Ferrokrom cüruf agregasının betonun mekanik özelliklerine etkisi
The effect of the ferrochrome slag aggregate on mechanical properties of concrete
Yazar: FATİH SALİHPAŞAOĞLU
Danışman: DOÇ. DR. ÖZKAN ŞENGÜL
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / İnşaat Mühendisliği Ana Bilim Dalı / Yapı Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2017
Konu: İnşaat Mühendisliği = Civil Engineering

Özet:
Endüstriyel üretimin yan ürünü olarak ortaya çıkan cüruflar, üretildekileri materyalden, üretim koşullarına kadar birçok etken sonucunda özelliklerini kazanırlar.  Kazanılan son özelliklere bağlı olarak; betonda bağlayıcı malzeme yerine kullanılabildikleri gibi agrega olarak da kullanılabilirler. Bu tez çalışmasında, ferrokrom cüruf agregasının betonda kullanılabilirliği ve betonun mekanik özelliklerine etkisi incelendi.
Toplamda üç seri üretim yapıldı. Her bir seride beş farklı su/bağlayıcı oranına sahip beş farklı üretim yapıldı. Tüm serilerde kullanılan su/bağlayıcı oranları sırasıyla; 0,83, 0,67, 0,45, 0,33 ve 0,28 olarak belirlendi. Tüm serilerde, su/bağlayıcı oranının yeterli işlenebilirliği vermediği durumlarda süper akışkanlaştırıcı kimyasal katkı kullanıldı ve kullanım miktarı, bağlayıcı miktarının ağırlıkça %1-3 arasında değişkenlik göstermiştir.
Öncelikli olarak, kontrol grubunu oluşturacak 1. Serinin üretimleri yapıldı.  Bu seride kullanılan malzemeleri kırma taş agregası, doğal kum ve bağlayıcı olarak Portland çimentosu oluşturmaktadır. 1. Seri üretimi sonrasında agregalarda değişikliğe gidildi ve 2. Serinin üretimleri yapıldı. Bu seride agrega olarak ferrokrom cüruf agregası, doğal kum ve bağlayıcı olarak Portland çimentosu kullanıldı. Son olarak 3. Serinin üretimi yapıldı. Bu seride agrega olarak ferrokrom cüruf agregası, doğal kum, bağlayıcı olarak yüksek fırın cürufu ve yüksek fırın cüruflarını aktif etmek için alkalin aktivatörler kullanıldı. 
3. seride yüksek fırın cüruflarını aktifleştirmek için alkalin aktivatörlerden faydalanıldı. Kullanılan alkalin aktivatörler sodyum hidroksit (NaOH) ve sodyum silikat ((SiO2)(Na2O)(H2O)) olup, kullanım miktarları üretim öncesinde yapılan ön deneyler sonucu bulunmuştur. Bulunan oranlar, sodyum silikat ((SiO2)(Na2O)(H2O)) için bağlayıcı miktarının ağırlıkça %17,34'u ve sodyum hidroksit (NaOH) için bağlayıcı miktarının %7,1'i olarak belirlendi. 
Üretilen tüm numuneler oda sıcaklığındaki kür havuzlarında 28 gün bekletildi. 35. Günde basınç dayanım tayini ve yarmada çekme dayanımı tayini için deneyler yapıldı. Bu deneyler sonrasında elastisite modülü ve gevreklik indisi için komparatör yardımı ile numuneler üzerinde okumalar yapıldı.
Yapılan deneyler sonucunda; ferrokrom cüruf agregası ile Portland çimentosunun beraber kullanılmasıyla üretilen 2. Seriye ait beton numunelerin mekanik özellikleri, kontrol grubu ile benzer özellikler göstermiş, yer yer ise daha iyi sonuçlar vermiştir. Ulaşılan en yüksek basınç dayanım değeri 80,8 MPa, yarmada çekme dayanımı 6,69 MPa, elastisite modülü ise 52,42 GPa ve gevreklik indisi değeri 2,88'dir.
Yine yapılan deneyler sonucunda; ferrokrom cüruf agregası ile yüksek fırın cürufunun beraber kullanılıp, alkalinler ile aktif edilmesi ile üretilen 3. Seriye ait beton numuneler kontrol grubu ile kıyaslandı. Kıyas sonucunda; 3. Seri numuneleri basınç dayanımında en iyi performansı 0,33 su/bağlayıcı oranında verdi ve 78,1 MPa değerine ulaştı. Yarmada çekme dayanım sonuçlarında ise genel olarak 3. Seri beton numuneler, kontrol grubundan daha iyi sonuçlar verdi. Ulaşılan en yüksek dayanım değeri 0,28 su/bağlayıcı oranında, 6,8 MPa olarak bulundu. Elastisite modülü kıyası yapıldığında ise 3. Seri üretimleri, kontrol grubuna göre oldukça düşük değerler verdi. Ulaşılan en büyük elastisite modülü değeri 0,33 su/bağlayıcı oranına sahip üretimlerde elde edildi ve 37,31 GPa olarak bulundu. Son olarak gevreklik indislerine bakıldığında, 3. Seri beton numunelerinin kontrol grubu ile benzer sonuçlar verildiği görüldü ve ulaşılan en yüksek değer 2,79'dur. 
Bu tez çalışmasında yapilan deneyler sonucunda, ferrokrom cüruf agregasının beton üretiminde agrega olarak kullanılmasının betonun mekanik özellikleri açısından son derece uygun olduğu sonucuna varıldı.

Abstract:
Slags, which emerge as by-product of industrial production, show different properties as a result of their sources, production conditions, cooling process etc. Depending on the last properties obtained, slags can be used in concrete as either cementitious material which is in glassy form or can be used as aggregates which is in crystalline form. In this dissertation, effect and usability of ferrochrome slag aggregate on mechanical properties of concrete were investigated.
As it known, composition of materials is very important for mechanical properties of the concrete. That's why, it is a necessary to consider the interaction of materials which are used in concrete. At the experiment process of this dissertation, 3 series of production were made total. Each series includes 5 productions which vary according to their water/binder ratio. The water/binder ratio was settled as 0,83, 0,67, 0,45, 0,33, 0,28 respectively. In all series, superplasticizer (which is known as high range water reducer) was used when the workability of concrete was not enough. Amount of superplasticizer was ranged between 1-3% of the amount of cementitious material. 
Initially, first series productions were made which will form the control group. The materials used in this series are crushed stone aggregate, natural sand and Portland cement as a binder. After the production of the first series, only the aggregates were changed and the second series was produced. The materials used in this series are ferrochrome slag aggregate, natural sand and Portland cement as a binder. Finally, the third series was produced. The materials used in this series are ferrochrome slag aggregate, natural sand and ground granulated blast furnace slag as a binder. At the third series, alkaline activators were utilized to activate ground granulated blast furnace slags. The used alkaline activators are sodium hydroxide ((SiO2)(Na2O)(H2O))  and sodium silicate (NaOH). Amount of the used activators were determined by preliminary tests and results of the tests were found to be 17,34% of the amount of binder for sodium silicate ((SiO2)(Na2O)(H2O)) and 7,1% of the amount of binder for sodium hydroxide (NaOH).
The concrete production for the three series was made using a concrete mixer which is made of stainless steel and has 50 litre capacity. The materials were mixed for about 5 minutes after poured into the concrete mixer. Superplasticizer was only used when the workability of concrete was not enough. 
The concrete production for the three series was made using a concrete mixer which is made of stainless steel and has 50 litre capacity. The materials were mixed for about 5 minutes after poured into the concrete mixer. Superplasticizer was only used when the workability of concrete is not enough.
The concrete mixture obtained after the production was placed with 10 pieces of cylinder molds having dimensions of 100mm x 200mm and 4 pieces of prism molds having dimensions of 7mm x 7mm x 280mm. Before the placement of concrete, molds were cleaned and a thin layer of mold oil was applied. During the placement of the concrete into molds, a shake table was used for the exact placement of the concrete and an ideal placement was achieved. After the concrete was placed, the molds were kept in damp conditions and tried to prevent water loss which may occur during hydration. The molds are dismantled 24 hours after the concrete is placed. After that, they were numbered and placed in curing pools at room temperature.
The test process can be divided into two categories. The first is the tests which is made when the concrete is fresh and the second is the tests which is made when the concrete is hardened. 
Fresh concrete tests are made after the producing of concrete. Name of the tests are unit weight test and slump test. After the producing and dismantled of concretes from molds, they were placed in curing pools at room temperature. Concrete specimens were kept in the curing pool for 28 days. After being removed from the curing pool, it was left to dry for 1 day. Then the head is made using the sand-cement mixture to distribute the load properly to be applied to the cylinder specimens. On the day 35., all hardened concrete tests were carried out on the specimens. 
The first test was applied on hardened concrete is compressive strength test and it is based on TS EN 12390-3. The surfaces of the specimens were carefully cleaned before the test. Likewise, before the test, care has been taken to ensure that the loading heads of the pressure machine are also clean. The specimens were placed in the exact center of the lower loading head and at a constant loading rate, the specimens were loaded up to the maximum value they could carry. The maximum value read from the load indicator is recorded and the compressive strengths are found with the help of the necessary equations.
The second test was applied on hardened concrete is splitting tensile strength test and it is based on TS EN 12390-6 (2010). The cylinder samples were thoroughly cleaned before the test. Then, in order to distribute the load to be applied properly, a lath was placed horizontally in the center of the machine, opposite to the upper and lower parts of the cylinder specimens. The test was continued until samples were cut at a constant loading rate. The maximum value read from the load indicator is recorded and the tensile strengths on the surface are found with the help of the necessary equations.
The final test was made to determine the modulus of elasticity and the brittle index. These two value were found in the same test with different calculations. First, to measure the longitudinal shape changes of the specimens, a comparator frame with a precision of 1/1000 mm was attached to the specimens. The specimens were loaded centrally between the lower and upper loading head, while the comparator frame was installed, and loaded at constant speed. The specimens were placed centrally between the lower and upper loading head, while the comparator frame was installed, and loaded at constant speed. At every 1000 kilograms, the longitudinal shape changes corresponding to these loads are read. For each production, these readings continued to the loading values corresponding to 80-90% of the average compressive strength which was found at results of the compressive strength test. Since these values are not definite, the loads are stopped in regions where the strain rate has significantly increased, and the load is read back at the same speed. These readings continued until the load value reached zero. At the last stage, the specimens are reloaded at the same speed and new shape change values are read up to the maximum strength value that the specimens can reach. After this point, stress-strain diagrams were drawn from the data obtained from the tests and modulus of elasticity and brittle index were calculated with using necessary equations. 
The test results showed that; the mechanical properties of concrete specimens of the second series produced by the use of ferrochrome slag aggregate and Portland cement showed similar properties when it was compared to the control group and gave better results at some points. As a result of comparison; second series specimens gave the best performance in compressive strength at 0.28 water/binder ratio and reached level of 80,8 MPa, while the control group series reached level of 78,9 MPa at the same water/binder ratio. For splitting tensile strength test results, specimens of the second series gave best performance at 0.28 water/binder ratio and reached level of 6,69 MPa, while the control group series reached level of 6,45 MPa at the same water/binder ratio. When the modulus of elasticity was compared, the second series productions showed similar results with control group. The greatest modulus of elasticity was obtained at 0.28 water/binder ratio and found to be 52,42 GPa, while the control group series reached level of 49,58 GPa at the same water/binder ratio. Finally, when brittle index was compared, it was seen that the second series concrete specimens gave similar results to the control group and the highest value reached 2.88.
The test results of the third series produced by using ferrochrome slag aggregate and blast furnace slag together and activated by alkaline activators were compared with the concrete sample control group. As a result of comparison; third series specimens gave the best performance in compressive strength at 0.33 water/binder ratio and reached level of 78.1 MPa, while the control group series reached level of 69,8 MPa at the same water/binder ratio. For splitting tensile strength test results, specimens of the third series gave best performance at 0.28 water/binder ratio and reached level of 6,8 MPa, while the control group series reached level of 6,62 MPa. When the modulus of elasticity is compared, the third series productions are much lower than the control group. The greatest modulus of elasticity was obtained at 0.33 water/binder ratio and found to be 37.31 GPa. Finally, when brittle index was compared, it was seen that the third series concrete specimens gave similar results to the control group and the highest value reached 2.79.
Considering the test results obtained from second series specimens which is produced by using ferrochrome slag as a concrete aggregate and Portland cement as binder, it can be said that the use of this material as an aggregate in the production of concrete is very suitable in terms of the mechanical properties of the concrete.
The main constituents of third series were ferrochrome slag and ground granulated blast furnace slag, which are completely industrial waste materials. Moreover there was no Portland cement used in this series. Also considering the test results obtained from third series specimens, it can be said that using these materials together both will give sufficient mechanical properties and not effect enviroment in a negative way. From the point of sustainability, this features are very important to have.