Rob B. Polder

Corrosion of steel in concrete : prevention, diagnosis, repair

Reinforced concrete has been developed and applied extensively in the 20th century. It combines the good compressive strength of concrete with the high tensile strength of steel and has proven to be successful in terms of structural performance and durability. However, there are instances of premature failure of reinforced concrete and prestressed concrete components due to corrosion of the reinforcing steel with very high economic implications of such damage. This book focuses on the chloride and carbonation induced corrosion of steel in concrete, presenting transport mechanisms and electrochemical concepts. Other types of corrosion of steel and degradation of concrete are also treated. The main emphasis lies on design and execution aspects related to durability of new and existing structures. New methods and materials for preventative measures, condition assessment and repair techniques are discussed. This makes this book an invaluable reference for any engineer and materials scientist involved in research and practice of corrosion protection, rehabilitation and maintenance of reinforced concrete structures and components. Owners, designers and contractors will profit by this updated state of the art.

Test methods for on site measurement of resistivity of concrete — a RILEM TC-154 technical recommendation

Abstract This paper describes methods to assess concrete resistivity on site for various purposes related to corrosion and protection of reinforcement. It is based on the first draft of a forthcoming RILEM Technical Recommendation. The electrical resistivity of concrete can be related to the two processes involved in corrosion of reinforcement: initiation (chloride penetration) and propagation (corrosion rate). The resistivity of a structure exposed to chloride indicates the risk of early corrosion damage, because a low resistivity is related to rapid chloride penetration and to a high corrosion rate. Once damage has occurred, resistivity is relevant for electrochemical maintenance methods. The resistivity of the cover (near surface) concrete can be measured non-destructively by placing electrodes on the concrete surface, applying a voltage and measuring the current. Several arrangements can be used, one electrode (the reinforcement is the second electrode), two electrodes, and four electrodes. Practical aspects of these arrangements are discussed. Procedures for calibration are proposed. Guidelines for the interpretation and reference values for various exposures and concrete compositions are given.

CHARACTERISATION OF CHLORIDE TRANSPORT AND REINFORCEMENT CORROSION IN CONCRETE UNDER CYCLIC WETTING AND DRYING BY ELECTRICAL RESISTIVITY

Concrete prisms were made with four cement types including cements with fly ash and/or blast furnace slag and three waterto- cement (w/c) ratios. Chloride penetration and corrosion of rebars were stimulated by subjecting prisms to cyclic loading with salt solution and drying. Concrete resistivity, steel potentials and corrosion rates were measured up to one year of age. Chloride penetration profiles were determined after salt loading. It was found that the resistivity of a particular concrete reflects its properties with regard to chloride penetration, corrosion initiation (probability of corrosion) and corrosion propagation (corrosion rate). Blending the cement with blast furnace slag, fly ash or both is beneficial with regard to delaying the onset of corrosion and subsequently limiting its severity under simulated de-icing salt load. The fly ash cement shows increased resistivity compared to Portland cement from eight weeks. Cement with a high percentage of slag develops a significantly higher resistivity after one week

Corrosion initiation and propagation in cracked concrete - a literature review

The major degradation mechanism in civil engineering concrete structures is corrosion of reinforcement due to chloride penetration. Corrosion reduces serviceability and safety due to cracking and spalling of concrete and loss of steel cross section. Recently, service life design has moved from prescriptive performance based. The current approach aims at postponing initiation of corrosion until the end of the required service life with a predetermined reliability, based on simplified modelling of transport in uncracked concrete and testing of laboratory samples for chloride diffusion. Real structures under service load contain cracks and execution defects. Cracks are fast transport routes for chloride, but the effect is mitigated by poorly known mechanisms such as self-healing and crack blocking. Current models do not cover the effect of cracks, voids and compaction defects in concrete on chloride transport and corrosion initiation, rendering them less robust than desired. A project is carried out aimed at modelling the influence of cracks on the initiation and propagation of reinforcement corrosion. As the first phase, a literature review was made, which is reported in this paper.

Possibilities for improving corrosion protection of reinforced concrete by modified hydrotalcites – a literature review

Modified Hydrotalcites (MHTs) represent a group of technologically promising materials for improving corrosion protection in concrete owing to their low cost, relative simplicity of preparation, and plenty of composition variables. Numerous academic and commercial studies on MHTs have been carried out, but few of them on cementious materials particularly in exploiting their potential application in corrosion protection of reinforced concrete. In this paper, the corrosion mechanism in reinforced concrete and concrete properties that affect it are briefly inroduced. In addition, the existing knowledge with regard to synthesis and characterization methods of MHTs, ion exchange within the MHT structure as well as the application of MHTs in cementitious materials were reviewed.

Chloride ingress of carbonated blast furnace slag cement mortars

In the Netherlands civil engineering structures, such as overpasses, bridges and tunnels are generally built using blast furnace slag cement (BFSC, CEM III/B) concrete, because of its high resistance against chloride penetration. Although the Dutch experience regarding durability performance of BFSC concrete has been remarkably good, its resistance to carbonation is known to be sensitive, especially when the used slag percentage is high. In a field investigation on a highway overpass damage was found in sheltered elements such as abutments and intermediate supports, which was attributed to chloride induced corrosion enhanced by carbonation that occurred prior to the chloride exposure.

Influence of Anolyte on Lithium Migration in Concrete

Alkali-silica reaction (ASR) affects concrete structures worldwide. During this deleterious process, alkali and hydroxyl ions react with reactive siliceous components of the aggregate, producing a hygroscopic gel. Once the gel absorbs water from the surrounding cement paste, it swells. Consequently, the reaction might lead to expansion and cracking of concrete elements. Lithium is known to prevent those detrimental effects. In fresh mixtures, the incorporation of lithium-based admixtures as a preventive method has been acknowledged for years. However, in hardened concrete lithium ions need to be driven into it. Ionic migration seems to be the most effective method, when compared to other transport mechanisms. Even though several investigations have been conducted on the use of electric field to transport lithium ions into concrete, so far, there is no agreement on the findings. The present paper aims to investigate the influence of the type and concentration of lithium solution used as anolyte.

A proposal for determining the remaining time to chloride induced corrosion initiation of existing reinforced concrete structures

Asset managers would benefit from knowing when to expect corrosion initiation in a particular reinforced concrete structure. However, accepted approaches to test existing structures for the remaining time to corrosion initiation are lacking. This paper proposes such an approach, based on experience in the field and additional considerations. From say 20 years age, existing structures embody the concrete’s response to actual environmental loads, e.g. in chloride profiles. Based on measuring the actual cover depth, taking (at least six) chloride profiles, some assumed parameters and a simple model, the expected time to corrosion initiation for a particular test area can be predicted. Sampling frequencies are given. Uncertainties can be taken into account by applying a safety margin to the cover depth. Results of at least six tests are classified and suggestions for interpretation are given. Because the accuracy is limited, the results are classified in three broad ranges: 5 years or less, 5 to 15 years, or more than 15 years. The procedure is applied to a field case and results are discussed.

Accelerated testing for chloride threshold of reinforcing steel in concrete

Testing for the chloride threshold (also called critical chloride content) for corrosion initiation of steel in concrete has been found difficult and, at best, time consuming. Nevertheless, the chloride threshold is an important parameter in service life design of new structures and for evaluation of the remaining service life of existing structures. This paper reports on an accelerated test on mortar specimens that produces results within one week to a few weeks. It is based on accelerating chloride penetration by a mild electrical field while the steel potential is monitored. Upon corrosion initiation, specimens are sampled to obtain the chloride content that initiates corrosion. Results are reported of testing in CEM I (OPC) mortar on multiple specimens. Results for reference mortar are compared to specimens with application of a hydrophobic surface treatment. The results show that in reference CEM I mortar values for the critical threshold were obtained that agree well with previous experiments using the same method. This is taken as a validation of the method. The method is thought to be suitable for comparative chloride threshold studies of different binders, without or with corrosion inhibiting additions. Results for mortar with surface applied hydrophobic treatment, however, are unexpectedly low, which is taken to suggest that the method is not suitable for (e.g. surface treated) material with inhomogeneous electrolytic conduction.

25 Years of Experience with Cathodic Protection of Steel in Concrete in the Netherlands

This paper reviews 25 years of experience with cathodic protection of steel in concrete in The Netherlands. Three phases are distinguished from the late 1980s until present: pioneering, development and maturity. The application has grown considerably over these years, up to a total number of 150 structures with CP by the end of 2010. Technical and non-technical developments are highlighted and further growth is foreseen.