Deterioro del Concreto

00:15:54
https://www.youtube.com/watch?v=XiltW6okYU4

Zusammenfassung

TLDRIl video descrive quanto il rapporto acqua-cemento influisce sulla qualità e durabilità del calcestruzzo utilizzato nelle costruzioni. Ogni anno, milioni di metri cubi di calcestruzzo sono prodotti, essendo il materiale da costruzione più usato. Il video spiega come l'idratazione del cemento produce fibre che determinano le caratteristiche meccaniche del calcestruzzo. Aggiungere troppa acqua porta a una miscela porosa di bassa resistenza, vulnerabile a agenti chimici come biossido di carbonio e cloruri che corrodono il calcestruzzo e le barre d'acciaio al suo interno. I solfati possono causare espansione e fessurazione. Processi naturali come il gelo e disgelo inducano stress che portano ad ulteriori danni. Si raccomanda l'uso di additivi chimici per ottenere un calcestruzzo compatto e durabile, migliorando la vita utile delle strutture di cemento armato. Le norme europee e americane forniscono linee guida sul rapporto acqua-cemento nei diversi ambienti.

Mitbringsel

  • 🔍 La qualità del calcestruzzo dipende dal giusto rapporto acqua-cemento.
  • 🧱 Il cemento è l'elemento legante nel calcestruzzo, costituito da water e polvere di cemento.
  • 🧪 Troppa acqua compromette la resistenza del calcestruzzo rendendolo poroso.
  • 🌬️ Agent di carbonatazione possono alterare le barre d'acciaio nel calcestruzzo.
  • 🔗 I cloruri causano corrosione localizzata delle barre di rinforzo.
  • 🧊 Cicli di gelo e disgelo danneggiano il calcestruzzo.
  • 🌊 Solfati e cloruri in ambiente marino sono particolarmente dannosi.
  • 🛡️ Additivi chimici moderni possono migliorare la durabilità del calcestruzzo.
  • 📏 Normative europee e americane guidano il rapporto acqua-cemento.
  • ⌛ La longevità delle strutture dipende dalla gestione del rapporto acqua-cemento.

Zeitleiste

  • 00:00:00 - 00:05:00

    Il video introduce il cemento come uno dei materiali da costruzione più utilizzati al mondo, particolarmente in Italia con 120 milioni di metri cubi prodotti ogni anno. Il cemento è una miscela di pietre e una pasta di cemento che le unisce. La qualità del cemento dipende dal rapporto acqua-cemento: troppo acqua lo rende poroso e debole, mentre meno acqua lo rende più forte e durevole.

  • 00:05:00 - 00:10:00

    La carbonatazione è uno dei processi di deterioramento più comuni per il cemento, causato dalla penetrazione dell'anidride carbonica che riduce il pH, esponendo le barre d'acciaio all'ossidazione. Anche i cloruri possono causare gravi danni a cemento e barre di rinforzo, inducendo corrosione localizzata e frammentazioni: il cloruro di calcio trasforma l'idrossido di calcio in ossicloruro, mentre il cloruro di sodio è dannoso per cementi con aggregati reattivi.

  • 00:10:00 - 00:15:54

    I solfati e le escursioni termiche possono drammaticamente deteriorare il cemento. I solfati reagiscono con l'idrossido di calcio creando gesso e successivamente ettringite, che causa espansione e danni alla struttura. Le variazioni termiche, particolarmente il gelo, causano un'espansione deleteria dell'acqua all'interno del cemento. Gli strumenti moderni aiutano a diagnosticare questi problemi, e gli additivi chimici possono migliorare la resistenza e la durabilità del cemento, riducendo il rapporto acqua-cemento mantenendo una buona lavorabilità.

Mind Map

Video-Fragen und Antworten

  • Qual è il componente legante nel calcestruzzo?

    Il componente legante nel calcestruzzo è la pasta di cemento, che è una miscela di acqua e cemento.

  • Cosa succede se si aggiunge troppa acqua al cemento?

    Se si aggiunge troppa acqua al cemento, il materiale diventa più poroso e meno resistente.

  • Qual è l'effetto della carbonatazione sul calcestruzzo?

    La carbonatazione riduce il pH e altera la protezione delle barre di rinforzo d'acciaio, causando ruggine e danni strutturali.

  • Come si formano i prodotti della reazione di idratazione del cemento?

    I prodotti si formano come fibre interconnesse che determinano le proprietà meccaniche del calcestruzzo.

  • Qual è l'effetto dei cloruri sul calcestruzzo?

    I cloruri possono causare corrosione localizzata delle barre di rinforzo in acciaio e danni alla pasta di cemento.

  • Cosa causa il ciclo di gelo e disgelo nel calcestruzzo?

    Il ciclo di gelo e disgelo può causare stress interno nella struttura, portando a deterioramento.

  • Quali agenti chimici in mare sono dannosi per il calcestruzzo?

    Il cloruro di sodio e i solfati presenti nell'acqua di mare sono molto dannosi per il calcestruzzo.

  • Come si può prevenire il deterioramento del calcestruzzo?

    Utilizzando additivi chimici per mantenere un basso rapporto acqua-cemento pur mantenendo la lavorabilità.

  • Che tipo di danno causa il solfato nel calcestruzzo?

    Il solfato reagisce chimicamente causando un aumento di volume e un effetto distruttivo sulla struttura.

  • Perché è importante mantenere un basso rapporto acqua-cemento nel calcestruzzo?

    Un basso rapporto acqua-cemento produce un calcestruzzo più resistente, impermeabile e durabile.

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    concrete is one of the most important
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    construction materials used today at
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    least as regards quantity it has been
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    calculated that every year over ,000
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    million cubic M of concrete are produced
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    in the
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    world in Italy alone 120 million cubic M
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    are produced every year which is
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    equivalent to about 2 cubic met of
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    concrete per year per
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    [Music]
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    person concrete is a mixture of loose
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    Stones held together by a cement paste
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    which acts as a binding glue
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    [Music]
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    the stones are called Aggregates and can
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    be as fine as sand or as large as
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    gravel whereas The Binding component the
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    cement paste is a mixture of water and
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    cement now let's see in detail what
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    happens when water is added to
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    cement mixing Portland cement in the
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    form of very fine grains with water a
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    hydration reaction
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    occurs the products of this reaction are
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    calcium hydrosilicates of a mainly
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    fibrous nature hydrous calcium
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    illuminates and calcium
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    hydroxide during the hydration of the
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    cement the calcium hydrosilicates
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    develop in the form of interlacing
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    fibers thus determining the mechanical
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    properties and the durability of
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    [Music]
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    concrete when we add too much water it
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    gets between the cement grains and keeps
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    them further
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    apart the fibers are less tightly
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    interlaced and the whole material is
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    more
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    porous the result is a cement paste with
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    low strength porous and permeable to
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    water as well as to the aggressive
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    chemical agents to be found in
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    [Music]
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    water on the other hand if we reduce the
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    amount of water in the mixture the
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    cement grains come closer to one another
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    a more dense and compact interlacing of
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    fibers is the result
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    therefore the formation of a less porous
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    micr structure of the cement paste is
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    obtained by lowering the water cement
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    ratio this is how concrete with high
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    strength should be made waterproof and
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    therefore with excellent
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    durability using as little water as
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    possible in the cement paste is main
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    Rule and the more aggressive the
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    environment in which the construction is
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    built the lower the water cement ratio
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    to be
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    used when this rule is not observed
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    deterioration of the concrete structure
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    is inevitable with the passing of
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    time the latest statistics show that the
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    most widespread cases of deterioration
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    are due to the chemical effects of
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    carbon dioxide in the
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    air in these cases the structure of the
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    concrete is in very bad
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    condition in many points the concrete
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    cover has been forced out and the rebars
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    can be
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    seen the aggressive agent is carbon
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    [Music]
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    dioxide the calcium hydroxide present in
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    the cement mixture creates inside the
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    cement Mass a basic environment with a
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    pH generally above
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    13 in these conditions the steel bar is
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    covered with a stable and compact rust
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    layer which protects it from corrosion
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    this condition of passivity however is
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    altered through the effect of
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    carbonation when the carbon dioxide
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    present in the air penetrates into the
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    concrete it reacts with calcium
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    hydroxide and neutralizes
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    it there is a lowering of the basicity
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    of the
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    environment and with a pH below 11 the
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    steel reinforcing bars inside the
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    carbonated concrete are no longer
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    protected from the outside water and
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    oxygen also penetrate thus increasing
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    the rusting reaction of the reinforcing
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    bars the rust which forms occupies a
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    volume of about six times more than the
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    metal from which it
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    originated and so causes the cracking
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    and expulsion of the concrete cover
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    let's imagine we can blow up this
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    picture and get a better look at the
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    causes of the
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    deterioration as you can see in this
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    case carbonation has caused considerable
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    damage causing the cover to come away
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    completely cases of carbonation are very
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    common and almost always associate with
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    the use of lowquality concrete porous
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    and thus easily attacked by the carbon
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    dioxide water and the oxygen in the
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    air this phenomenon is completely absent
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    in good Quality Concrete which is
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    Compact and made with a water cement
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    ratio of less than
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    0.6 even more dangerous for concrete is
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    the effect of chlorides
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    chloride in the form of calcium or
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    sodium chloride is used frequently to
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    melt
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    ice these chlorides can do serious
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    damage to reinforcing
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    bars the thin rust layer which encloses
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    and protects the steel bars remains
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    stable and compact as long as the amount
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    of chloride remains below 0.2 0.3% by
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    weight of
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    cement if however the percentage of
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    chlorides increases the rust layer
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    becomes porous and no longer guarantees
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    any protection to the steel reinforcing
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    buz the metal undergoes localized
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    pitting corrosion which dangerously
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    reduces its
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    diameter apart from the corrosive action
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    on the steel rebar
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    these salts can also damage the
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    concrete calcium chloride especially
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    attacks the cement
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    paste what it does is react with the
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    calcium hydroxide present in the cement
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    Matrix forming calcium oxychloride
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    hydrate and this reaction produces an
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    expansion it causes swelling cracking
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    and
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    sping Ive action of calcium chloride is
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    exacerbated at low
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    temperatures sodium chloride on the
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    other hand is an aggressive agent that
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    is damaging only to concrete with alkal
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    reactive Aggregates that is capable of
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    reacting with sodium and
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    potassium sodium
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    sodium already present in cement or
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    penetrating from the outside as we can
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    see in the cartoon reacts in particular
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    with certain silus
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    Aggregates in this case too there is
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    expansion and cracking above all in
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    unprotected structures or those exposed
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    to
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    moisture this last kind of phenomenon
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    apart from Road works on roads and
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    motorways is also to be found in
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    concrete structures in direct contact
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    with seawater which also contains sodium
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    chloride the sea is also the place where
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    we find apart from sodium chloride the
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    most feared of aggressive agents for
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    concrete sulfate which is also to be
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    found in certain soils or natural
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    Waters sufate rea acts chemically with
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    the calcium hydroxide present in the
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    concrete mass and transforms it into the
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    more voluminous
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    gypsum this product reacts in its turn
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    with the hydrous calcium illuminates
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    here shown as
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    cah transforming it into
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    anite this transformation also results
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    in an increase in volume in the material
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    with a disastrous effect on the
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    [Music]
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    structure in particular
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    in certain very special environmental
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    conditions the effect of the sulfate on
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    the concrete can be even more
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    [Music]
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    dramatic at a temperature of between 0
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    and 5° C with relative humidity of over
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    95% and in the presence of carbon
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    dioxide the sulfate combines with
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    calcium hydroxide and transforms it into
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    [Music]
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    gypsum the gypsum in its turn react with
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    the calcium silicate hydrates here
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    indicated as
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    CSH and the calcium carbonate
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    ca3 producing
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    [Music]
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    thorite thorite breaks down concrete
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    changing its internal characteristics
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    completely
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    observation with a scanning electron
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    microscope shows that the cement paste
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    has been completely broken
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    down natural thermal excursions can also
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    cause deterioration of
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    concrete the most serious results are
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    seen in freezing thawing
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    Cycles when the concete is
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    [Music]
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    wet as the liquid water contained in the
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    concrete mass is transformed into ice it
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    expands and its volume increases by
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    about
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    9% the increase in volume causes
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    internal
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    stress when this internal stress is
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    repeated cyclically the effect on the
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    structure is
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    [Music]
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    disastrous this is the kind of
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    deterioration which affects concrete
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    constructions exposed to very low
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    [Music]
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    temperatures the instruments which we
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    have today at our disposal to analyze
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    these
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    phenomena the scanning electron
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    microscope x-ray defract meter
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    thermoanalysis the spectrograph and
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    chromatograph allow a precise
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    [Music]
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    diagnosis we have seen how the main
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    cause of all kinds of deterioration of
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    concrete is the excessive water cement
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    ratio used to make concrete placement
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    easier more water means better
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    workability of the con
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    and so greater facility in
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    placement this greater facility however
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    is paid for later in terms of durability
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    of concrete
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    structures the European Standard Norms
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    EnV 206 as well as the American ACI
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    recommendations indicate in each case
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    the water cement ratio not to be
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    [Music]
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    exceeded there exist chemical ad
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    mixtures today which make it possible to
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    produce concrete with a very low water
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    cement ratio while maintaining excellent
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    workability with these ad mixtures all
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    the kinds of deterioration that we have
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    examined can be
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    prevented add mixtures for the
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    production of compact concrete
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    waterproof and therefore resistant to
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    aggressive agents studied to lengthen
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    the service life of reinforced concrete
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    structure is
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    [Laughter]
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    d
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    a
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Tags
  • calcestruzzo
  • cemento
  • rapporto acqua-cemento
  • carbonatazione
  • corrosione
  • cloruri
  • solfati
  • deterioramento
  • durabilità
  • additivi chimici