Beton yollarda korozyon
Corrosion in concrete pavements
Yazar: SALİH İLTEKİN
Danışman: PROF. DR. ABDULLAH HİLMİ LAV
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / İnşaat Mühendisliği Ana Bilim Dalı / Ulaştırma Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2017
Konu: Ulaşım = Transportation ; İnşaat Mühendisliği = Civil Engineering

Özet:
İnsanlar için yer değiştirme her dönemde önemli bir eylem olmuştur. Önceleri sadece yayalar daha sonraları hayvanlarla çekilen basit taşıtlar sadece ulaştırmanın birer ögesiyken günümüzde motorlu ve motorsuz taşıtlar ve bunların sürücüleri ve yayalar karayolu ulaşımının birer ögeleridir. 
Her geçen gün gelişmekte olan karayolu ulaştırmacılığında karayolları esnek veya rijit yapılabilmektedir. Esnek kaplamada kullanılan asfaltın hem pahalı oluşu hem sıcaklığa karşı çok duyarlı oluşu hem de çevreye olan zararı betona göre daha fazla olduğundan rijit kaplamalar tercih edilmeye başlamıştır. Özellikle yoğun ve ağır taşıt trafiğinin olduğu noktalarda beton yollar tercih edilir. ABD, Avustralya, Belçika, Fransa, Almanya, Avusturya ve Hindistan gibi ülkeler beton yolların yoğun olarak kullanıldığı ülkelerdir. Bu ülkelerde beton yolların performansının gayet yüksek olduğu gözlenmiştir. 
Beton yolların asfalt yollara göre çeşitli üstünlükleri vardır. Özellikle beton yolların daha uzun ömürlü ve ekonomik oluşu beton yolu asfalt yola göre daha cazip kılmaktadır. Trafiğe açılış ve onarım süresinin uzun olması beton yolun dezavantajlarından olup beton yol yapımının ciddi bir altyapı ve ekipman istediğinin göstergesidir.
Beton yollar asfalt yollar gibi dökülemediği için enine ve boyuna derzler bırakılır. Bu derzlere ise yük aktarımı için demir donatı yerleştirilir. Daha sonra derzlere yapılan mühürleme işlemi çok sağlıklı olmalıdır. İşte tam da bu noktada bu çalışmada anlatılan beton yollarda oluşabilecek korozyon devreye girmektedir. Beton yollardaki donatı korozyonu bu derzlerde yer alan donatılarda meydana gelmektedir. Derzlerdeki mühürlemenin zamanla yıpranması veya ilk yapım aşamasında kalitesiz uygulama yapılması bu noktalardaki demirlerin direkt atmosferle temas etmesine neden olur. Bu safhada ise korozyon devreye girer.
Beton yolda incelenen korozyona iklim koşulları, betonun kritik özellikleri ve beton yolun yapıldığı yerin konumunun sebep olduğu gözlenmiştir. Yolun inşa safhasında veya daha sonrasında betonun özelliklerinden dolayı betonda meydana gelebilecek çatlama, kırılma, hidratasyon malzemesi oluşması gibi olumsuzluklar beton yolda korozyon oluşmasında önemli bir etkiye sahiptir. 
Korozyona etki eden en önemli sebeplerden biri de iklim özellikleridir. Derzlerdeki demir donatıların direkt olarak atmosferle temas edebilme olasılığı korozyonu etkiler. Soğuk bölgelerde özellikle kar yağışının olduğu ve karla kaplı gün sayısının fazla olduğu yerlerde buz çözücü olarak kullanılan tuzlar betona etki ederek dolaylı yoldan, derz bölgesindeki donatı demirlerine etki ederek direkt olarak korozyona sebep olabilir. Tuzun bileşenlerine ayrılmasıyla klorür iyonları demire etki ederek korozyon oluşumunu başlatır. Ayrıca kar suyu da korozyon için tehlikeli maddelerden biridir. Sıcak bölgelerde ise nem etkisi korozyona sebep olan önemli etmenlerden biridir. Gece beton yol yüzeyinde kalan su buharı damlacıkları gündüz yüksek sıcaklık etkisiyle kuruyarak hem betona hem de donatıya zarar verir. Özellikle denize yakın konumda ve sıcak bir bölgede bu olaydan bahsediyorsak yüksek klorür içeren bu su buharı damlacıkları gündüz klor iyonlarını yüzeyde bırakarak donatı korozyonunu oldukça hızlandırır. Konum olarak deniz kenarına yakın yerlere yapılan beton yollarda yağmur etkisi ile ıslanma, dalga etkisi, denizden esen rüzgar ve yoğunlaşma sebebiyle tuz birikimi meydana gelir ve korozyon için oldukça elverişli bir ortam hazırlanmış olur.
Bu çalışmada ayrıca beton yoldaki kayma demiri için ABD'de yapılan bir deney incelenmiştir. Bu deneyde kullanılan çeşitli kayma demirleri için korozyon performansları ölçülmüş ve sonuçlar elde edilmiştir. 
Bütün bu sonuçlar değerlendirilerek Türkiye'den yedi farklı coğrafi bölgeden yedi farklı il seçilmiş ve bu illerde beton yol uygulanacak olsa, iklimden ve konumdan yola çıkılarak beton yol yapılmadan önce ne gibi önlemler alınması gerektiği ve beton yol yapılırken ve donatıları seçilirken ne gibi hamlelerde bulunulması gerektiği açıklanmıştır.

Abstract:
Relocation for people has always been an important act. Priority is only a matter of transporting simple vehicles transported by animals only after the spring, and nowadays motorized and non-motorized vehicles and their drivers and vehicles are the objects of highway transportation.
Highways can be made flexible or rigid every day in developing road transport. Since the asphalt used in the flexible coating is both expensive and very sensitive to heat and has more damage to the surrounding than concrete, rigid coatings have begun to be preferred. Concrete roads are especially preferred where there are heavy and heavy vehicle traffic. Countries such as USA, Australia, Belgium, France, Germany, Austria and India are countries where concrete roads are used extensively. It has been observed that the performance of concrete roads in these countries is very high.
Concrete roads have various advantages over asphalt roads. In particular, the longer life and economic form of concrete roads make the concrete road more attractive than the asphalt road. The length of the opening and repair time of the traffic is due to the disadvantages of the concrete road and it is a sign that concrete road construction requires serious infrastructure and equipment.
The increased use of concrete roads has led to many problems with it. Some agencies such as municipalities and general directorate of highways have completed sufficient scientific infrastructure work, they have to prepare the road construction specifications and activate serious control mechanisms during implementation. Otherwise, it is inevitable that the concrete roads which are attracting attention with their positive aspects in many scientific platforms will be shorter in life than the asphalt roads.
When a road is planned to be concrete, the issue should be assessed in terms of sustainability and all the conditions should be taken seriously and the precautions should be taken especially for the negligence and abuse that may be caused by them.
Many of the factors that negatively affect the service life of concrete roads are interrelated. The emergence of a negative factor can bring along other negative factors. For example, due to heavy vehicle loads, breakage can occur in the road cover, resulting in increased permeability, road-based and floor deformation, which can lead to increased cracking in the cover.
Factors causing damages in concrete roads can be explained as vehicle loads and traffic, errors in concrete design and applications, freezing-thawing and salting studies, chemical degradation and other factors.
Corrosion occurs as an important resistance problem in reinforced concrete structures. Major economic losses also occur due to corrosion. For these reasons it is necessary to take measures against corrosion.
Direct contact with concrete grounds and atmosphere, heavy vehicle loads and any leaks that may occur in the joints contribute indirectly and directly to corrosion. Concrete roads must therefore be protected against corrosion. Since the average lifespan of concrete roads is 50 years, corrosion in concrete roads is usually neglected, but with measures taken against corrosion in concrete roads, we can extend service life and save the economy.
Concrete mix designed for road coating should be done considering the adverse factors that the road may be exposed to. Especially breaks, erosions, permeability, deterioration due to freeze-thawing and salting studies, and consequent deterioration caused by chemical reactions can be avoided in a great way with the right mix design.
The purpose of this study is; corrosion mechanism and construction of concrete roads, concrete properties and corrosion mechanism, and how corrosion in concrete roads can occur and what precautions can be taken against concrete and fixtures.
Concrete roads are not paved like asphalt roads, therefore, transverse and longitudinal joints are left. These joints are placed in reinforcement for load transfer. Afterwards, the sealing process to the joints should be very healthy. At this point, there is corrosion that can occur in the concrete roads described in this study. Reinforcement corrosion in the concrete roads occurs in the joints in these joints. If the seals in the joints are worn over time or poorly applied during the first construction phase, the bar in these points will cause direct contact with the atmosphere. In this phase, corrosion occurs.
The corrosion on the concrete road was observed to be caused by the climatic conditions, the critical properties of the concrete and the location of the place where the concrete road was made. Cracks in the concrete due to the properties of concrete during the construction phase or afterwards, and the formation of hydration material which can lead to the formation, have an important effect on corrosion of the concrete road.
One of the most important causes of corrosion is climate. The possibility that the bar fittings in the joints can directly contact with the atmosphere affects the corrosion. In cold regions, especially where there is snowfall and the number of snow-covered days is high, salts used as defrosters can act directly on the reinforcing bars in the joint area, acting indirectly on the concrete, causing corrosion. By separating into salt components, chloride ions act as a demure to initiate corrosion formation. With water frost, the volume is increased by about 10%. In the case of freeze-thawing, this can lead to cracks in the concrete, which in turn cause damage to the reinforced concrete bars and cause corrosion. A similar situation is the salting work done to prevent the icing on the roads during the winter months. It becomes molten with salt snow waters and seeps into the concrete, but when the weather is hot, this water evaporates, but the salt is transformed into a crystal, causing internal pressure in the concrete and causing cracks and cracks in the concrete. The aggressive materials that leak from these cavities and cracks are the biggest cause of corrosion.
In addition, snow water is one of the dangerous substances for corrosion. Moisture effect in hot areas is one of the important factors causing corrosion. 
The water remaining on the concrete road surface at night damages both concrete and reinforcement by drying the vapor droplets with high temperature effect during daytime. Especially if we are talking about the sea in close proximity to the sea and in a hot zone, this water with high chlorides will accelerate the corrosion of the revetment by leaving the chlorine ions on the surface at daytime. As a result of the wetness effect, the wave effect, the wind blowing from the sea and the condensation, the salt accumulation occurs on the concrete roads made near places near the seaside and a suitable environment for corrosion is prepared.
There is also a chemical reaction in concrete roads called carbonation over time. This reaction is especially effective in concrete roads where the rate of carbon dioxide is high in the open air. The carbon dioxide in the environment transforms into calcium carbonate by entering into the cavities of the concrete. This conversion plays an important role in the rusting of reinforcement or steel fibers in the concrete as it reduces the pH value of the concrete. Carbonation proceeds from the surface of the concrete that comes into contact with the air. At the same time, it increases the impermeability of the concrete. Theoretically, with the increase of the impermeability, there is no expectation of a decrease in the strength of the concrete over time, whereas the reinforcement which is given for the high energy holding of the concrete tends to rust with the reason of carbonation. The service life of the construction is shortened due to the decrease in the amount of energy absorption of the concrete with the corrosion result.
This study also examined a test made in the USA for concrete dowels. Corrosion performances for various dowels used in this experiment were measured and results were obtained.
Seven different provinces were selected from seven different geographical regions in Turkey and all these results were evaluated and it is explained what kind of precautions should be taken before the concrete road is made by climbing from the climate and from the location and if the concrete road is to be applied to these roads and what kind of movements should be made while making the concrete road and choosing the equipment.