Agrega konsantrasyonunun betonun kırılmasına etkisi
Effect of aggregate volume concentration on mechanical behaviour of concrete
Yazar: ÇAĞRI ÖZDEMİROĞLU
Danışman: DOÇ. DR. HASAN YILDIRIM
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / İnşaat Mühendisliği Ana Bilim Dalı / Yapı Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2014
Konu: İnşaat Mühendisliği = Civil Engineering

Özet:
Tez çalışmasında bazalt, beyaz kalker, cebeci kalkeri ve dolomit olmak üzere dört farklı agrega kullanılarak agrega hacim konsantrasyonunun betonun kısa süreli elastik ve elastik olmayan mekanik davranışına etkisi araştırıldı. Üretilen betonlarda en büyük agrega boyutu, granülometri ve su/çimento oranı sabit tutularak agrega konsantrasyonu değiştirildi. Yarma deneyleri yardımıyla betonların şekil değiştirme kapasiteleri ölçüldü ve agrega konsantrasyonunun bu dolaylı çekme halindeki şekil değiştirme kapasitesine etkileri incelendi.Üretilen Bazalt serileri, Cebeci Kalkeri serileri, Dolomit serileri ve Beyaz Kalker serileri, %0, %20, %40, %60, %75 agrega konsantrasyonularıyla üretildi. Agrega konsantrasyonu %0 - %75 arasaında değişirken, su/çimento oranı ve en büyük tane çapı sabit tutuldu. Su/çimento oranı 0,28, en büyük agrega çapı 20mm alındı. Bütün testlerde standart silindir ve küp numuneler kullanıldı. Silindir için yükseklik 300mm, çap 150mm; küp için 150mm x 150mm boyutlarına üretilen numunelere 28. günde yarma ve basınç deneyleri uygulandı. Yapılan deneylerde taze beton özellikleri, elastik ve elastik olmayan davranış özellikleri, gerilme – şekil değiştirme ilişkisi, ultrasonik ses hızının değişimi ve elastisite modülü araştırıldı. 
Deneylerde ulaşılan sonuçlara göre, agrega konsantrasyonu artıkça taze betondaVe-Be değerinin arttığı çökmeninde azaltığı görülmüştür. Su/çimento oranı sabit tutulan deneylerde, agrega konsantrasyonunun artışıyla artan agrega yüzeyini ıslatmak için daha fazla suya ihtiyaç duyuldu. Bu nedenle %60 ve %75 konsantrasyonlu numunelerde süper akışkanlandırıcı kullanıldı. Taze Beton birim ağırlığı, agrega konstrasyonunun artışıyla, agrega özgül ağırlığının betondan fazla olmasına bağlı olarak artış gösterdi.Elastisite modülü deneysel yöntemlelerle bulundu. Kırmataş agregalarının elastisite modülü hamur ve beton fazlarına göre yüksek olduğu için, kırmataş agrega konsantrasyonundaki artışın, betonun elastisite modülünü arttırdığı gözlendi.Agrega konsantrasyonundaki artışın süreksizlik sınırındaki Poisson oranını bir minimumdan geçtikten sonra arttığı görüldü. Aynı şekilde basınç dayanımı, çözülme sınırı ve süreksizlik sınırı değerlerinin de bir minimumdan geçtikten sonra arttığı gözlendi. 
Yapılan ultra ses deneylerinde, ultra ses hızının agrega konstrasyonu arttıkça, arttığı görüldü.
Agrega konsantrasyonundaki artışın yarma-çekme dayanımını artırdığı gözlendi. Betonda agrega konsantrasyon artışıyla basınç dayanımındaki birim kısalmaların ve kırılma işinin azaldığı bulundu.

Abstract:
I want in this study to establish the effect of aggregate volume ratio on concrete elastic and unelastic mechanical behavior. I will do so, by using four different types of aggregates and the affects of aggregate. These aggregates are Kırklareli region dolomite aggregates series, Cebeci region limestone aggregate series, white limestone aggregates series and Çorlu region basalt aggregate series.
I will also point to the influence of aggregate concentration on the splitting tensile behavior and the strain capacity of concrete. I used a split tension test to measure the tensile strain capacity, due to the fact that an uniaxial tension test is difficult to perform. As a final statement, I experimentally measured the modulus of elasticity of concrete.Composite materials are the mixes of minimum two type of materials with different mecanical and chemical properties. These materials are coming together with contact surfaces. Contact surfaces are effecting the properties of concrete. New material has mostly different properties than the initial ones. Concrete is a heterogen and composite material. Also concrete shows elastic and inelastic features. I tried to see experimentals results in this inelastic phases.
In the experiments, crack can be starts in contact surfaces, in cement paste or in aggregate. Cracks are phase of micro cracks till 60% of compression strengt of concrete. Crack spread will start to make stable links till 80%. Between 80% - 95% of compression strengt of concrete, crack spread will make unstable links.
The concreates used in the experiments are belonging to five different aggregates volumes as follows: 0 %, 20 %, 40 %, 60 %, 75 % with basalt series (BA20, BA40, BA60, BA60, BA75), cebeci limestone series (CE20, CE40, CE60, CE75), dolomite series (DO20, DO40, DO60, DO75), and white limestone (BE00a, BE00b, BE20, BE40, BE60a, BE60b, BE75) series. For this study i had to change the aggregate volume concentrations in the range of 0 % - 75 %, but i kept constant the aggregate grading of concrete, water/cement ratio and the maximum particle size for all concrete series. The water/cement ratio and the maximum size of aggregate were 0,28 and 20 mm, respectively.
I used 55dm3 concrete mixer. 60% and 75% aggregate concentration series prepared in steel formwork. I poured concrete in 3 step and each times I used steel bars 25 times for settle concrete. All concrete series are waited in formworks 24 hours. 28 days I kept them in pool with temperature 20 °C ± 2 °C. I made the experiments in 28th day of concretes.All mechanical tests were based on the standard cylinder specimens, the height=300 mm and the diameter=150 mm and standard cube specimens 150 x 150mm  at the age of 28 days. 
Splitting tensile tests were based on disk specimens which were prepared from the standard cylinder as the height=l50 mm and the diameter=l50 mm. In the end, the test results that were made are evaluated in terms of following properties: Fresh concrete properties, elastic properties of concrete, inelastic properties of concrete, fracture energy, under compression, splitting tensile strength, tensile strain capacity, ultrasonic pulse velocity, the modulus of elasticity.I have split the investigations into four chapters: First chapter refers to general information. The second is the objective of the investigation. Third chapter is experimental studies and the results of these experiments. And the last chapter I put the conclusions of study and suggestions for further studies, if given.
The results obtained in the experimental studies:Fresh concrete behaviour:Increasing of aggregate concentration is effecting workability of concrete negative. Concrete is passing from to dry concrete consistency.Composite is decreasing with increasing aggrega concentration.Ve-Be values are increasing slowly with increasing aggrega concentration till 60% concentrate. We used superplasticizer in 60% ans 75% series. Because of that Ve-Be values decreasing in 60% series. 75% series is passing from plastic consistency to dry concrete consistency and value of Ve-Be is increasing rapidly.Results related to elastic behaviour:Aggregate concentration has an important effect on the modulus of elasticity, as an example when i chosen higher the modulus of elasticity of aggregate, the concrete increases also.Results related to inelastic behavior:The compressive strengths aggregates series decreases till one minimum limit and after that increases, when the aggregate volume concentration increases. The strains of all series at the maximum stress is decreasing as the aggregate volume concentration increases.
Increasing of aggrega concentration is effects dislocation point of concrete. It is decreasing till one minimum point after that it is starting increase.Increasing of aggrega concentration is effects yielding point of concrete. It is decreasing till 35% - 40% concentration values after that it is starting increase.Compressive strength of concrete in DO, CE and BA series is decreasing till 35% - 40% aggregate concentrations, then it is increasing. BE series increasing continuously with increasing of aggrega concentration.The results related to the toughness and the relative toughness are as followed: as the aggregate volume concentrations of all concrete series increase the toughness of concretes decreases. The relative toughness of concrete series does not change much, as the aggregate volume concentration increases.Experimental results related to the splitting tensile strength and the tensile strain capacity: In normal aggregate concretes, as the aggregate volume in the mixes increases the splitting-tensile strength also increases. The tensile strain capacity is independent on the type and texture of aggregates within the limits of this work. The tensile strain capacity as defined and measured in this work is strongly dependent on the volume of aggregate in the mix and it decreases with the increase of aggregate concentration.The results related to the ultrasonic pulse velocity:
In all concrete series, as the aggregate volume concentration increases the ultrasonic pulse velocity also increases.Proposals for further studies:It can be performed with different origin of aggregates, at different ages than those chosen in this study, and different water/cement ratios other than 0,28.We can also assume that issue can give more different results using a biaxial loading.By using different types of aggregates, the results obtained may vary in a wide range and line spacing must be set for summaries.