دورات هندسية

 

 

ليسمح لي الاعضاء بتقديم اول مشاركاتي ( corrosion )

النتائج 1 إلى 5 من 5
  1. [1]
    عبدالعزيز 1
    عبدالعزيز 1 غير متواجد حالياً

    عضو

    تاريخ التسجيل: May 2006
    المشاركات: 13
    Thumbs Up
    Received: 0
    Given: 0

    ليسمح لي الاعضاء بتقديم اول مشاركاتي ( corrosion )

    وهي تقرير بحث بسيط عن تاكل الخرسانة وطرق علاجها
    Introduction


    Reinforced concrete is the most multiform, economical and successful constraction

    material. It can be moulded to a variety of shapes and finishes. Usually it is durable

    and strong so it is a widely used for bridges, buildings, utility and marine construction,

    and underground structures such as tunnels and reinforced concrete pipe lines.

    There are still a large number of failures of concrete structures as a result of

    reinforcement corrosion. The corrosion of reinforcing steel in concrete is a major

    problem facing civil engineers and surveyors today.

    In this report, the types of cracks and method of repair will be definite.



    2 Basics of corrosion of reinforcement in concrete


    Some engineering says the concrete is alkaline that means it contains microscopic

    pores with high concentration of soluble calcium, sodium and potassium oxides (when

    Concrete is alkaline the PH number between 12-13) and if concrete is high alkaline

    that means the concrete contains high PH.

    The alkaline condition creates a passive layer, which is a dense and prevents the

    steel from corrosion, around the steel surface. Through the permeability of the

    concrete many different kinds of gases such as carbon dioxide, sulphr dioxide and

    calcium chloride will penetrate into concrete. As a result, the reinforcing steel

    will be rusted









    2.1 The corrosion processes


    The processes, which will destroy a passive layer, may be classified on the basis of

    whether they belong to the carbonation or the chloride attack. The first process is

    carbonation which is the result of the interaction of carbon dioxide gas in the

    atmosphere with the alkaline hydroxides in the concrete. This reaction occurs when

    there is a low cement ******* , high water cement ratio , poor curing of the concrete and

    a little concrete cover over the reinforcing steel.

    Carbonation is common in old structures but it is rare on modern highway

    bridges and other civil engineering structures where water cement ratio (W/C) are low,

    cement *******s are high with good compaction and curing. wet and dry cycling on the

    concrete and high of temperature will accelerate carbonation. As a result, coastal areas

    and the Middle East which the temperature excess of 40 degrees Celsius throughout

    the year.

    The second process chloride attack when the chloride ion attacks the passive layer

    but unlike carbonation, there is no overall drop in ph. According to John (1997) there

    are three sources of chlorides, use of sea water in the mix, contaminated aggregates and

    use of chemical materials in the mix.



    3 Corrosion damage

    Corrosion leads to many cracks in the reinforcement concrete and it will be do

    to remove the concrete cover. Which cause many problems that often result of

    corrosion which lead to significant problems that may cause a big collapse in many

    deterioration building particularly near the coast and underground facilities. Therefore

    engineers are now examining and analysing the concrete to determine the types of

    cracks to treat the situation based on the type of cracking.



    3.1 Type of cracks


    Cracking can be an important sign that reinforcement is rusting. Because the

    significance of each type of crack is different. Cracks can be classified according to its

    direction into tow types, longitudinal cracks which caused by corrosion of reinforcing

    steel and transverse cracks which caused by shrinkage, thermal contraction , structural

    overloading , movement of the foundation and accident damage.

    No all cracks result from rusting so some cracks such as transverse cracks do

    not normally indicate that the reinforcement is rusting but transverse cracks, which

    caused by structure overloading , need immediately action to keep the structure safe .




    4 repairing cracks


    Inspection and testing of the structural will defined the kind and cause of cracking.

    The repair cracks can be classified according to the type of the cracks. First, repair

    transverse cracks which caused by overload should all the overload are removed then

    should the cracks are injected with special materials to product reinforcement from

    weather facts . Second repair longitudinal cracks, which run directly over

    reinforcing bars and this cracks caused by corrosion so it will be leads to removing of

    cover concrete . It is a symptom of deterioration and it seems that they cannot be

    treated without removing and renewing the concrete cover and deterioration concrete

    with used special materials.


    4.1 Removing concrete cover


    The concrete cover, which is damage, must be cut away until the affected

    reinforcement and usually up to 50 mm beyond it . This distance depends on

    contaminated concrete because the chloride can spread from contaminated concrete

    into new concrete . As a result, all contaminated concrete are removed.

    Before removing any concrete should support the structure first by add the

    temporary support for the transfer of loads from section that will be treated.



    4.2 Cleaning reinforcement

    When the concrete cover has been removed the reinforcement can be inspected. Then

    the reinforcement will be cleaned by special material and must be removed all rust

    from the reinforcement . But according to John (1997), if rusting reduced cross-sectional

    area of reinforcement by more than 20 % extra reinforcement must be added.



    4.3 Replacing and curing concrete

    Before adding new concrete, the old one must be very clean so that the new

    paste can bond with it . And must be saturated so that water needed for curing is not

    sucked from the new concrete. And also the concrete must be contains polymer

    admixtures or other special materials to bond old and new concrete together.

    All types of cementations repair need curing by spray water for at least 3 days

    in temperate weather or 7 days under hot drying conditions.





    5 conclusion

    Although many older structures still not need repair, there are many other structures

    which built during last three decade are showing signs of deteriorations. In many causes

    early deterioration can be linked to chloride in the concrete. Such as in cold regions,while

    the engineers in this countries add more chloride to the mix because the chloride

    accelerate the time of sitting. And the States that suffer from severe weather conditions

    such as high temperature and high humidity .So should engineers have to deal

    with deteriorating buildings as soon as possible and to maintain modern structures with

    decrease the percent of a mount of chloride in the mix and decrease the permeability of

    concrete.

  2. [2]
    descovery_2000
    descovery_2000 غير متواجد حالياً
    عضو متميز


    تاريخ التسجيل: Jul 2006
    المشاركات: 496
    Thumbs Up
    Received: 11
    Given: 0
    بارك اللة فيك اخي العزيز على هذا المجهود الرائع وجعلة اللة في ميزان حسناتك
    مع تحيات

    0 Not allowed!



  3. [3]
    عبدالعزيز 1
    عبدالعزيز 1 غير متواجد حالياً
    عضو


    تاريخ التسجيل: May 2006
    المشاركات: 13
    Thumbs Up
    Received: 0
    Given: 0
    والشكر موصول لك اخي

    0 Not allowed!



  4. [4]
    AMSE
    AMSE غير متواجد حالياً
    عضو فعال


    تاريخ التسجيل: Sep 2006
    المشاركات: 146
    Thumbs Up
    Received: 0
    Given: 0
    نرجوا الاستمرار.....

    0 Not allowed!



  5. [5]
    zzz
    zzz غير متواجد حالياً
    عضو فعال


    تاريخ التسجيل: Nov 2006
    المشاركات: 66
    Thumbs Up
    Received: 0
    Given: 0
    شكراً لك على هذه المشاركة

    0 Not allowed!



  
الكلمات الدلالية لهذا الموضوع

عرض سحابة الكلمة الدلالية

RSS RSS 2.0 XML MAP HTML