Chloride Profiles Research Articles

Free and bound chloride relationships affecting reinforcement cover in alkali activated concrete

This paper investigates the free chloride profiles, diffusion parameters and chloride binding capacity of an alkali activated concrete (AACM) together with a control Portland cement (PC) concrete. Ggbs based AACM concrete specimens with different molarity of activator were exposed to a 5% NaCl solution for 540days to determine their free chloride diffusion properties. The relationships between the free and bound chloride concentration were determined by applying Freundlich and Langmuir isotherms. The required cover to steel reinforcement for corrosion prevention is derived to satisfy the limiting thresholds of free and bound chloride concentrations.The results show that Fick's second law of diffusion applies to the free chloride profiles of AACM concrete and provides higher values of diffusion coefficients than a similar grade of PC concrete. The relationship between the free and bound chlorides is defined by the Langmuir isotherm. PC concrete has higher chloride binding capacity than AACM concrete for both water and acid soluble chlorides. Less concrete cover to steel reinforcement is required in AACM than PC concrete when calculated by using the bound chloride concentration threshold limit. The values of cover based on the corresponding free chloride limit in AACM concrete are higher than its bound chloride values.

Profiles of chloride in matrix porewater as natural tracer for matrix diffusion in crystalline rocks

Matrix porewater from low permeable Grimsel granodiorite was successfully characterised using indirect methods applied to originally saturated core samples. Core samples were taken from a 17 m long borehole originating from a tunnel of the Grimsel Test Site into the crystalline bedrock intersecting a tectonic shear zone with a water-conducting fracture. Matrix porewater chloride profiles on the meter scale were determined on both sides of the water-conducting fracture. To evaluate transport processes within the bedrock formation, a series of diffusive model calculations were performed, which to fit the porewater data. Boundary and initial conditions were varied according to the geological conditions, whereas other required parameters such as the connected porosity and pore diffusion coefficients were determined by laboratory experiments on the cores and extrapolated to in situ conditions. The main conclusions can be summarized as follows: (1) Chloride porewater profiles at the meter scale can be simulated using diffusive transport models. This provides evidence that diffusive exchange with active fractures occurs over a range of a few meters in the low-permeable crystalline bedrock; (2) the best fit of the diffusion profile was achieved by a model approach, which takes asymmetric initial Cl-concentrations into account. This indicates that prior to the activation of the present water-conducting fracture, the porewater system in the bedrock was already active showing a concentration gradient in chloride; (3) the water-conducting fracture was activated at least between 850 and 1700 years before present, with a best-fit 1200 years before present; and (4) the hydraulic were affected by the construction of the rock laboratory 20 years ago, resulting in a rapid dilution of the fracture groundwater by advection.

Nutritional composition and toxicity profile of Cantharellus species (Purple Mushroom) in rats

Cantharellus species (Purple mushroom) natively known as Ero ububa in Southeastern Nigeria is used for nutritional and medicinal purposes. This study evaluated the nutritional composition of ero ububa and its toxicity profile in rats. Proximate, phytochemicals, minerals, vitamins, fatty acids and amino acids were analyzed using standard biochemical methods. The acute toxicity experiment was performed by administering a single dose of upto 5g/kg of the mushroom extract (n=5/group/sex) and rats were monitored for any toxic signs or mortality. For subacute toxicity experiment, the mushroom extract was orally administered at the doses of 500, 1000 and 1500 mg/kg for 14 days. The haematological, biochemical and histopathology of the rats were evaluated. Ero ububa had high carbohydrate (64.24%) and protein (13.71%) contents and low lipid content (3.12%). The phytochemical analysis revealed the presence of important bioactive compounds: alkaloid (0.51%) and flavonoids (1.60%). Mineral content showed a high trend in mg/100g in the order of Ca2+>K+>P>Mg2+>Na+>Zn2+>Fe2+. The results revealed high amount of vitamins A, B3 and C; reasonable amount of essential and non-essential amino acids as well as high unsaturated fatty acid (oleic acid (12.45%). In acute toxicity test, oral administration of 5g/kg body weight did not produce any mortality or toxic effects. The subacute toxicity study showed significant increase (p<0.05) in packed cell volume and platelets, however no effects (p>0.05) were observed in the other white blood cell and red blood cell indices. Biochemical studies revealed significant decrease (p<0.05) in urea, creatinine, sodium and alkaline phosphatase. No significant (p>0.05) effects were recorded in aspartate and alanine aminotransferases , potassium, bicarbonate, chloride and lipid profile parameters. Histopathological examination of the liver and kidney did not show any pathological changes. The results of this study revealed that purple mushroom (ero ububa) is highly nutritious and non-toxic in rats at the tested doses and therefore can be used for medicinal and culinary purposes.

Corrosion assessment of reinforced concrete structures exposed to chloride environments in underground tunnels: Theoretical insights and practical data interpretations

Field investigations were conducted to assess the corrosion status of reinforcements in the underground metro tunnels built between 1980 and 2006. The carbonation depth, half-cell potential, and concrete resistivity were measured on-site, and the chloride profile of cored concrete specimens was analyzed in the laboratory. A theoretical analysis was conducted based on Nernst equation and Butler-Volmer equation. The nature of corrosion potential (half-cell potential) and its relationship with corrosion rate in different corrosion status were revealed. The impact of galvanic coupling on localized corrosion and macrocell corrosion was also analyzed. Connecting the theoretical analysis with the test results, the drop of the half-cell potential that occurred near the NaCl crystallization on some tunnel segments can serve as an indicator of chloride-induced corrosion. However, for the segments showing damp patches and relatively low resistivity, it will be challenging to assess the corrosion status based simply on the half-cell potential due to the impact of galvanic coupling. The corrosion assessment in similar environments should be conducted carefully with the determination of corrosion sources and considering the impact of concrete mix proportion and galvanic coupling.

Multi-term time fractional diffusion equations and novel parameter estimation techniques for chloride ions sub-diffusion in reinforced concrete.

In this paper, searching for a better chloride ions sub-diffusion system, a multi-term time-fractional derivative diffusion model is proposed for the description of the time-dependent chloride ions penetration in reinforced concrete structures exposed to chloride environments. We prove the stability and convergence of the model. We use the modified grid approximation method (MGAM) to estimate the fractional orders and chloride ions diffusion coefficients in the reinforced concrete for the multi-term time fractional diffusion system. And then to verify the efficiency and accuracy of the proposed methods in dealing with the fractional inverse problem, two numerical examples with real data are investigated. Meanwhile, we use two methods of fixed chloride ions diffusion coefficient and variable diffusion coefficient with diffusion depth to simulate chloride ions sub-diffusion system. The result shows that with the new fractional orders and parameters, our multi-term fractional order chloride ions sub-diffusion system is capable of providing numerical results that agree better with the real data than other models. On the other hand, it is also noticed from the numerical solution of the chloride ions sub-diffusion system that setting the variable diffusion coefficient with diffusion depth is more reasonable. And it is also found that chloride ions diffusion coefficients in reinforced concrete should be decreased with diffusion depth which is completely consistent with the theory. In addition, the model can be used to predict the chloride profiles with a time-dependent property. This article is part of the theme issue 'Advanced materials modelling via fractional calculus: challenges and perspectives'.

Analysis of Service Life of Surface Coated-Concrete Structures Considering Climate Change and Chloride Ingress

Mortar surface coating is widely used as a finishing material to extend the service life and improve chloride ingression resistance of marine concrete structures. This study proposes a model for estimating the service life of surface-coated marine concrete considering climate change. First, the increase of chloride diffusivity due to climate change is considered using Arrhenius’ law. A two-layered chloride ingress model is used to analyze chloride profile. The probability-based approach is used to find the service life of concrete structures. Second, parameter analysis is performed considering the effects of various factors on service life. The influences of thickness and chloride diffusivity of the coating and substrate concrete on service life are highlighted. The reduction of service life due to climate change is clarified based on the regression of results of parameter analysis. For marine concrete with 50 years’ service life, 6% service life reduction occurs because of climate change.

Influence of artificial cracks and interfacial defects on the corrosion behavior of steel in concrete during corrosion initiation under a chloride environment

In this study, the effect of both artificial crack and defects of the steel-concrete interface on the initiation and propagation of steel reinforcement corrosion in concrete under a chloride environment is investigated. This work was based on two groups of reinforced concrete blocks, with or without artificial crack. The microstructures of the steel-concrete interface, the cement hydration products at the steel-concrete interface, the chloride profiles, the galvanic corrosion current, and the distribution of pitting corrosion on steel rebar were studied and compared. Experimental results show that the location of initial corrosion is related to top-casting defects but not to the location of air bubbles. Pitting corrosion mainly initiated at the rib foot of the bottom side of the deformed steel rebar with top-casting defects. Steel in concrete with an artificial crack exhibited a fast initiation period immediately followed by a propagation period. The presence of both artificial crack and top-bar effect thus led to faster deterioration than in un-cracked structures.

The effect of artificial leaching with HCl on chloride binding in ordinary Portland cement paste

This study investigates how the pH in the pore solution influences the chloride binding in Portland cement pastes. Cement paste samples were exposed to NaCl, CaCl2 and HCl solutions. The mechanisms of changes in chloride binding were investigated using a wide variety of techniques both for the liquid and solid phase. Lowering the pH from 13 to 12 with CaCl2 or HCl greatly increased chloride binding compared to NaCl, which was associated with increased amounts of chlorides in the AFm-phases. Lowering the pH below 12 lead to reduced chloride binding in part due to dissolution of AFm. Chloride binding approached zero at a pH of 9. The influence of C-S-H on changes in chloride binding could not be conclusively determined. The impact of leaching and low pH on chloride binding is key to explaining the peaking behaviour of chloride profiles in concrete submerged in chloride containing solutions like sea water.

Comparison of Three Different Methods for Measuring Chloride Transport in Predamaged Concretes

Chloride transport is an important subject for the durability of steel-reinforced concrete structures in chloride-laden environments. There are several different types of tests for determination of the chloride-transport properties of concretes. The understanding of the differences between these tests is critical for choosing the most suitable type of test. Besides, there are different factors affecting the chloride transport in concrete, such as the water/binder (w/b) ratio, cement type or mineral additives, and the stress levels (since concrete structures are designed to withstand different loads). This work aims to evaluate the applicability and feasibility of different chloride-transport tests on concretes predamaged by compression. Moreover, the combined effect of predamage caused by different stress levels and the concrete mix design (w/b ratio, mineral additives) on chloride transport in concrete were investigated. The results show that the chloride profiles and the chloride diffusion coefficients in the chloride sorption + diffusion tests are much higher than those in the chloride diffusion tests, especially for the concretes subjected to higher stress levels. This indicates that the effect of sorption on the increase of chloride ingress into concrete is more significant when the concrete has more microcracks. Sorption was found to have minimum influence on the surface chloride content. The chloride migration coefficients were found to be higher than the chloride diffusion coefficients, especially for the concretes with a higher stress level. The partial replacement of ordinary Portland cement (OPC) with ground granulated blast-furnace slag (GGBS) can significantly reduce the detrimental effects caused by the high stress levels on chloride transport in all three methods.

Influence of load-induced cracks coupled or not with top-casting-induced defects on the corrosion of the longitudinal tensile reinforcement of naturally corroded beams exposed to chloride environment under sustained loading

This paper discusses the effect of both load-induced cracks and top-casting-induced defects on the corrosion characteristics of the tensile bars in reinforced concrete beams under sustained loading and exposure to a chloride environment. Four reinforced concrete beams exposed to climate accelerated natural corrosion were used in the present work. The cracking maps, chloride profiles and cross-sectional loss of four beams were studied and compared with each other. Experimental results show that the presence of load-induced cracks is not the sole cause of early propagation of corrosion. As a result, top-casting-induced defects are the most significantly impacting factor accelerating the deterioration of reinforced concrete. With top-casting-induced defects, corrosion starts at service cracks and then develops preferentially at the bottom surface of the tensile bar. Without top-casting-induced defects, corrosion starts at service cracks but does not develop along the tensile bar. It is only when the chloride content at the depth of reinforcement reaches a critical value that corrosion develops along the tensile bar – preferentially at the outside surface of the rebar because of its probable higher chloride content.

Long term effect of corrosion inhibitor and associated cation type of chloride ions on chloride profile of concrete exposed to composite chloride-sulfate environment

This paper experimentally investigated the effect of nitrite-based corrosion inhibitor and cation type namely Na+, Mg2+ and Ca2+ associated with chloride ions on free chloride (CF) and total chloride (CT) ion concentrations of concrete exposed to composite chloride-sulfate (Cl-+SO42-) environment. Concrete cubes were prepared using Portland pozzolana cement and w/c ratio of 0.55. Sodium nitrite (NaNO2) was used as a corrosion inhibitor at an admixed dosage of 3% by weight of cement. After curing, the cubes were subjected to composite Cl-+SO42- solutions such as NaCl + MgSO4, MgCl2 + MgSO4, and CaCl2 + MgSO4. Powder samples were collected at different depth intervals from the cubes to determine the CF and CT concentrations. Fourier transform infrared (FTIR) spectroscopy and Field emission scanning electron microscope (FESEM) analyses were carried to examine the microstructure of concrete. The experimental results indicated that addition of NaNO2 in concrete reduced the penetration of chloride ions. Concrete exposed to CaCl2 + MgSO4 solution mostly showed higher CF and CT concentrations than NaCl + MgSO4 solution followed by MgCl2 + MgSO4 solution. Results of microstructure study indicated the formation of different compounds in concrete exposed to composite Cl-+SO42- solutions.

Level of sodium chloride (NaCl) and profile of cervical mucus of dairy cattle at various age synchronized by prostaglandine

Objectives of this study were to compare the percentage of Sodium Chloride (NaCl) and cervical mucus profile which includes potential of Hydrogen (pH), abundance of cervical mucus, spinnbarkeit and ferning of dairy cattle at different age during estrus cycle. Thirty Two head of dairy cattle were used as materials which are 2 years old (n = 2), 3 years old (n = 18), 4 years old (n = 8) and 5 years old (n=4). Dairy cattle were estrus synchronized using 50 mg/head of prostaglandin. Data was collected on 48, 72, 78, 84, 90, 120, 144 and 408 hours after prostaglandin administration. The data were analyzed by using non parametric statistic which was Kruskal-Wallis H test. The significant data was tested with Mann-Whitney U test. The result showed that the abundance of cervical mucus was significantly different (P&lt;0.05; χ2 = 0.011) on 84 hours after estrus synchronization. However, level of NaCl, abundance, spinnbarkeit and ferning of cervical mucus was not sigificantly different. In conclusion, the age of dairy cattle did not affected to the condition NaCl percentage, spinnbarkeit, pH and ferning of cervical mucus, but affected to the abundance of cervical mucus on 84 hours after adminitration of prostaglandine.

Effect of polymer modified cementitious coatings on chloride‐induced corrosion of steel in concrete

AbstractThe paper deals with the study of the effect of polymer modified cementitious mortars on chloride‐induced corrosion of steel reinforcement in concrete. Nowadays, many results obtained by standard and short‐term tests are available in the literature. The paper reports more than 15 years exposure testing on two commercial coatings, with different polymer/cement ratio. The effect of coatings on corrosion initiation and propagation has been studied by the monitoring of corrosion potential and corrosion rate of rebars in concrete subjected to chloride ponding; chloride profiles, coating adhesion, water content, and corrosion morphology have been also analyzed. It was demonstrated that polymer modified cementitious mortars can delay corrosion initiation caused by chloride penetration into concrete. Owing to high resistivity of coated concrete, corrosion rate is reduced. The protective effect is more pronounced as the polymer content increases from 0.35 to 0.55. The results have been elaborated to estimate the possible increase of service life gained with this additional protection method, compared with other solutions.

Experimental studies on the chloride ion permeability of concrete considering the effect of freeze–thaw damage

A series of laboratory experiments were conducted to investigate the effect of freeze–thaw (FT) cycles on mechanical properties and chloride permeability of concrete with the strength class of C30 in this paper. The mechanical property tests were performed on the specimens subjected to 0, 5, 15, 30, 50, 75 and 100 standard FT cycles to determine the compressive strength, normalized dynamic elastic modulus (NDEM) and mass loss. Also, the chloride natural diffusion tests of concrete specimens, after 0, 5, 15, 30 and 50 FT cycles, were conducted in a self-design tidal cycling simulation device to investigate the chloride ingress into concrete in marine environment of tidal zone. Based on the Fick’s second law, a time-dependent model was developed to predict the chloride profiles of frost-damaged concrete. Additional FT cycling tests at different minimum temperatures of freezing process (−4 and −11 °C) and the chloride natural diffusion tests were conducted to study the effect of minimum temperature on the chloride diffusion in concrete. The experimental results revealed the significant influence of FT action on the mass loss, compressive strength and NDEM. After 50 FT cycles, the mean of NDEM dropped to 60%, indicating that the specimen was destroyed by FT action. With the decrease of minimum freezing temperature, the loss of NDEM increased apparently, performing a good linear relation. A substantial effect of FT damage on the chloride profiles was observed: compared to the counterparts of the control groups without being exposed to FT attack, chloride concentration was larger for the frost-damaged concrete, and this difference increased with the extension of exposure duration. A linear relation between the apparent chloride diffusion coefficient and the loss of NDEM was also obtained regardless of the exposure time. Moreover, it was found that the proposed model was applicable for the prediction of chloride profiles in concrete subjected to FT cycles at different minimum freezing temperatures. In other words, the proposed model can be used to describe the chloride ingress into frost-damaged concrete, regardless of the cause of the damage (due to the number of FT cycles or the minimum freezing temperature).

Effect of Seasonal Characteristics of Temperature and Relative Humidity on Chloride Diffusion Process in Concrete: A Preliminary Theoretical Study

The chloride diffusion process can be greatly affected by the temperature and relative humidity. Annual average temperature and relative humidity are often adopted in analytical models to calculate chloride profiles. These models, however, cannot consider the seasonal characteristics of temperature and relative humidity. This paper presents a theoretical study to solve the above problem. The temperature and relative humidity in several major cities in China are first collected. Then, the governing equation of one-dimensional chloride diffusion is solved by both analytical and numerical methods using the annual and monthly average temperature and relative humidity, respectively. Based on these two methods, a parameter called “seasonal correction coefficient” is introduced into the analytical models. The values of the coefficient for major cities in China are obtained. Based on the results, it is found that: (1) the analytical solution with annual average temperature and relative humidity is questionable to calculate chloride profiles for typical cities, (2) the seasonal correction coefficient is independent on the apparent chloride diffusivity, affected slightly by the activation energy of chloride ions during diffusion and greatly by the critical relative humidity for common water-to-cement ratios of ordinary Portland cement (OPC) mortar and concrete.

Sensor-based time-dependent formation factor in prediction of chloride ingress in mortar

Characterisation of chloride ingress rate is crucial for service life predictions in reinforced concrete. In this study, the time-dependent chloride diffusion coefficient (DCl(t)) was determined using real-time non-destructive embedded sensors. First, the time-dependent formation factor was established based on continuous electrical conductivity data from the sensors, which provided DCl(t) by the Nernst–Einstein equation. Twelve mortar mixtures were included that varied in water/cementitious materials ratio (w/c) and supplementary cementitious material (SCM) content. A numerical model of chloride diffusion using the established DCl(t) was developed by solving Fick's second law of diffusion using the finite-difference method. The model's predictions agreed well with experimental chloride profiles available in the literature. The results of chloride ingress simulation for all tested mixtures clearly showed the effect of reducing the w/c and using more SCM on slowing the rate of chloride ingress. Furthermore, the developed DCl(t) relations were used to establish a diffusion decay coefficient (mdiff) for all tested mixtures, leading to the development of empirical formulations for DCl(t) and mdiff as a function of w/c and SCM content. The results of this study demonstrate the potential of the implemented non-destructive technique in efficient assessment of transport properties of mortar related to chloride ingress.

Eco-durability index of self-compacting concrete incorporating high volume fly ash

Designing concrete meeting the principles of sustainability becomes urgent in the construction of buildings and other civil engineering infrastructures. Sustainability of concrete can be assessed by considering its environmental, economic and social impact. Each impact may cover multi-criteria and parameters for the assessment. In this respect, the designers require practical tools so as to select the best alternative concrete mix design fulfilling the multi-criteria. This paper proposed an eco-durability index (EDI) as such tool for assessing the balance performance in term of environmental impacts and durability of self-compacting concrete (SCC) incorporating high volume fly ash. The fly ash content is in the range of 50%-70% of replacement level i.e. a fraction of cement replaced by weight of fly ash. The parameters adopted for assessing the environmental impacts (ecological index) are embodied primary natural resources depletion, embodied energy and embodied CO2; while the time to corrosion initiation period due to chloride ion ingress by diffusion mechanism is taken as durability parameter. The chloride ion diffusions of the concretes under study were determined following ASTM C1556 from the chloride profiles. The chloride profiles were obtained by salt ponding test according to AASHTO T259. The amount of chloride ion with respect to the depth of its penetration was determined by XRF method. Within the scope of this study, it is shown that an increase of fly ash will reduce the environmental impacts of SCC. However, the durability of concrete does not show a similar trend. Therefore, a balance performance considering the environmental impacts and durability is searched for by using the value of EDI. Based on the EDI, it is indicated that SCC with 70% fly ash replacement level gives the best alternative of SCC with respect to balance performance of environmental impacts and durability.

Manure plume modeling in feedlot pen soils

The generation of large amounts of manure by confined cattle feeding operations (feedlot) in reduced areas is a concern due to its potential to act as pollutant for ground and surface water. Studies have revealed that leaching may occur in pen soils, with negative effects on water quality. The objective of this work was to develop a mathematical model for predicting manure plume vertical advancement in soil beneath feedlot pens. The study was carried out in feedlot pens situated in a Argentine region called the Sandy Pampa (Pampa Arenosa). Five areas or treatments were selected, four of which were located in pens (considerably impacted by beef cattle operations) with 1, 4, 8 and 15 years of use, and the remaining one in natural soil area as control. The soil in the study areas was morphologically characterized. Applying standard procedures, the following variables were quantified: gravimetric moisture content and chloride concentration in soil solution. Chloride ion was used as a tracer to estimate manure flux. Data of different chloride profiles adjusted to a first-order model, from which it was possible to predict the depth of penetration of the manure, and the factor of plume advance in the underlying soil. In addition, the dominance of flows was analyzed from the development of a flow number indicator (Nf), which could be useful for environmental regulatory purposes bringing a base for easy estimation of pollutant transport mechanism in water–soil systems.

Chemical speciation, distribution and leaching behavior of chlorides from municipal solid waste incineration bottom ash

Municipal solid waste incineration (MSWI) bottom ash is an environmentally harmful solid waste that cannot be recycled without pre-treatment. The chloride content in bottom ash (BA) is a major obstacle that restricts its application as secondary building materials. Here, the chemical speciation of the chlorides in BA is systematically studied with multiple analytical techniques, i.e., quantitative XRD, microanalysis and XPS. In addition to halite (NaCl), several chloride-rich minerals are present in BA. These phases are hydrous metal oxides, ettringite, decomposed hydration products (C4A3) and incineration slag with a chloride content of 3.2%, 1.4%, 2.1% and 1.3%, respectively. For the first time, the real-time leaching profiles of chloride (up to 80 h) from BA were obtained with a chloride-ion specific electrode to explain the leaching mechanism. In the initial stage of leaching, highly soluble alkali salts (NaCl) and physisorbed chlorides (especially those adsorbed on hydrous metal oxides) are released, which is controlled by diffusion. Later, the leaching is controlled by the solubility/reactivity of the chloride-containing phases, such as ettringite and incineration slag. The results show that the release of chloride is not only a diffusion-controlled process, as reported in the literature, but also a reaction-controlled phenomenon, during which the chloride-rich phases decompose and release chlorides that are associated with them via sorption/incorporation.

Evaluation of chloride ion penetration through concrete surface electrical resistivity of field naturally degraded structures present in marine environment

As reinforcement corrosion due to chlorides action is the main cause degradation of reinforced concrete structures in marine environment, concrete electrical resistivity has been used as a non-destructive methodology in order to evaluate the service life of these structures, since it is a simple and fast field methodology that presents confiable results. At this point, many works have been carried out in order to stablish a correlation between concrete electrical resistivity and chlorides penetration. However, observing the literature and standards about this issue it was noted significant differeces between the values presented for stablish this correlation. Furthermore, a significant part of the literature studies were conducted under controlled laboratory conditions, which can differ from the real aggressiveness that a structure is exposed. Thus, this paper presents a new proposal of range values and classes between the chlorides penetration and the concrete surface electrical resistivity, based on the analysis of real chloride profiles from structures present for more than 40 years in different marine aggressive zones under natural degradation. The results shown that standard parameters were close from the values proposed in this work; however a refinement in the range values and the insertion of new parameter classes are necessary for better evaluation of chlorides penetration in concrete structures present in marine environment.