Luca Bertolini

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.

Steel corrosion and service life of reinforced concrete structures

This paper illustrates the mechanisms of corrosion of steel in concrete, and analyses its influence on the service life of reinforced concrete structures. Even though other types of corrosion are mentioned, attention is focused on the effects of carbonation and chloride penetration. Factors affecting the time to corrosion initiation are described with regards to both concrete properties and environmental exposure conditions. Propagation of corrosion and its consequences on the serviceability and performance of the structures are illustrated. Approaches for the design of durable reinforced concrete structures, as well as options available to increase the service life of structures exposed to aggressive environments, are described.

Cathodic protection and cathodic prevention in concrete: principles and applications*

The paper deals with the principles of cathodic protection for atmospherically exposed concrete structures, the various protecting effects induced by the cathodic polarization and tests and field experience results. The differences between the cathodic protection applied for controlling the corrosion rate of chloride contaminated co nstructions and that applied to improve the corrosion resistance of the reinforcement of new structures expected to become contaminated are then underlined and discussed. The more recent applications of cathodic protection on carbonated concrete are also illustrated. The operating conditions (voltage and current applied), the throwing power, the protection conditions which avoid the risk of hydrogen embrittlement in prestressed structures are also discussed. Examples of cathodic protection and of cathodic prevention are also presented.

Prevention of steel corrosion in concrete exposed to seawater with submerged sacrificial anodes

This paper presents the results of a study of the effectiveness of submerged sacrificial anodes in preventing the onset of pitting corrosion in the emerged part of marine piles. Experimental tests were carried out on reinforced concrete columns with steel embedded both in chloride free concrete and chloride contaminated concrete in order to compare the effects of sacrificial anodes on passive steel and on corroding steel. Results have shown, at least under the present testing conditions, that sacrificial anodes may be more effective in preventing corrosion initiation (i.e. in providing cathodic prevention) than in controlling ongoing pitting corrosion (i.e. in guaranteeing cathodic protection). Monitoring criteria for this type of prevention are also discussed.

Cathodic protection of new and old reinforced concrete structures

Current and potential distributions measured on concrete slabs and simulated by computer modelling are discussed in relation with the application of cathodic protection to new reinforced structures as a corrosion preventive method. The results show high penetration of cathodic protection over the depth of uncontaminated concrete, so that even a rebar relatively distant from the anode can be polarized, whereas the penetration is limited to the rebars near to the anode in chloride contaminated slabs with corroding rebars. The great throwing power and the wide range of protection potentials for uncorroding concrete structure enable safe application of the cathodic protection even to new prestressed structures.

Behaviour of Stainless Steel in Simulated Concrete Pore Solution

AbstractThe localised corrosion behaviour of austenitic, martensitic, and duplex stainless steels has been studied in several solutions simulating the liquid present in the pores of both alkaline and carbonated concrete in the presence of chloride ions. The work aimed to evaluate the suitability of these types of stainless steel as rebars in reinforced concrete structures exposed to very aggressive environments. Electrochemical tests have been performed in solutions with pH values in the range 7·6-13·9, chloride concentration in the range 0-10%, and temperatures of 20 and 40°C. The adverse effect of a decrese in pH on the critical chloride content is discussed, as a function of stainless steel composition and temperature, and the inhibitive effect of high carbonate/bicarbonate concentrations is also shown.

Simulation of chloride penetration in cement-based materials

Abstract Corrosion of reinforcement in concrete can initiate when chloride ion concentration in contact with steel bars exceeds a threshold value. It is then of crucial importance to describe Cl− penetration through models based on fundamental physico-chemical relationships avoiding the use of empirical parameters. Here, the multicomponent diffusional process was simulated by means of the percolation concepts. Furthermore, the adsorption of chloride within hardened cement paste was also considered. General relationships were derived to calculate binding coefficients and effective diffusivity of ions as a function of technological concrete parameters. The model explains experimental trends in a wide range of operating conditions (e.g., with and without superimposed current) both for cement paste and concrete.

LABORATORY AND FIELD EXPERIENCE ON THE USE OF STAINLESS STEEL TO IMPROVE DURABILITY OF REINFORCED CONCRETE

This paper reviews studies on the corrosion resistance of stainless steels in concrete exposed to chloride environments. Laboratory research and field applications of stainless steels of different compositions and microstructures are summarized. Fields of applicability for stainless steel grades used for reinforcing bars are drawn in terms of expected chloride contamination of concrete and carbonation. Requirements for stainless steel bars for reinforcing concrete are also discussed.

Corrosion Behavior of a Particulate Metal-Matrix Composite

Abstract The corrosion behavior of a particulate-reinforced metal-matrix composite (MMC) with an Al 6061-T6 (UNS A96061, Al-Mg-Si) matrix and 10 vol% alumina (Al2O3) particles was studied. The mate...

Steel Corrosion Monitoring in Normal and Total-lightweight Concretes Exposed to Chloride and Sulphate Solutions. Part I: Potential Measurements

The paper reports on long time testing of reinforcement corrosion in normal and total-lightweight concretes exposed to cycles consisting of 4 phases: chloride salt fog, drying, sulphate solution immersion, drying. Potential monitoring evidenced a passive condition for all reinforcements embedded in normalweight concretes. The initiation of the corrosive attack in total-lightweight concretes could not be evidenced, although low potential values were found on corroding reinforcements.