Civil Engineering / İnşaat Mühendisliği
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Review Citation - WoS: 42Citation - Scopus: 49Utilization of Waste Materials in the Stabilization of Expansive Pavement Subgrade: an Extensive Review(Elsevier, 2023) Tanyıldızı, Muhammed; Uz, Volkan Emre; Gökalp, İslamExpansive soils, also known as swell-shrink soils, are one of the most problematic soils in highway construction and exhibit significant volume changes by swelling and shrinking while wet and dry, respectively. These changes in soil cause cracks, heaves, differential settlements, and damages to the overlying pavements leading to high maintenance costs. The annual average maintenance cost of structures built on expansive soils ranges from $9 to $15 billion, with 50% of the expenses associated with highways and streets. Chemical stabilization techniques such as cement and lime stabilization are one of the most efficient ways to treat expansive soils. However, there is a need to develop environmentally friendly approaches to stabilize expansive soils due to worldwide growing interest in sustainable developments and concerns about greenhouse gas emissions and climate change. In this context, using waste materials in soil stabilization has been considered an important issue for sustainability concerns. The aim of the current study is to review the relevant studies performed to improve the geotechnical and engineering properties of expansive subgrade soils of pavements by using waste materials arising from industrial, agricultural, and other activities in the last decade. In the organization of this study, characteristics of expansive soils including plasticity, compaction, strength & stiffness, microstructural characteristics, shrink-swell properties, and durability were focused to point out the effect of the waste materials. The overall results obtained throughout the scope of the current study indicated that the use of waste materials in soil stabilization improves the engineering properties of expansive soils, significantly. This paper also provides key information and creates awareness for researchers and sector representatives about sustainable soil stabilization.Article Citation - Scopus: 1Relationship Between Abrasion, Fragmentation and Thermal Weathering Resistance of Aggregates: Regression and Artificial Neural Network Analyses(Springer, 2023) Gökalp, İslam; Kaya, Orhan; Uz, Volkan EmreFor being used in pavement construction, properties of aggregates must satisfy the minimum requirements specified by highway agencies or institutions. The properties of the aggregates are determined by many tests lasting anywhere between a couple of hours to a few weeks depending on the type of the test. If good correlations can be established between the tests taking longer time and the ones taking comparably shorter time, there might be no need to conduct these longer time-taking tests for the sake of time. The aim of this study is to investigate the relationships between abrasion, fragmentation, and thermal weathering resistances of different aggregate types. To accomplish this aim, aggregates with different origins (natural and slags) were tested and correlative analyses utilizing regression analysis and artificial neural network (ANN) models were performed to establish relationships between the results of these test methods. It was found that good correlations can be established especially with ANN models and significant amount of time and effort can be saved with these developed models. © 2023, The Author(s), under exclusive licence to Chinese Society of Pavement Engineering.Article Investigation of the Effect of Aggregate Specific Gravity on Optimum Bitumen Content of Hot Mix Asphalt(2022) Saltan, Mehmet; Karadağ, Öznur; Uz, Volkan Emre; Kaçaroğlu, Gizem; Gökalp, İslamIn this study, effect of aggregate specific gravity, which is directly related to origin of aggregates used in hot mix asphalt on optimum bitumen content, indirect tensile strength and tensile strength ratio of hot mix asphalt, was investigated. Specific gravity (SG) values of one kind of limestone aggregate were calculated according to Turkish Standard (TS), American Society for Testing and Materials (ASTM) and American Association of State Highway and Transportation Officials (AASHTO) standards, separately. Although one kind of limestone aggregate and 50/70 penetration grade bitumen are used in the mixtures, different values were obtained in terms of optimum bitumen content, indirect tensile strength and moisture sensitivity due to differences in the specific gravity values of the aggregates. Optimum bitumen contents were found by using TS, ASTM and AASHTO standards as 5.03%, 4.75% and 4.59%, respectively. According to the cost – benefit analysis, it can be said that changes in aggregate specific gravity values, which were calculated, based on different standards provide economic benefit. Overall, the results indicated that specific gravity values of one kind of limestone aggregate used in hot mix asphalt have significantly affected optimum bitumen content and indirect tensile strength of the mixtures.Article Citation - WoS: 2Citation - Scopus: 3Site Assessment of Surface Texture and Skid Resistance by Varying the Grit Parameters of an Sma(American Society of Civil Engineers (ASCE), 2022) Gökalp, İslam; Uz, Volkan Emre; Saltan, Mehmet; Tepe, MehtapFor the sale operation of vehicles, pavement should provide adequate skid resistance, which can be achieved by using high polishing-resistant aggregate in wearing courses. However, supplying high-quality aggregate is not always feasible due to high transportation costs. For this reason, a method called gritting was adapted to meet the Highway Technical Specification (HTS) of Turkey in 2013. According to the method, for certain parts of the country, the wearing course can be constructed with local aggregates that have minimum polished stone value (PSV) of 40 (PSV >= 40), but, in this case, the surface must be covered with a high polishing-resistant aggregate (PSV >= 50), after the rollers' first pass. The objective of this study was to improve the present gritting method by investigating the effect of grit parameters on pavement performance under real traffic conditions. In this regard, during its construction, the wearing course of 0-51 Highway was gritted with different aggregate types (slags and natural), sizes (1-3; 1-5 mm), spreading amount (1.5; 2; 2.5 kg/m(2)), and spreading time (before and after the first pass of a roller) on eight test sections. Then, the macrotexture and skid resistance performance of these sections were evaluated under real traffic and environmental conditions for longer than 4 years. Changes in surface texture and skid resistance with respect to traffic were determined for each section. The results showed that higher skid resistance values were obtained at the sections gritted with metallurgical slags. Additionally, the sections gritted with 1-5 mm aggregates had better skid resistance than those gritted with 1-3 mm, while the change in mean texture depths were not very significant.Article Citation - WoS: 4Dönel Kavşak Geometrik Elemanlarının Kavşak Güvenliği Üzerine Etkisinin Literatür Işığında Değerlendirilmesi(2021) Özinal, Yağmur; Uz, Volkan EmreUlaşım sistemi içerisindeki trafik akımının güvenli ve etkin biçimde işlemesi üzerinde büyük rolü bulunan kavşaklar, faaliyet alanı, geometrik özellikleri ve denetim şekillerine göre farklı kategorilere ayrılmaktadır. Kontrollü eş düzey kavşak kategorisindeki dönel kavşaklar, trafik akımının merkezi ada etrafında yönlendirildiği ve ada içerisindeki araçların ilk geçiş hakkına sahip olduğu kavşak tipidir. Dönel kavşakların her bir geometrik elemanı kavşağın işleyiş, kapasite ve güvenliği üzerinde rol oynamaktadır. İyi tasarlanmış bir dönel kavşak, araçların dolaşım yolu boyunca hızlarının sabit kalmasını sağlayarak kavşak güvenliğinin optimize edilmesine yardımcı olur. Bu makalede, dönel kavşakların geometrik elemanlarının kavşak güvenliği üzerine etkilerinin incelendiği çalışmalar derlenmiştir. Dönel kavşakların her bir geometrik elemanın literatürde yer alan çalışmalar ışığında kavşak güvenliğiyle olan ilişkileri ve bazı ülkelerin standart/kılavuzlarında yer alan tasarım kriterleri incelenmiştir. Bu çalışmayla amaçlanan, yapılmış çalışmalar doğrultusunda, dönel kavşak geometrik elemanlarının tasarımlarının kavşak güvenliği açısından hayati önem taşıdığını ortaya koymaktır. Ülkemizde bu konuyla ilgili olarak daha önce yapılmış detaylı çalışmalara rastlanılmaması çalışmamızın motivasyon kaynağı olmuştur. Ülkemizdeki dönel kavşakların hangi standart/kılavuzlara bağlı olarak yapıldığı ile ilgili bilgi yetersizliği olduğu da görülmektedir. Çalışma sonucunda dönel kavşaklardaki güvenliğin sağlanabilmesi için geometrik elemanların birbirleriyle etkileşim içinde ve uygun fiziki boyutlarda tasarlanması gerektiği belirtilmiştir. Ayrıca trafik güvenliği bakımından ülkemizde bu konuyla ilgili ivedilikle çalışmalara başlanılması ve ülkemiz koşullarına özgü tasarım standart/kılavuzu hazırlanması gerektiği ifade edilmiştir.Article Citation - WoS: 5Citation - Scopus: 6Sustainable Production of Aging-Resistant Bitumen: Waste Engine Oil Modification(American Society of Civil Engineers, 2021) Gökalp, İslam; Uz, Volkan EmreUsing waste engine oil (WEOIL) within bituminous binders might be one of the most energy-efficient and sustainable means of producing aging-resistant bitumen due to the antioxidative properties of WEOIL. In this paper, the use of WEOIL to obtain aging-resistant bitumen and its optimum rates for short and long terms were investigated. In this regard, a base bitumen was modified with WEOIL in certain rates ranging from 1% to 5% by weight of bitumen. Then base and oil-modified bitumen samples were subjected to aging. To define the changes in rheological properties of bitumen based on rutting, fatigue, and thermal cracking resistance, dynamic shear and bending beam rheometer tests were performed on each sample. Furthermore, an aging index (AI) analysis was performed for both the short- and long-term aging conditions to express the effect of WEOIL on aging resistance of the bitumen. According to the AI analysis, short-term-aging-resistant bitumen is obtained by adding 3.5% WEOIL to the base bitumen, while a 5.8% contribution rate is required to avoid the long-term aging effect. Moreover, the increase in rate of WEOIL content improved the low-temperature cracking resistance. Consequently, utilizing WEOIL for production of aging-resistant bitumen can provide environmental and economic benefits based on conservation of natural resources and waste recycling.Article Citation - WoS: 19Citation - Scopus: 19Effect of Aggregate Microtexture Losses on Skid Resistance: Laboratory-Based Assessment on Chip Seals(American Society of Civil Engineers, 2020) Ergin, Basri; Gökalp, İslam; Uz, Volkan EmreSkid resistance has long been recognized as one of the most important pavement surface characteristics for safer roads. Evaluation of skid resistance of pavement is crucial but it is not an easy task. Moreover, it depends on numerous parameters such as pavement type, materials and tire properties, and environmental conditions. Aggregate texture changes significantly according to its origin and affects the skid resistance performance of the road surfaces. In the current study, chip seal samples were produced with different aggregate types at different polishing levels to evaluate the effect of aggregate microtexture on skid resistance performance. The Micro-Deval (MD) test device was utilized to obtain polished aggregates. Different polishing levels were provided by distinct revolutions of the MD drum. To monitor the change in aggregate surface with the polishing process, aggregates were monitored by scanning electron and optical microscopes at each level. Mean texture depths (MTDs) of chip seals were determined with outflow meter test. On the other hand, dynamic friction tester (DFT) and British pendulum tester (BPT) were implemented for assessment of skid resistance according to the relevant ASTM standards. Skid resistance and texture measurements were further used to identify the International Friction Index (IFI) for each sample. In addition, a correlational analysis was conducted between DFT and BPT results, and variable relationships were set for different speeds. Consequently, better skid resistance values were observed for chip seals produced by slags than the ones with natural aggregates at each polishing level. After fulfilling the economic and environmental requirements, using metallurgical by-products is recommended for long-lasting skid-resistant pavement surfaces. Additionally, it can be concluded that MD apparatus may be considered an easier, more cost-effective, and faster way to assess the polishing resistance of aggregates.Article Citation - WoS: 28Citation - Scopus: 31Sustainable Recovery of Waste Vegetable Cooking Oil and Aged Bitumen: Optimized Modification for Short and Long Term Aging Cases(Elsevier, 2020) Uz, Volkan Emre; Gökalp, İslamBitumen ages in the short and long-term due to environmental conditions. As the bitumen ages, it loses its original properties and flexibility. Hardened bitumen causes certain distresses in pavement that may endanger traffic safety and reduce travel comfort. Bitumen is one of recoverable material, however some techniques may not be ecological due to considerable energy, time, and cost. On the other hand, recovering of aged bitumen might be eco-friendlier, energy-efficient, and economic by using bio-based waste materials such as waste vegetable cooking oils (WVCO). In this perspective, this paper was established on the idea of sustainable recovery of aged bitumen and WVCO. Base bitumen was aged in case of short-term (ST) and long-term (LT) in laboratory condition and modified with WVCO ranging from 2 to 10% by weight of bitumen. To determine the effect of WVCO modification on aged bitumen conventional and rheological test methods were utilized. To find the optimum rate of WVCO for full recovery of aged bitumen, an index called Pure Rejuvenation Index (PRI) was specified and applied for each test results. It can be concluded from PRI analyses that WVCO can be used as rejuvenator to recover aged bitumen and approximately 3% and 6% of WVCO are required for ST and LT aged bitumen cases, respectively. However, different test methods yield different optimum rates of WVCO for ST and LT aged bitumen. Recovering of WVCO and aged bitumen by using together may provide environmental protection and conservation of resources.