Browsing by Author "Aksoylu, Ceyhun"

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Highly Effective Injection Composites With Fly Ash and Microsilica for Soil Stabilization
(MDPI, 2025) Ozkilic, Yasin Onuralp; Beskopylny, Alexey N.; Aksoylu, Ceyhun; Stel'makh, Sergey A.; Shcherban', Evgenii M.; Madenci, Emrah; Kosykh, Alexey
Injection composites based on mineral binders are widely used for soil stabilization, using jet grouting technology to solve various geotechnical problems. Cement, which contains toxic components and worsens the ecology of the environment, is typically the main mineral component used to manufacture injection composites. Reducing cement consumption in the production of building materials is currently of great importance. This study developed highly effective, environmentally friendly injection composites for soil stabilization based on three mineral components: Portland cement, fly ash (FA), and microsilica (MS). FA was introduced into the composites as a partial Portland cement substitute, in amounts ranging from 5 to 50% in 5% increments. The properties of fresh and hardened composites, including the density, flow rate, water separation, compressive strength at 7 and 28 days, and the structure and phase composition of the composites, were studied. The inclusion of FA in the composition of composites contributes to a decrease in density by 16.9%, from 1.89 g/cm3 to 1.57 g/cm3, and cone spread by 9%, from 30.1 cm to 27.4 cm, and an increase in water bleeding by 91.4%, from 3.5% to 6.7%, respectively. Based on the results of the experimental studies, the most effective dosage of FA was determined, which amounted to 20%. An increase in compressive strength was recorded for composites at the age of 7 days of 8.3%, from 33.6 MPa to 36.4 MPa, and for compressive strength at the age of 28 days of 9.4%, from 41.3 MPa to 45.2 MPa, respectively. SEM and XRD analysis results show that including FA and MS promotes the formation of additional calcium hydrosilicates (CSH) and the development of a compact and organized composite structure. The developed composites with FA contents of up to 50% exhibit the required properties and can be used for their intended purpose in real-world construction for soil stabilization.
The Influence of Fiber-Form Waste Tire Aggregates on the Flexural Strength, Ductility, and Energy Dissipation of Pultruded GFRP-Rubberized Concrete Hybrid Beams
(MDPI, 2025) Ecemis, Ali Serdar; Karalar, Memduh; Beskopylny, Alexey N.; Stel'makh, Sergey A.; Shcherban, Evgenii M.; Aksoylu, Ceyhun; Ozkilic, Yasin Onuralp
This study investigates the effects of different proportions of waste rubber fiber aggregates on the flexural behavior of reinforced concrete beams. Beam specimens were prepared with different proportions (5%, 10%, and 15%) of waste rubber fiber aggregates, and composite beams formed with pultruded GFRP profiles were tested under vertical load. According to the results of this study, cube compressive strength, cylinder tensile strength, and beam flexural strength decreased by 27.5%, 50%, and 47.6%, respectively, with the use of a 15% waste rubber aggregate. As a result of the four-point bending tests performed on reinforced concrete beams, the maximum load-carrying capacity of the beams decreased significantly after increasing the waste rubber aggregate ratio to 10% and 15%. However, a general improvement in the ductility of the beams was observed. One of the main results of this study is that when the waste rubber aggregate content is 5%, the best balance between strength and ductility is achieved, and the performance closest to the reference beams is obtained. The tests also revealed that the & Oslash;10-5% specimen exhibited higher performance in terms of both load-carrying capacity and yield stiffness. On the other hand, although the 15% waste rubber aggregate ratio caused a decrease in the maximum load-carrying capacity. along with an increase in the diameter of the tensile reinforcement, this decrease was quite low. Finally, an overall decrease in energy consumption capacity was observed with increasing waste rubber aggregate content in all test beams. This can be attributed to the acceleration of shear damage in the beam and the shrinkage of the area under the load-displacement curve as the amount of waste increases. Additionally, SEM analyses were conducted in order to investigate the microstructural behavior of the rubberized concrete. This study has shown that the use of waste rubber aggregates can be environmentally and economically beneficial, especially at the 5% level.
Nonlinear Finite Element Evaluation of the Seismic Performance of the Historic Ayvat Masonry Weir
(Springer, 2025) Mollamahmutoglu, Cagri; Ozturk, Mehdi; Aksoylu, Ceyhun; Madenci, Emrah; Ozkilic, Yasin Onuralp
A nonlinear seismic assessment of the 18th-century Ayvat masonry weir was performed by integrating three-dimensional finite-element (FE) modeling with Ground-Penetrating Radar (GPR) surveys. A detailed ABAQUS model of approximately 70000 continuum elements was developed and calibrated using laboratory-measured stone-mortar properties and GPR-derived foundation profiles. Nonlinear time-history analyses were carried out under Turkish Earthquake Code (TEC-2018) hazard levels DD1 (2%/50 yr) and DD2 (10%/50 yr) for both principal-axis and 45 degrees-rotated records. Under the 45 degrees-rotated DD1 record (EQ1R), crest-to-base displacements reached up to 0.30 m, and the isolated local maximum damage parameter (PEMAX*) reached 0.47. In contrast, under the 45 degrees-rotated DD2 record (EQ2R), maximum displacements remained below 0.01 m and PEMAX* did not exceed 0.14, thereby preserving global stability while inducing residual strains at the abutments. Stress concentrations were consistently detected at material discontinuities and joint zones. Based on these results, targeted retrofitting measures, including joint reinforcement and localized strengthening, are recommended to ensure the structural safety and preserve the heritage integrity of historic masonry weirs.
Sustainable Concrete with Waste Tire Rubber and Recycled Steel Fibers: Experimental Insights and Hybrid PINN-CatBoost Prediction
(MDPI, 2025) Ecemis, Ali Serdar; Yildizel, Sadik Alper; Beskopylny, Alexey N.; Stel'makh, Sergey A.; Shcherban', Evgenii M.; Aksoylu, Ceyhun; Ozkilic, Yasin Onuralp
The growing environmental concern over waste tire accumulation necessitates innovative recycling strategies in construction materials. Therefore, this study aims to develop and evaluate sustainable concrete by integrating waste tire rubber (WTR) aggregates of different sizes and recycled waste tire steel fibers (WTSFs), assessing their combined effects on the mechanical and microstructural performance of concrete through experimental and analytical approaches. WTR aggregates, consisting of fine (0-4 mm), small coarse (5-8 mm), and large coarse (11-22 mm) particles, were used at substitution rates of 0-20%; WTSF was used at volumetric dosages of 0-2%, resulting in a total of 40 mixtures. Mechanical performance was evaluated using density and pressure resistance tests, while microstructural properties were assessed using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The findings indicate systematic decreases in density and compressive strength with increasing WTR ratio; the average strength losses were approximately 12%, 20%, and 31% at 5%, 10%, and 20% for WTR substitution, respectively. Among the WTR types, the most negative effect occurred in fine particles (FWTR), while the least negative effect occurred in coarse particles (LCWTR). The addition of WTSF compensated for losses at low/medium dosages (0.5-1.0%) and increased strength by 2-10%. However, high dosages (2.0%) reduced strength by 20-40% due to workability issues, fiber clumping, and void formation. The highest strength was achieved in the 5LCWTR-1WTSF mixture at 36.98 MPa (approximate to 6% increase compared to the reference/control concrete), while the lowest strength was measured at 16.72 MPa in the 20FWTR-2WTSF mixture (approximate to 52% decrease compared to the reference/control). A strong positive correlation was found between density and strength (r, Pearson correlation coefficient, approximate to 0.77). SEM and EDX analyses confirmed the weak matrix-rubber interface and the crack-bridging effect of steel fibers in mixtures containing fine WTR. Additionally, a hybrid prediction model combining physics-informed neural networks (PINNs) and CatBoost, supported by data augmentation strategies, accurately estimated compressive strength. Overall, the results highlight that optimized integration of WTR and WTSF enables sustainable concrete production with acceptable mechanical and microstructural performance.