Farklı agrega kökenlerinin bitümlü sıcak karışımlarda soyulma mukavemeti üzerine etkisi
The effect of different aggregate origins on the stripping strength of hot bituminous mixes
Yazar: BİLAL FARUK KOÇ
Danışman: PROF. DR. HASAN YILDIRIM
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / İnşaat Mühendisliği Ana Bilim Dalı / Yapı Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2023
Konu: İnşaat Mühendisliği = Civil Engineering

Özet:
Artan dünya nüfusu ve yeni yerleşim yerlerinin oluşmasına bağlı olarak  ulaşım ağları büyüyerek genişlemiş ve genişlemeye devam etmektedir.  Ulaşımın ve taşıt kullanımının artması beraberinde trafik yüklerini de getirmektedir. Yüksek trafik yükleri ise   karayolu üstyapısında kalıcı deformasyonlara sebep olmaktadır.  Oluşan karayolu üstyapı bozulmaları ise trafik güvenliğini tehlikeye atmasının yanında bakım-onarım masrafı olarak geri yansımaktadır.  Ülkemizde 2021 yılında -yerel yönetimler hariç olmak üzere- yaklaşık 3,5 milyar TL karayolu bakım-onarımına harcanmıştır ve bu maliyet her sene katlanarak artmaktadır. Bu gibi sebeplerden dolayı karayollarını servis ömrü uzun olacak şekilde tasarlamalı ve üstyapı bozulmalarını minimum seviyelerde tutacak çalışmalar yapılmalıdır. 
Karayolu üstyapılarında oluşan bir çok bozulma tipi olmakla birlikte bu tez çalışması kapsamında "soyulma" tipi üstyapı bozulması  incelenerek bitüm sıcak karışımlarda kullanılan  agreganın soyulma mukavemetine olan etkisi incenlenmiştir. Agregaların -fiziksel kimyasal özelliklerinin soyulma davranışı üzerindeki etkilerini incelemek amacıyla bu çalışmada bazalt, beyaz kalker, çakıl, dolomit, kalker ve kumtaşı olmak üzere  altı farklı agrega kullanılmıştır. Çalışma kapsamında agregaların fiziksel özellikleri, fiziksel deney metodları; kimyasal özellikleri, petrografik ve kimyasal analizler ile   ortaya konulmuştur. 
Tez çalışması kapsamında soyulma davranışını daha iyi belirleyebilmek ve soyulma tipi bozulmanın etmenlerini ortaya koyabilmek  amacıyla  çalışma kapsamına ilki karıştırma sıcaklığı (Tm), ikincisi su içerisinde bekletme işlemi (water conditioning) olmak üzere iki farklı parametre daha eklenmiştir.  Deneysel çalışmalar TS EN 12697-11:2020 standartının Statik Metodu ve Karayolları Teknik Şartnamesinin Soyulma Mukavemeti Deneyi kısımlarına göre yapılarak sonuçlandırılmıştır. 
Elde edilen bulgulara göre agreganın kökeni değiştikçe bitümlü sıcak karışımlardaki soyulma karşısında göstermiş olduğu  mukavemetler de değişiklik göstermektedir.  Fiziksel olarak daha yassı olanların ya da los angeles parçalanma direnci daha yüksek olan agregaların daha düşük soyulma mukavemeti göstererek yüksek soyulmalara maruz kaldıkları gözlemlenmiştir. Kimyasal olarak incelendiğinde sertlik sınıfına göre durabilitesi ve sertliği yüksek, yüksek homojenliğe sahip yapıdaki kayaçlardan elde edilen agregalar ile üretilen karışımların daha yüksek soyulma mukavemeti gösterdikleri gözlemlenmiştir.  
Karıştırma sıcaklığı açısından bakıldığında ise yüksek karıştırma sıcaklıklarının agrega bitüm benzeşmesini artırarak yüksek adezyon sağladığı ve bu sebeple düşük soyulmalar meydana getirdiği ortaya konulmuştur. Karıştırma sıcaklıkları düştükçe soyulma miktarlarında artışlar meydana gelmiştir. 
Su içerisinde bekletme işlemi (water conditioning) kapsamında TS EN 12697-11 ve Karayolları Teknik Şartnamelerinin önerdiği metodlar ayrı ayrı ve birleştirilerek çalışma kapsamına dahil edilmiştir. Su içerisinde belirli bir süre boyunca sabit sıcaklıkta  bekletme işlemlerinin soyulma mukavemetine olan etkisi de bu sayede deneysel çalışmalarda incelenmiş oldu.  Bu işlem sırasında KTŞ'nin önerisi olarak yüksek sıcaklık tercih edildiğinde soyulma miktarlarında artış olduğu  tespit edilmiştir. Yani su içerisinde bekletme işleminde de (Water conditioning) sıcaklık arttığında süre düşse dahi soyulma mukavemetine negatif etki yaptığı gözlemlenmiştir.

Abstract:
Depending on the increase in the world population and the formation of new settlements, the transportation network is gradually developing. The developing transportation network, on the other hand, causes an increase in the traffic load and causes deterioration in the highway pavement. In addition to endangering traffic safety, the occuring deterioration of the pavement also causes many economic drawbacks. In our country, as of 2021, excluding local governments, approximately 3.5 billion TL has been spent on highway pavement  maintenance and repair. The spent maintenance and repair costs continue to increase exponentially every year. Highway pavements should be designed to have a longer service life and studies should be carried out to keep pavement deterioration at minimum levels. Based on these reasons, in this study, "stripping"  which is one of  the deteriorations that occurs in highway flexible pavement, is examined in detail. 
It is known that the stripping behavior depends on the adhesion between the aggregate and the bitumen. This situation reveals that the chemical and physical properties of the aggregate will affect the stripping strength. For this reason, 6 different aggregates; basalt, white limestone, gravel, dolomite, limestone and sandstone were used in the experimental studies. Before starting the stripping strength tests the physical properties of aggregates such as specific gravity, water absorption, los angeles abrasion test; chemical properties such as microscopic imaging, chemical components, mohs hardness classes, origins were determined by experimental methods. Bitumen 50/70 was used in all experimental work.
While conducting the experimental study, the static method of TS EN 12697-11 (2020): Determination of the affinity between aggregate and bitumen standard and the Stripping Strength Test section of the Turkish Highways Technical Specification were used.
In order to present and prove other parameters affecting the stripping behavior mixing temperature (Tm) and water conditioning parameters were also included as variables in the experimental study. The mixing temperature (Tm) affects the viscosity of the bitumen and changes the quantity of adhesion to the aggregate. Therefore, it is necessary to use high mixing temperatures to ensure high adhesion. As a result of the interaction of the aggregate bitumen interface with high adhesion, it also causes a decrease in deterioration such as stripping caused by water. In the scope of the experimental study 3 different mixing temperatures 165 °C, 150 °C and 135°C, were applied in order to understand the effects of mixing temperature. Thus, the effects of decreasing mixing temperatures on stripping strength were examined in detail. 
The water conditioning process, which is used as another variable in the thesis, is the place where literally stripping type deterioration occurs. In water conditioning process, TS EN 12697-11 standard recommended that 19°C should be applied for 48 hours. In addition, it is mentioned in the standard that the process can be continued by using different temperatures and time intervals. On the other hand, Turkish Highways Technical Specification recommends 60°C water condtioning for 24 hours. In the light of this information, 3 different types of water conditioning were chosen respectively 1- 48 hours 19°C, 2- 24 hours 60°C ve 3- 24 hours 19°C + 12 hours 60°C. By this way, the effects of water conditioning processes on stripping strength were examined.
First of all, the effects of the origins of the aggregates namely the physical and chemical properties on the stripping strength were determined. According to the findings, aggregate origin plays an important role in the stripping behaviour of hot bitumen mixes. The six aggregates used showed differences in stripping behavior. It has been determined that specific gravity and water absorption have no observed effect on stripping strength. Major stripping differences were observed between aggregates with very close eachother in terms of aggregate specific gravity. Likewise, it has been observed that aggregates with similar water absorption properties have different stripping strengths in their stripping behavior. However, when the los angeles abrasion value was examined, it was observed that the aggregates with high abrasion value had lower stripping strength. When the stripping behavior was examined in terms of mohs aggregate hardness class, it was determined that aggregates with low hardness class were tend to high stripping. It has been shown that aggregates with smoother and flatter surfaces are subject to high stripping, even if their other physical properties are better. When the photomicrograph of the aggregates was evaluated, it was determined that those with homogeneous distribution in terms of chemical components exhibited higher stripping strength.
Although the physical properties of the dolomite aggregates are similar compared to other aggregates, it performed very poorly in stripping. This is caused by chemical properties. When the chemical components were examined, it was understood that the stripping strength of the aggregates with high Fe2O3 content was good. It is considered that the SiO2 value has an optimum value in aspect of stripping behavior and when this value is exceeded it is considered that it adversely affects the stripping strength of mixes. 
In the effects of the mixing temperature on the stripping strength, it was determined that the mixtures using high mixing temperature showed higher stripping strength. This can be explained by the decrease in the viscosity of the bitumen at high temperatures and the increase in bitumen aggregate adhesion. In addition, as the mixing temperatures increased, it was evaluated that the bitumen penetrated the micro-voids in the aggregates and reduced the amount of stripping.
When the effects of the water conditioning process applied to the produced samples were examined, it was observed that the amount of stripping increased as the water conditioning temperature increased, even if the time was shortened. In the study, it was determined that when water conditioning conditions were applied at 19°C for 48 hours, the amount of stripping decreased compared to 60°C for 24 hours. When 60°C conditions are applied, it is understood that the 50/70 bitumen that used in mixes exceeds the softening point, therefore the bitumen softens and strips off easily. Since the bitumen type and class was kept constant for each set and aggregate, the effect of water conditioning could be easily demonstrated.
Aggregates used in hot bituminous mixtures should be in crushed stone and angular forms rather than flat and smooth in order to increase the stripping strength. Aggregates with high hardness class should be preferred in places where stripping type deterioration is commonly seen. Bitumen with high softening point should be chosen as binder for hot bituminous mixtures to be used in both humid and high temperature climate residential areas. In places where stripping is not desired, bitumen should be modified or additives that increase adhesion should be added to the mixture in order to prevent this deterioration. In addition, using high mixing temperatures can be considered as an option for mixtures where low stripping is desired.