Ultrasonik tomografi ve ultrases geçiş hızı yöntemiyle betonda kusur tespiti
Ultrasonic tomography and ultrasonic pulse velocity method for detecting defects in concrete structures
Yazar: EMRE TAVLI
Danışman: DOÇ. DR. BEKİR YILMAZ PEKMEZCİ
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / İnşaat Mühendisliği Ana Bilim Dalı / Yapı Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2018
Konu: İnşaat Mühendisliği = Civil Engineering
Dizin: Donatılı beton = Reinforced concrete ; Tahribatsız muayene = Nondestructive inspection ; Tahribatsız muayene yöntemleri = Nondestructive inspection methods ; Ultrases geçiş süresi yöntemi = Ultrasonic pulse transit time ; Yapı malzemeleri = Building materials ; İnşaat malzemeleri =

Özet:
Türkiye dünyanın en aktif fay hatlarından birinin üzerinde yer almaktadır ve eski yapıların veya yeni yapılan bina, köprü, baraj, viyadük ve endüstriyel zemin gibi beton yapıların, belli bir kalite standartına uygun olması gerekmektedir. Bu nedenle, beton yapılar üzerinde yapılan deneylerle beton yapı kalitesinin tahribatlı veya tahribatsız deney yöntemleriyle belirlenmesi günümüzde önemli bir konu haline gelmiştir.
Tahribatsız deneylerin tahribatlı deneylere göre daha kolay uygulanıp, sahada hızlıca sonuç alınması ve beton yapılara hasar vermemesi, tahribatsız deney yöntemlerinin ön plana çıkmasına neden olmaktadır. Bu tez kapsamında, son çıkan tahribatsız deney yöntemlerinden biri olan Ultrasonik Tomografi ve yıllardır yapı kusur tespitinde kullanılan ultrases geçiş hızı yöntemiyle özel üretilen numuneler üzerinde yapay kusurlar ve donatı tespitleri yapılıp, bu iki deney yöntemi uygulama açısından ve deney sonuçların açısından karşılaştırılacaktır. Özel olarak üretimi yapılan 3 farklı 60 cm x 60 cm boyutlarındaki beton numuneler üzerinde önce ultrasonik tomografi, daha sonra ultrases geçiş hızı deneyleri yapılmıştır.
Ultrasonik tomografi deneyleri sonucunda ulaşılan 3 kesitten alınan 2 boyutlu görüntüler neticesinde, beton numuneler içerisine yerleştirilen yapay çatlaklar, yerleşmemiş beton blok, şekilsiz bazalt taş blok, doğal taşlar, boşluklu yapıya sahip eps köpük ve gazbeton, yapay beton içi boşluk ve korozyonlu/korozyonsuz çelik donatıların boyutları yüksek doğruluk oranıyla (%91) tespit edilmiştir. Ayrıca bu kusurların beton içerisindeki koordinatları doğruya yakın mertebelerde belirlenmiştir. Fakat boyut ve beton içi konumları yüksek doğrulukla belirlenen bu kusurların türleri hakkında bir yorum yapılamamış ve donatı korozyonuyla, çelik donatı çapları tespit edilememiştir.
Ultrases geçiş hızlarıyla aynı numuneler üzerinde yapılan deney sonuçlarında, beton numuneler içerisinde bulunan yapay kusurların ve çelik donatıların bulunduğu bölgelerde meydana gelen hız değişimleri sayesinde beton içerisindeki konumları yaklaşık olarak tespit edilmiştir. Diğer yandan, kusur ve donatıların boyutları, çapları ve türleri hakkında ayırt edici verilere ulaşılamamıştır.
Yapılan deneyler sonucunda, ultrasonik tomografi tahribatsız deney yöntemiyle kusur ve donatıların boyutlarının, beton içerisindeki konum belirlemelerinin doğruluk oranı yüksek bir şekilde tespit edildiği, ayrıca bu yöntemle 2 boyutlu 3 kesite görsel olarak ulaşılabilmesi, deneylerin hızlı yapılıp, sonuçlara kolay ulaşılmasına olanak sağlamasıyla ultrases geçiş hızı deney yöntemine göre bir çok avantaj sağladığı sonucuna ulaşılmıştır. Ultrasonik tomografi deney yönteminin sağladığı bu avantajlar sayesinde, sahada servis ömrü biten, içerisinde kusur barındıran veya yetersiz donatı bulunan beton yapılar tespit edilebilir, ortaya çıkabilecek sorunlar önceden belirlenip önlemler alınabilir.

Abstract:
Turkey is located one of the world's most active fault lines. Concrete constructions such as old buildings or newly constructed buildings, bridges, dams, viaducts and industrial floors must conform to a quality standard. Therefore, determination of the quality of the concrete structures has become an important issue today with destructive or non-destructive test methods.
Non-destructive test methods are easier to implement than destructive test methods, faster results can be taken on the site with NDT methods and non-destructive methods do not damage to the concrete structure. On account of these reasons, non-destructive test methods come into the forefront and have begun to be preferred rather than destructive test methods. In the scope of this thesis, Ultrasonic Tomography that is one of the recent non-destructive test method and ultrasonic pulse velocity method used for detecting defects of concrete structures for years will be investigated. In the experimental studies, "Mira A1220 Monolith Advanced" for ultrasonic tomography experiments and "Proceq Pundit Lab (+)" for ultrasound pulse velocity experiments were used. 2 specimens of 60 cm x 60 cm x 13.5 cm and 1 specimens of 60 cm x 60 cm x 15 cm were produced. In order to detect defects and steel reinforcements with 2 non-destructive test methods, simulated cracks, coarse aggregate concrete block, shapeless basalt stone block, natural stone blocks, eps foam, autoclaved aerated concrete, simulated air-filled void, and steel reinforcements are located in the specimens. Ultrasonic tomography and ultrasound pulse velocity method results were compared in terms of defect size, defect coordinates and defect types.
Sand, crushed stone sand, angular aggregate-1 aggregates and CEM 1 PÇ 42,5 cement which have the largest grain size of 16 mm were used in the produced samples. The cement dosage in the concrete mixture is 300 kg / m3 and the W / C ratio is 0.55. Naphthalene sulphonate based superplasticizer has been used as a concrete admixture.
Two 60 cm x 60 cm x 13.5 cm concrete specimens and one 60 cm x 60 cm x 15 cm concrete specimen were produced for this study. Dimensions of Specimen-1 is 60 cm x 60 cm x 13.5 cm and it contains a coarse aggregate concrete block, 6 steel reinforcements, 2 simulated cracks materials. When the coarse aggregate concrete block was produced, no target strength was determined and the concrete mixture was made randomly. The reason for the use of coarse aggregate concrete block in the sample is to test whether the non-homogeneous and inhomogeneous concrete can be detected by ultrasound pulse velocity and ultrasonic tomography non-destructive
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testing methods. Then, there is 2 simulated cracks in specimen-1 is located for detecting cracks in concrete in specimen-1. Dimensions of Specimen-2 is 60 cm x 60 cm x 13.5 cm and it contains a shapeless basalt stone block, 2 natural stone blocks and 4 steel reinforcements. The reason for the use of basalt and natural stone samples in concrete design is to determine whether different materials with different intensities in the concrete can affect the sound waves and sound velocity and whether the ultrasonic tomography can be determined by non-destructive test method. Dimensions of Specimen-3 is 60 cm x 60 cm x 15 cm and it contains an eps foam, an autoclaved aerated concrete and a simulated air-filled void.
For the ultrasonic tomography test, the points to be measured are marked on the sample to be measured at intervals of 6 cm x 3 cm. Then a project in "MAP mode" was created and measured at every point marked by the ultrasonic tomography instrument. After the measurements to be made on the sample have been completed, the project opened in the device is transferred to the computer.
For ultrasound pulse velocity test, the measurement points were marked on the samples to be tested at intervals of 10 cm x 10 cm. Subsequently, the 3 specimens were tested with ultrasound pulse velocity instrument and time values and sample thicknesses were used to reach ultrasound pulse velocities.
Ultrasonic tomography and ultrasound pulse velocity test results were evaluated in terms of location, type and size of the target defect or steel reinforcement to be identified. In all defects in specimens (except reinforcements and simulated cracks) the accuracy rate is calculated by taking the arithmetic mean of the accuracy ratios calculated in each of the three dimensions. (Diameters of steel reinforcements and the widths of simulated cracks are neglected when calculating the accuracy of these dimensions inasmuch as they can not be determined.) Accuracy rates are classified as follows ; high accuracy rate (%90 - %100), moderate accuracy rate (%80 - %90), low accuracy rate (%70 - %80), very low accuracy rate ( < %70).
As a result of two dimensional images taken from the three different sections reached by ultrasound tomography tests, simulated cracks, coarse aggregate concrete block, shapeless basalt stone block, natural stone blocks, eps foam, autoclaved aerated concrete, simulated air-filled void, and steel reinforcements determined in concrete samples (91%) with high accuracy. In addition, the location of these defects in the concrete has been determined with high accuracy too. On the other hand, no data has been obtained about the types of defects and reinforcement corrosion. Moreover, steel reinforcement diameters were not determined with ultrasonic tomography test method because of the small dimensions.
Within the scope of this study, 3 different concrete specimens produced by using different types of defects and steel reinforcements were tested with ultrasonic pulse velocity and ultrasonic tomography non-destructive test methods. The results obtained in the ultrasonic tomography and ultrasound pulse velocity experiments were evaluated and the results of these two different non-destructive testing methods were compared with each other.
Experimental results of ultrasound pulse velocity tests on the same specimens show that the locations in the concrete of the simulated defects and steel reinforcements have been approximately determined by velocity changes. Furthermore, about the dimensions of the simulated defects, diameters of steel reinforcements and types of the simulated defects could not determined with ultrasonic pulse velocity test method.
End of the tests, the dimensions of simulated defects (simulated cracks, coarse aggregate concrete block, shapeless basalt stone block, natural stone blocks, eps foam, autoclaved aerated concrete, simulated air-filled void, and steel reinforcements) were determined and it has been achieved the location determinations in the concrete is determined with high accuracy. Besides, 2 dimensional 3 sections can be visually reached with ultrasonic tomography method. The experiments are also made faster and the results can be reached easier. As seen, ultrasonic tomography method has many advantages compared to ultrasound pulse velocity method. Thanks to these advantages provided by ultrasonic tomography test method, it is possible to detect concrete structures with defective or inadequate reinforcements that have reached the service life, and problems that may arise can be determined in advance and precautions can be taken.