Çok hafif yalıtım betonlarının mekanik ve ısıl iletkenlik özellikleri
Mechanical and thermal properties of lightweight insulation concrete
Yazar: SİBEL ELDEN
Danışman: PROF. DR. BEKİR YILMAZ PEKMEZCİ
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / İnşaat Mühendisliği Ana Bilim Dalı / Yapı Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2011
Konu: Mühendislik Bilimleri = Engineering Sciences

Özet:
Normal beton inşaat mühendisliğinde yaygın kullanılan iyi bir taşıyıcı olmasına karşın birim ağırlığı büyük, dolayısıyla ısı iletkenlik katsayısı yüksektir. Birim ağırlığı normal betonlardan belirgin şekilde düşük olan hafif betonların, normal betona oranla yapı ağırlıklarını, dolayısıyla taşıyıcı elemanların kesitlerinin azaltılmasını sağladığından inşaat sektöründe kullanımı artmaya başlamıştır. Yapıların kendi (zati) yüklerinin azaltılması özellikle yapının düşük deprem kuvvetlerinin etkisinde kalması açısından önemlidir. Hafif beton kullanımı ile taşıyıcı elemanların kesit boyutları küçültülmesi nedeniyle betonarme elemanlarda donatı azalır; taşıma ve yerleştirme masraflarından ekonomi sağlanır. Ayrıca ısı iletim katsayısı çok düşüktür. Yüksek ısı yalıtımına sahip oldukları için yangına ve dona dayanımı normal betondan daha iyidir.  Hafif beton üretiminde en sık başvurulan yöntem, bileşimde normal ağırlıklı agregaların tamamen ya da kısmen hafif agregayla yer değiştirilmesidir. Bu çalışmada hafif agrega olarak genleştirilmiş perlit, EPS, XPS ve cam köpüğü kullanılmıştır. Çalışmalar sırasında özellikle yalıtım etkisi bulunan farklı agregalar kullanılması ile üretilen numunelerin üzerinde ısıl iletkenlik etkileri ve mekanik etkileri incelenmiştir.
Deneysel çalışmalarda öncelikle su ve çimentodan oluşan çimento hamuruna perlit agregası eklenerek beton üretimleri yapılmıştır. Daha sonra agrega olarak kullanılacak polistrenlerden %10 eps ve %90 xps'ten oluşan polistren agregalı beton üretimi yapılmıştır. Son olarak da çimento dozajı 200 ve 250 olan cam köpüğü agregalı beton serileri üretilmiştir.
Üretilen hafif betonlara yapılan deneyler sonucunda, beton karışımındaki agrega cinsinin hafif betonun mekanik özellikleri üzerinde çok fazla etkisi olduğu görülmüştür. Üretilen hafif betonlar birbirlerine göre karşılaştırıldığında; perlit agregalı hafif betonların birim ağırlıkları, basınç dayanımları ve elastisite modülleri düşük, ısı yalıtım özellikleri oldukça iyi fakat su geçirimlilikleri fazladır. Polistren agregalı hafif betonlarda, birim ağırlık ve basınç dayanımları yüksek, elastisite modülü düşüktür. Isı iletkenlik katsayısı yüksek, su emme ve kılcallık değerleri düşüktür. Cam köpüğü ile üretilen hafif betonların birim ağırlıkları, basınç dayanımları ve elastisite modülleri yüksek, ısı iletkenliği perlitli hafif betona göre daha yüksek fakat su geçirimlilikleri azdır. 250 dozajlı cam köpüğü agregalı hafif betonların ısı iletkenlik ve mekanik özellikleri 200 dozajlı cam köpük agregalı hafif betona göre daha iyi olduğu tespit edilmiştir.
Bu çalışmada deneyleri yapılan hafif betonlara ilişkin sonuçlar topluca değerlendirildiğinde; cam köpük agregalı betonun bu kapsamdaki üretilen hafif betonlar içinde en verimli hafif beton olduğu ortaya konulmuştur.

Abstract:
In construction engineering normal concrete has commonly used, but it has large density and large thermal conductivity constant. Using of lightweight concrete, which is defined as general to have lower density than 2400kg /m3, is gaining in building sector because of its lower density. It is preferred to use porous aggregate instead of normal aggregate in production of lightweight concrete since 70% - 80% of concrete consists of aggregate.
In addition to this, it decreases the structure weight and also provides reducing the cross section of bearing component. Especially decreasing in the proper weight of structure is important for getting lower seismic force effect. When lightweight aggregate concrete uses, numbers of reinforcement reduces, transportation and placement expense decreases. They also have more resistant of fire and freeze than normal concrete. Besides, the production time is fast due to availability of the prefabrication. They can be easily cut, drilled and fixed, especially when produced according to this type of intended use.
Relocating all or partly of aggregates with lightweight aggregate is the method which is most commonly applied. In this study, expanded perlite with 50kg/m3 density and 0,040W/mK thermal insulation-rating factor, EPS with 21kg/m3 density and 0,037W/mK thermal insulation-rating factor, XPS with 29kg/m3 density and 0,033W/mK thermal insulation-rating factor and glass foam with 50kg/m3 density and 0,042W/mK thermal insulation-rating factor are used as lightweight aggregates. At the time of this study, the specimens were produced with different types of aggregates that have isolation properties. They were tested in order to determine the effects of the aggregates on the mechanical and thermal conductivity.
In the experimental study, trial concrete mixes with different water/cement ratio were prepared and to be used ratio in real concrete mix with perlite was determined. Then new trial concrete mixes with different eps and xps ratio in fixed water/cement ratio were produced to define convenient concrete mix. Additionally, trail concrete with different cement dosage in constant water/cement ratio were produced for lightweight concrete with glass foam aggregate.
Finally, 4 series of lightweight concretes with expanded perlite, polystyrene and glass foam aggregates were produced according to trial mixes results. All polystyrene aggregates were produced from polystyrene boards. Perlite and glass foam were provided as ready-made products.
In lightweight concretes with polystyrene included %10 eps and %90 xps as aggregates. Cement rate were 200 and 250 kg in 1 m3 concrete in lightweight concrete with glass foam aggregate.
Different experiments are made on produced speciments such as determining unit weight of fresh concrete. Then ultrasound test was done to view the affect of pore structure. Compressive stress and elasticity modeles were deteremined with uniaxial compression test on specimences with 100mm diameter and 200mm height.
Additionally, the weight of oven-dry and saturated water samples are measured and water abservation ratio for specimens are calculated. The other test on oven-dry samples is capillarity. The surfaces that are contact with water are coated with paraffin. Cappilarity ratio was calculated according to absorbed water and absorbation time.
As a latest test, heat flow plate was prepared. Thermal conductivity coefficient was determined considering the duration of cold and hot surface temperatures reach stabilized.
As a result of all this experiments which was made on the produced lightweight concretes; too much influence of the lightweight aggregates on the mechanical properties of the lightweight concrete was found. When produced lightweight concrete compared to each other, lightweight concrete with perlite aggregates has low unit weight, low compressive strength and low elasticity modules due to low cement dosage. Unit weight is increasing when the density of aggregate is increasing. Therefore, unit weight of fresh and hardened concrete for concrete with glass foam is higher than the concrete with polystyrene.
More air gaps in concrete causes low ultrasound transmission velocity. As a result of this, ultrasound transmission velocity of concrete with perlite aggregate is very low. The concrete with glass foam aggregate has the highest ultrasound transmission velocity than the others.
Compressive strength for the concrete with perlite aggregates is low because of low cement dosage. Concrete with glass foam has higher compressive strength than concretes with polystyrene and perlite depending on the cavity. The concrete produced with glass foam and 200-dosage cement has low strength than the concrete produced with 250-dosage cement. 
The unit weight of the concrete with perlite aggregate is higher than the concrete with polystyrene aggregate but the elasticity modules is less than it. The concrete produced with glassfoam aggregates has very high elasticity modules due to features of the aggregate in the content. The concrete produced with glass foam and 250-dosage cement has high elasticity modules than the concrete produced with 200-dosage cement since the increasing of cement dosage causes to increasing the unit weight and also elasticity modules.
Capillarity ratio for the concrete with perlite is high enough due to capacity of water absorbation. The concrete with polystyrene and glass foam are not absorb more water due to lack of air gaps. So it is seen that the capillarity is too low, as well. Besides, it is observed that the relation between capillarity and unit weight is similar with the relation between capillarity coefficient and unit weight.
Thermal conductivity coefficients of the produced concretes are acceptable values. The concrete with polystyrene aggregate has the highest thermal conductivity coefficient. The concrete with perlite aggregate has the lowest coefficient. It is found that thermal conductivity features of the glass foam is the expected value. 
When the all results of lightweight concrete compositions are evaluated as a whole, lightweight concrete with glass foam is the most efficient lightweight concrete in lightweight concretes produced in this contex.