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 - 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.