This paper presents an experimental investigation into the residual capacity of corroded reinforcing bars. By performing both accelerated and simulated corrosion tests on bare bars and on bars embedded in concrete, the mechanism of the reduction of the capacity of corroded reinforcement was investigated. The influence of type and diameter of reinforcement on its residual capacity is discussed. The experimental results show that, due to local attack penetration, the residual cross-section of a corroded bar is no longer round and varies considerably along its circumference and its length. Although the force–extension curves of corroded bars are similar to those of non-corroded bars for up to 16% corrosion, their residual yield and ultimate forces decrease more rapidly than their average cross-sectional area and, therefore, their residual strength decreases significantly. Even though the residual capacity of corroded small diameter and/or plain bars reduces more than that of large diameter or ribbed ones, di...

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Residual capacity of corroded reinforcing bars

One of the most important causes for reinforcing steel corrosion is the presence of chloride ions. They cause localised breakdown of the passive film that initially forms on steel as a result of the alkaline nature of the pore solution in concrete. The harmful chloride ions can be originated from the use of contaminated mix constituents or from the surrounding environment. The determination of a critical level, above which serious problems can occur, has been one of the main goals of investigation. Unfortunately, it is difficult to establish such a value since the chloride level is influenced by several factors. Thus, after concrete contamination, it is of fundamental importance to follow the activity of chlorides and the state of the reinforcing rebars. In this respect, the use of electrochemical techniques such as polarisation resistance, electrochemical impedance, galvanostatic pulse and potential measurements have shown to be powerful tools. Nevertheless, the interpretation of the results becomes sometimes a difficult task. A large number of authors have dedicated several studies to the interpretation of such measurements and a highly dispersed number of interpretations can be found in literature. The aim of this paper is to present an overview on the state-of-the-art of the most important aspects of the corrosion process initiated by chlorides, its development and monitoring techniques.

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Chloride-induced corrosion on reinforcing steel: from the fundamentals to the monitoring techniques

The durability of reinforced concrete is influenced by those physical characteristics of concrete that control the diffusion of gases, such as CO2 and O2 or of liquids (mainly water) through its pores, and the diffusion of ions, such as Cl-, dissolved in the pore water. These physical characteristics depend on the composition of concrete, the chemical composition and type of cement, and the relative humidity and temperature of the environment. In the present paper, these characteristics of concrete are determined analytically and/or experimentally in terms of the composition parameters and environmental condtions; the molar concentration of those constituents that are susceptible to carbonation; the porosity and pre-size distribution; the degree of saturation of the pores; and effective diffusivity of gases through the concrete.

Physical and Chemical Characteristics Affecting the Durability of Concrete

This paper presents the formulation of a time-dependent seismic fragility format for bridges, as well as new insights into the potential effects of aging and deterioration on seismic vulnerability traditionally neglected in fragility modeling, including joint impacts of multiple component deterioration not investigated to date The study evaluates the impact of lifetime exposure to chlorides from deicing salts on the seismic performance of multispan continuous highway bridges, considering corrosion of reinforced concrete columns and steel bridge bearings The components' degradation and their influence on seismic response are illustrated through three-dimensional nonlinear dynamic analysis A full probabilistic analysis accounting for variation in bridge, ground motion, and corrosion parameters is conducted to develop time-dependent seismic fragility curves These fragility curves indicate the evolving potential for component and system damage under seismic loading considering time-dependent corrosion-induced deterioration The results indicate that while corrosion may actually decrease the seismic vulnerability of some components, most critical components suffer an increase in vulnerability Quadratic models depicting the change in lognormal seismic fragility parameters are proposed to capture the time-dependent effect of aging on the fragility of the bridge system Overall, the seismic vulnerability significantly increases throughout the lifetime of the representative bridge geometry, with a 32% shift in the median value of complete damage fragility near the end of the bridge's life

Aging Considerations in the Development of Time-Dependent Seismic Fragility Curves

This paper reviews the effect of incorporating recycled aggregates, sourced from construction and demolition waste, on the carbonation behaviour of concrete. It identifies various influencing aspects related to the use of recycled aggregates, such as replacement level, size and origin, as well as the influence of curing conditions, use of chemical admixtures and additions, on carbonation over a long period of time. A statistical analysis on the effect of introducing increasing amounts of recycled aggregates on the carbonation depth and coefficient of accelerated carbonation is presented. This paper also presents the use of existing methodologies to estimate the required accelerated carbonation resistance of a reinforced recycled aggregate concrete exposed to natural carbonation conditions with the use of accelerated carbonation tests. Results show clear increasing carbonation depths with increasing replacement levels when recycled aggregate concrete mixes are made with a similar mix design to that of the control natural aggregate concrete. The relationship between the compressive strength and coefficients of accelerated carbonation is similar between the control concrete and the recycled aggregate concrete mixes.

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Carbonation behaviour of recycled aggregate concrete

The author details the reactions of various concretes on steel reinforcement. Although portland cements, slag cements and high alumina cements are all hydraulic binders, each possess special properties which are examined. The discussion of causes and methods of preventing the corrosion of steel reinforcement covers such aspects as galvanised steel reinforcement, effects of concrete composition, corrosion of steel reinforcments in concrete and prestressed reinforcement. It is concluded that the most significant influences on the corrosion of prestressing wire in concrete are: the presence of chloride; the presence of nitrates; the composition of the concrete; the degree of carbonation of the concrete; concrete compaction and, chlorides and sulphates should be used as far as possible when steel is embedded. (TRRL)

A C Smith

Papers

Corrosion of steel by concrete