additional treatment in five consecutive cycles. • The second repeated reaction provided the highest FAME content of 97.7% after 5 h. Abstract Crude biodiesel was proven as a cosolvent in the methanolysis of sunflower oil catalyzed by calcined CaO. This reaction was modeled and optimized statistically in terms of reaction temperature (33.2–66.8 °C), methanol-to-oil molar ratio (3.5:1–8.5:1) and catalyst concentration (0.219–1.065 mol/L). The cosolvent loading was 10 wt% (based on oil weight). The optimum reaction conditions were found to be: the methanol-to-oil molar ratio of 7.1:1, the catalyst concentration of 0.74 mol/L and the reaction temperature 52 °C, ensuring the best esters content of 99.8%, for the reaction time of 1.5 h, which is close to the reported experimental value of 98.9%. Also, the used catalyst was recycled with no additional treatment in the further four consecutive cycles under the following reaction conditions: methanol-to-oil molar ratio 6:1, the concentration of catalyst 0.642 mol/L (only in the first run), the reaction temperature 50 °C, cosolvent-crude biodiesel loading 10 wt% to oil weight. The second recycling reaction provided the highest FAME content of 97.7% after 5 h. [ABSTRACT FROM AUTHOR]

Abstract Salt frost deterioration of concrete is an important durability problem to concern. Prior to clarifying the salt frost damage mechanisms, the salt effect on mechanical behavior of concrete needs to be clarified. To quantitatively understand the damage effects, this paper experimentally investigated meso-scale mortar samples suffered from sodium chloride (NaCl) attack, including mechanical degradation in meso scale and chemical analysis of calcium hydroxide and Friedel's salt in micro scale. The test results showed that calcium (Ca2+) leaching and salt crystallization occur along with the solution absorption process, and the kinetics is depending on water to cement ratio (W/C) and solution concentrations. Higher W/C has more severe Ca2+ leaching and strength loss, while the leaching amount and strength loss are changed in fluctuating manner with the solution concentrations. The amount of crystallized salt is increasing with the solution concentration. The mechanical degradation degree agrees with the Ca2+ leaching amount. The results indicated that the deterioration of mortar is mainly resulting from increasing porosity due to Ca2+ leaching. [ABSTRACT FROM AUTHOR]

Highlights • Electrochemical impedance spectroscopy is applied to evaluate the leaching behavior. • A new electrical equivalent circuit is proposed to extract parameters from impedance spectra. • A linear relationship between x L and R′ CCP is suggested to quantify the leaching depth. Abstract This study employed EIS (electrochemical impedance spectroscopy) as a non-destructive method to study the leaching behavior of the cementitious materials subjected to aggressive environments. A novel electrical equivalent circuit was established based on a microstructure assumption concerning the leaching-induced degradation. Electrochemical parameters were extracted from the impedance spectra by fitting the established equivalent circuit. On the basis of the understanding of the physical meanings, a proper equivalent-circuit parameter was defined as the indicator of leaching depth. Then the relationship between the leaching depth and the indicator was estimated. As a result, leaching depths can be quantitatively estimated using EIS method. [ABSTRACT FROM AUTHOR]

Chloride-induced corrosion of steel bars can shorten the service life of concrete structures in marine environment. Therefore, a numerical model that can accurately characterize the chloride diffusion in marine concrete can help to evaluate the service durability of structures. In this paper, a novel chloride diffusion model considering the coupling effect of calcium leaching and sulfate attack in cement-based materials is proposed. The model can not only simulate the increase of porosity structure and the desorption of bound chloride caused by calcium leaching, but also characterize the competitive antagonism between sulfate and chloride salts in cement-based matrix, which produces expansive products to fill pores and promotes the desorption of bound chloride. The proposed model was further developed in COMSOL, and verified by two groups of literature experimental data. Then, the verified model was applied to investigate the coupling effect of calcium leaching and external sulfate attack on chloride diffusion process in cement-based materials. The results show that the proposed model can effectively reproduce the chloride diffusion process in both groups of tests well. In contrast to the single influencing factor, the coupling effect of calcium leaching-sulfate attack on the chloride diffusion process in cement-based materials shows that there is a phenomenon of inhibiting chloride diffusion in the early stage of erosion, but it shows a promoting effect in the later stage. Compared with sulfate attack, calcium leaching always dominates the influence of chloride diffusion in cement-based matrix. Furthermore, considering the coupled effect of leaching-sulfate attack, the initial corrosion time of reinforced concrete is about 24.5% earlier than that without considering the coupling effect. Increasing the thickness of steel bar cover layer and reducing the initial porosity of matrix can effectively delay the occurrence of steel bar corrosion in cement-based matrix. [ABSTRACT FROM AUTHOR]

Impressed current cathodic protection and prevention techniques are efficient methods to stop or prevent corrosion in steel reinforced concrete structures. The inevitable side effect of the current exchange is acidification at the anode–concrete interface. Accelerated test methods can be used to investigate the long-term performance of the system. However, a linear relation will not hold between the accelerated and normal conditions because of the influence of the current density. This paper presents results of an accelerated test. A power-relation conversion model is proposed and an acceleration factor is introduced. [ABSTRACT FROM AUTHOR]

One of the key issues associated to mineral carbonation is the slow kinetic rate of leaching process. Hence it is highly important to study the kinetics of the leaching process in detail. This paper deals with the detailed analytical and statistical studies of calcium leaching from waste concrete sample. For comparison, another potential waste i.e. CKD was also selected. Different analytical approaches such as ICP, EDS, XRD, and SEM were used. Based on the preliminary results, at the experimental conditions of 2 M solution of each ligand for 2 h at 70 °C, HNO 3 was found to be more proficient as compared to the rest of ligands (propionic acid, NH 4 Cl, and NaOH) used. In addition, detailed kinetic study was also performed for different temperatures and HNO 3 concentrations. Different heterogeneous (M1-M9), homogeneous (M10, M11), and nucleation i.e. JMAEK (M12) models were implemented to represent the experimental data. Statistical tools such as SSE, SEE, R 2 , F-value, and t-values of the regression parameters were used to discriminate various kinetic models and among them, nucleation model (M12) was found best to describe the experimental data. A low activation energy (25 kJ/mol) indicates that diffusion could be the rate controlling step for the dissolution of waste concrete sample. [ABSTRACT FROM AUTHOR]

In this study, the effects of accelerated carbonation and hydraulic retention time (HRT) on the lead (Pb) removal in pervious concrete filter (PCF) were investigated. The Pb containing solution of 8 mg/L concentration was constantly passed for 60 min through three PCF monoliths that were arranged in series with progressively decreasing water heads. This three-tier filtration experiment was conducted on PCFs, which were tested right after initial curing as well as after an accelerated carbonation exposure. Cumulatively, the Pb removal in 7-day cured and carbonated PCFs were found to be 97.2% and 99.1%, and thus it showed that the CO 2 uptake by PCF marginally improved the Pb fixation, and further these results strongly recommend the HRT consideration in concrete filter design for real-field applications. Moreover, the leachability test results suggests that the change in physical characteristics of treated water from carbonated PCF was found lesser than 7-day cured PCF regardless of the inlet solution pH. The Ca ions removed from both PCFs post-treatment were found well below drinking water acceptable limits. The cost of both PCFs were estimated, which appeared inexpensive unlike treatment units that are currently in practice. On the whole, this study effectively demonstrated the potential of 7-day cured and carbonated PCFs for cost-effective Pb removal. [ABSTRACT FROM AUTHOR]

Calcium-leaching processes can potentially degrade the structure of a concrete matrix. This problem is studied here through the progressive dissolution of Ca 2+ in both ordinary Portland cement pastes (C-0) and binary cement blends (C-20) containing 20% thermally Activated Coal Mining Waste (ACMW). 1 A series of accelerated tests are conducted that involve the immersion of these cement pastes in a 6 M ammonium nitrate solution at a temperature of 20 °C for 7 and for 21 days. A rise in paste porosity was observed, due to increased capillary pore sizes of between 5 and 0.1 μm. In the case of the 20% ACMW pastes (C-20), calcium leaching decreased, probably as a consequence of the pozzolanic effect of the ACMW, while potassium and magnesium leaching increased, due to the presence of the phyllosilicates in the ACMW. The paste compounds most affected by leaching were Ca(OH) 2 , C 6 AS 3 H 32 , and C 4 A C ¯ H 12 . In general terms, it can be concluded that the incorporation of ACMW into binary cements slightly reduces the calcium leaching phenomena. Concerning the environmental impact assessment, the substitution of 20% OPC by ACMW reduced CO 2 emissions by as much as 12% and improved energy efficiency by using approximately 19% fewer fossil resources. [ABSTRACT FROM AUTHOR]

In this paper, a newly developed lattice Boltzmann method based reactive transport model to simulate changes in microstructure of ordinary Portland cement paste due to calcium leaching is presented. The model takes three-dimensional digitized cement paste microstructure as input and is capable to capture an evolution of microstructure due to leaching, accounting for the dissolution of portlandite and corresponding increase in capillary porosity and the decalcification of C-S-H resulting in increase in gel porosity. The developed model has been applied to microstructures generated using two cement hydration models, CEMHYD3D and HYMSOTRUC, for three water-to-cement ratios. It was observed that the rate of leaching is directly proportional to ability of microstructure to transport calcium ions and higher fraction of percolated capillary pores result in higher rate of leaching. The model qualitatively reproduces experimentally observed changes in cement paste porosity and pore size distribution due to leaching. The quantitative validation of model at this scale is not possible by comparison of leaching obtained experiments and simulations which can be attributed to several factors including the differences in the scales of experiment and modelling study presented in this paper. [ABSTRACT FROM AUTHOR]

Wastewater structures, such as treatment plants or sewers can be easily affected by bio-corrosion influenced by microorganisms living in waste water. The activity of these microbes results in deterioration and can cause the reduction in structural performance of such structures. In order to improve the durability of mortar and concrete, different admixtures are being used and the best impact is observed in cement based materials combined with blast furnace slag. In this study, mortar samples with blast furnace slag were exposed to bacterial sulphate attack for 90 and 180 days. The leaching of calcium ions from the cement matrix and equivalent damaged depths of studied mortar samples were evaluated. The results showed more significant leaching of samples placed in bacterial environment, compared to the samples placed in non-bacterial environment. Similarly, the equivalent damaged depths of mortars were much higher for the bacteria-influenced samples. The slag-based cement mortars did not clearly show improved resistance in bacterial medium in terms of calcium leaching. [ABSTRACT FROM AUTHOR]

Carbonation is generally considered beneficial for the calcium leaching resistance of cement-based materials. However, many studies have demonstrated that early accelerated carbonation has detrimental effects on the calcium leaching resistance. In this study, the calcium leaching behavior of an early-carbonated cement paste was investigated in detail. The results showed that 8–16 h of carbonation mitigated the reduction in compressive strength caused by calcium leaching; however, further prolongation of carbonation caused an increased decline in strength at the later leaching stage. In contrast to the calcium leaching results for the powdered samples, the decalcification level of calcium silicate hydrate during the leaching test for the cubic specimens was similar to or even higher than that of the early-carbonated specimens. CaCO 3 and silica gel played key roles in these phenomena; the former provided ideal hardness and calcium sequestration, with the potential to generate protective films, while the latter acted as an ideal filler and binder. Nonetheless, considering the risk of rapid degradation during long-term calcium leaching, excessive carbonation curing of cement-based materials should still be avoided in aqueous environments. [ABSTRACT FROM AUTHOR]

[Display omitted] • The contact angle of calcium silicate hydrate is tested through molecular simulations. • A strategy is proposed to control the surface wettability of C-S-H. • The chloride adsorption and penetration mechanism on C-S-H surface is uncovered. • The effect of surface wettability on chloride invasion and calcium leaching are elucidated. Solid substrates of cementitious composites served in high salinity and humidity environments are invariably covered by a layer of fluid water. Thus wetting behavior of cement hydrates is critical to their durability due to calcium leaching. Meanwhile, chloride ingress phenomena are highly dependent on it. These effects severely aggravate the microstructural degradation of calcium silicate hydrate (C-S-H), with mechanisms that are pronounced at molecular level. Here, we investigate here the nanoscale wetting behaviors of C-S-H and report a surface modification strategy to control its hydrophobicity. Molecular dynamic simulation results reveal that the surfactant, fluoroalkylsilane (FAS), furnishes superhydrophobic surfaces, which hinders ionic interactions and stabilizes the interlayer calcium to eliminate calcium leaching in C-S-H. Further, FAS layer provides a rougher and highly electronegative surface, blocking the chloride adsorption and invasion. This work portrays atomistic insights in C-S-H surface properties, improving the chemical and physical stability of cementitious composites in saline solutions and providing strategies for their surface modifications. [ABSTRACT FROM AUTHOR]