Extent of corrosion damage for RC structures exposed to chloride-bearing environment

In industrialized countries, most of the reinforced concrete (RC) structures and infrastructures have more than 40 years, since they were built around 1960 − 1980, and were designed for a service life of 50 years. Consequently, in the next years, the number of structures and infrastructuresthat will need to be repaired will steeply increase. Several techniques, characterized by a different durability, environmental impact and economic impact, are available for the repair of a reinforced concrete structure damaged by the corrosion of reinforcement. To help the designers in the choice of the most suitable one, a preliminary assessment of the condition of the structure is essential, aimed at diagnosing the causes of deterioration, the extent of damage, i.e. the extent of corroding reinforcement, and its evolution in time. An approach, with a wide consensus, for the evaluation of the extent of corroding reinforcement is available for carbonation-induced corrosion, whilst it is still lacking forchloride-induced corrosion. In this paper two approaches for the evaluation of the extent of corroding reinforcement for a RC structure subject to chloride-induced corrosion are presented and compared, showing similar results. These approaches can be useful to properly plan a restoration intervention as well as to assess the reliability of the recently proposed model for service life design

Cathodic protection with localised galvanic anodes in slender carbonated concrete elements

A combined experimental and numerical investigation was carried out with the aim of determining whether few localised galvanic anodes per unit length could protect the reinforcement of slender carbonated concrete elements, exposed to atmospheric conditions, which could not be repaired with traditional methods. Initially, the cathodic behaviour of steel under galvanostatic polarisation was determined on small-size specimens obtained from a real element. A correlation of potential versus applied current was obtained. The current distribution in slender elements was then determined through finite elements simulations, considering various scenarios of carbonation and humidity. Results showed that, in spite of the high electrical resistivity of carbonated concrete, anodes with spacing of 0.45 m are enough to protect corroding reinforcement in most exposure conditions, even in thin parts of element. Estimated anode durations were of the order of several years or even decades; however, it was shown that also reinforcement in dry (carbonated or alkaline) concrete, which does not need to be protected, contributes to anode consumption. Although other aspects play a role on the performance of a cathodic protection system (such as the effectiveness of anode-encasing material and of electrical connection to reinforcement), the results obtained are supportive of a repair strategy based on the use of localised galvanic anodes and can be generalised to slender elements exposed to atmospheric conditions suffering carbonation induced corrosion

A study on the cement-based decorative materials in the San Fedele Church in Milan

Cement-based materials have been used since the 19th century for different decorative purposes, and a high levels of expertise has often reached in reproducing or restoring even quite elaborated stoneworks. An important example is the application of cement-based decorative materials on the façades of the San Fedele church in Milan. The church, built in the 16th century and characterized by the presence of pinkish-yellowish Angera stone on the façades, was subjected, especially in the 20th century, to several restoration works. Damaged decorative elements of the façades as well as portions of its structural elements were replaced or covered in the last century by â\u80\u9cstone imitating renderâ\u80\u9d, made with cementitious materials which imitate the original Angera stone. In this study, several samples of cement-based decorative materials, collected from different elements of the external façades of the Church, were characterized by several analytic techniques (thermogravimetric analysis, X-ray diffraction, scanning electron microscopy and IR analysis), in order to investigate both their microstructure and composition, how the chromatic aspect of the cementitious materials were obtained and their conservation state and to provide useful information for the possible reproduction of materials with comparable appearance to be used in a further restoration project. Results showed that the cement-based materials and decorations were obtained by the application of different layers of renders; in particular, the colour and texture of finishing layer were achieved by blending the binder with fine dolomite particles, probably obtained by grinding the Angera stone. This technique not only allowed an amazing reproduction of the original stone, but also resulted in a durable protection, since the cement-based decorative materials did not show any significant degradation phenomena in the polluted environment of the centre of Milan

Investigation on the effect of supplementary cementitious materials on the critical chloride threshold of steel in concrete

open3noThe critical chloride threshold is a key parameter in the service life design of reinforced concrete structures exposed to chloride-bearing environments. This paper investigates the role of concrete composition, and particularly the effect of supplementary cementing materials, on the chloride threshold. To simulate real exposure conditions, ponding tests were carried out on reinforced concrete specimens with bars in free corrosion conditions and corrosion initiation was detected through corrosion potential and corrosion rate measurements. After two and a half years, the ponding was followed by an ageing period and the initiation of corrosion was further detected with anodic potentiostatic polarisation tests. Results of the tests showed several limitations of the approach based on chloride penetration and monitoring of free corrosion parameters to investigate the chloride threshold. In spite of this, a possible role of natural pozzolan and coal fly ash additions in leading to higher values of the chloride threshold and ground limestone in promoting lower values of the chloride threshold could be observed.Lollini, Federica; Redaelli, Elena; Bertolini, LucaLollini, Federica; Redaelli, Elena; Bertolini, Luc

The Promise of Preventive Cancer Vaccines

Years of unsuccessful attempts at fighting established tumors with vaccines have taught us all that they are only able to truly impact patient survival when used in a preventive setting, as would normally be the case for traditional vaccines against infectious diseases. While true primary cancer prevention is still but a long-term goal, secondary and tertiary prevention are already in the clinic and providing encouraging results. A combination of immunopreventive cancer strategies and recently approved checkpoint inhibitors is a further promise of forthcoming successful cancer disease control, but prevention will require a considerable reduction of currently reported toxicities. These considerations summed with the increased understanding of tumor antigens allow space for an optimistic view of the future

The challenge of the performance-based approach for the design of reinforced concrete structures in chloride bearing environment

The performance-based approach, published by the International Federation for Structural Concrete (fib), was applied for the design of a RC element in a marine environment, with corrosion resistant reinforcement, to analyse the potentiality of the model as well as the possible reasons which limit its use. Results showed that the fib model allows to compare different solutions and to consider the benefits connected with the use of preventative measures. However the definition of reliable values for some input parameters, as the critical chloride threshold for corrosion resistant reinforcement, is demanded to the designer and this aspect clearly limits a widespread use

Corrosion of Steel in Concrete and Its Prevention in Aggressive Chloride-Bearing Environments

This keynote paper deals with the durability of reinforced concrete (RC) structures exposed to aggressive environments characterized by high concentration of chloride ions, namely, marine environments or the use of de-icing salts. The mechanism of chloride-induced corrosion of steel in concrete is introduced, and its influence on the service life of RC structures is analyzed. Factors affecting the time to corrosion initiation are described with regard to both concrete properties and environmental exposure conditions. Design approaches available for achieving durability targets associated with the design service life are analyzed, focusing on studies carried out by the authors in recent years at the mCD Concrete Durability lab of Politecnico di Milano, which were aimed at improving the protection provided to the steel bars by the concrete cover, investigating the advantages of using corrosion-resistant stainless steel bars and developing the electrochemical technique of cathodic prevention

Recycling of RAP (Reclaimed Asphalt Pavement) as aggregate for structural concrete: experimental study on physical and mechanical properties

The replacement of natural aggregate in concrete with artificial and/or recycled one has recently gained attention as meaningful strategy to reduce the environmental impact of structural concrete and promote circular economy principles. This study investigated the possibility to use Reclaimed Asphalt Pavement (RAP), in the “as received conditions”, as a partial or complete substitution of natural aggregate for structural concrete. RAP aggregate was firstly characterized in terms of grain size distribution, density, assessment of fines, chloride content, moisture content and water absorption. Subsequently, a total of twenty-four concrete mixes were designed, considering two cement types, two w/c ratios and several aggregate substitution percentages. For each mix, properties at the fresh and hardened state were investigated, such as workability, density and total open porosity, compressive strength, dynamic modulus of elasticity, and electrical resistivity. Results showed that RAP has a good potential to be used in reinforced concrete, provided that different water absorption and moisture content are considered in the mix design. RAP concrete was characterized by a lower density and increased total open porosity; however, an accurate tailoring of the concrete recipe could compensate the strength loss for several applications. Other properties, such as electrical resistivity and the relationship between dynamic modulus of elasticity and compressive strength did not result significantly altered by the presence of RAP

Sustainable Concrete with Seawater and Corrosion Resistant Reinforcement: Results of Monitoring of Corrosion Behaviour

The use of seawater for mixing concrete for reinforced concrete structures is prohibited, since it can promote steel corrosion. However, the use of seawater would contribute to decrease the environmental impact of concrete, in particular in those regions of the world where potable water is a precious resource. The project SEACON-INFRAVATION between University of Miami and Politecnico di Milano, with various industrial partners, aims at investigating the use of seawater for the construction of sustainable and durable reinforced concrete structures and infrastructures. Within the project, that included a vast campaign of laboratory tests, also two demo projects – one in Italy and another one in the US – were designed and executed with the aim of testing the technology on-site and allowing long-term monitoring of the durability behavior. In Italy, a reinforced concrete culvert was built next to A1 motorway, close to Piacenza. The culvert collects the waters coming from the roadway that, during winter season, is subjected to de-icing salts; in addition, it is unsheltered from the rain and exposed to wetting and drying cycles. The culvert is divided into different segments, and each segment is representative of a given scenario in terms of type of concrete and type of reinforcement. Besides a reference segment, with carbon steel and chloride-free concrete, some segments were built using seawater concrete in combination with corrosion-resistant reinforcement. Three types of corrosion-resistant reinforcement were considered: an austenitic grade of stainless steel (1.4311), a duplex grade of stainless steel (1.4362) and GFRP. The corrosion conditions of the metallic reinforcements are monitored by means of potential measurements. The electrical resistivity of concrete is also measured in time, and the evolution of carbonation and chloride penetration are periodically analysed on concrete cores taken from the culvert. This note presents the results that have been obtained during more than one year of monitoring of the corrosion conditions of the various types of reinforcement embedded in seawater concrete and compares them with results obtained in the laboratory