Determination of pH in Powdered Concrete Samples or in Suspension

Concrete is a material that is widely used by mankind. Although different deterioration mechanisms can lead to degradation of the concrete itself, reinforcement corrosion is the biggest durability issue for reinforced concrete structures. One of the key parameters influencing the corrosion rate is pH value. Accordingly, this work presents two capacitive sensor platforms—one based on parallel plate electrodes and the other based on a planar interdigitated electrode structure. The first platform is used to determine whether the pH value is lower or higher than a predetermined limit (around 11) and this device was successfully tested using concrete suspensions. The second platform can determine the pH value by establishing a relationship between pH and measured capacitance from a powdered concrete specimen. Both multi-layered platforms were manufactured by means of a cost-effective xurography technique, which provides technically and mechanically robust structures very quickly

A New Corrosion Sensor to Determine the Start and Development of Embedded Rebar Corrosion Process at Coastal Concrete

The corrosion of reinforcements induced by chloride has resulted to be one of the most frequent causes of their premature damage. Most corrosion sensors were designed to monitor corrosion state in concrete, such as Anode-Ladder-System and Corrowatch System, which are widely used to monitor chloride ingress in marine concrete. However, the monitoring principle of these corrosion sensors is based on the macro-cell test method, so erroneous information may be obtained, especially from concrete under drying or saturated conditions due to concrete resistance taking control in macro-cell corrosion. In this paper, a fast weak polarization method to test corrosion state of reinforcements based on electrochemical polarization dynamics was proposed. Furthermore, a new corrosion sensor for monitoring the corrosion state of concrete cover was developed based on the proposed test method. The sensor was tested in cement mortar, with dry-wet cycle tests to accelerate the chloride ingress rate. The results show that the corrosion sensor can effectively monitor chloride penetration into concrete with little influence of the relative humidity in the concrete. With a reasonable corrosion sensor electrode arrangement, it seems the Ohm-drop effect measured by EIS can be ignored, which makes the tested electrochemical parameters more accurate

Sistema de Sensores Embebidos para Monitorizar la Corrosión de Estructuras de Hormigón Armado. Fundamento, Metodología y Aplicaciones

La durabilidad de una estructura de hormigón armado puede verse seriamente comprometida por la corrosión de las armaduras. En una inspección visual la corrosión solo se detecta cuando el daño está ya muy avanzado, lo que supone un elevado riesgo estructural e implica unas reparaciones muy costosas. Por tanto, es fundamental incorporar a las estructuras sistemas de monitorización capaces de detectar la aparición de procesos de corrosión con suficiente antelación. El presente trabajo recoge el diseño, desarrollo e implementación de un sistema de sensores embebidos para monitorizar la durabilidad de estructuras de hormigón armado. Se trata de un sistema totalmente automatizado que muestra en tiempo real el estado de la estructura en múltiples zonas de forma simultánea. El elemento principal del sistema de monitorización es el sensor de corrosión, diseñado para determinar de forma fiable y precisa la velocidad de corrosión de las armaduras embebidas. Para ello este sensor emplea un novedoso método de medida que integra la exactitud y precisión de los métodos de laboratorio, y la rapidez y versatilidad de los métodos para medidas in situ. Esta nueva técnica se ha desarrollado a partir de un modelo teórico que simula fielmente el comportamiento de la interfase acero-hormigón. Esto permite obtener, además de la velocidad de corrosión, otros parámetros relacionados con la naturaleza del proceso de corrosión y con las propiedades físico-químicas del hormigón. Para gestionar de forma automatizada la monitorización se ha desarrollado un sistema electrónico específico (hardware y software) en colaboración con otros investigadores del mismo grupo de trabajo. El sistema de sensores ha sido finalmente implementado para monitorizar la durabilidad de varias estructuras de hormigón armado. Actualmente el sistema permanece operativo de forma exitosa, pues el mantenimiento requerido hasta ahora ha sido mínimo.Corrosion of the steel reinforcement is a major deterioration problem of concrete structures. In a visual inspection corrosion is detected when the damage is already very advanced, which involves a high structural risk and involves very expensive repairs. Therefore, it is essential to integrate into the structures monitoring systems capable of detecting emerging corrosion processes sufficiently in advance. The present work includes the design, development and implementation of an innovative system of embedded sensors to monitor the durability of reinforced concrete structures. It is a fully automated system that real-time monitors the state of the structure in multiple zones simultaneously. The main component of the monitoring system is the corrosion sensor, designed to reliably and accurately determine the corrosion rate of embedded reinforcements. This sensor uses a novel measurement method that integrates the accuracy and precision of laboratory methods, and the speed and versatility of the methods for in situ measurements. This technique has been developed using a theoretical model that faithfully simulates the behavior of the steel-concrete interface. This allows obtaining, in addition to the corrosion rate, other parameters related to the nature of the corrosion process and to the physical-chemical properties of the cover concrete. To manage the monitoring sensor network in an automated way, a specific electronic system (hardware and software) has been developed in collaboration with other researchers of the same researching group. The sensor system has been finally implemented to monitor the durability of several reinforced concrete structures. Currently the system remains operational successfully, in fact the maintenance required so far has been minimal.La durabilitat d'una estructura de formigó armat pot veure's seriosament compromesa per la corrosió de les armadures. En una inspecció visual la corrosió només es detecta quan el dany està ja molt avançat, la qual cosa suposa un elevat risc estructural i implica unes reparacions molt costoses. Per tant, és fonamental incorporar a les estructures sistemes de monitorització capaços de detectar l'aparició de processos de corrosió amb suficient antelació. El present treball comprén el disseny, desenrotllament i implementació d'un sistema de sensors embeguts per a monitoritzar la durabilitat d'estructures de formigó armat. Es tracta d'un sistema totalment automatitzat que mostra en temps real l'estat de l'estructura en múltiples zones de forma simultània. L'element principal del sistema de monitorització és el sensor de corrosió, dissenyat per a determinar de forma fiable i precisa la velocitat de corrosió de les armadures embegudes. Per a això este sensor empra un nou mètode de mesura que integra l'exactitud i precisió dels mètodes de laboratori, i la rapidesa i versatilitat dels mètodes per a mesures in situ. Esta nova tècnica s'ha desenrotllat a partir d'un model teòric que simula fidelment el comportament de la interfase acer-formigó. Açò permet obtindre, a més de la velocitat de corrosió, altres paràmetres relacionats amb la naturalesa del procés de corrosió i amb les propietats fisicoquímiques del formigó. Per a gestionar de forma automatitzada la monitorització s'ha desenrotllat un sistema electrònic específic (hardware i software) en col·laboració amb altres investigadors del mateix grup de treball. El sistema de sensors ha sigut finalment implementat per a monitoritzar la durabilitat de diverses estructures de formigó armat. Actualment el sistema roman operatiu de forma reeixida, de fet el manteniment requerit fins ara ha sigut mínim.Ramón Zamora, JE. (2018). Sistema de Sensores Embebidos para Monitorizar la Corrosión de Estructuras de Hormigón Armado. Fundamento, Metodología y Aplicaciones [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/111823TESI

Development of Local and Global Corrosion Sensing Technique to Monitor Structural Behavior of Prestressed Concrete Structures

Corrosion of steel rebar in reinforced concrete structures is a concern for highway bridge owners. According to 2002 study by the Federal Highway Administration, ~15% of the highway bridges in the US are structurally deficient due to corrosion and have an estimated annual direct cost of $8.3 billion. Generally, in post-tensioned bridges, ducts filled with poor or incomplete grouting can allow the tendons to come into contact with water, leading to corrosion and fracture. Although new and improved procedures of grouting have been developed to reduce the instances of poor grouting, the problem of how to reliably inspect tendons on existing structures remains. This research aimed to evaluate the feasibility of using currently available local and global corrosion sensing techniques to monitor the performance of concrete structures. This dissertation explores the use of three local corrosion sensors (resistivity sensors, relative humidity sensors, and resistor-inductor- capacity [RLC] sensors). In this research, local sensors (i.e. RH sensors and four-point resistivity sensors) placed at an interval of every three foot were able to detect corrosion conducive environment in PT ducts by measuring the electrical properties and moisture contents of the grout. However, the measured RH was consistently lower in the low point of the specimens compared to the high points for all the specimens. The four-point resistivity sensors were able to detect a clear difference between the grouted ducts with good grout compared to ducts with chloride-rich grout with voids and layered-chloride rich grout without voids. To evaluate destructive testing and monitor the global response, two full-scale prestressed concrete inverted-tee (IT) beams were constructed and instrumented with vibrating wire strain gauges (VWSGs) located in multiple planes along the length. The VWSGs were able to clearly detect the initiation of corrosion in the first prestressing strand in each beam. The local corrosion damage in the first strand resulted in a change in the behavior of the beam, which was detected by the VWSGs (through a change in slope of curvature versus time)

Improving Passive Magnetic Inspection for Reinforced Concrete Condition Assessment

Life quality, industrial productivity, and community safety can be assured by the reliability and the safety of infrastructure such as highways, bridges, and energy-supply systems. Reinforced concrete is the most-commonly used massive construction material in urban, road and industrial infrastructure because of its mechanical properties, durability, and mouldability. Concrete has acceptable compressive strength but relatively low tensile strength, so steel reinforcement rods (rebar) are usually added to concrete to enhance its tensile strength. However, steel rebar is subject to the serious and costly problem of corrosion, which eventually can significantly degrade the mechanical properties of concrete. Quantifying the corrosion condition of reinforcing steel can help manage associated risks arising from the unexpected function failure of reinforced concrete structures. In efforts to avoid such failures, engineers rely on quantitative time-history condition monitoring of reinforcing steel to help make decisions on rehabilitation, decommissioning, or replacement of concrete infrastructure. The self-magnetic behaviour of ferromagnetic materials can be used for quantitative condition assessment. Inspection of reinforced concrete structures by a method based on this concept is under development. Improving the data recording, mathematical simulation and interpretation so as to obtain more-reliable outcomes from this novel NDT technology (Passive Magnetic Inspection (PMI)) is the main aim of this research project. This thesis, consisting of eight chapters, investigates various experiments and simulations, and delineates future work: Chapter 1 includes the introduction, theoretical background, and research objectives; Chapter 2 consists of numerical simulations and experimental results on the passive magnetic behavior of a rebar with pitting; Chapter 3 represents the simulations and experimental results of the investigations on rebars with local longitudinal defects; Chapter 4 investigates the self-magnetic behaviour of rebars with different sizes of crack; Chapter 5 covers numerical simulations and experimental results of passive magnetic behavior of an intact rebar and a rebar with general corrosion; Chapter 6 compares the magnetic flux density values generated from rebars with different degrees of general corrosion; Chapter 7 describes a successful fieldwork project; Chapter 8 outlines a general conclusion and future works that can help the further improvement of the inspection technology. To explain the content of the thesis in more detail, through the analysis of magnetic data, Chapters 2, 3, and 4 cover methods for identifying the local defects in steel reinforcements, and Chapters 5 and 6 focus on realizing the general corrosion of steel rebars. Applicable findings generated from Chapter 2 to Chapter 6 are used in detecting and categorizing the local defects and general corrosion in steel rebars. For instance, it is shown that a certain percentile threshold can be applied on magnetic data to accurately detect longitudinal defects. It is also demonstrated that medium and large cracks are detected by magnetic values’ absolute gradients of greater than 0.87 (µT/mm) and 0.95 (µT/mm), respectively. In addition, it is shown that the average of standard deviations calculated for a magnetic data set decreases when the degree of general corrosion increases. The findings in the first six chapters are implemented to establish the data gathering, data analysis, and interpretation approaches used in the field work described in Chapter 7. In the field work, the condition of culvert C072’s reinforced concrete (RC) bridge structure (located in the north of Markham, Ontario, Canada) is inspected. The inspection, supervised by the Corporation of the City of Markham, uses PMI technology. The inspection outcomes demonstrate that the sections close to the south and north ends of the bridge display the most-severe reinforcement anomalies: roughly, maximums of 20% and 14% of the reinforcement’s cross-sectional area loss are detected close to the bridging structure’s south and north ends, respectively. Additionally, an area in the middle of the bridge is found to have a noticeable anomaly in the reinforcement. The results generated from the magnetic data, collected using a PMI scanner, are in good agreement with visual-investigation results and the culvert’s historical information, such as the concrete’s chloride content and compressive strength values, as well as information from a half-cell potential survey. Culvert C072’s condition is considered moderately deteriorated and corrective actions are recommended