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

Web-Based Networked Music Performances via WebRTC: A Low-Latency PCM Audio Solution

Nowadays, widely used videoconferencing software has been diffused even further by the social distancing measures adopted during the SARS-CoV-2 pandemic. However, none of the Web-based solutions currently available support high-fidelity stereo audio streaming, which is a fundamental prerequisite for networked music applications. This is mainly because of the fact that the WebRTC RTCPeerConnection standard or Web-based audio streaming do not handle uncompressed audio formats. To overcome that limitation, an implementation of 16-bit pulse code modulation (PCM) stereo audio transmission on top of the WebRTC RTCDataChannel, leveraging Web Audio and AudioWorklets, is discussed. Results obtained with multiple configurations, browsers, and operating systems showthat the proposed approach outperforms theWebRTC RTCPeerConnection standard in terms of audio quality and latency, which in the authors' best case to date has been reduced to only 40 ms between twoMacBooks on a local area network

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

Effect of cracks on the service life of RC structures exposed to chlorides

To move towards a more sustainable concrete, the enhancement of its durability is strongly encouraged and, dealing in particular with reinforced concrete (RC), this mainly means to prevent the damage due to environmental actions, e.g. due to chloride-induced corrosion. Therefore, there is the need of models aimed at designing durable structures. Usually the service life design models consider concrete in uncracked condition. In real structures, however, several phenomena can generate cracks on concrete surface, leading to an acceleration of the corrosion of steel rebar. A number of studies have been recently carried out in order to evaluate the influence of cracks on reinforced concrete durability in chloride-contaminated environment, however the knowledge of the effect of cracks on the initiation and propagation periods is still lacking. Furthermore, few studies have considered additional protection strategies, such as the use of stainless steel rebar. In this work, experimental results are presented concerning the influence of cracks on the service life of reinforced concrete structures in order to evaluate if cracks lead to an earlier corrosion initiation induced by chlorides. Prismatic specimens, reinforced with carbon steel and 304L stainless steel bars, were longitudinally cracked and exposed to ponding with 3.5% NaCl solution. The monitoring of corrosion behaviour showed that when cracks reached the steel surface corrosion initiated immediately