https://hdl.handle.net/20.500.12809/211 2026-04-07T12:02:11Z 2026-04-07T12:02:11Z Kasap Keskin, Özlem Keskin, Süleyman B. Tekin, Kamil https://hdl.handle.net/20.500.12809/11014 2023-10-11T08:28:42Z 2023-01-01T00:00:00Z

Predicting the Ultimate Properties of Engineered Cementitious Composites by Maturity Method Kasap Keskin, Özlem; Keskin, Süleyman B.; Tekin, Kamil This study examines the application of the maturity method to obtain the ultimate properties of ECC. Within the scope of the study, the maturity method according to the Arrhenius equation was applied to four different ECC mixtures encountered in the literature: the activation energies and the ages at which they achieve ultimate properties were determined. Subsequently, the mixtures were subjected to standard and accelerated curing to reach an equivalent age of 1 year. The properties of the specimens at 1-year equivalent age were determined after both standard curing at 23°C and accelerated curing at 60°C. Thus, both the validity of the maturity method and the effect of accelerated curing in ECC were evaluated. Mechanically, compressive and flexural tests were performed, while non-destructive tests such as ultrasonic pulse velocity, rapid chloride ion penetration, and resonant frequency were used to determine ECC properties. As a result, it was determined that all ECC mixtures achieved their ultimate properties in less than a year. Furthermore, it was revealed that ECC retains its distinctive properties even in the ultimate state. Additionally, while accelerated curing led to a slight decrease in all properties compared to normal curing, it contributed to a slight improvement in deformation capacity. Nevertheless, considering the proximity of the results between normal and accelerated curing, it can be concluded that accelerated curing has the potential to be applied in ECC, and based on the findings, the maturity method has the potential to predict the long-term properties of ECC mixtures.

2023-01-01T00:00:00Z Gülkan, H. Polat Akansel, Vesile Hatun Kalkan, Erol https://hdl.handle.net/20.500.12809/10905 2023-08-22T11:43:15Z 2023-01-01T00:00:00Z

Response spectrum shapes implied by earthquakes in Turkey: comparisons with design spectra Gülkan, H. Polat; Akansel, Vesile Hatun; Kalkan, Erol Design spectrum shape in many recent standards and codes is defined by spectral accelerations for two periods, Ts,(~0.2s) and T1,(~1 s), modified by multiplicative factors that account for the site class and strength of the ground shaking. This article draws attention to apparent discord between spectra from actual recordings at a number of stations of the national strong motion network of Turkey with the design spectra for the same location and site characteristics as given by the national seismic hazard map. We find that, for deep basins with Site Class D or E profiles, the design spectrum seems not to recognize consistently the constant velocity and longer period demand. If this conjecture is true, it may foreshadow unsafe designs for the building stock in Turkey in similar environments. Many more earthquake recordings than are currently at hand are needed to verify the applicability of using the two-point design spectrum that is embedded in the regulation. This is not a unique problem only to the Turkey Building Earthquake Regulation (TBER 2018). The recently recorded strong ground motion records from the 06 February 2023, M 7.7 and M 7.5 Kahramanmaraş, earthquakes support the conjecture of this study and provide strong evidence for a need to revise the corner periods of the design spectrum in the Regulation.

2023-01-01T00:00:00Z Özkılıç, Yasin Onuralp Zeybek, Öze Bahrami, Alireza Çelik, Ali İhsan https://hdl.handle.net/20.500.12809/10868 2023-08-09T08:25:42Z 2023-01-01T00:00:00Z

Optimum usage of waste marble powder to reduce use of cement toward eco-friendly concrete Özkılıç, Yasin Onuralp; Zeybek, Öze; Bahrami, Alireza; Çelik, Ali İhsan In this study, waste marble powder (WMP) was used to replace cement of concrete in specific amounts. To accomplish this aim, WMP was replaced at 10%, 20%, 30%, and 40% of the cement weight, and a reference concrete sample without WMP (REF) was created to compare the compressive strength, splitting tensile strength, and flexural strength. The replacement of WMP at 10%, 20%, 30%, and 40% of the cement weight resulted in 5.7%, 21.7%, 38.1%, and 43.6% decreases in the compressive strength compared with REF. Furthermore, the splitting tensile strength results commonly followed the same trend as the compressive strength. However, WMP at 10%, 20%, 30%, and 40% led to 5.3%, 8.6%, 19.4%, and 26.7% decreases in the flexural strength compared with REF. In addition, three different calculations, ranging from simple to complex, were proposed to compute mechanical resistances of concrete with WMP. These proposed calculations for practical applications were validated using values from the literature and the implications obtained from the current research. While the simple calculations were based on the strength of REF and the WMP percentages, the complex calculations were dependent on the design of the concrete mixture, age of the samples, and the WMP percentages. For the complex calculations, the ANN approach was used with the help of the coefficient of determination (R2) for the K-fold cross validation method. All the proposed methods provided high accurate estimation to predict the properties of concrete with WMP. Based on the studies, utilizing 10% WMP as the replacement of cement is recommended to obtain the optimum benefits considering both mechanical and environmental aspects. Moreover, scanning electron microscope (SEM) and energy dispersive X-ray (EDX) analyses were then conducted to observe the interaction of WMP in concrete. According to the SEM analyses, some pores were detected and the interfacial transition zone was observed in the reaction zone. On the other hand, based on the EDX analyses, the presence of WMP in concrete was manifested by the presence of high levels of calcium.

2023-01-01T00:00:00Z Arslan Kaya, Tuğçe Nagihan Sarı, Erol Gül, Murat https://hdl.handle.net/20.500.12809/10830 2023-08-02T12:28:33Z 2023-01-01T00:00:00Z

Assessment of eco-toxicological and health risks of core sediment from İzmit Gulf, Marmara Sea, Türkiye Arslan Kaya, Tuğçe Nagihan; Sarı, Erol; Gül, Murat A comprehensive geochemical study was carried out to evaluate the environmental and human health effects of metal pollution in the Gulf of İzmit. For this purpose, the toxic and ecological risk distributions of a sediment core collected from 156 m water depth were determined. The mean concentrations of the studied metals as mg/kg dry weight in the İzmit Gulf core sediments were found to be in the following order: Cr (150.3) > Zn (122.7) > Pb (48.3) > Cu (35) > As (28) > Co (19.7) > Cd (3.6). A Contamination Factor (CF), Pollution Load Index (PLI), and Geo-Accumulation Index (Igeo) were used to assess sediment pollution. Increased industrial and agricultural activities around the İzmit Gulf has caused contamination in metals concentration, such as Cu (CF = 1.2), Zn (CF = 1.7), and Pb (CF = 1.5). This finding showed that Cu, Zn, and Pb contamination levels in the inspected core samples were moderate. Additionally, mean PLI values (1.2) point to human-induced contamination in the Izmit Gulf. The adverse effects of toxic metals on the organisms living in benthic environments were determined according to the Sediment Quality Guidelines (SQGs). According to SQG, living is exposed to toxic effects in terms of Cr, As, and Cd. The impacts of these toxic metals on human health were investigated by the Hazard Index (HI) and Cumulative Cancer Risk (LCR) parameters. Adults are not at risk from HI-As, however children have a value greater than 1 and require attention. LCR is another risk factor for Cd in adults and Cd and Cr in children.

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