Browsing by Author "Cakir, Ozgur"

Now showing 1 - 6 of 6

Durability Properties of Treated Recycled Aggregate Concrete: Effect of Optimized Ball Mill Method
(Elsevier Sci Ltd, 2021) Cakir, Ozgur; Dilbas, Hasan
In this paper, effects of optimized Ball Mill Method (oBMM) with silica fume (SF) and/or basalt fiber (BF) on durability of untreated recycled aggregate concrete (RAC) and treated recycled aggregate concrete (RAiC) are investigated. 84 concrete series were designed in the experimental program and it is aimed to find the best series objectively depending on experimental results. In the program, many concrete series included natural aggregate (NA), recycled aggregate (RA) and treated RA by oBMM (RAi) and SF, BF SF + BF at various ratios were produced. The physical and the mechanical properties of concretes were determined at the age of 28 days. TOPSIS (Technique for Order Preference by Similarity to Ideal Solution) was considered to select the best concrete series among 84 series. Then, the durability properties of the selected series were determined at the age of 28 days and the test results were compared. According to the test results, it was found that RAi decreased the performance of concrete marginally and oBMM caused a significant improvement compared to RAC. TOPSIS was a useful method to determine the best concrete series and could be used objectively if the weighting coefficients of TOPSIS depended on literature data. It was interesting that the best concrete series determined by TOPSIS were found including 10% SF only for each RA replacement proportions (these are 20%, 40% and 60% by volume) and the best series had satisfactory durability properties in comparison to control concrete. In addition, the durability performance of the best series included up to 60% RAi was generally superior to that of RA. (C) 2020 Elsevier Ltd. All rights reserved.
An Experimental Investigation on Fracture Parameters of Recycled Aggregate Concrete With Optimized Ball Milling Method
(Elsevier Sci Ltd, 2020) Dilbas, Hasan; Cakir, Ozgur; Yildirim, Hasan
In this paper, Ball Milling Method (BMM) is employed on recycled aggregate (RA) with an optimization process which is conducted to enhance RA efficiently eliminating attached old mortar (AOM) content in RA. Various combinations of drum rotation (R) (100-200-300-400-500) and the steel balls (S) (0-2-5-7-10-12) applied to the recycled aggregate during the BMM process and treated recycled aggregates (RAi) are obtained. The mechanical properties (compressive, splitting tensile and flexural strength values and elasticity modulus) and the non-linear fracture parameters (effective crack length, crack mouth opening displacement, crack tip opening displacement, initial cracking toughness, unstable fracture toughness and fracture energy) of concretes including untreated and treated recycled aggregate (RAi) are determined. The test results proved that the water absorption values of recycled aggregates in the size of 4-11.2 mm and 11.2-22.4 mm reduced from 8.80% to 1.40% and 8.95% to 0.84%, respectively, after treatment process. It is also found that the compressive strength of concretes are marginally affected with the use of treated recycled aggregate (RAi) up to 60% which is twofold of the optimum recycled aggregate proportion given in the literature. Moreover, 60% RAi content in concrete can be recommended in terms of fracture characteristics (a(c), CMODc, CTODc, K-ic(ini), K-ic(un) and G(F)). (C) 2020 Elsevier Ltd. All rights reserved.
Influence of Basalt Fiber on Physical and Mechanical Properties of Treated Recycled Aggregate Concrete
(Elsevier Sci Ltd, 2020) Dilbas, Hasan; Cakir, Ozgur
This paper investigates the effect of the treatment methods on the physical and the mechanical properties of recycled aggregate concrete (RAC). The optimized Ball Mill Method (oBMM) and the incorporation of basalt fiber (BF) in concrete were employed as treatment process and the combination of oBMM and BF were utilized in this experimental study. It was intended using the treatment methods that the application of oBMM on recycled aggregate (RA) cleaned the most part of attached old mortar (AOM) content in RA and the incorporation of BF in concrete eliminated the adverse effects of remaining AOM in treated RA (tRA) strengthening mortar phase of concrete. Hence, to observe the improvement impact of treatment on the performance of concretes, twenty-eight concrete series including natural aggregate (NA), 20-40-60% RA and 20-40-60% tRA with 0-0.25-0.50-1.0% BF were produced in the laboratory. The physical and the mechanical tests were conducted on concrete specimens at the age of 28 days. According to the test results, although the physical properties were negatively affected by the incorporation of RA and tRA with/without BF in concrete, the mechanical properties of RACs and tRACs were improved by the incorporation of BF. Besides, the impact of treatment were significantly observed, especially for higher rates of RA (60%). The optimum proportion of BF was found as 0.50% BF with 60% tRA regarding compressive strength test results only. (C) 2020 Elsevier Ltd. All rights reserved.
Physical and Mechanical Properties of Treated Recycled Aggregate Concretes: Combination of Mechanical Treatment and Silica Fume
(Asce-amer Soc Civil Engineers, 2021) Dilbas, Hasan; Cakir, Ozgur
This paper presents the combined effect of the mechanical treatment of recycled aggregate (RA) and the use of silica fume (SF) in the concrete mixes. In the first step, the RA is treated by the optimized ball mill method (oBMM) to decrease mortar content. In the second step, the SF is used to enhance the negative effects of the attached old mortar (AOM) that has remained in the RA. In this method, natural aggregate (NA), RA, and treated RA (tRA) at various ratios (20%-40%-60%) with 0%-5%-10% SF are used in the mixes. After 28 days, tests are carried out on the specimens. The results show that the mechanical treatment followed by the SF combination significantly enhances the performance of recycled aggregate concretes (RACs). Satisfactory test results are generally obtained for treated recycled aggregate concrete (tRAC) produced with up to 60% tRA and 10% SF. This improvement can be explained as the consequence of the removal of AOM by oBMM and eliminating the adverse effects of the remaining part of AOM in tRA by SF addition in concrete.
Silica Fume Effect on Fracture Parameters and Cracking Pattern Maps of Recycled Aggregate Concrete
(Gazi Univ, Fac Engineering Architecture, 2019) Cakir, Ozgur; Dilbas, Hasan
The paper demonstrates the determination of the fracture parameters of concretes included recycled aggregate (RA) and silica fume (SF) and the crack pattern of a reinforced concrete beam. Double-K fracture model (DKFM) is considered in this paper and the required parameters for DKFM are obtained from the model simulated using finite element method (FEM) in Abaqus. In the simulation parts geometric nonlinearity and material nonlinearity is considered and the parameters of materials for modelling applications depends on the experiments. The fracture parameters are calculated after obtaining the FEM model analyses. The implemented study of fracture behavior of the conventional and recycled aggregate concretes with and without SF and RA reveals that the conventional concrete fracture models (double-K fracture model) could be used to determine the fracture parameters and fracture behavior of RAC and both SF and RA use in concrete has an effect on fracture properties is found. Moreover, crack pattern of a reinforced concrete beam with and without RA and SF is investigated. According to the results, number of cracks decrease but the depth of cracks increase and initial cracking toughness increases if both RA and SF are used at various ratios in the concretes. Although RA inclusion in concretes decreases the rigidity of the beam, approximately equal elastic bearing capacity of the beam is found.
Silis Dumanı Katkılı Geri Kazanılmış Agregalı Betonların Elastisite Modüllerinin Karşılaştırmalı Analizi
(2018) Dilbas, Hasan; Cakir, Ozgur
Atık malzemelerin geri dönüşümü, doğal kaynakların korunmasından ve yaşanabilir bir gelecek için öncülük edecek çevresel etkilerinin azaltılmasından dolayı, yapı sektöründe sürdürülebilirlik kavramı üzerinde önemli bir etkiye sahiptir. Yapım işlemleri, genellikle, yüksek miktarda yapı ve yıkıntı atığı (YYA) oluşumuyla sonuçlanmakta ve geri dönüşüm işlemi ardından YYA bertaraf edilmesi için inşaat mühendisliği uygulamalarında, özellikle geri kazanılmış agregalı betonda (GKA-B), geri kazanılmış agrega (GKA) olarak kullanımı büyük potansiyele sahiptir. Bu bağlamda, çeşitli oranlarda GKA (0-30-40-70-100%) ve çeşitli oranlarda silis dumanı (SD) (0-5-10%) içeren beton karışımları GKA-B‘ nun elastisite modülünü belirlemek üzere üretilmiştir. Bu çalışma, çeşitli standartlar tarafından ve çeşitli araştırmacılar tarafından önerilen teorik elastisite modülü formüllerince hesaplanan GKA-B elastisite modülü değerlerinin deneysel olarak elde edilen GKA-B elastisite modülü değerlerine yakınlıklarının olup olmadığını göstermeyi amaçlamaktadır. Analitik ve istatistik değerlendirmeler yapılmıştır. Sonuç olarak, GKA oranının betondaki artışı ile elastisite modülü azalmaktadır. GKA-B’da SD kullanımı elastisite modülünü ve basınç dayanımını artırmaktadır. İrdelenen standartlar göz önüne alındığında, Amerikan standardı (ACI 318-05) elastisite modülünü deneysel sonuçlara göre, en yüksek standart sapma göstermesine rağmen, yakın tahmini vermektedir. Diğer taraftan araştırmacılar tarafından GKA-B elastisite modülü tahmini için önerilen denklemler, irdelenen standartların ve deney sonuçlarının üzerinde sonuç vermektedirler. SD içeren ve içermeyen betonlar için bir elastisite modülü denklemi de bu çalışmada önerilmektedir.