Concrete plays an important role in construction industry and every year several billion tonnes of raw natural materials are consumed for its production. In the last years, also construction industry has become very attentive to environmental sustainability, focusing the research into alternative solutions to limit the consumption of raw materials. At this regard, seawater might be an alternative to fresh water. However, the main problem of using seawater to cast reinforced concrete is the presence of chlorides. Similarly, recycled concrete aggregates from demolition industry can be an alternative to the use of virgin aggregates; however, chloride contamination may hinder the use of recycled concrete aggregates. It is well known that chlorides can promote the initiation of corrosion on the bars embedded in concrete. In most instances, the use of seawater and salt-contaminated aggregates is prohibited by standards and codes due to associated risks of corrosion of steel reinforcements and limits on chlorides content in reinforced concrete are introduced. This leads to avoid the use of seawater or other potential constituents like recycled or contaminated aggregates. This thesis is part of a larger project called Seacon, that have involved several academic and industrial partners, and it was aimed at demonstrating the safe utilization of salt- contaminated raw materials, such as seawater, cement and contaminated aggregates (natural or recycled), when combined with corrosion-resistant reinforcements. Within the present study, besides the reference concrete, with virgin constituents, four different types of concrete were made, with raw materials contaminated with chlorides, ad seawater, recycled concrete aggregates and cement with a high content of chlorides. Both alkaline and carbonated specimens were considered. In the concretes four different grades of stainless steel (304L, 22-05, 23-04 and XM-28) and common carbon steel was embedded. Alkaline specimens were exposed to wet/dry cycles with a 3.5% NaCl solutions, whilst carbonated specimens to ponding with the same solutions. During the exposure the corrosion behaviour of the bars embedded in the different types of concrete were monitored. Results showed a lower corrosion resistance of stainless steel of grade XM-28 in comporison to the other stainless steel bars both when embedded in alkaline and carbonated concretes.
Il calcestruzzo svolge un ruolo importante nell’industria delle costruzioni e ogni anno miliardi di tonnellate di materie prime, come l’acqua dolce e le rocce naturali, vengono consumate per la sua produzione. Negli ultimi anni, anche l’industria delle costruzioni è diventata molto attenta alla sostenibilità ambientale, focalizzando la ricerca su soluzioni alternative che limitino proprio il consumo delle materie prime. L’acqua di mare potrebbe essere una valida alternativa a quella dolce. Il problema principale dell’uso di materiali alternativi, come l’acqua di mare, nella produzione di calcestruzzo è legato alla presenza di cloruri. Essi infatti possono causare la depassivazione delle armature in acciaio al carbonio e, di conseguenza, la loro corrosione. Questo è il motivo per il quale il contenuto di cloruri viene limitato dalle normative esistenti, portando così ad impedire l’uso di acqua di mare o di altri potenziali componenti del calcestruzzo come aggregati riciclati contaminati da cloruri. Il presente elaborato di tesi si colloca in un più ampio progetto denominato Seacon, al quale hanno partecipato diversi partners sia accademici che industriali, che riguarda la realizzazione di calcestruzzo sostenibile utilizzando materie prime contaminate da cloruri, come acqua di mare, cemento e aggregati contaminati (naturali e riciclati), in combinazione con armature resistenti alla corrosione. Nell’ambito del presente studio sono stati considerati, oltre al calcestruzzo di riferimento, quattro diversi tipi di calcestruzzo confezionati con materie prime contaminate da cloruri, quali acqua di mare, aggregati contaminati da cloruri e cemento contaminato da cloruri. Per ogni calcestruzzo sono stati considerati sia provini alcalini sia carbonatati. Nei calcestruzzi analizzati sono state inglobati quattro diversi tipi di acciaio inossidabile (304L, 22-05, 23-04 e XM-28) e il comune acciaio al carbonio al fine di studiare il loro comportamento a corrosione. I provini alcalini sono stati soggetti a cicli di asciutto/bagnato con una soluzione 3.5% NaCl, mentre quelli carbonatati a ponding continuo con la medesima soluzione. Durante l’esposizione è stato monitorato il comportamento a corrosione delle diverse barre di armatura inglobate nei diversi tipi di calcestruzzo. Le prove sperimentali hanno mostrato una minore resistenza alla penetrazione dei cloruri delle armature in acciaio inossidabile XM-28 rispetto alle altre armature in acciaio inossidabile, sia quando inglobati in calcestruzzi alcalini sia carbonatati.
Comportamento a corrosione di rinforzi in acciaio inossidabile inglobati in calcestruzzi con cloruri
VILLA, FEDERICO;NANA, MATTIA
2018/2019
Abstract
Concrete plays an important role in construction industry and every year several billion tonnes of raw natural materials are consumed for its production. In the last years, also construction industry has become very attentive to environmental sustainability, focusing the research into alternative solutions to limit the consumption of raw materials. At this regard, seawater might be an alternative to fresh water. However, the main problem of using seawater to cast reinforced concrete is the presence of chlorides. Similarly, recycled concrete aggregates from demolition industry can be an alternative to the use of virgin aggregates; however, chloride contamination may hinder the use of recycled concrete aggregates. It is well known that chlorides can promote the initiation of corrosion on the bars embedded in concrete. In most instances, the use of seawater and salt-contaminated aggregates is prohibited by standards and codes due to associated risks of corrosion of steel reinforcements and limits on chlorides content in reinforced concrete are introduced. This leads to avoid the use of seawater or other potential constituents like recycled or contaminated aggregates. This thesis is part of a larger project called Seacon, that have involved several academic and industrial partners, and it was aimed at demonstrating the safe utilization of salt- contaminated raw materials, such as seawater, cement and contaminated aggregates (natural or recycled), when combined with corrosion-resistant reinforcements. Within the present study, besides the reference concrete, with virgin constituents, four different types of concrete were made, with raw materials contaminated with chlorides, ad seawater, recycled concrete aggregates and cement with a high content of chlorides. Both alkaline and carbonated specimens were considered. In the concretes four different grades of stainless steel (304L, 22-05, 23-04 and XM-28) and common carbon steel was embedded. Alkaline specimens were exposed to wet/dry cycles with a 3.5% NaCl solutions, whilst carbonated specimens to ponding with the same solutions. During the exposure the corrosion behaviour of the bars embedded in the different types of concrete were monitored. Results showed a lower corrosion resistance of stainless steel of grade XM-28 in comporison to the other stainless steel bars both when embedded in alkaline and carbonated concretes.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/150791