Reinforced concrete is a versatile, economical and successful construction material: "the combination of high compression strength of concrete and high tensile properties of reinforcing steel gives an ideal composite material which offers, compared to other materials, a wide range of applications in structural engineering” [1]. Worldwide, more concrete is used than any other man made material: every year, the global consumption of cement is on the rise; it was estimated a global market consumption of about 50 billion tons of cement in 2017 [2]. The big demand of reinforced concrete in construction engineering stays on its ability to be durable and strong, with high performances throughout its service life. However, in some cases it does not act adequately due to poor design, poor construction or inadequate material selection to withstand the environmental conditions to which it is subjected [3]. An affected or limited state of serviceability is thus consequent. The corrosion of the steel reinforcements is globally the major problem of premature end of infrastructure service life and its study gained considerable importance at the end of 1980s [4]. The economic loss and damage caused by the corrosion of steel in concrete makes it the largest infrastructure problem facing industrialized countries. Billions of dollars are spent every year in protecting and replacing corrosion damages [3]. The highly alkaline pore solution (pH around 13), formed during cement hydration, allowed to protect the steel reinforcements embedded inside concrete, promoting their passivation. Nevertheless, the passivity condition can decay (i.e. depassivation effect) with consequent Reinforced concrete is a versatile, economical and successful construction material: “the combination of high compression strength of concrete and high tensile properties of reinforcing steel gives an ideal composite material which offers, compared to other materials, a wide range of applications in structural engineering” [1]. Worldwide, more concrete is used than any other man made material: every year, the global consumption of cement is on the rise; it was estimated a global market consumption of about 50 billion tons of cement in 2017 [2]. The big demand of reinforced concrete in construction engineering stays on its ability to be durable and strong, with high performances throughout its service life. However, in some cases it does not act adequately due to poor design, poor construction or inadequate material selection to withstand the environmental conditions to which it is subjected [3]. An affected or limited state of serviceability is thus consequent. The corrosion of the steel reinforcements is globally the major problem of premature end of infrastructure service life and its study gained considerable importance at the end of 1980s [4]. The economic loss and damage caused by the corrosion of steel in concrete makes it the largest infrastructure problem facing industrialized countries. Billions of dollars are spent every year in protecting and replacing corrosion damages [3]. The highly alkaline pore solution (pH around 13), formed during cement hydration, allowed to protect the steel reinforcements embedded inside concrete, promoting their passivation. Nevertheless, the passivity condition can decay (i.e. depassivation effect) with consequent breakdown of the protecting oxide layer on the rebars surface. The two main reasons are attributed to the presence of chlorides at the carbon steel surface, in a content higher than a critical threshold, and to the concrete pore solution pH reduction, generated by the reaction with atmospheric carbon dioxide (CO2). Once corrosion has initiated, the reduction of reinforcements cross section and the concrete cover cracking and spalling arise, leading to a loss of performance of the structure. Measures to prevent the reinforcements damage or to keep it within tolerable limits could be necessary during the design lifetime of the structure. Among these methods, external coatings have been widely applied for preventing corrosion in many and varied technical fields for years, due to their low costs and easy handling. Indeed, they can delay the corrosion initiation time and reduce its propagation rate. The aim of the following experimental thesis is to study the effects of a hydrophobic coating in the form of a gel to be applied on the surface of reinforced concrete structures for the contrast of reinforcement corrosion. In particular, its effect on specimens exposed to atmosphere and against corrosion due to chlorides were evaluated. The first two chapter illustrates the main types of degradation of reinforced concrete, the prevention and protection from degradation and describes the surface treatments, in particular the hydrophobic treatments. The third chapter describes the experimental methodology adopted in the present study to identify the effects of the hydrophobic treatment in the form of a gel. The fourth chapter reported the results obtained and their discussion. Finally, the conclusions of the work carried out are presented.
Il cemento armato è un materiale da costruzione versatile, economico e di successo: “la combinazione di un'elevata resistenza alla compressione del calcestruzzo e delle proprietà ad alta resistenza dell'acciaio di rinforzo fornisce un materiale composito ideale che offre, rispetto ad altri materiali, un’ampia gamma di applicazioni nell'ingegneria strutturale” [1]. Nel mondo viene utilizzato più calcestruzzo di qualsiasi altro materiale artificiale: ogni anno il consumo globale di cemento è in aumento; è stato stimato un consumo del mercato globale di circa 50 miliardi di tonnellate di cemento nel 2017 [2]. La grande richiesta di cemento armato nell'ingegneria edile sta nella sua capacità di essere durevole e forte, con prestazioni elevate per tutta la sua vita utile. Tuttavia, in alcuni casi non agisce adeguatamente a causa di cattiva progettazione, cattiva costruzione o inadeguata selezione dei materiali per resistere alle condizioni ambientali a cui è sottoposto [3]. Ne consegue uno stato di servizio limitato o compromesso. La corrosione delle armature in acciaio è globalmente il problema principale della fine prematura della vita utile delle infrastrutture e il suo studio ha acquisito notevole importanza alla fine degli anni ‘80 [4]. La perdita economica e i danni causati dalla corrosione dell'acciaio nel calcestruzzo ne fanno il più grande problema infrastrutturale per i paesi industrializzati. Miliardi di dollari vengono spesi ogni anno per proteggere e sostituire i danni causati dalla corrosione [3]. La soluzione porosa altamente alcalina (pH intorno a 13), formatasi durante l'idratazione del cemento, ha permesso di proteggere le armature in acciaio annegate all'interno del calcestruzzo, favorendone la passivazione. Tuttavia, la condizione di passività può decadere (cioè effetto di depassivazione) con conseguente rottura dello strato di ossido protettivo sulla superficie delle armature. I due motivi principali sono attribuiti alla presenza di cloruri sulla superficie dell'acciaio al carbonio, in un contenuto superiore ad una soglia critica, e alla riduzione del pH della soluzione porosa del calcestruzzo, generata dalla reazione con l'anidride carbonica atmosferica (CO2). Una volta che la corrosione è iniziata, si verificano la riduzione della sezione trasversale delle armature e la rottura e la scheggiatura del copriferro in calcestruzzo, con conseguente perdita di prestazioni della struttura. Misure per prevenire il danneggiamento delle armature o per mantenerle entro limiti tollerabili potrebbero essere necessarie durante la vita di progetto della struttura. Tra questi metodi, i rivestimenti esterni sono stati ampiamente applicati per anni per prevenire la corrosione in molti e svariati campi tecnici, grazie ai loro bassi costi e alla facile manipolazione. In effetti, possono ritardare il tempo di inizio della corrosione e ridurre la sua velocità di propagazione. Scopo della seguente tesi sperimentale è studiare gli effetti di un rivestimento idrofobo sotto forma di gel da applicare sulla superficie di strutture in cemento armato per il contrasto della corrosione delle armature. In particolare, è stato valutato il suo effetto su campioni esposti all'atmosfera e contro la corrosione dovuta ai cloruri. I primi due capitoli illustrano le principali tipologie di degrado del cemento armato, la prevenzione e protezione dal degrado e descrivono i trattamenti superficiali, in particolare i trattamenti idrofobici. Il terzo capitolo descrive la metodologia sperimentale adottata nel presente studio per identificare gli effetti del trattamento idrofobico sotto forma di gel. Il quarto capitolo riportava i risultati ottenuti e la loro discussione. Infine, vengono presentate le conclusioni del lavoro svolto.
The effect of hydrophobic treatment on concrete durability
Singh, Akashdeep
2019/2020
Abstract
Reinforced concrete is a versatile, economical and successful construction material: "the combination of high compression strength of concrete and high tensile properties of reinforcing steel gives an ideal composite material which offers, compared to other materials, a wide range of applications in structural engineering” [1]. Worldwide, more concrete is used than any other man made material: every year, the global consumption of cement is on the rise; it was estimated a global market consumption of about 50 billion tons of cement in 2017 [2]. The big demand of reinforced concrete in construction engineering stays on its ability to be durable and strong, with high performances throughout its service life. However, in some cases it does not act adequately due to poor design, poor construction or inadequate material selection to withstand the environmental conditions to which it is subjected [3]. An affected or limited state of serviceability is thus consequent. The corrosion of the steel reinforcements is globally the major problem of premature end of infrastructure service life and its study gained considerable importance at the end of 1980s [4]. The economic loss and damage caused by the corrosion of steel in concrete makes it the largest infrastructure problem facing industrialized countries. Billions of dollars are spent every year in protecting and replacing corrosion damages [3]. The highly alkaline pore solution (pH around 13), formed during cement hydration, allowed to protect the steel reinforcements embedded inside concrete, promoting their passivation. Nevertheless, the passivity condition can decay (i.e. depassivation effect) with consequent Reinforced concrete is a versatile, economical and successful construction material: “the combination of high compression strength of concrete and high tensile properties of reinforcing steel gives an ideal composite material which offers, compared to other materials, a wide range of applications in structural engineering” [1]. Worldwide, more concrete is used than any other man made material: every year, the global consumption of cement is on the rise; it was estimated a global market consumption of about 50 billion tons of cement in 2017 [2]. The big demand of reinforced concrete in construction engineering stays on its ability to be durable and strong, with high performances throughout its service life. However, in some cases it does not act adequately due to poor design, poor construction or inadequate material selection to withstand the environmental conditions to which it is subjected [3]. An affected or limited state of serviceability is thus consequent. The corrosion of the steel reinforcements is globally the major problem of premature end of infrastructure service life and its study gained considerable importance at the end of 1980s [4]. The economic loss and damage caused by the corrosion of steel in concrete makes it the largest infrastructure problem facing industrialized countries. Billions of dollars are spent every year in protecting and replacing corrosion damages [3]. The highly alkaline pore solution (pH around 13), formed during cement hydration, allowed to protect the steel reinforcements embedded inside concrete, promoting their passivation. Nevertheless, the passivity condition can decay (i.e. depassivation effect) with consequent breakdown of the protecting oxide layer on the rebars surface. The two main reasons are attributed to the presence of chlorides at the carbon steel surface, in a content higher than a critical threshold, and to the concrete pore solution pH reduction, generated by the reaction with atmospheric carbon dioxide (CO2). Once corrosion has initiated, the reduction of reinforcements cross section and the concrete cover cracking and spalling arise, leading to a loss of performance of the structure. Measures to prevent the reinforcements damage or to keep it within tolerable limits could be necessary during the design lifetime of the structure. Among these methods, external coatings have been widely applied for preventing corrosion in many and varied technical fields for years, due to their low costs and easy handling. Indeed, they can delay the corrosion initiation time and reduce its propagation rate. The aim of the following experimental thesis is to study the effects of a hydrophobic coating in the form of a gel to be applied on the surface of reinforced concrete structures for the contrast of reinforcement corrosion. In particular, its effect on specimens exposed to atmosphere and against corrosion due to chlorides were evaluated. The first two chapter illustrates the main types of degradation of reinforced concrete, the prevention and protection from degradation and describes the surface treatments, in particular the hydrophobic treatments. The third chapter describes the experimental methodology adopted in the present study to identify the effects of the hydrophobic treatment in the form of a gel. The fourth chapter reported the results obtained and their discussion. Finally, the conclusions of the work carried out are presented.| File | Dimensione | Formato | |
|---|---|---|---|
|
2020_10_SINGH.pdf
non accessibile
Descrizione: The effect of hydrophobic treatment on concrete durability
Dimensione
2.56 MB
Formato
Adobe PDF
|
2.56 MB | Adobe PDF | Visualizza/Apri |
I documenti in POLITesi sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
https://hdl.handle.net/10589/166363