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    Investigation of mechanical properties of high-performance hybrid fiber concretes adding nanomaterials using with coarse aggregate
    (Elsevier Science Inc, 2021) Oksuzer, Nurullah; Anil, Ozgur; Aldemir, Alper; Sahmaran, Mustafa
    High-performance hybrid fiber cement composites have more ductility and higher strength than traditional concrete. This is because crack development is limited due to multiple small cracks are formed instead of a single large crack as the fibers enter the matrix. It is customary to produce these concrete composites with fine aggregates. In this study, concrete composites with coarse aggregates were strived to be produced to gain some feasibility. To this end, different mixtures composed of different aggregate/binder ratios and different fly ash/ binder ratios were designed. In order to compare the effectiveness of the combination of different fibers were utilized in these mixtures. The volumetric ratios of fibers (excluding reference samples) were kept constant at a value of 2%. For each mixture, four-point bending and compressive tests were performed. The increase in the aggregate ratio was observed to cause a more ductile flexural behavior in mixtures composed of PVA and steel fibers. In contrast, the ductility was reduced in mixtures with Nylon-mono and steel fibers. In addition, the ductility values were enhanced with the increase in FA/PC ratio. In addition, the possibility to use the cheaper Nylon-mono fibers in hybrid fiber mixtures was proved with optimization of aggregate-binder (A/B) and FA/PC ratios, enabling more feasible high-performance concrete mixtures.
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    Upcycling marble waste into construction materials and heavy metal adsorbents via hot-pressed geopolymerization technique
    (Academic Press Ltd- Elsevier Science Ltd, 2026) Oksuzer, Nurullah; Uslu, Emin; Gokce, H. Suleyman
    This study presents a sustainable approach to utilizing marble dust waste by producing bifunctional metakaolinbased geopolymers via a synchronized hot-pressing technique. In this study, the environmental footprint was minimized by designing mixtures in which marble waste constituted 50% of the total volume. Three stoichiometric series were investigated by varying the activator modulus (SiO2/Na2O = 3 and 4) and the Si/Al ratio (2 and 3) under two curing temperatures (150 and 300 degrees C) and three compaction stresses (5, 25, and 50 MPa). Thus, a high-volume industrial byproduct was transformed into a functional component. In this context, it investigated the transformation of industrial products into next-generation materials by using them to produce cementless composite geopolymers for civil engineering and to adsorb heavy metal (Cu2+). As a result of the research, an early compressive strength of 58 MPa was obtained through heat treatment and pressing applied at 300 degrees C and 50 MPa. This optimum strength was achieved in the SiO2/Na2O = 3, Si/Al= 3 series, whereas excess silica (SiO2/ Na2O = 4) and excess aluminum (Si/Al = 2) limited the strength to 16.8 and 35.2 MPa, respectively. Micro-structural analyses (SEM/EDS and FT-IR) revealed that marble dust was used as a filler material in the microstructure to produce an N-A-S-H-containing matrix. The produced materials were then ground after their service life and used to purify water containing heavy metals. More than 99.75% of Cu2+ was removed through ion exchange between copper ions used as heavy metals. The residual Cu2+ concentration fell below 0.25 mg/L from an initial concentration of 100 mg/L, and the released Na+-to-adsorbed Cu2+ molar ratio of approximately 1.8-2.3 confirmed an ion-exchange-dominated uptake mechanism. This structural and environmental impact demonstrates that marble waste, which is otherwise discarded as waste, is considered inert, offering an alternative model for the circular economy and environmental applications.