The steel–concrete interface

Although the steel–concrete interface (SCI) is widely recognized to influence the durability of reinforced concrete, a systematic overview and detailed documentation of the various aspects of the SCI are lacking. In this paper, we compiled a comprehensive list of possible local characteristics at the SCI and reviewed available information regarding their properties as well as their occurrence in engineering structures and in the laboratory. Given the complexity of the SCI, we suggested a systematic approach to describe it in terms of local characteristics and their physical and chemical properties. It was found that the SCI exhibits significant spatial inhomogeneity along and around as well as perpendicular to the reinforcing steel. The SCI can differ strongly between different engineering structures and also between different members within a structure; particular differences are expected between structures built before and after the 1970/1980s. A single SCI representing all on-site conditions does not exist. Additionally, SCIs in common laboratory-made specimens exhibit significant differences compared to engineering structures. Thus, results from laboratory studies and from practical experience should be applied to engineering structures with caution. Finally, recommendations for further research are made

Cathodic protection of reinforcement in concrete – experience and development over 30 years

This paper presents developments over 30 years in the field of cathodic protection of steel reinforcement in concrete in The Netherlands and elsewhere. From the late 1980s major developments have been: application to large numbers of precast elements corroding due to mixed-in chloride with drilled in titanium anodes and conductive coatings; analysis of working life of systems and components and end-of-life considerations; application to prestressed structures; new anode types including galvanic systems with associated life and design considerations; numerical modelling and preventative applications. Presently, CP has become a fully accepted method of securing safety and serviceability of buildings and infrastructure. Major successes and lessons learned will be presented. Technical and non-technical developments are highlighted and some recent innovative CP systems are discussed

Cathodic protection of steel in concrete – experience and overview of 30 years application

This paper presents an overview of 30 years' experience with cathodic protection of steel in concrete in The Netherlands. Principles and practical aspects of CP and its design and installation are presented. Three phases have passed from the late 1980s until present: pioneering, development and maturity. In the first period CP was mainly applied to precast elements corroding due to mixedin chlorides. The parties involved worked together to draw up a Technical Guideline. In the second period, application to bridges came up, including post-tensioned structures, which was then innovative. Furthermore, galvanic anode systems were introduced. In the third period, CP became a fully accepted method of securing durability and safety. Renewed collaboration led to a database that allowed analysis of various aspects of CP system working life, including shortcomings in early systems. Major successes and lessons learned will be presented. Technical and non-technical developments are highlighted and some recent innovative CP components and systems are discussed

Forensic Investigation Concerning Inspection and Diagnosis of Condition of Water Storage Systems in the Gulf

Sandberg were asked to visit and comment on a sizeable project in the Gulf involving water storage towers, ground reservoirs and ancillary buildings in contemplation of legal proceedings. The structures had been built by a contractor but some problems had occurred in construction due to the high temperatures and issues with the concrete placement. The main issue that needed to be resolved was whether the problems that occurred were within acceptable limits for that type of construction and what repair recommendations were appropriate. The Client for the project had rejected the structures and was aiming for demolition and reconstruction which was a draconian step, given the level of problems – all of which were easily repairable. A significant amount of misdiagnosis had occurred with dark flecks on the surface of reservoirs being attributed to corrosion of reinforcement, for example, when in fact they were due to mould growth on the surface of the concrete and were literally surface deep only. There were also significant questions to be answered as to what constituted an acceptable level of leakage from water storage towers. An issue was also present with very severe corrosion to some reinforcing bars close to ground level in several ground reservoirs, despite the reinforcement being epoxy coated. It was considered highly likely that this damage was in fact due to stray current corrosion from current leakage from the cathodically protected water pipelines that delivered water to the facilities in question.This paper will discuss the inspection and diagnosis of the problems and the feasibility and need for appropriate repairs

6th International RILEM PhD Workshop

This book presents key advances in the modeling of reinforcement corrosion and concrete durability. It also examines various further aspects of reinforcement corrosion and concrete durability, striking a balance between modeling and testing. Particular attention is paid to innovative treatments for avoiding deterioration, and to methods for modeling performance in a real environment. Some basic aspects related to non-destructive testing techniques are also discussed. Deterioration-related topics addressed in the book include the basis for modeling alkali-silica reactions, chloride diffusion and the development of concrete microstructure; measurement-related topics include cathodic protection, polarization resistance and resistivity. A combined approach using the AFM technique and polarization measurements is examined, and the relation between cracking and corrosion and the treatment of concrete with hydrophobes or innovative products such as hydrotalcite is also discussed

Procedure for determining the remaining time to initiation of chloride induced reinforcement corrosion for existing concrete structures

For efficient asset management of reinforced concrete infrastructure, owners want to know when to expect corrosion in structures. At present, no widely accepted procedures for testing of existing structures for the remaining time to corrosion initiation are available. This paper describes such a procedure, based on the authors’ long-time experience. From about 20 years age, the concrete contains its mature response to actual environmental loads, e.g. chloride ingress. By measuring the mean and standard deviation of the actual cover depth, taking chloride profiles, assuming a few parameters and a simple, pragmatic model, the expected time to corrosion initiation for a particular test area can be predicted. Required numbers of cores and samples per core are given. Uncertainties are taken into account by subtracting a safety margin from the measured concrete cover depth. Results of six cores per test area are classified and interpretations are given. Because of large variability, the results are classified in three ranges of time to corrosion initiation: five years or less, five to fifteen years, or more than 15 years. The procedure has been approved by the relevant national Standards committees and was issued as a CUR Recommendation in 2018. It is illustrated based on a field case and the obtained results are discussed

Cathodic Protection Of Reinforcement In Concrete – Overview And Experience Over 30+ Years

This paper gives an overview of long term performance up to 30 years in the field of cathodic protection of steel reinforcement in concrete in The Netherlands, focusing on impressed current systems based on activated titanium anodes. Case studies are presented including applications to large numbers of precast elements corroding due to mixed-in chloride with drilled in titanium anodes, parking garages with titanium strips in cementitious overlays and industrial floors with titanium mesh in overlay. Based on observed failures and replacements, analysis of working life of various types of systems and components and end-of-life considerations are given. CP has become a fully accepted method of securing safety and serviceability of buildings and infrastructure that are prone to corrosion. Observations show that with activated titanium based systems, very long service lives can be obtained. The activated titanium itself keeps working well beyond the observed period of 30 years. Some other components have relatively higher failure rates. The repairs that were required in the cases discussed are dominated by failing anode-copper connections and to a minor extent power sources and potential sensors

Long term performance of reference electrodes for cathodic protection of steel in concrete

This paper will report on long term behaviour of potential sensors used in cathodic protection of steel reinforcement in concrete. Cathodic protection (CP) systems, both impressed current CP (ICCP) and galvanic CP (GCP), need regular testing to establish the quality of protection. In addition, ICCP may require adjustment of output voltage or current. Various types of potential sensors have been used in relatively large numbers, comprised of true reference electrodes (RE) based on silver/silver chloride or Mn/MnO2 and decay probes (DP) based on a.o. activated titanium. Failures may occur due to loss of contact, drying out or cable defects. Test methods for potential sensors are discussed. Monitoring of about one hundred CP systems with several thousands of potential sensors over more than ten years allows to analyse their performance and failures. It appears that limited numbers of potential sensors fail over time, but in some cases an insufficient number of working potential sensors are left to properly monitor a CP system or zone. It is recommended to install more potential sensors than strictly needed in order to allow for failures and to maintain testability and save the high cost of installing new potential sensors later

The effect of two types of modified Mg-Al hydrotalcites on reinforcement corrosion in cement mortar

Two modified Mg-Al hydrotalcites (MHTs), (MHT-pAB and MHT-NO2) were incorporated into mortar (with different w/c ratios) in two different ways: (1) as one of the mixing components in bulk mortar; (2) as part of cement paste coating of the reinforcing steel. Accelerated chloride migration, cyclic wetting-drying and diffusion tests were performed to investigate their effect on reinforcement corrosion. The results indicated that MHTs could be promising alternatives for preventing chloride-induced corrosion when an appropriate dosage is adopted and applied in a proper way, particularly, replacing 5% mass of cement by MHT-pAB in bulk mortar or as a coating of reinforcing steel (MHT-pAB/MHT-NO2 to replace 20% mass of cement). The effect of MHT-pAB on time-to-corrosion initiation (TTC) of reinforcing steel was estimated using the DuraCrete model. It was found that the incorporation of 5% MHT-pAB in bulk mortar led to a more than double TTC relative to reference mortar without MHTs