Article

A new system for early chloride detection in concrete

IOP Publishing
Smart Materials and Structures
Authors:
  • TFB Romandie SA
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Abstract

In a national and worldwide context, countless reinforced concrete structures are in an advanced state of deterioration. A principal cause of such degradation is chloride induced corrosion of reinforcement bars. This phenomenon is accentuated in countries where de-icing salts are used for road safety, as well as in maritime zones. To date, no non-destructive method quantifying chloride content during the corrosion initiation phase has been established. Measurement of such a parameter is important for the development of a better understanding of the complexity of corrosion phenomena and, more practically, for better management of existing structures. This paper proposes a new method for non-destructive measurement, for monitoring continuously and in real time free chloride content in concrete pores. In this context, a chemical sensor that employs optical fibers was developed and tested. The sensor functions using the fluorescence of an indicator dye that is sensitive to chlorides. Through fluorescence spectroscopy, variations in the concentration of free chlorides are related to intensity fluctuations of fluorescence. The use of optical fibers also provides an advantage compared with existing electric non-destructive detection systems due to superior electromagnetic stability. Theoretical and experimental studies calibrated and validated the sensor for implementation within mortar samples. Free chloride concentrations between 30 and 350 mM can be detected. Two experiments reproduced climatic variations in a controlled environment. The first test simulated a hot maritime climate and the second test simulated a cold continental climate. These tests confirmed that it is possible to determine with precision the free chloride content. Also, fluorescence spectroscopy with optical fibers offers an innovative means for early and non-destructive detection of free chloride content in concrete. As a result, this new method has potential for improving the science of corrosion process understanding and for planning appropriately for preventive action in practical situations.

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... Such penetration can undermine the protective passive film on steel reinforcement, accelerate the corrosion process, diminish structural performance, and ultimately compromise the safety of a structure [1,2]. Chloride ions within concrete exist in two distinct forms: free chloride ions and those bound within hydration products [3,4]. It is the presence of free chloride ions that predominantly contributes to the corrosion of reinforcing bars. ...
... In recent years, the deployment of fiber optic sensing technology for the structural monitoring of concrete has been notable, leveraging its compact size, high sensitivity, strong anti-interference capabilities, and resilience in challenging environments [3,8,12,13]. To date, fiber optic sensors have predominantly been used for post-corrosion monitoring, in which they are used to measure corrosion-induced strain or mass loss [14,15], which limits their utility for early corrosion warning. ...
... (a) Concrete simulation solution test: This study used Ca(OH) 2 powder and a NaHCO 3 standard solution to configure concrete simulation solutions with different pH values. The configuration process started with adding excess Ca(OH) 2 powder to deionized water to obtain a supersaturated Ca(OH) 2 solution. ...
Article
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Coastal concrete structures, such as cross-sea bridges and tunnels, are susceptible to the penetration of chloride ions, which can lead to the deterioration of the passive film on the rebar surface, consequently accelerating the corrosion process. Conventional methods for monitoring chloride ions typically require in situ drilling for sample collection, thereby compromising efficiency and accuracy. Additionally, real-time monitoring and early warning cannot be achieved. To address these challenges, this work introduces a fluorescent-probe-based fiber optic sensor for monitoring chloride levels in concrete structures. Quinine sulfate was chosen as the fluorescent material due to its exceptional sensitivity to chloride ions and its stability in concrete environments. The proposed sensor was manufactured using sol–gel and 3D-printing techniques. Tests were conducted using concrete simulation fluid and cement mortar specimens. The results demonstrate that the sensitivity of the proposed sensor is greater than 0.01 M, and its accuracy in penetration depth measurement is better than 3 mm. The findings confirm that the designed fiber optic sensor based on quinine sulfate enables real-time monitoring of chloride ions in concrete structures, offering high sensitivity (0.1% in concentration and 2.7 mm in terms of penetration depth), unique selectivity (as it is immune to other ions whose concentrations are 10 times higher than those of Cl−), and a compact size (10 × 20 mm). These attributes render it promising for practical engineering applications.
... However, the local core samples are sometimes not representative for the whole concrete structure [26,68]. In addition, the destructive methods are usually time consuming, and the complicated sample preparation procedure may result in errors for the determined chloride content [27,77,78]. ...
... Optical fiber sensor is consisted of three key components [87][88][89][90][91]: the sensing conversion module, optical signal carrier (usually a special optical fiber) and light source and spectrum (which have already been widely commercialized). The related mechanisms for determining chloride content by the optical fiber sensor include: (1) long-period fiber grating (LPG) based on refractive-index sensitivity [88][89][90] and (2) fluorescence quenching principle [78,91] (as shown in Fig. 3). The chloride concentration is corresponding to a specific resonance wavelength shift or specific spectrum produced by fluorescence, respectively. ...
... Chlorides present quenching effect when they react with specific sensitive fluorescence indicator [78], as shown in Fig. 3 (b). Therefore, by measuring the relative fluorescence intensity of the optical fiber sensor, the chloride concentration in concrete can be calculated by the following Stern-Volmer equation [78]: ...
Article
The accurate measurement of chloride content in concrete is of great importance, because chloride-initiated corrosion of the reinforcement significantly influences the durability of reinforced concrete. This paper summarizes the research status of Ag/AgCl ion-selective electrode (ISE) used for non-destructive chloride detection in concrete. In general, four main topics are reviewed, including preparation of Ag/AgCl-ISE, main factors influencing the potential of Ag/AgCl-ISE, detection limit/potential response of Ag/AgCl-ISE, and novel composites/electrochemical methods based on Ag/AgCl-ISE for chloride detection in concrete. Further, the existing problems and research strategies are also discussed in detail in this present review.
... Those sensors are also employed in fields such as environment, space, automobile, medicine or biochemistry [14] to detect, in-situ, chemicals in a reversible and noninvasive manner [15]. This technology has been recently adapted for monitoring invasive and harmful chemicals in concrete structures for corrosion monitoring [16]. Such new sensors provide an accurate knowledge of chloride concentration at the steel rebar level allowing new opportunities for comparisons with model predictions. ...
... Chloride OF sensors were embedded within the cementitious matrix at 20 mm from the surface and used in the laboratory with a capillarity test in order to observe the free chloride content evolution in the pore solution at a given penetration depth (20 mm) [16,17]. The OF sensors overcame the difficulty encountered in measuring the capillary suction with the actual experimental methods previously described because https://doi.org/10.1016/j.cemconres.2020.106033 ...
... The calibration curve (Fig. 3b) of the Stern-Volmer's Eq. (1) was carried out against 250 measurements [16]. The I 0 /I linearity was verified from 30 mol/m 3 (0.1%) to 350 mol/m 3 (1.2%) ...
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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 ad-sorption 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.
... In designing reinforced concrete, chloride profiles are calculated based on different times using equation 2-1 (Laferriere, et al., 2008). ...
... C(x,t): the concentration C at the distance x, after time t (Laferriere, et al., 2008) ...
... To date, no non-destructive method quantifying chloride content during the corrosion initiation phase has been established. Measurement of such a parameter is important for the development of a better understanding of the complexity of corrosion phenomena and, more practically, for better management of existing structures (Laferriere, et al., 2008). To evaluate the durability of reinforced concrete structures the measurement of the chloride content is necessary. ...
Article
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... with the Stern-Volmer's equation[1] was defined based on 250 calibration measurements(Laferrière et al. 2008). The 0 linearity is verified from 30 mol/m³ (0.1%) to 350 mol/m³ (1.2%). ...
... The 0 linearity is verified from 30 mol/m³ (0.1%) to 350 mol/m³ (1.2%). The free chloride concentration in the pore solution of the concrete [ − ] depends on the fluorescence intensity with and without 0 chloride ions: (a) Instrumental setup and (b) Calibration of the sensor(Laferrière et al. 2008) ...
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Corrosion that is induced by the presence of chloride ions in reinforced concrete structures is an important cause of premature degradation. This phenomenon has a high economic and ecological impact, especially near coastal areas and in countries where de-icing salts are used for road safety during winter periods. The transport of chloride ions in those materials is not only due to diffusion but also to the effects of water transport and capillarity mostly present with wet-dry cycles. These two last phenomena are currently very poorly modeled. A new system for the detection of free chloride ions in pore concrete was previously developed. It consists of a chemical sensor that undergoes fluorescent quenching in the presence of chlorides and optical fibers that transmit light and retrieve results. With this system, the presence of free chloride concentration as low as 350 mol/m³ in pore concrete solution can be detected without damaging the material. This work, therefore, aims to create a numerical model of multi-species and reactive transport of chloride ions by capillarity in a cementitious material. The model considers the diffusion of chloride ions and water transport by capillarity, as well as the chloride adsorption by the material with isotherms interaction. In a larger perspective, this study let to improve knowledge in concrete durability structures in severe environmental condition and the numerical model that can be created to predict their life service to better maintenance.
... However, in the long-term, fiber material degradation, the necessity of protection of the transducing element in aggressive environment, mechanical stability and temperature dependence are some critical issues, which should be solved. Mostly, research has been done on the opto-chemical transducing part as it defines the sensitivity, selectivity, and long-term performance of the sensor [74][75][76][77]. There are two approaches for opto-chemical transduction: (a) fluorescence-based and (b) optical grating (refractive index) based. ...
... This sensing mechanism is based on the collisional quenching of the fluorescence molecule by chloride ions [77]. Such an optochemical transducer is also referred to as an optode. ...
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In this work, the different techniques for non-destructive in situ measurement of chloride ion concentration are presented. Non-destructive (ND) in situ measurement is crucial for reliable and continuous determination of chloride ion concentration in concrete. Over the last 20 years, several studies have been performed on ND measurements. These were mainly focused on the application of electrochemical and electromagnetic techniques. Each technique has its advantages and disadvantages. Depending on the requirement of assets managers and constructors and considering the limitations, these techniques can be well applied. The main concepts and comparative analysis, in view of possibilities and limitations, of these non-destructive techniques are presented in this paper.
... A fibre optic sensor consists of a fibre with an optical transducer, sensitive to chloride ions. The lifetime of optical transducers, protection of fibres and the bulky measurement setup are the limitations of this technique [60]. ...
... An overview of the available techniques for measuring the chloride content in concrete[29,[52][53][54][55][56][57][58][59][60][61][62]. ...
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... Examples of conventional direct measurement techniques include corrosion coupons, electrical resistance (ER) probes [10], and linear polarization resistance (LPR) probes [11]. Indirect corrosion measurement technologies based on fiberoptic sensors monitor various factors that affect the rate of corrosion processes (pH [12][13][14], humidity [15][16][17][18][19], temperature [17,20], concentrations of certain chemical species [21][22][23][24][25]), or their consequences, such as the presence of corrosion products [26], a reduction in wall thickness [27], changes in hoop strain [28][29][30], or leaks that occurred due to the loss of integrity [20,31]. The sensor described in this work falls into the category of indirect measurements because it does not provide the actual rate of external corrosion on the pipe wall in real-time. ...
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A sensor for monitoring of the external corrosion of small-diameter aboveground oil and gas pipelines (called flowlines), based on fiber-optic strain sensing, is proposed. The working principle of our proposed sensor relies on the use of a pre-stressed sacrificial structure made of the same material as the pipeline and monitoring changes in the measured strain that occur due to deterioration caused by corrosion to the structure. We present the development of analytical equations that allow designing the sensor structure to achieve the desired strain values. The analysis was verified using commercial finite element analysis (FEA) software. The proposed sensor is simple and cost-effective and can be easily manufactured. It can be deployed on existing overground pipelines without any modification to the pipeline structure. While it is not capable of measuring the corrosion rate continuously, it can provide a measurement of the average corrosion rate over the life span of its sacrificial metal structure.
... Therefore, the study does not provide information on the sensitivity thresholds of the sensors. Laferrière et al. [93] described a sensor based on an indicator dye lucigenin, which is a blue-green, fluorescent chloride-sensitive ion indicator. The study demonstrated the possibility of accurately detecting chlorides within the concentration range from 0.030 to 0.35 M. ...
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Non-destructive monitoring methods and continuous monitoring systems based on them are crucial elements of modern systems for the management and maintenance of assets which include reinforced concrete structures. The purpose of our study was to summarise the data on the most common sensors and systems for the non-destructive monitoring of reinforced concrete structures developed over the past 20 years. We considered systems based on electrochemical (potentiometry, methods related to polarisation) and physical (electromagnetic and ultrasonic waves, piezoelectric effect, thermography) examination methods. Special focus is devoted to the existing sensors and the results obtained using these sensors, as well as the advantages and disadvantages of their setups or other equipment used. The review considers earlier approaches and available commercial products, as well as relatively new sensors which are currently being tested.
... With respect to non-invasive inspection methods, ultrasonic evaluation of the damage to concrete [7,8], X-ray fluorescence (XRF) to measure the amount of chloride ion [9] were developed. The special distribution of airborne salt amount was directly observed by exposure tests at marine coasts using mortar thin plates [10]; wet candle methods and dried gauze methods are also widely known [11] apart from nuclear magnetic resonance (NMR) [12,13], laser-induced break down spectroscopy (LIBS) [14], and electro chemical measurements [15,16,17]. As vibrational spectroscopy, Fourier transformed infrared spectroscopy (FTIR) [18], Raman scattering [19], and surface enhanced Raman spectroscopy [20] are also studied; thus weatherproof Raman substrates [21] are fabricated. ...
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This is a fundamental study of a non-destructive and contactless equipment to evaluate the chloride ion on concrete, with near infrared spectroscopy. Non-destructive measurements on Friedel’s salt, generated by ingress of chloride ion into concrete, have been studied; characteristic absorption unique to each substance was utilized to qualitative and quantitative analyses. However, there has been a difficulty in separating absorption peak of Friedel’ salt from that of other hydrates. This study investigates the method to extract the absorption peak of Friedel’s salt by Bayes’ theorem for quantitative evaluation, and its validity was confirmed using some conventional methods.
... Therefore, these traditional techniques are mostly destructive and time-consuming; further, the real-time monitoring of chloride content in concrete structure cannot be achieved. In the recent three decades, different non-destructive methods were investigated for in-situ monitoring of chloride content in concrete, mainly including electrochemical sensors, optical sensors and etc. [11,[15][16][17][18][19][20][21][22][23][24]. Among them, the electrochemical sensors based on Ag|AgCl electrode was considered as the most suitable non-destructive method due to its high chloride selectivity, low detection limit and robustness with low-cost [11,16,25,26]. ...
Article
The electrochemical behavior of Ag|AgCl electrode for chloride detection is closely related to the microstructure of AgCl film on the electrode surface. In this study, the surface properties and electrochemical behavior of Ag|AgCl electrode prepared with different current density were investigated. With a higher current density, the distance for ions diffusion through the boundaries of AgCl grains was reduced, due to the tended growth of AgCl at crystal plane (111) and formation of more spherical AgCl grains and porous AgCl film. As a result, both the electrical resistivity of AgCl film and Rct of Ag|AgCl electrode decreased.
... Based on the results, the authors claimed that the developed sensor could be successfully applied for Cl − monitoring in concrete structure. Laferrière et al. [60] has developed optical fiber for real-time and continuous monitoring of Cl − concentrations in concrete pores. It uses Cl − sensitive fluorescence indicator dye. ...
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In this work, technological feasibility of autonomous corrosion assessment of reinforced concrete structures is studied. Corrosion of reinforcement bars (rebar), induced by carbonation or chloride penetration, is one of the leading causes for deterioration of concrete structures throughout the globe. Continuous nondestructive in-service monitoring of carbonation through pH and chloride ion (Cl−) concentration in concrete is indispensable for early detection of corrosion and making appropriate decisions, which ultimately make the lifecycle management of RC structures optimal from resources and safety perspectives. Critical state-of-the-art review of pH and Cl − sensors revealed that the majority of the sensors have high sensitivity, reliability, and stability in concrete environment, though the experiments were carried out for relatively short periods. Among the reviewed works, only three attempted to monitor Cl− wirelessly, albeit over a very short range. As part of the feasibility study, this work recommends the use of internet of things (IoT) and machine learning for autonomous corrosion condition assessment of RC structures.
... Two fiber optic based chloride ion sensing devices in concrete environment are found in the literature. One is based on suspended-core optical fiber [18] and the other one uses chloride ion sensitive fluorescence indicator dye [19]. The fiber optic pH sensing device based on pH sensitive optic fluorescence polymer has been proposed by Nguyen et al. [15]. ...
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... Two fiber optic based chloride ion sensing devices in concrete environment are found in the literature. One is based on suspended-core optical fiber [18] and the other one uses chloride ion sensitive fluorescence indicator dye [19]. The fiber optic pH sensing device based on pH sensitive optic fluorescence polymer has been proposed by Nguyen et al. [15]. ...
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We present a conceptual framework for continuous in-service durability monitoring and assessment of reinforced concrete (RC) structures. Conventional durability assessments are carried out through laboratory testing of samples taken destructively from the structures, which are labor intensive, time consuming and costly. By employing internet of things, continuous nondestructive in-service monitoring of structures can be realized in a cost-effective manner. The availability of long-term monitored data along with the use of intelligent data analysis enables capturing of the complex nonlinear interaction of durability controlling parameters, making the structures' condition assessment more reliable. The reliability of the assessment results is highly beneficial for stakeholders to plan proactive maintenance, which in turn extends the service life of the structures.
... More advanced instrumental analytical methods, such as X-ray fluorescence [11,12,24], laser-induced breakdown spectroscopy [11,12,[16][17][18][19][20][21][22][23][24][25][26][27][28][29] and fiber optic sensor [14,16,[30][31][32][33] are examples of electromagnetic techniques that have already been used for the determination of chloride in concrete. Other techniques to determinate chloride content in concrete are also mentioned in the literature: nearinfrared, millimeter and microwave spectroscopy [16], laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) [34], nuclear magnetic resonance (NMR) [16], grounding penetrating radars (GPR) and capacitive technique [14,35,36], electrical resistivity tomography [17,36] and terahertz time-domain spectroscopy (THz-TDS) [37]. ...
Article
Full-text available
The technique of X-ray fluorescence spectroscopy is a non-destructive method used in several applications in Civil Engineering for the qualitative and quantitative determination of chemical elements in different materials. This technique allows the analysis of materials by atomic excitations and identification of spectra obtained from defined wavelengths interpreted for each chemical element present in the material in a precise and fast quantification, optimizing characterization analysis in a laboratory. Although the benefits obtained from this technique are clear, problems regarding the quantification of chloride ion in concrete powder samples, obtained from real structures, end up, giving significant errors in relation to its quantification, which, in turn, overestimate the chloride concentration in the profiles more than 500%. In this way, this work presents a correlation between two methodologies using concrete powder samples from structures present in a marine environment for more than 40 years. These samples were analyzed by X-ray fluorescence spectroscopy and potentiometric titration techniques in order to establish a correlation between the methods. The obtained results showed that there is a relationship between both techniques with a determination coefficient close to 1.
... High sensitivity measurement of Chlorides is typically carried out using indicator based sensing (Chalk and Tyson 1998;Fuhr et al. 1996;Laferriere et al. 2008). In the case of long term in situ application, there are issues with long term calibration and durability of indicator based approaches. ...
Chapter
Two parameters are used to assess the maturity of fresh hydraulic cement during the curing process: temperature and water content. This chapter describes the preparation and the application of two optical fiber sensors for simultaneous measurement of temperature and moisture. The temperature sensor utilizes Europium beta diketonates, a luminescent complex with an emission signal that provides temperature data. The moisture sensor utilizes the intrinsic optical properties of the water molecule used for the quantitative measurement of the liquid phase moisture content. These probes were tested in fresh cement paste during the curing processes.
... High sensitivity measurement of Chlorides is typically carried out using indicator based sensing (Chalk and Tyson 1998;Fuhr et al. 1996;Laferriere et al. 2008). In the case of long term in situ application, there are issues with long term calibration and durability of indicator based approaches. ...
Chapter
In this chapter we discuss an optical method used for direct measurement of pH in Portland cement concrete with high spatial and temporal resolution. This approach is designed to better enable the study and analysis of high pH dependent degradation reactions, and hydration reaction in cement-based composites. We demonstrate that the halochromic sensor molecule is suitable for this purpose. Results of experiments showing spatial distribution of early stage carbonation and reaction involving silica aggregates are highlighted at pH levels between ~11.0 to ~13.5. Results are compared with the commercially available pH indicator Phenolphthalein.
... High sensitivity measurement of Chlorides is typically carried out using indicator based sensing (Chalk and Tyson 1998;Fuhr et al. 1996;Laferriere et al. 2008). In the case of long term in situ application, there are issues with long term calibration and durability of indicator based approaches. ...
Chapter
Molecular probes, also referred to as chemosensors, are molecules capable of transforming chemical information, such as the presence or concentration of a specific target species, into an analytically useful, identifiable signal. These signals are commonly either electrical or optical. This chapter is an introduction to molecular probes and the respective optical signatures used for chemical sensing. Features reviewed include the categories of chemo-optical response including absorbance or fluorescence, as well as methods for calibration.
... High sensitivity measurement of Chlorides is typically carried out using indicator based sensing (Chalk and Tyson 1998;Fuhr et al. 1996;Laferriere et al. 2008). In the case of long term in situ application, there are issues with long term calibration and durability of indicator based approaches. ...
Chapter
Porphyrins, or more generally, porphyrinoids, have played a big role as chromophores in sensing applications. This is due to the intense absorption they exhibit over a wide section of the UV-vis spectrum, their large fluorescence yields, high chemical stability, and the multiple options for functionalization. Therefore, porphyrinoids and their metal complexes have been used as optical chemosensors for a range of analytes. This chapter provides some details on the characteristic of these indicators for sensing high pH levels, including options for tuning and matrix immobilization.
... These well-established monitoring techniques have reliable accuracy, yet are destructive in nature, require experienced labor, and are timeconsuming (Montemor et al. 2006). Consequently, researchers are motivated to investigate alternative, nondestructive techniques for corrosion initiation monitoring, such as Ag/AgCl electrodes, optic sensors, conductivity sensors (Duffó and Farina 2009;Montemor et al. 2006;Gao et al. 2010;Laferriere et al. 2008;Elsener et al. 2003;Climent-Llorca et al. 1996). ...
Article
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... Destructive testing is mainly characterized by taking samples from the element to be examined, and then testing them either in situ or in the lab according to the ASTM [21,22] and AASHTO [23] standard testing procedures. Recently researchers started investigating non-destructive testing approaches such as the use of embedded chloride detection sensors [19,20,[24][25][26][27][28][29]. Two main types of sensors were mainly examined, optic fiber sensors and sensors that rely on Ag/AgCl electrodes to measure chloride content. ...
Article
Abstract Chloride induced reinforcement corrosion is one of the most common causes of deterioration of reinforced concrete structures. Condition assessment of such structures is typically based on comparing the chloride content at steel level to the critical threshold chloride concentration. This study aims at developing a robust non-destructive structural health monitoring (SHM) methodology for assessing the state of the structure and predicting its remaining corrosion free service life. The presented methodology relies on embedded sensors that measure the chloride concentration at certain locations, and a predictive model that governs the dynamics of chloride ingress. The system is propagated forward in time using a finite element/finite difference scheme, and the Ensemble Kalman Filter (EnKF) is employed to calibrate the predictive model parameters. The calibrated parameters are then used to assess the remaining corrosion free service life of the structure. The robustness of the presented methodology is demonstrated on 1-D and 2-D numerical examples yielding accurate estimation of the spatial and temporal variability of the chloride content and consequently enhancing maintenance efficiency and structural sustainability.
... Therefore, measuring Clˉ ions in concrete is inevitable to predict the service life and maintenance cycle of a structure 4,5 . Different sensing principles have been reported for chloride ion measurement in concrete such as electrochemical 6,7 , optical 8,9 and electromagnetic 10,11 . However, optical and electromagnetic methods have bulky setups, are difficult to integrate as a stand-alone system and have issues with selectivity 12 . ...
Article
Full-text available
This protocol describes the dynamic measurement of chloride ions using the transition time of a silver silver chloride (Ag/AgCl) electrode. Silver silver chloride electrode is used extensively for potentiometric measurement of chloride ions concentration in electrolyte. In this measurement, long-term and continuous monitoring is limited due to the inherent drift and the requirement of a stable reference electrode. We utilized the chronopotentiometric approach to minimize drift and avoid the use of a conventional reference electrode. A galvanostatic pulse is applied to an Ag/AgCl electrode which initiates a faradic reaction depleting the Cl- ions near the electrode surface. The transition time, which is the time to completely deplete the ions near the electrode surface, is a function of the ion concentration, given by the Nernst equation. The square root of the transition time is in linear relation to the chloride ion concentration. Drift of the response over two weeks is negligible (59 µM/day) when measuring 1 mM [Cl-]using a current pulse of 10 Am(-2). This is a dynamic measurement where the moment of transition time determines the response and thus is independent of the absolute potential. Any metal wire can be used as a pseudo-reference electrode, making this approach feasible for long-term measurement inside concrete structures.
... real time ingress profile without destroying the structures [8]. In recent years many groups have investigated in situ measurement of chloride in concrete using mainly electrochemical91011 and optical methods121314. However, optical methods have bulky setups, are difficult to integrate as a standalone system and have other disadvantages such as the photo bleaching of dyes (optical transducers ) and the leaching of transducer (polymer matrix) due to the high pH environment inside concrete. ...
Article
In this paper, a novel approach is reported for the electrochemical measurement of chloride ions in aqueous solution. This sensor is based on the stimulus/response principle of chronopotentiometry. A current pulse is applied at the Ag/AgCl working electrode and the potential change is measured with respect to another identical Ag/AgCl electrode in the bulk electrolyte. The potential difference is related to the Clˉ ion concentration via the Nernst equation and follows an inverse logarithmic trend. By varying the applied current pulse, the sensitivity of the sensor is tunable to different concentration ranges. The potential response is also influenced by the pH of the electrolyte, this effect is pronounced at lower concentration of Clˉ ions (< 1 mM KCl) and at high pH values (>12 pH). The advantage of this approach is the use of a bare Ag/AgCl electrode as a pseudo-reference electrode, which enables this system for long term application such as the in-situ measurement of Clˉ ions in concrete.
... A similar approach can be used for detection of chloride ion penetration, using a sensitive membrane at the distal end of a fiber optic bundle, in contact with the material. This sensor has been successfully embedded in mortar cubes and tested in simulated maritime environments [54]. ...
Article
Structural Health Monitoring (SHM) can be understood as the integration of sensing and intelligence to enable the structure loading and damage-provoking conditions to be recorded, analyzed, localized, and predicted in such a way that nondestructive testing becomes an integral part of them. In addition, SHM systems can include actuation devices to take proper reaction or correction actions. SHM sensing requirements are very well suited for the application of optical fiber sensors (OFS), in particular, to provide integrated, quasi-distributed or fully distributed technologies. In this tutorial, after a brief introduction of the basic SHM concepts, the main fiber optic techniques available for this application are reviewed, emphasizing the four most successful ones. Then, several examples of the use of OFS in real structures are also addressed, including those from the renewable energy, transportation, civil engineering and the oil and gas industry sectors. Finally, the most relevant current technical challenges and the key sector markets are identified. This paper provides a tutorial introduction, a comprehensive background on this subject and also a forecast of the future of OFS for SHM. In addition, some of the challenges to be faced in the near future are addressed.
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Hydrophilic lucigenine doped P(VDF-TrFE) based chloride sensitive films were prepared by three different methods. These include increased pore size and distribution, introduction of alumina nanoparticles and addition of amphiphilic copolymer. The properties of the films were characterized by scanning electron microscope (SEM), contact angle meter (CAM), fourier transform infrared absorption spectroscopy (FT-IR) and photoluminescence (PL) spectroscopy. The PL intensity of chloride sensitive films is chloride concentration-dependent and the evolution of the lucigenine related PL intensity as a function of the chloride concentration follows the Stern–Volmer equation. From all the results, addition of amphiphilic copolymer shows the best effect on the hydrophilic modification of the film as well as the chloride sensitivity, and one of the optimal linear calibration formula I0/I=1+15.069[Cl-] (R2=0.981) was obtained in the concentration range 0.02 M-0.10 M of a standard sodium chloride solution with a detection limit of 0.01M (S/N=3). Graphical abstract
Conference Paper
The ever-increasing need to maintain aging existing reinforced concrete structures, especially in severe winter environments, in good condition and a cost-effective manner arises mainly in structural health monitoring methods, where it is necessary to adopt approaches that allow early detection of corrosion. Chloride-induced corrosion is a significant durability issue in cold regions where de-icing salts are used. This paper presents an embedded optical fiber chemical sensor that detects reliable free chloride concentrations into concrete cover in a precise non-destructive manner. It is based on fluorescence measurements using a chloride-sensitive fluorescent calcium-alginate sol-gel. Optical fibers were not affected by environmental factors, ions presences, or cold climate. Nevertheless, the fluorescent chemical sensor showed sensitivity towards alkalinity, temperature, leaching, and photo-bleaching. These restraints were encountered by applying a successfully validated ratiometric fluorimetry approach. Also, the durability and long-term stability of the sensor were studied. This sensor detects low chloride concentrations in a range of 0.045–0.45 M present in pore solution. It demonstrates a robust behavior, and excellent long-term stability so that it can withstand harsh environments. Thus, this sensor could provide a new approach towards the rapid, simple, and non-destructive monitoring of the structural health for detected the onset of corrosion damage.
Chapter
The dissolution of a “structure breaking reagent” such as NaCl results in reduction of hydrogen bonds between water molecules and a corresponding change in the absorption of electromagnetic energy at specific absorption bands (Chap. 1). This change in energy absorption is proportional to the amount of salt dissolved in water. Sodium and Calcium Chlorides are among the strongest structure-breaking reagents, a quality which is used in deicing agents. As part of a program investigating the use of optical spectroscopy for applications to the subsurface monitoring of infrastructure materials, a study was carried out involving analysis of the Near-Infrared (NIR) spectra of EM radiation when interacting with aqueous solutions containing dissolved Sodium Chloride (NaCl). This chapter described results of sensitivity and calibration procedures for in situ intrinsic sensing of dissolved Chlorides.
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In this work, we designed a ratiometric core-shell nanoarchitecture composed of an indium UV plasmonic core, an internal reference (Rhodamine B), a pH-sensitive probe (fluorescein), and a halide ion sensor (6-methoxyquinolinium). Immobilizing the fluorophores in distinct silica layers at precise distances from the core modulates the plasmon coupling and tunes the linear concentration range of halide ion detection.
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Optical Fiber sensors can be attached or embedded in reinforced concrete structures to provide continuous data on the state of these structures. This paper provides an overview of the state-of-the-art FOS sensors for monitoring of aging concrete structures in the nuclear industry. Cracks, corrosion, chloride and water ingress, excessive strain and deformation and stress relaxation in tendons are among the parameters that can be monitored using these sensors. Fiber optic sensors can be used either as distributed sensors or as a large number of multiplexed localized sensors. The ability to use these sensors in different configurations makes them very versatile for long-term monitoring of different degradation processes in concrete structures. The advantages and disadvantages of different types of FOS sensors are discussed in this paper.
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An overview is presented of the determination of chlorides in concrete ranging from simple on-site methods to detect the presence of chlorides to complex laboratory methods using NMR and γ-ray absorption for the non-destructive visualization of chloride and moisture penetration profiles. The requirements for chloride analysis are considered in the light of statistical service life prediction and computer models which simulate the mechanisms of chloride ingress.
Chapter
The new regulations imposed by the environmental protection agency (EPA) in the USA and REACH in Europe has forced manufacturers to use chromate-free corrosion protection. These new treatments and paints may perform differently to the traditional protection coatings based on chromates. Therefore, quantitative information about corrosion is a key parameter in these structures treated with the new protection. This chapter covers the different techniques and devices for the detection of corrosion by means of optical methods. Most of these methods pursue a nondestructive evaluation of the structure to be monitored that can be from a civil construction to an aircraft. In the former case the detection of corrosion has to be performed in reinforced concrete. In the latter, the whole structure is metallic. Usually, these sensors measure the by-products generated by corrosion, and therefore, are in fact chemical sensors that monitor specific substances that can give information about corrosion. Other approaches involve the coating of an optical fiber with a metallic film that can suffer a similar corrosion to the structure that the device is monitoring. This chapter reviews all of these techniques.
Article
In this paper, conducting polymer film modified electrodes were applied to fabricate paper-based chips (PCs), and different concentrations of chloride ions (Cl(-)) in water can be selectively detected based on the potential response towards Cl(-). The three-electrode system was screen-printed on paper and the polypyrrole (PPy) film doped with Cl(-) was electrochemically polymerized on working electrodes through cyclic voltammetry in aqueous solution. Open circuit potential-time method was used to measure the potential response. Based on such PCs, Cl(-) can be selectively detected in the range of 10(-7)-10(-2)M. Moreover, such PCs were utilized for Cl(-) analysis in real water samples and resulted in good results with recoveries between 113% and 124%. Besides, following the strategy we also employed this method to detect F(-) in water to demonstrate its general applicability. In view of its novelty, simplicity, sensitivity and low price, such PCs will potentially be utilized for the monitoring of anions in the environment, and our method made a start for the application of CMEs to PCs to design electrochemical sensors.
Article
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Concrete is the primary construction and repair material of many structural systems in Canada, such as highway bridges, high-rise buildings, parking structures, and dams. Today, many of the concrete structures, which have been exposed to aggressive environments, suffer from durability problems and fail to fulfill their design service life requirements. The problem is particularly serious in reinforced concrete structures where corrosion of reinforcing steel can impair their safety. Carbonation and chloride-induced corrosion are two major causes of deterioration of concrete structures in Canada and several other countries. The cost of the repair and rehabilitation of corrosion-damaged structures in the United States, Canada, and most European countries constitutes a large portion of their infrastructure expenditures. The limited knowledge of the field performance of corrosion-damaged structures and the lack of systematic approaches for their inspection, maintenance and repair contribute to the increase of their life-cycle costs, and result in the loss of functionality and safety. Le béton est le principal matériau utilisé pour la construction et la réparation de nombreuses structures au Canada, comme les ponts autoroutiers, les gratte-ciel, les stationnements multi-étagés et les barrages. De nos jours, nombre de structures en béton ayant été exposées à des environnements agressifs éprouvent des problèmes de durabilité et risquent de ne pas atteindre leur durée de vie utile anticipée. Le problème est particulièrement grave dans le domaine des structures en béton armé, où la corrosion de l'acier d'armature peut affecter leur sécurité. La corrosion due aux chlorures et/ou la carbonatation est la principale cause de détérioration des structures en béton. Leurs coûts de réparation et de restauration, aux USA, au Canada et dans la plupart des pays européens, constituent un fort pourcentage des dépenses de ces pays en matière d'infrastructure. Les connaissances limitées en matière de performance des structures endommagées par la corrosion ainsi que l'absence de démarche systématique en matière d'inspection, d'entretien préventif et de réparation contribuent à l'augmentation des coûts du cycle de vie des structures et provoquent une perte de fonctionnalité et de sécurité. PRAC
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Various types of errors during the measurements of ion-selective electrodes, ionsensitive field effect transistors, and fibre optic chemical sensors are described. The errors were divided according to their nature and place of origin into chemical, instrumental and non-chemical. The influence of interfering ions, leakage of the membrane components, liquid junction potential as well as sensor wiring, ambient light and temperature is presented.
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The compromised optima for high intensity chemiluminescence (CL), using superoxide generators, were all above pH 9.0 for the CL probes luminol and lucigenin. With luminol the optima were at pH 9.0 and 9.4 for the generators KO2 and hypoxanthine/xanthine oxidase (HX/XO), respectively. Lucigenin, with the same generators, produced optima at pH 9.5 and 10.0, respectively. The probe methyl-Cypridina-luciferin analogue (MCLA) produced optima closer to neutral pH, which is preferred for physiological assessments. MCLA had optima at pH 6.0, 8.7 and 9.5 with KO2 and with HX/XO optima at pH 4.8, 6.0, 7.0 and 8.7. When CL was assessed at physiological pH, MCLA observed superoxide radicals with a sensitivity of 100- and 330-fold more than luminol or luicigenin respectively. For singlet oxygen, the sensitivity of MCLA at this pH was 45- and 5465-fold more than for the said probes respectively. H2O2 did not elicit CL between pH 4 and 9.5 with any of the probes and did not influence the production of superoxide or singlet oxygen when co-assessed. Therefore CL could only be obtained when enzymes were used as converters. The optima for the enzyme-conversion system horseradish peroxidase (HRP)/H2O2, and luminol, were at pH 8.0 and 9.2. Lucigenin and HRP/H2O2 also had a biphasic CL profile with optima at pH 7.4 and 9.6. MCLA and HRP/H2O2 had five optima, with the major ones at pH 6.1 and beyond 10. The optima for the myeloperoxidase/H2O system were at 8.6 and beyond 10.0 when luminol and 0.15 mol/L NaBr were used.
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To study vacuolar chloride (Cl−) transport in the halophilic plant Mesembryanthemum crystallinum L., Cl− uptake into isolated tonoplast vesicles was measured using the Cl−-sensitive fluorescent dye lucigenin (N,N′-dimethyl-9,9′-bisacridinium dinitrate). Lucigenin was used at excitation and emission wavelengths of 433 nm and 506 nm, respectively, and showed a high sensitivity towards Cl−, with a Stern-Volmer constant of 173 m −1 in standard assay buffer. While lucigenin fluorescence was strongly quenched by all halides, it was only weakly quenched, if at all, by other anions. However, the fluorescence intensity and Cl−-sensitivity of lucigenin was shown to be strongly affected by alkaline pH and was dependent on the conjugate base used as the buffering ion. Chloride transport into tonoplast vesicles of M. crystallinum loaded with 10 mm lucigenin showed saturation-type kinetics with an apparent K m of 17.2 mm and a V max of 4.8 mm min−1. Vacuolar Cl− transport was not affected by sulfate, malate, or nitrate. In the presence of 250 μm p-chloromercuribenzene sulfonate, a known anion-transport inhibitor, vacuolar Cl− transport was actually significantly increased by 24%. To determine absolute fluxes of Cl− using this method, the average surface to volume ratio of the tonoplast vesicles was measured by electron microscopy to be 1.13 × 107 m−1. After correcting for a 4.4-fold lower apparent Stern-Volmer constant for intravesicular lucigenin, a maximum rate of Cl− transport of 31 nmol m−2 sec−1 was calculated, in good agreement with values obtained for the plant vacuolar membrane using other techniques.
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The expansion of optical sensors and the interest of the sol-gel process for the working out of new materials, have led us to develop a sensor applied to cryogenic temperature measurement in harsh environments. The measurement technique uses the decay-time of the luminescence emitted by doped crystals, in response to a short duration excitation pulse. The principle of the measurement has already been demonstrated by a prototype with crystals under bulk shape, and we present here a non contact version of the sensor, using fluorescent layers deposited on mechanical parts. These layers are composed of photoluminescent crystals reduced to powder and mixed to a binder. The originality of this work is that the binder is a silica-based hybrid gel. Such a gel has a good adherence to metallic substrates in cryogenic mediums and it can be used in chemically oxidizing environments. The fluorescence decay-time technique associated with the sol-gel process can then provide an interesting alternative in the development of new noncontact optical fiber sensors, working in hostile conditions.
Article
An optical sensor highly sensitive to hydrogen peroxide has been prepared by incorporating the indicator dye Meldola Blue (MB) into sol-gel layers, prepared from (a) pure tetramethoxysilane (TMOS) and (b) variation of TMOS and methyltrimethoxysilane (Me-TriMOS). Sensor layers based on TMOS doped with MB were found to be most appropriate for purposes of sensing hydrogen peroxide in giving large signal changes and displaying rapid response times over the wide concentration range of 10(-8)-10(-1) M.
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Sol-gel technology has been used to fabricate fiber optic and integrated optic chemical sensors for environmental monitoring and process control applications. These multi-sensing element sensors offer many advantages, the most prominent being that they are miniaturized, lightweight, and immune to electromagnetic interference. We are developing versatile, multi-analyte, micro-miniaturized fiber optic chemical sensor (FOCS) and integrated optic chemical sensor (IOCS) technologies for use in closed-loop control and process monitoring for industrial and environmental applications.
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Corrosion of structures is a serious problem involving man and material safety. Over the years, though several methods of monitoring corrosion have been devised with some success, but there is a persistent need for devising non-destructive and in-situ techniques for monitoring corrosion in structures. Fiber optic techniques are capable of meeting these requirements, besides offering several other important advantages. Fiber optic corrosion sensors have thus become quite attractive and are currently being investigated to address the high costs associated with the existing structural maintenance procedures. Fiber optics based direct absorption spectroscopic techniques investigated by some groups for estimating corrosion have used single fiber elements for recording the signal reflected from specimen at different wavelengths. As the light coupling efficiency of the single fiber elements is relatively poor in comparison with that of fiber bundles and the signal available for processing is weak, the paper presents a simple and alternate technique based on the color matching principle of fiber optic colorimetry to detect corrosion induced color changes. It employs a thin Y- shaped fiber optic bundle which increases the quantity of light energy coupled from a whitelight source. The light reflected off the sample is made incident on a PIN photo- detector through a complementary filter. A series of such probes can be safety embedded and or bonded to structures at pre-determined locations. The experimental set up for this sensor was implemented and feasibility of in-situ corrosion detection in structures demonstrated. Measurement data was acquired for steel samples corroded both in concrete embedded and open ambience conditions and results analyzed.
Article
This project is part of a global research program aimed at studying the durability of steel-fiber-reinforced concrete exposed to severe winter conditions. It was carried out to determine if the use of steel fibers can have a significant influence on the deicer salt scaling resistance of concrete. Sixteen steel-fiber-reinforced concrete mixtures were investigated. The test variables were the water/binder ratio, the use of silica fume, the type of fiber and the quality of the air-void network. The results of the tests show that the fibers have no apparent influence on the deicer salt scaling resistance of concrete. Furthermore, it has been observed that a very small difference in the minimal freezing temperature could have a great influence on the deicer salt scaling resistance.
Article
A chloride-selective optode is presented which is based on a polymer-stabilised emulsion system consisting of a hydrogel with entrapped plasticizer droplets. The droplets contain a neutral chloride-selective ionophore and a polarity-sensitive cationic fluorescent dye (PSD) located near the droplet surface. The ionophore extracts chloride out of the aqueous solution through the hydrogel into the plasticizer droplets, followed by a displacement of the positively charged PSD into the plasticizer droplet. This concerted process causes a decrease of micro-polarity near the dye, resulting in a dramatic increase in its fluorescence intensity. The sensing scheme can be used for reversible sensing of chloride in the 1–80 mM concentration range with response times on the order of less than 3 min. The sensor membrane has been investigated in terms of signal change, stability, limits of detection and selectivity for the analyte over interferents.
Article
pH sensitive fluorescent sol–gels were obtained by both covalent immobilization of aminofluorescein (AF) via isocyanate or epoxy groups, and by co-condensation of tetramethoxysilane (TMOS) and phenyltrimethoxysilane (Ph-TriMOS) in the presence of AF. The gel precursors were deposited on glass supports, cured, and characterized in terms of response to pH, pKa values, effects of ionic strength, response time, leaching, long-term stability, and photostability. The addition of Ph-TriMOS is found to exhibit a pronounced effect on the performance of the materials. Sensor layers based on TMOS doped with AF were found to be most appropriate for purposes of sensing pH in giving large relative signal changes and displaying rapid response times over the pH range 4–9.
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Many components contain welds which represent regions where defects most often initiate or are latent as a result of material and geometrical irregularity. However, it is difficult to inspect welds due to these irregularities. Correspondingly, there is no established method for inspection of welds. In this study, is developed a new Remotely Induced Current Potential Drop (RICPD) technique for highly sensitive inspection of defects in welds which is based on electromagnetic induction. The features of RICPD are investigated and a comparison is made between the performance of RICPD and existing Induced Current Focusing Potential Drop (ICFPD) technique, which is also potential drop technique based on electromagnetic induction. It turns out that the S/N ratio is significantly larger in RICPD due to the positioning of the induction wire far from the surface of the specimen.
Article
A hand-held dissolved oxygen optical sensor based on solid-state electronics and highly oxygen-sensitive luminescence material has been developed. Oxygen-sensitive dye absorbed on silica gel particles was dispersed in a 0.2 mm homogenous silicone rubber film (optode membrane) and coated on a 580 nm long-pass filter. The O2-sensitive dye was excited by an ultra-bright blue light-emitting diode and the emission intensity was captured by a silicon photodiode. The long-pass filter efficiently reduced the scattered light from the light source. The emission signal of the optode membrane was converted to the voltage signal which was processed by a single-chip Micyoco controller, and the dissolved oxygen concentration was automatically displayed on a liquid crystal display unit. The developed hand-held optical sensor is a single-piece device which can provide instant and reliable dissolved oxygen measurement. The sensor showed good repeatability, photostability and long-term stability. Satisfactory results were obtained when its analytical performance was compared with that of a typical Clark-type amperometric oxygen electrode. The developed oxygen optical sensor possesses the advantages of portability, low cost and long lifetime.
Article
Optical techniques developed for sensing purposes proved to be essential in many application fields, ranging from aerospace, industry, process control, to security, and also medicine. The capabilities of these sensors are generally enhanced when a bulk-optical configuration is replaced by optical fibre technology. In the past few years, research programmes and also the market for fibre sensors have assumed a relevant role. This is undoubtedly due to the growing interest in optoelectronics, but also to the very satisfactory performance and reliability that optical fibre sensors are now able to provide. This paper focuses on the advantages that optical fibre sensors offer to the biomedical field, recalls the basic working principles of sensing, and discusses some examples. This review was received in July 1995
Article
In the last century the production and application of halides assumed an ever greater importance. In the fields of medicine, dentistry, plastics, pesticides, food, photography etc many new halogen containing compounds have come into everyday use. In an analogous manner many techniques for the detection and determination of halogen compounds and ions have been developed with scientific journals reporting ever more sensitive methods. The 19th century saw the discovery of what is now thought of as a classical method for halide determination, namely the quenching of fluorescence. However, little analytically was done until over 100 years after its discovery, when the first halide sensors based on the quenching of fluorescence started to emerge. Due to the typical complexity of fluorescence quenching kinetics of optical halide sensors and their lack of selectivity, they have found little if any place commercially, despite their sensitivity, where other techniques such as ion-selective electrodes, x-ray fluorescence spectroscopy and colorimetry have dominated the analytical market. In this review article the author summarizes the relevant theory and work to date for halide sensing using fluorescence quenching methods and outlines the future potential that fluorescence quenching based optical sensors have to offer in halide determination.
Article
The authors justify their choice concerning the water absorption test for assessing both cover concrete porosity and largest capillary size, which are significant factors for concrete durability. In this way they extend to concrete an existing model used for terra cotta. The criterion used is the amount of water absorbed after one hour. This value is sufficiently representative of the mean radius of the largest capillaries. The results show that the absorption test can assess the effects of cement content on cover concrete porosity. Relating to these same results, the absorption test makes it possible also to take into account the beneficial effects of curing on capillary size. Correlations between carbonation depth and amount of water absorbed after one hour confirm the validity of these tests to assess the resistance of concrete to carbonation.
Article
The chloride threshold to develop active corrosion of the reinforcing steel does not seem to be a unique value and it depends on several factors, such as concrete mix proportions, cement type, C3A content of cement, blended materials, water/cement ratio, temperature, relative humidity, steel surface conditions and source of chloride penetration among others. Numerous studies have been already devoted to the study of the chloride threshold value for depassivation of the steel embedded in concrete. One of the reasons found for the scatter is the large number of variables that influence the chloride amount for depassivation. The other reason is the lack of accordance for the definition of the chloride threshold itself, either on the determining parameters (visual observation, corrosion potential or corrosion current) or on the expression of the threshold (as Cl−/OH− ratio or by weight of cement or concrete).The present paper presents chloride thresholds that were studied in mortar based on corrosion current measurements and expressed as total, free and Cl−/OH− ratio. For this study, mainly smoothed bars were used, but also some ribbed bars were tested. Chloride thresholds in the range of 1.24–3.08% and 0.39–1.16%, by weight of cement, for total and free chlorides, respectively, and in the range of 1.17–3.98 for Cl−/OH− ratio were found for chlorides admixed in the mixing water. Active corrosion is considered when, in a small exposed area, the corrosion rate of the rebar is higher than 0.1 μA/cm2. The threshold in the case of Cl−/OH− results a bit higher than that found in a previous work for synthetic pore solution, although the two types of data can be fitted together finding a good correlation.
Article
Two lipophilic derivatives of Reichardt’s phenolbetaine were dissolved in thin layers of plasticized poly(ethylene vinyl acetate) copolymer. These layers were coated with microporous white PTFE in order to allow reflectance (transflectance) measurements to be performed. The sensor layers respond to aqueous ethanol with a colour change from green to blue when increasing the ethanol content. The highest signal changes are observed at a wavelength of 750 nm with a linear calibration function up to 20% v/v ethanol and a detection limit of 0.1% v/v. The layers also exhibit strong sensitivity to acetic acid which affects real measurements of beverages. However, this limitation can be overcome by adjusting the basic pH of the sample solution. The correlation of ethanol content measured by enzymatic tests or gas chromatography correlates well with the data obtained using the ethanol sensor described here.
Article
The realization of an optical fibre sensor applied to cryogenic temperature measurement in harsh environments is presented. The measurement principle is based on the analysis of the decay-time of the fluorescence emitted by special doped crystals, the excited state lifetimes of which are greatly dependent on temperature. The sensor is intended to work in the presence of strong perturbations encountered on the testing benches of the liquid hydrogen and liquid oxygen turbo-pumps of the Ariane 5 Vulcan engine developed by ‘la Societé Européenne de Propulsion (SEP)’.
Article
The microcracking and self healing mechanisms of concrete exposed to rapid freezing and thawing in water and subsequently kept in water have been investigated by Scanning Electron Microscopy (SEM). Non air entrained concretes of ratio 0.40 with 0 and 5 % silica fume were studied. Damage was measured as loss in resonance frequency and compressive strength. After frost exposure, concrete beams were stored three months in water. During this time resonance frequency largely recovered, whereas compressive strength showed smaller recovery. On Secondary Electron Images (SEI) of fractured surfaces hydration products mainly of the C-S-H type were seen traversing cracks at several locations after self healing, but not directly after freeze/thaw. Back Scattered Electron Images (BSEI) showed that the cracks due to freeze/thaw testing were of 1–10 μm width. The cracks traversed the paste and followed the interfaces of most larger aggregate particles. On BSEI self healing was seen on 300–1000 X magnification as partly closing of several cracks smaller than 5 μm. This was most clearly seen by switching between SEI and BSEI modes. In BSEI-mode the re-hydration products appeared less dense and the cracks appeared wider than in the SEI-mode.
Article
The goal of this study was to develop long-wavelength fluorescent Cl indicators that have improved optical properties over quinolinium compounds. A series of quaternized tricyclic heterocycles was screened. We found that N,N-dimethyl-9,9-bisacridinium (lucigenin) had very high halide sensitivity with Stern-Volmer constants for collisional quenching of 390 M-1 (Cl), 585 M-1 (Br), 750 M-1 (I), and 590 M-1 (SCN), much higher than those for the reference compound 6-methoxy-N-(3-sulfopropyl)quinolinium (SPQ) (118 M-1 (Cl)); lucigenin fluorescence was insensitive to phosphate, sulfate, and nitrate. Lucigenin fluorescence at 505 nm was excited with molar absorbances of 34,000 M-1 cm-1 (368 nm) and 7500 M-1 cm-1 (455 nm). To examine structure-activity relationships, five 9-substituted N-methylacridinium compounds were synthesized (9-amino, 9-carboxaldehyde, 9-carboxamide, 9-N,N-dimethylcarboxamide, and 9-methylcarboxylate), of which N-methylacridinium-9-carboxamide (MACA) had the best optical properties. MACA had excitation and emission maxima at 424 and 500 nm, and Stern-Volmer constants of 225 M-1 (Cl), 480 M-1 (Br), 550 M-1 (I), and 480 M-1 (SCN). The quantum yields of lucigenin and MACA were 0.6-0.7. The acridinium compounds are useful as Cl indicators in liposomes and membrane vesicles, but are not stable in cell cytoplasm.
Article
Nitrite- and chloride-selective, ion correlation-based, nano-optodes have been prepared for application in vitro. These fluorescent, liquid polymer based sensors have theoretically predictable responses to anion activities and good selectivity. The nitrite sensor, prepared with a vitamin B12 derivative ionophore, would be useful for determination of oxidized nitric oxide. Chloride nano-optodes, as well as micro-optodes, prepared with an indium porphyrin ionophore, were utilized to determine chloride levels both on the surface and inside the visceral yolk sac of organogenesis-stage rat conceptuses.
Article
Article
An optical sensor for the measurement of salinity in seawater has been developed. It is based on a chloride-quenchable fluorescent probe (lucigenin) immobilized on a Nafion film. Two approaches for measuring salinity via chloride concentration are presented. In the first, a change in salinity corresponds to a change in the fluorescence intensity of lucigenin. In the second, the fluorescence intensity information is converted into a phase angle information by adding an inert phosphorescent reference luminophore (a ruthenium complex entrapped in poly(acrylonitrile) beads). Under these conditions, the chloride-dependent fluorescence intensity of lucigenin can be converted into a chloride-dependent fluorescence phase shift which serves as the analytical information. This scheme is referred to as dual lifetime referencing (DLR). The sensor was used to determine the salinity in seawater and brackish water of the North Sea.