The use of electrical resistivity as a NDT for the specification of concrete durability

The calculation of the time to reinforcement corrosion and service life duration is a subject of increasing interest. In present communication is explained how to use the electrical resistivity to calculate both the initiation and propagation periods in the case of carbonation and chloride penetration, although only the case of chlorides is illustrated here. The main advantage is that resistivity is an inexpensive non destructive measurement that can be used for routine quality control. The resistivity is an indication of the porosity and pore connectivity. It increases with time as hydration proceeds which is an indication of aging or pore refinement. In addition to the measurement of the resistivity it is necessary to calculate a "reaction factor" for accounting of the binding with cement phases. Conceming the propagation period, the electrical resistivity is an indication of the moisture content of concrete and therefore, it has a relationship with the corrosion cement. A model is proposed in which the resistivity is introduced in the square root of time la

Concrete Mixture Design Based on Electrical Resistivity.

Current codes have requirements for the durability design of concrete based on compressive strength and provisions related to cement content and water - cement ratio. However, such requirements do not take into account important parameters related to the behaviour of concrete against to aggressive attack. The electrical resistivity of the hardened concrete is related to connectivity of pores network under saturated condition.. This paper proposes a methodology of design based on the Archie law, which is originated from the concept of diffusion and provides properties such as electrical resistivity, porosity, and tortuosity, for estimating the ideal mix of concrete (maximum water cement, the minimum content of cement and cement type) for a specific environmental class and service life. It also considers the chemical reaction of chloride and carbonation with the phases of cement, so called factor of reaction (r) which depends on the type of cement and indicates the delay on the agressi vc penetratio

Electrical resistivity as microstructural parameter for the calculation of reinforcement service life

There is an increasing interest in developing models for prediction of the service life regarding reinforcement corrosion. In present communication a proposal is made based on the electrical resistivity to calculate both the initiation and propagation periods as well as for predicting concrete aging related to durability and for measuring the efficiency of curing. The model is fundamented in that the Resistivity is a property depending on the concrete porous system and its degree of moisture, and then from its values in saturated conditions, it is possible to find relations between diffusivity and resistivity, then linking concrete microstructure and transport resistance. The relation of resistivity and time is quantified through the square root law, either for chloride penetration as for carbonation. However some additional information is needed due to the reaction of chlorides and carbon dioxide with cement phases: the resistivity has to be factorised by a "reaction factor" accounting for it. Concerning the corrosion propagation period the relation between corrosion and resistivity is provided by an expression previously developed by one of the authors. Aging is introduced by measuring the evolution of the resistivity with time. The paper presents an example of application of the model. Finally it is mentioned that the concrete mix can be designed for a target resistivity and that this parameter can also be used as a performance parameter (Corrosion indicator). Being the measurement of resistivity a non destructive method, it can be as well used for on-site quality control

Metodología para la evaluación de estructuras de horigón corroídas.

El hormigón ha resultado ser un material que se puede utilizar en múltiples aplicaciones con unas prestaciones muy eficientes y una buena durabilidad. Sin embargo es necesario reconocer el creciente número de estructuras que presentan corrosión de la armadura debido al creciente envejecimiento del parque construido. La corrosión está causada principalmente por la carbonatación del recubrimiento y por la penetración de cloruros que provocan la despasicación del acero de la armadura. Los efectos que se producen en la estructura cuando la armadura se empieza a corroer se muestran en la Figura 1 y son: a) Fisuración del recubrimiento, b) Pérdida de adherencia c) Pérdida de sección efectiva de acero y d) Pérdida de sección efectiva de hormigón. La consecuencia de la evolución progresiva de todos estos factores produce una pérdida de la capacidad portante del elemento estructural con el tiempo

A la sustentabilidad por la durabilidad del hormigón estructural

- Referencias a ingenieros ilustres - Hormigón estructural: el material del siglo XX: barato, funcional y resistente - Retos del siglo XXI: Efecto invernadero del CO2 Objetivos de Desarrollo Sostenible de la ONU El hormigón como sumidero de CO2: Re-carbonatación Método de calculo en un inventario de estructuras Duración Vida útil ¿es posible predecirla? Códigos: métodos probabilistas, métodos avanzados de cálculo Método de la resistividad eléctricaDisertación de la ingeniera María del Carmen Andrade Perdrix en el marco de la recepción de la misma como nuevo miembro de la Academia de la Ingeniería de la provincia de Buenos Aires.Academia de la Ingeniería de la provincia de Buenos Aire

Non contacting corrosion method applied to the steel corrosion rate determination in different solutions and reinforced concrete specimens.

All the current techniques used to measure the metallic corrosion require contact with the metal. Particularly, in the case of reinforcement corrosion, this signifies the need to reach the bar that is embedded in the concrete, which may consequently result in the disruption of the integrity of the real structures. This paper explores the feasibility of using a new method for polarizing the reinforcement or any metal in an electrolyte, without the need of direct contact with it. The polarization is obtained through the induction of current from an external electrical field. The current runs through the electrolyte and the metal in parallel, depending on the electrode arrangement. The resulting Polarization Resistance calculated is termed as Inductive, Rp = Rpi . The Inductive is calculated by the model of resistances in parallel, which requires a separate measurement of the electrolyte ohmic resistance. In this study, solutions with several resistivities and concrete specimens with and without chlorides have been used. The results indicate that electrolytes of low resistivity mask the measurement, and consequently, Rpi could not be calculated. In electrolytes with high resistivity, such as concrete, the feasibility is found to depend on the relative values of Re and Rp

Correlación entre ancho de grieta del recubrimiento del concreto y corrosión del refuerzo en elementos expuestos a un ambiente natural contaminado por cloruros

La corrosión del refuerzo genera daños variados a estructuras de concreto que influyen en la capacidad de carga; entre estos daños se puede mencionar el agrietamiento del recubrimiento del concreto. Este trabajo proporciona resultados de campo en el tema de propagación de grietas del recubrimiento del concreto por corrosión del refuerzo después de una exposición natural por varios años. Los elementos estructurales evaluados fueron una viga T y una columna cuadrada expuestos al ambiente atmosférico de Madrid, España. Dos formulas empíricas fueron usadas para correlacionar los valores obtenidos del agrietamiento del recubrimiento por corrosión: w=k Px/(C/φ), y w=k Px/Ro, en donde w es el ancho de la grieta por corrosión, k es una constante de proporcionalidad, Px es la penetración por la corrosión en el tiempo, C/φ es la relación recubrimiento de concreto/diámetro del refuerzo, y Ro es el radio original del refuerzo

Bond response in structural concrete with corroded steel bars. Experimental results

The growing interest in upgrading existing reinforced concrete structures or extending their service life, and in ensuring greater durability in new designs, has led to a need for resistance models that take deterioration processes into account to verify structural safety. Bond activation between reinforcing steel and concrete is of cardinal importance in this context. A number of experimental studies have been conducted in recent years on bond failure, which normally leads to brittle behaviour. The findings have diverged rather widely, however, due primarily to differing test conditions. The present paper presents an experimental programme for eccentric pull-out tests in which specimens were subjected to both accelerated and natural corrosion in an attempt to surmount these inconsistencies. It also introduces an embedded fibre-optic sensing system with corrosion-resistant fibre Bragg grating sensors and discusses some of the finding

Hydrothermal monitoring using embedded sensors of the actual roof system of the prado museum

El Prado Museum in Madrid has been recently submitted to a refurbishment of its roof which from been made with the traditional tiles has been changed to the use of modern waterproofing layers covered with a metallic lead finishing. Due to an unexpected damp patch that produced leaking in the hall in which Las Meninas by Velázquez was exhibited, the authors were commissioned by the Ministry of Education and Culture to study the suitability of the roof and its waterproofing properties. The study led to suggestions of modifications in the design of the roof layers, which are out of the scope of present paper. In present paper are given the behaviour of the sensors embedded in two specific areas of the roof. The sensors installed were of: temperature, relative humidity, measurement of local strain and detection of liquid water. The liquid water sensors reveal that some water is withheld in the layer just below the thermal insulation material, although it is standing. The results of over four years of readings show that the temperature attenuates over distance away from the outermost layer, where the readings are very high in summer, due to it consists of lead. During the colder seasons, in turn, the temperature in the inner layers of the roof is higher than in the outer layers. The strain recorded follows the logical evolution of temperature with no abnormal behaviour being detected. Some of relative humidity sensors had measuring problems due to water condensing on them. In summary however, if the behaviour in this area is extrapolated to the rest of the roof, it can be considered to perform correctly as intended. No more leaking events have been detected from the design modifications were incorporated to the existing roof

Relation Between Corrosion Degree And Pressure Needed To Produce The First Crack And Evolution Of Crack Width In Natural Exposure

Reinforcement corrosion leads into several damage types which influence the structural loadbearing capacity, among which can be mentioned the cracking of concrete cover. This work presents results of crack width generated in concrete elements fabricated in 1990 with chlorides added in the mix and exposed to the natural atmosphere of Madrid-Spain climate. These elements, one T beam and one column. Two expressions have been fitted to the results: w = k Px / (c/φ) and w = k Px / Ro, where w is a crack width in the time, k is a proportional factor, Px is the corrosion penetration in the time, c/φ is the concrete cover/diameter relation and Ro is the original radius of the bar. The expressions were also fitted to results taken from the literature made applying a current. The beam shows larger crack widths than the beam and the accelerated tests give intermediate results. Based in all the results, although the scatter is important, it has been calculated the k and k’ slopes which resulted respectively in values of 9.5 and 35.