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Knowing the chloride ingress rate is crucial in predicting the service life of reinforced concrete in chlorine environment. While empirical diffusion model is available, fundamental knowledge of Cl− diffusion in calcium silicate hydrate (C-S-H) is largely lacking as it is experimentally challenging to prepare a bulk pure C-S-H. In this study, synthesized C-S-H powder was compacted to form pellets of controlled pore structure and Ca/Si. Effective diffusion coefficients of Cl− in these C-S-H matrixes were measured using steady-state natural diffusion and electric-migration tests, as a function of Ca/Si and porosity. Increased pore tortuosity significantly reduced diffusivity even when porosity remains nearly unchanged. The influence of pore-solution pH to Cl− diffusion is distinct between natural-diffusion and electric-migration. Our data provides the first direct measure of Cl− diffusion coefficient in pure C-S-H matrix, and new insights into the surface effect for diffusion in extremely small pores. [ABSTRACT FROM AUTHOR]

Calcined layered double hydroxides (CLDH) and nano-SiO 2 are commonly added to cement-based materials to enhance their resistance against chloride ions (Cl−) and mechanical performance, respectively. In this work, the CLDH and nano-SiO 2 were combined to synthesize SiO 2 @CLDH, aiming for a synergistic effect between the two materials. The deposition of nano-SiO 2 on the CLDH substrate enhanced the utilization of nano-SiO 2 by promoting their dispersion in the cement pastes. Interestingly, the alkaline pore solution could induce a phase-transformation of SiO 2 @CLDH, leading to the formation of a hydrated calcium silicate (C-S-H) layer on the rehydrated LDH surface (i.e., C-S-H@LDH). The C-S-H layer could enhance the surface adsorption for Cl−; effectively hinder the displacement of interlayer Cl− by SO 4 2− and also improve the carbonization resistance of C-S-H@LDH. However, the amount of nano-SiO 2 loading on the CLDH surface exhibits a 'trade-off' effect. Excessive nano-SiO 2 loading leads to an overabundance of nascent C-S-H gel, which envelops the CLDH and hinders the rehydration of CLDH. Moreover, the nascent C-S-H gel layer could act as the cross-linker between rehydrated LDH and cement pastes, thereby increasing the compressive strength of cement. In general, the incorporation of SiO 2 @CLDHs into cement could significantly increase the hydration degree, the compressive strength, adsorption of Cl−, and optimize the pore size of cement pastes. This study highlighted that when investigating the effects of doping materials on cement performance, it is crucial to recognize that cement may concurrently influence the physicochemical properties of the doping materials. [Display omitted] [ABSTRACT FROM AUTHOR]

Cementitious materials exposed to marine and saline environments are commonly threatened by a combined attack of sulfate and chloride ions. This study developed a numerical framework to investigate two combined coupling mechanisms of 1) coupled solid-liquid chemical reactions for competitive chloride-sulfate attack and 2) electrostatic multi-ion coupling effect on reactive-transport mechanisms. Various chemical reactions including sulfate attack with anhydrous calcium aluminates, secondary precipitation of expansive minerals, competitive binding, and calcium leaching have been quantified. The electrostatic potential caused by multi-ions coupling was solved according to constitutive electrochemical laws. After model validation, the chemical coupling mechanisms for solid-liquid reactions during competitive chloride-sulfate binding were investigated. On this foundation, the influence of electrostatic multi-ionic coupling effects on ionic transport and its interaction with chemical coupling were disclosed. It was found that neglecting multi-ions coupling effect would result in an underestimated chemical coupling strength in competitive chloride-sulfate binding. • The chemical and electrochemical coupling mechanisms for combined chloride-sulfate attack was numerically analyzed. • Solid-liquid chemical reactions including competitive binding, minerals precipitation and calcium leaching was coupled. • The electrostatic multi-ions coupling effect was quantitively expressed by constitutive electrochemical laws. • Electrochemical coupling not only affects the ionic transport behavior but also the chemical coupling intensity. [ABSTRACT FROM AUTHOR]

Abstract Accelerated migration tests which are commonly used to measure chloride diffusion in ordinary cement-based materials cannot be directly applied to composite with very low permeability, such as Ultra High-Performance Fiber Reinforced concretes (UHPFRC). In order to assess the UHPFRC enhancement on the structural durability, there is a critical need to accurately assess the permeability level of the material to chloride ions. The objective of this work is to adapt an existing set-up of accelerated chloride migration test in order to (i) better characterize the resistance of chloride ion penetration in UHPFRC; and (ii) to compare the resistance of chloride ion penetration between UHPC and UHPFRC. The material characterization, the set-up modifications of the existing accelerated migration test, the results are presented. In conclusion, the modification of the test-set-up allowed to accurately measure chloride transport of very low permeability UHPFRC and to shed light on the effect of the fiber reinforcement. [ABSTRACT FROM AUTHOR]

There are several cases worldwide wherein sulfide-bearing aggregates in concrete elements/structures have undergone oxidation and caused extensive damage. Signs of observed deterioration include map cracking, pop-outs, and secondary products that were generated from swelling. Unfortunately, it takes years to detect these signs visibly. Thus, in this study, a new methodology is proposed to activate and accelerate the potential oxidation reaction of iron sulfide minerals in concrete aggregates using chloride ions as activators or catalysts for the oxidation reaction. To promote the rapid penetration of chloride ions through concrete specimens, an electrochemical treatment is proposed consisting of two main phases, namely chloride impregnation in the specimen and impressed voltage treatment. Concrete specimens each 100 mm in diameter and 200 mm in length were made using aggregates with or without iron sulfide minerals and a mix design resembling the one used for building house foundations in the Trois-Rivières case, Canada. The results showed that chloride ions could activate the reaction and act as catalysts for the oxidation reaction of sulfide-bearing aggregates under a constant current (impressed voltage). Finally, traces of iron oxides/hydroxides and the formation of secondary sulfates (i.e., gypsum and ettringite) were observed in the concrete made with sulfide-bearing aggregates. This new procedure is promising for evaluating the oxidation potential of concrete with sulfide-bearing aggregates over a reasonable testing period. [ABSTRACT FROM AUTHOR]

The interactions of water and chloride ions penetration into porous mortar have been investigated experimentally and modelled by molecular dynamics. The water distribution visualized by neutron radiography and chloride penetration by Electron Probe Micro-Analysis indicate that separation of chloride ions from water during the penetration process took place and water ran much deeper into the material than chloride ions. The relationship between the penetration depth of water and chloride ions can be described by a linear function despite different water-cement ratio. Furthermore, molecular dynamics attributes the different transport mechanisms of water and ions in porous cementitious materials to three reasons: the nanostructure of hydration product play filtering role to screen chloride ions with larger hydration shell; as compared with water, ions reside in the calcium silicate surface for longer time due to the strong interfacial bonding; chloride ions accumulate and form CaCl ionic cluster, slowing down the migrating rate. [ABSTRACT FROM AUTHOR]

For calculating ion transport in electro-migration experiments in concrete, the pore space is divided between free pore water and a double layer that compensates the surface charge of minerals lining the pore. The concentrations of counter-ions and co-ions in the double layer are averaged in a Donnan layer, which allows to solve the flux equation of the individual ions. A numerical model is developed for transient states, with the harmonic mean of the chemical activity coefficients and the physical parameters to adapt cell sizes in zones with high concentration gradients. Diffusion coefficients of the ions are corrected for temperature and ionic strength with an empirical equation with three parameters optimized on published transport numbers and specific conductances. The current and the Cl – breakthrough is calculated in an electro-migration experiment with a concrete sample. The surface charge is positive in the experiment, enhancing and reducing the diffusivity of anions and cations. [ABSTRACT FROM AUTHOR]

Stray current induced corrosion is a major technical challenge for modern electric railway systems. The leakage of stray current to surrounding reinforced concrete structures can lead to steel reinforcement corrosion and the subsequent disintegration of concrete. Steel fibre reinforced concrete has been increasingly used as the railway tunnel lining material but it is not clear if discrete steel fibres can still pick up and transfer stray current in the same way as conventional steel reinforcement and lead to similar corrosion reactions. The corrosion behaviour of steel fibres was investigated through voltammetry tests and electrochemical impedance spectroscopy. The presence of high concentration chloride ions was found to increase the pitting corrosion tendency of steel fibres in simulated concrete pore solutions and mortar specimens. The chloride threshold level for corrosion of steel fibres in concrete is approximately 4% NaCl (by mass of cement) which is significantly higher than that of conventional steel reinforcement. [ABSTRACT FROM AUTHOR]

State of rebar corrosion in concrete powder aqueous solution contaminated with chloride and sulfate ions has been determined by conducting a potentiodynamic polarization test. XRD analysis and FTIR spectroscopy were also performed. From the results, different zones of corrosion in terms of potential ranges have been identified. The presence of Na 2 SO 4 has mitigated the effect of chloride ions whereas the presence of MgSO 4 has stimulated the effect of chloride ions on reducing the passivity of steel reinforcement in a chloride environment. Ordinary Portland cement performed better against Mg-oriented sulfate attack whereas Portland pozzolana cement performed better against Na-oriented sulfate attack in the presence of chloride ions. [ABSTRACT FROM AUTHOR]

Chemical aggressions from the environment, such as salt ions, can damage reinforced concrete structures before they reach their service life. These deterioration mechanisms are coupled. The current research on cementitious material's durability has thus gradually shifted to the field of durability damage caused by the combined action of multiple factors. The research in this study concerns the case of combined chloride-sulfate attacks to provide a better understanding of the coupling phenomena by studying the mutual effect of the chloride and sulfate ions on the materials. The effect of the type of cement and curing duration on the chloride-sulfate attack is also investigated. Experimental results based on different investigation techniques (ICP, XRD, NMR, etc.) clearly show the competition between chloride and sulfate ions, and how the physico-chemical involved mechanisms completely change with respect to the cases of an exposure to a single type of ion. • The presence of sulfate ions reduces the chemical fixation of chloride ions. • This increases the possible risks of steel corrosion by increasing the propagation front. • The decalcification of C-S-H in the combined sulfate-chloride attack is drastically reduced. • The presence of sulfate ions decomposes the Friedel salt and turns it into ettringite. [ABSTRACT FROM AUTHOR]

A growing body of evidence has suggested an aggravated chloride diffusion in concrete exposed to seawater than to pure NaCl solution of the same chloride concentration, indicating the potential impact of other constitutional ions in seawater, e.g., sulphate and magnesium. This study aims to systematically investigate the impact of sulphate, magnesium and leaching, and their interaction on the chloride transport in alkali-activated slag (AAS) and ordinary Portland cement (OPC). The results indicate that the aggravating effect of magnesium on chloride diffusion overwhelms the suppressing effect of sulphate, leading to increased chloride diffusion in both AAS and OPC. Despite without the pore filling effect by ettringite formation as in OPC, the sulphate in seawater also suppresses the chloride transport in AAS, which is likely linked to the electrical coupling effect during multi-ion transport and the pore wall thinning effect by the aggregation of the formed Na–SO 4 clusters in the gel pore. The origin of the peaking behaviour is found to be contributed by not only the impact of leaching, but also the effect of sulphate and magnesium on releasing the bound chloride from the reacted phases at the exposure front. [Display omitted] [ABSTRACT FROM AUTHOR]

The impact of the addition of layered double hydroxides (LDHs) on binding of chloride ions was studied by pore expression experiments. A Mg-Al-NO 3 type of LDHs was added to paste samples blended with 3 % NaCl in different proportions (4 % and 10 % by mass of the binder). In addition, the influence of LDHs on the hydration process, morphology and porosity of samples containing Portland cement, calcium sulphoaluminate cement and silica fume was investigated. The potential physical and chemical contributions of LDHs to the system (e.g. AFm formation) were discussed comprehensively. According to the results, addition of LDHs by 10 % could reduce the chloride content in the pore solution by over 25 % and increase the carbonate AFm phases. Moreover, formation of reaction products on the LDH grains was observed. Finally, it was clear that a part of the Cl− ions is bound to the surface of LDHs and can be washed out. [ABSTRACT FROM AUTHOR]

To investigate the relationship between the chloride ion concentration of the expressed pore solution ( C e ) and the exposure solution ( C es ) of cement-based materials exposed to a chloride salt solution, a calculation of the C e , based on an electrical double layer (EDL) model was proposed. The C e values were calculated using the proposed equations, applying the measured parameters: relative potential ( δψ 0 ), dielectric constant ( ε ), porosity ( P ), bulk density ( D ), volume percentage ( p i ) of pores with diameter d i . The calculations explain why C e does not always equal to C es . The results indicate that the expression method does not test the concentration of free chloride ions in the bulk solution ( C Cl − b ) or the average concentration of the transportable chloride ions ( C ttr.a ) in the pores. However, the ratio ( C r ) of C e to C Cl − b and the relationship between C e and C ttr.a can be calculated to more accurately measure chloride ion migration in cement-based materials. [ABSTRACT FROM AUTHOR]

Understanding the energetics and kinetics of chloride in cement-based materials is critical to identify effective ways to control chloride diffusion. Here, we performed an ab-initio molecular dynamics (AIMD) simulation on interfacial activities to reveal the reaction mechanism and dynamic nature of chloride. Chloride ions mainly distributed in the electric double layer (EDL) of positively charged surface ([Ca 2 Al(OH) 6 ]+) through electrostatic interactions with calcium ions and protons, while sodium ions were mainly confined within the interface region between the negatively charged surface ([Cl·2H 2 O]−) and hydrocalumite main layer, forming various ionic complexes. The above interactions are driven from the nucleophilic nature of bound chlorides and electrophilic nature of water hydrogen and calcium ions. These findings were further confirmed by dynamic analyses, local structures and electronic properties as well as comparing with experiments and classical molecular dynamics (MD) simulations. We finally inferred that the chloride binding properties can be tailored by regulating the Ca/Al ratio of hydrocalumite main layer. [ABSTRACT FROM AUTHOR]

This paper studies chemical composition of partially and fully hydrated slag grains in a (nearly) 40-year-old field concrete from the Netherlands. The concrete samples were assumed to be sufficiently aged to contain fully hydrated slag grains as well as partially hydrated large slag particles with thick rims. Our analysis showed that three different elemental zoning could be identified depending on the original slag grain size. Upon full hydration of a small slag grain (i.e., <8 μm), two distinct regions were identified corresponding to a hydrotalcite-like phase in the outer rim and a C–S–H gel phase in the core, respectively. As for medium (8–17 μm) and large (>15 μm) slag grains, three distinct regions were clearly visible. Hydrotalcite-like phase was mainly observed in the outer rim and the core. C–S–H gel phase was found to be precipitated in the region between the outer rim and the core. [ABSTRACT FROM AUTHOR]

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

Well hydrated cement paste was exposed to MgCl 2 , CaCl 2 and NaCl solutions at 20 °C. The chloride binding isotherms for free chloride concentrations ranging up to 1.5 mol/l were determined experimentally. More chlorides were found to be bound when the associated cation was Mg 2 + or Ca 2 + compared to Na + . The chloride binding capacity of the paste appeared to be related to the pH of the exposure solution. In order to explain the cation dependency of the chloride binding a selection of samples was investigated in detail using experimental techniques such as TG, XRD and SEM–EDS to identify the phases binding the chlorides. The experimentally obtained data were compared with the calculations of a thermodynamic model, GEMS. It was concluded that the measured change in chloride binding depending on the cation was mainly governed by the pH of the exposure solution and thereby the binding capacity of the C-S-H. [ABSTRACT FROM AUTHOR]

Four different binders based on calcium sulfoaluminate cements have been submitted to accelerated chlorination through ionic exchange on hydrated pastes, in order to investigate their ability to chemically bind chloride ions that might reduce chloride penetration. The composition of hydrated cements before and after the treatment was evaluated by means of an X-Ray Diffraction– 27 Al Magic Angle Spinning Nuclear Magnetic Resonance Spectroscopy combined study, allowing to take into account even partially amorphous phases and to make quantitative assumption on the relative abundance of the different aluminium-containing phases. It was found that low SO 3 Sulfoaluminate–Portland ternary systems are the most effective in binding chloride ions and the active role played by different members of the AFm family in chloride uptake was confirmed. Moreover, a peculiar behavior related to the formation of Friedel's salt in different pH conditions was also established for the different cements. [ABSTRACT FROM AUTHOR]

Chloride ion transport driven by electrical potential gradients is discussed in concretes wherein OPC is partially replaced by limestone or a combination of limestone and fly ash/metakaolin at replacement levels of 20% or 35% (volume-basis). The ternary formulations demonstrate non-steady state Cl − migration (NSSM) coefficients that are comparable to or lower than those of the control OPC concretes, with metakaolin blends showing markedly better performance. A pore structure factor extracted through electrical conductivity measurements before the NSSM test is correlated with Cl − penetration depths after the migration test. The transport of all ionic species (Cl − , OH − , Na + , K + ) is modeled using an explicit finite element framework via the coupled Poisson–Nernst–Planck (PNP) equation with suitable consideration of: (a) concentration (depth)-dependent diffusion coefficients, (b) pore-structure factor, and (c) Cl − binding. With informed inputs of material properties, the simulations are able to reliably capture Cl − penetration behaviors in plain and blended binder formulations. [ABSTRACT FROM AUTHOR]

Cementation of aqueous radioactive waste contaminated with a significant 90Sr is challenging due to the potential radiolysis of water contents. Utilization of calcium aluminate cement (CAC) modified with sodium polyphosphate (CAP) is interesting as its water content can be reduced by thermal treatment. The present study investigated solidification and stabilization of Sr2+ and Cl− ions in CAC and CAP with or without thermal treatment. A leaching test showed a superior Sr2+ ion stabilization in CAP: apparent diffusion coefficient of Sr2+ was smaller than in the CAC by 5 orders of magnitude. CAC cured at 20 °C had the best stabilization for Cl− ions among the samples tested. Friedel's salt formed in CAC may have contributed to the immobilization of Cl− ions. The stabilization of Cl− ions by CAP was significantly improved by the thermal treatment likely because of the improvement in the microstructure previously reported. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, the effect of hydroxyl ions on chloride penetration depth measurement using the colorimetric method was studied. Equivalent silver nitrate solution (i.e. Ag+ =Cl−) was added to the NaCl+NaOH solution with different concentrations, then the amount of precipitated silver chloride and silver oxide were determined by chemical methods, and the color of the precipitated products was examined. Results show that the amount of silver chloride formed decreases linearly as OH− to Cl− ratio (r) increases. Thus, the chloride concentration at color change boundary changes with the pH value of the concrete. AgCl has a white color, while Ag2O has a dark brown color. When the value of r exceeds 4, the color of the mixture looks brown, and color change boundary cannot be easily distinguished. [Copyright &y& Elsevier]

Abstract: This paper concerns the proper selection of the electrochemical chloride removal (ECR) current and the ECR duration. Four constant ECR current densities, 100, 200, 400 and 800 μA/cm2, were applied to concretes for 1 to 6 weeks. The remaining chloride contents nearby the reinforcement were measured to understand how fast the ECR process can remove chloride ions out of concrete. The open circuit potential and corrosion rate measurements were performed to examine the corrosion status after ECR. In addition, the pH value nearby the reinforcement and the apparent electrical resistivity of concretes after ECR were measured. The results showed that the remaining chloride ions decreased, the open circuit potential became nobler, the corrosion rate decreased, the pH value increased and the apparent electrical resistivity increased as the ECR parameter, defined as the product of the ECR current density and the ECR duration, increased. The ECR parameter can provide a direction in designing the ECR process. [Copyright &y& Elsevier]

Currently, in Ontario, Canada, around 21.7% of the total hazardous waste (HZW) collected by municipalities is waste paint. Waste latex paint (WLP) alone constitutes 12% of the total HZW. It is estimated that only 10–30% of this waste is presently being collected but this proportion is growing with public education efforts. In addition, due to increasingly more stringent environmental regulations on volatile organic compounds (VOCs), more latex-based paints will be produced compared to solvent- and oil-based alkyds. This will result in more WLP being generated annually in Ontario and across North America. The disposal cost of such waste currently varies between Can$0.90 and Can$1.40 per litre. This study was conducted in collaboration with the City of London, Ontario and the Ontario Paints and Coatings Association and aims at investigating the benefits of recycling WLP in concrete with a special focus on concrete sidewalks. WLP was used in concrete mixtures both as a partial replacement for virgin latex and for mixing water. This paper demonstrates that concrete mixtures incorporating WLP can have improved workability, higher flexural strength, lower chloride ion penetrability, better resistance to deicing salt surface scaling and can be more economic because they require less water-reducing and air-entraining admixtures. The results also indicate that the annual urban concrete sidewalk construction could use the yearly production of WLP while producing sidewalks with enhanced properties and durability. [Copyright &y& Elsevier]

In this paper, chloride (Cl−) binding isotherms are developed for cement hydration compounds, specifically, calcium-silicate-hydrates (CSH) and AFm phases including mono-sulfate aluminate, hydroxy-AFm, monocarbonate-AFm, and hemicarbonate-AFm, in simulated concrete pore solutions to account for the effect of pH and the presence of other ions. pH and the presence of other ions have a strong influence on the Cl− binding capacity of cement compounds, which have not been taken into consideration in previous research. A novel experimental technique is developed to characterize the binding capacity from very low (1 mM) to very high concentrations (5 M). To overcome the existing challenges of measuring both low and high Cl− concentrations without significant dilution and in the presence of SO 4 2− and OH− ions, a potentiometric method was used. The amorphous CSH in the hydrated cement paste; thus, the heterogeneity of the hydrated components of the cement paste was also quantified and accounted for in this study. [ABSTRACT FROM AUTHOR]

In this study, the effect of chloride environment containing various concentrations of chloride ion (Cl−) on self-healing performance of pre-cracked cementitious composite containing crystalline admixture (CA) and MgO expansive agent (MEA) was investigated under wet-dry cycles in chloride solutions. The results revealed that the Cl− changed the mineralogy of self-healing products, and consequently, affected the crack closure ratio and mechanical strength recovery. When self-healing occurred in distilled water, a large amount of ettringite (AFt) were detected, whereas in Cl− solution, monosulfate (AFm) was consumed by Cl− to form Friedel's salt (Fs), and then the Fs was decomposed to Al(OH) 3 (AH 3) due to carbonation. During the multiphase conversion process, hydroxide (OH−) was released into crack solution, therefore the dissolved carbon dioxide (CO 2) concentration was increased. The carbonation of the crystals formed in cracks was accelerated with the volume expansion, which achieved rapid crack sealing but contributed little to the mechanical performance recovery. • Crack closure under wet/dry cycles in chloride solution is higher than the one in distilled water. • Element analysis shows that calcium is vital for crack healing either in water or chloride solution. • AFm is consumed by chloride ion to form Fs, and Fs were decomposed to AH 3 by carbonation. • Soluble reactive silica reacts with calcium hydrate to form C-S-H gel to heal concrete cracks. • Expansion of magnesium hydroxide facilitates crack self-healing by interconnected network. [ABSTRACT FROM AUTHOR]

The utilization of recycled concrete as an adsorbent to sequester NO 2 without additives or catalysts is an innovative, cost-effective, and sustainable approach to capture NO 2 from targeted industrial facilities. This paper presents the mechanical and durability performance of ordinary portland cement (OPC) concrete containing NO 2 sequestered recycled concrete aggregate (NRCA). NRCA was used as a partial replacement for natural fine aggregate at 20% and 40% rates by volume. The incorporation of NRCA in concrete resulted in increased compressive strength, decreased water-permeable porosity, and reduced chloride ion migration. Moreover, test mixtures comprising 40% NRCA showed a significant chloride binding capacity compared to control concrete mixtures. Furthermore, high replacement rates of NRCA noticeably enhanced the resistance to chloride-induced corrosion of steel in concrete or at least was on par with the performance of a commercially available calcium nitrite-based corrosion inhibitor. [ABSTRACT FROM AUTHOR]

Strength development and shrinkage and creep behavior of recycled aggregate concrete as well as durability aspects such as carbonation and chloride ion penetration were investigated. Except for Control concrete, natural fine aggregate was replaced by recycled fine aggregate at a rate of 0%, 15%, 30%, or 50% while natural coarse aggregate was completely replaced by recycled coarse aggregate (RCA). Two different recycled fine aggregates were used: Recycled fine aggregate (RFA) and CO 2 treated recycled fine aggregate (CRFA). Compressive strength of recycled aggregate concrete at all ages tested was reduced from that of the Control concrete. CO 2 treatment of recycled fine aggregate improved not only the aggregate physical properties but also the strength of recycled aggregate concrete. The compressive strength reduction was 19% or less at 100% RCA + 15%–50% RFA replacement level while it was 11% or less at 100% RCA + 15%–50% CRFA replacement level after 28 days. Shrinkage and creep strains were measured for up to 300 days. Shrinkage of concrete with 100% RCA was 12% larger than that of Control concrete, while shrinkage of concretes with 100% RCA + 30% RFA or 30% CRFA replacement increased by about 25%–30%. In the creep test, creep coefficient and specific creep of all recycled aggregate concretes increased by about 20–35% over that of the Control. CO 2 treatment of recycled fine aggregate resulted in up to 15% improved strength of recycled aggregate concrete, but showed little improvement on shrinkage and creep. Durability of recycled aggregate concrete evaluated in terms of carbonation and chloride ion penetration was reduced from that of the Control concrete. • Based on current test results, the maximum amount of CRFA replacing natural fine aggregate can be suggested as 30% (by vol.). The maximum 30% utilization is also limited by availability of long-term test data such as shrinkage and creep. • It should be noted that, due to reduction of concrete durability for carbonation and chloride ion penetration, cautious use of CO2 treated recycled aggregates is recommended where the application is potentially affected by carbonation and/or chloride ion penetration. [ABSTRACT FROM AUTHOR]

The transport properties obtained from the accelerated tests on the concrete mixtures that contain shrinkage-compensating cement have indicated that addressing the issue of shrinkage may come with the expense of increased permeability. This raised a fundamental question concerning the long-term durability of reinforced concrete structures made with this type of cement. In the absence of similar studies, a comprehensive experimental testing program was devised in the current study to understand the vulnerability of steel bars embedded in shrinkage-compensating cement concretes exposed to corrosive environments. This included a long-term corrosion monitoring of reinforced concrete specimens made with different dosages of shrinkage-compensating cement. In addition to finding the corrosion rate of embedded steel bars, air permeability, capillary absorption, and chloride diffusion tests were conducted to determine the transport properties of the concretes made with this type of cement. The experimental test results were then further supported and explained using mercury intrusion porosimetry analyses. [ABSTRACT FROM AUTHOR]

The effects of limestone replacement fraction, limestone specific surface area and water-to-binder (W/B) ratio on the threshold chloride concentration (TCC) for steel corrosion were evaluated. XRD and SEM analyses were conducted to examine the crystalline phases and microstructure of limestone-blended cement paste, respectively. The influence of pH value of concrete pore solution on the chloride binding capability was also investigated. The results demonstrate that the chloride threshold decreases as the limestone content or the W/B ratio increases, while limestone fineness shows negligible effect. XRD analyses indicate that addition of limestone inhibits the transformation from ettringite (AFt) to monosulfate (AFm), which exhibits superior chemical binding capability for chloride ions. SEM analyses suggest that addition of 15 wt% limestone contribute to a denser microstructure. Reduction in the pH value of pore solution compromises the chloride binding capability of concrete. [ABSTRACT FROM AUTHOR]

The high solution to solid ratio normally used for the measurement of chloride binding isotherms, leads to a leaching of ions and a decrease of pH. To make binding test more representative of on-site conditions, we investigated the influence of the increase of pH to compensate the leaching. The binding was characterized on plain cement and Limestone Calcined Clay Cements (LC3). The increase of pH leads to a decrease of the amount of bound chloride. This lower binding can be first explained by the lower chloride content in the solid solution of Friedel's salt and hemicarboaluminate hydrate. Moreover, a lower chloride ions adsorption on C-A-S-H is quantified. [ABSTRACT FROM AUTHOR]

The transport of chloride ions in concrete structures is not only due to diffusion but also to the advective effects of water movements and capillarity, mostly present with wet-dry cycles. These last two phenomena are currently very poorly modelled. A new system based on optical fibres was previously developed to measure the free chloride concentration in the pore solution without damaging the material. This work aims at developing a numerical model simulating the reactive transport of chloride ions by capillarity in a cementitious material, which considers the diffusion of chloride ions and water transport by capillarity, as well as the chloride adsorption by the material with chemical interaction. It led to the analysis of the main phenomena occurring during a capillarity test. In a larger perspective, this study improves the current understanding of the durability of concrete structures exposed to severe environmental conditions. [ABSTRACT FROM AUTHOR]

Numerical simulation of chloride diffusion through high-performance binding systems such as limestone-calcined clay cement (LC3) and its comparison to control and fly ash modified concretes is discussed. The simulation framework considers the pore structure of concrete, the concentration-dependence of diffusion coefficient, and Freundlich binding. The LC3 concrete and the companion fly ash concrete exhibit similar service lives (~8× control mixture), despite the LC3 system having a reduced clinker factor than the fly ash concrete (~0.5, as opposed to 0.7). The diffusion model is augmented with a scalar isotropic damage variable that accounts for random distribution of microcracks under fatigue loading (e.g., in a bridge deck). The impact of damage on service life at different stress levels, for the different concretes is elucidated. The modeling approach can be used to evaluate the influence of binder composition and damage on effective service life of chloride-exposed concrete structures, thereby aiding in binder selection. [ABSTRACT FROM AUTHOR]

Quantitative predictions for service-life modelling requires a strict approach to quantify the impact of each parameters. As an example, this paper presents the durability performance of cementitious materials composed of different supplementary cementitious materials (SCMs including limestone, calcined clay (CClay), slag and siliceous fly ash (FA)) with respect to chloride transport. Pore structure, binding capacity (combined with phase assemblage analysis) and pore solution were studied. In addition, the rate of diffusion of chloride ions through binary and ternary mortars were measured with an unidirectional bulk diffusion experiment. Results from the pore structure and the binding studies, and the bulk diffusion follow opposite trends. However, the alkali ions content in pore solution is shown to have a strong correlation, but the mechanisms are not yet fully understood. These results suggest that models need to be revised based on the physical mechanisms to obtain reliable predictions. [ABSTRACT FROM AUTHOR]