Sürdürülebilir Kalkınma Amaçları

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• MakaleYalnız künye2026Scopus SJRQ2/r/munzur/1112
  Drying Shrinkage and Microstructural Properties of Geopolymers Including Steel and Iron Particles

  Gulmez, Nihan; Kockal, Niyazi Ugur

  Geopolymer mortars show significantly higher shrinkage than normal Portland cement mortars. So, one of the most important disadvantages of these promising alternative binding materials for their wider applications is the cracking occurring by shrinkage. Different inserts and fibers are used in fresh mixtures in order to control drying shrinkage cracks and to provide mechanical capacity. The aim of this study is to investigate the effectiveness of using both metal particles (iron particles) and metallic fibers (steel particles) in geopolymer composites to reduce drying shrinkage. In addition, microstructural properties of composites were determined by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses and causes of shrinkage were investigated in detail. Mixtures containing 20% ​​silica fume have 38.4% lower drying shrinkage than slag-based mixtures. In slag-based composites, decreases in drying shrinkage were found as 18.8% and 49.1% when adding 10% iron particles or 10% steel particles compared to metal-free composites.

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• MakaleAçık Erişim2026Scopus SJRQ1/r/munzur/852
  Enhancing the mechanical and durability properties of fly ash/GGBS-based geopolymer mortars using dunite and polypropylene fibers

  Cemalgil, Selim; Gülmez, Nihan; Yön, Merve Şahin; Karataş, Mehmet

  Polypropylene (PP) fiber-reinforced geopolymer mortar reduces the high brittleness of conventional geopolymer made with natural aggregates. However, the effects of different precursor materials on the performance of PP fiber-reinforced self-compacting geopolymer mortar (SCGM) remain unclear. This study investigates the feasibility of using dunite (D), a magnesium-rich ultramafic rock with consistent mineralogy and low processing energy demand that enhances thermal stability and durability, as an alternative precursor for fly ash (FA)/ground granulated blast furnace slag (GGBS)-based geopolymers. The study examined the workability, flexural and compressive strengths, and sorptivity of mortars cured at 20 ± 2°C and 60 ± 5% relative humidity, as well as their durability under freeze–thaw cycles and high-temperature exposure. Interfacial interactions between aggregates and the geopolymer matrix, along with microstructural and morphological changes caused by fire, were analyzed using scanning electron microscopy (SEM). X-ray diffraction (XRD) and thermogravimetric analysis (TGA) were also performed for detailed material characterization. The mix containing 30% dunite exhibited the highest flexural strength, reaching 5.70 MPa at 28 days, the highest among all mixes. Under fire exposure, the mix containing 10% dunite significantly reduced mechanical strength loss and retained about 33.3% higher residual flexural strength than the FA–slag control mix at 600°C.

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  AtıfScopus1·WoS1·OpenAlex1

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• MakaleYalnız künye2026Scopus SJRQ1/r/munzur/621
  High-temperature, freeze–thaw, and sulfate resistance of mortars incorporating ternary blends of fly ash, chromite, and waste glass

  Gülmez, Nihan; Kanellopoulos, Antonios

  The demand for sustainable construction materials promotes the use of industrial waste in cement-based systems. This study examines mortars incorporating fly ash (FA) (0%, 7.5%, and 15%), waste glass, and chromite aggregates for mechanical and durability performance. Specimens underwent compressive strength, freeze–thaw, high-temperature, sulfate attack, and ultrasonic pulse velocity tests, while microstructure was characterized by x-ray diffraction, thermogravimetric analysis, and scanning electron microscopy–energy-dispersive spectroscopy. Mortars with 7.5% FA exhibited relatively high compressive strength and improved freeze–thaw resistance. The combined use of chromite and FA improved strength retention at 800°C, reaching 23 MPa with 7.5% FA and 50% chromite. The greatest sulfate resistance occurred in mortars containing 15% FA and 15% waste glass, maintaining compressive strengths of 61 and 70.9 MPa after MgSO4 and Na2SO4 exposure, respectively.

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• MakaleAçık Erişim2025/r/munzur/5997
  Effects of Alternative Binder and Aggregate Use on the Compressive Strength of Concrete

  Gülmez, Nihan; Pala, Mustafa

  The use of industrial wastes in concrete production is of significant importance in reducing environmental impacts and lowering costs. In this study, concrete mixtures were designed by using olivine minerals as a substitute for Portland cement (PC), chromite powder as fine aggregate, and ferrochromium slag as coarse aggregate. The effects of different binder and aggregate ratios on the compressive strength of the concrete were examined after a 7-day curing period. Experimental results showed that mixtures with 5% olivine substitution achieved the highest compressive strength of 22.30 MPa, particularly in mixtures with a cement dosage of 500 kg/m³. This result indicates that the low water/cement ratio and the addition of olivine contribute to increased early-age strength. Furthermore, increasing the chromite powder content to 20% in mixtures with a water/cement ratio of 0.61 led to an 11.7% increase in compressive strength, demonstrating the positive impact of chromite powder on the mechanical performance of the concrete. These findings highlight that cement replacements and aggregate types can significantly affect the mechanical properties of concrete, emphasizing the need for careful selection of both material compositions.

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• MakaleYalnız künye2023Scopus SJRQ2/r/munzur/1686
  Engineering Properties of Geopolymer Mortars Containing Industrial Steel Shavings

  Gülmez, Nihan; Koçkal, Niyazi Uğur

  The purpose of using waste materials is to prevent the unnecessary use of resources and to reduce the amount of waste. Geopolymer, developed as an alternative to cementitious materials, prevents the depletion of natural resources and saves a large amount of energy. This paper presents the effect of waste steel shavings on the improvement of physical and mechanical properties of geopolymer mortars. For this purpose, geopolymer mortars were produced by using two binder types [slag (BFSb) and silica fume] as well as steel shavings in five different replacement percentages (0%, 2.5%, 5%, 7.5% and 10%) by volume instead of aggregate. A series of experiments on geopolymer mortars were carried out to determine properties such as bulk density, water absorption, apparent porosity, sorptivity coefficient, splitting tensile strength, flexural strength and compressive strength. Results showed that steel shavings recovered from metal processing and forming sector were highly effective at improving engineering properties of geopolymer mortars. Furthermore, although replacement of 20% by volume of BFSb with silica fume improved properties of geopolymer mortar, it was observed that the use of silica fume at higher ratios reduced mechanical properties by increasing porosity and sorptivity of BFSb-based geopolymer mortars.

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  AtıfScopus1·OpenAlex1

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• MakaleYalnız künye2023Scopus SJRQ2/r/munzur/1601
  Computer-aided Optimization of Geopolymer Mortars

  Gülmez, Nihan; Koçkal, Niyazi Uğur

  The optimum mix design of geopolymers involves the purpose of determining which mixture will have high engineering properties without compromising the importance of each variable. This experimental study aimed to investigate the effects of some critical geopolymer mixture parameters on engineering properties by using historical data design in response surface methodology (RSM). Statistical models were developed between factors (binder and aggregate content, curing conditions and aggregate type) and their response surfaces (oven dry (OD) bulk density, water absorption, compressive strength and flexural strength). The final mathematical models for the response surfaces were constructed in terms of coded factors defined as dimensionless. In addition, a multipurpose optimization technique was used to achieve the desired design with the desired maximum strength.

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• MakaleYalnız künye2022Scopus SJRQ1/r/munzur/3063
  Experimental and material characterization of composites, including waste iron and marble powder

  Gülmez, Nihan

  Due to its fine particle size, waste marble slurry originating in cutting and processing units mixes into the air after drying, causing environmental and health problems in nearby areas. On the other hand, large amounts of iron particles are generated as metalworking industry waste, affecting the environmental system. In this study, 0%, 10%, and 20% marble powder (instead of cement) and iron particles (instead of fine aggregate) were used in mixtures, and the composites produced were subjected to two different curing periods: 7 and 28 days. The physical, mechanical, microstructural, and thermal properties of the fresh and hardened composites were ascertained via bulk density, consistency, porosity, water absorption, capillary water absorption, strength tests, particle size distribution, X-ray diffraction (XRF), X-ray fluorescence (XRF), scanning electron microscopy and energy dispersive spectroscopy (SEM–EDS), and thermogravimetric analyses (TGA). The results revealed that minimum water absorption (8.5%) and porosity (19.8%) values were achieved in 28-day composites produced with 10% marble–20% iron wastes among all composites. Thus, iron particles substituted for natural aggregates were mainly responsible for the increase in mechanical performance. A maximum flexural strength of 5.9 MPa and a compressive strength of 26.7 MPa were observed in 28-day composites containing 0% marble–20% iron wastes. Furthermore, capillary water absorption tended to decrease with the substitution of 10% marble powder.

  AtıfScopus3·WoS2

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• MakaleYalnız künye2022Scopus SJRQ2/r/munzur/2399
  Corrosion potential and electromagnetic shielding effectiveness of geopolymer tiles produced with waste metal particles

  Gülmez, Nihan; Koçkal, Niyazi Uğur; Özen, Şükrü; Ateş, Kayhan

  This study is related to the production of special geopolymer specimens, where high effectiveness is provided in terms of electromagnetic interference (EMI) shielding and corrosion resistance. The study is important for the preparation of silica fume/slag based geopolymers by using waste steel and iron powder as a partial substitute for slag aggregate and thus to provide an effective solution to the disposal problems of waste metals. The electromagnetic interference shielding effectiveness (SE) of geopolymer tiles of 7.6 ± 0.1 mm thickness with different metal contents was measured at 4.9–7.05 GHz. Corrosion activity was monitored by measuring the half-cell potential of copper/copper sulphate (Cu/CuSO4) on specimens kept under controlled laboratory conditions for a period of 90 days at %60 relative humidity according to ASTM C876. In addition, anextensive evaluation of the optimization research on the design and proportion of mortar mixtures is presented here. EMI shielding effectiveness of slag based geopolymer tile with 10% steel particles has been determined as 26.1 dB in the frequency range 4.9–7.05 GHz. The results show that the shielding effectiveness reached a maximum of 23.1 decibels (dB) for geopolymer tiles in 40% iron powder content. Also, from experimental results, it was learned that geopolymer specimens with high slag content as binders in the mixtures showed better corrosion resistance.

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  AtıfScopus10·WoS10·OpenAlex10

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• MakaleAçık Erişim2021/r/munzur/5889
  Reuse of Industrial Metal Wastes as Partial Replacement of Aggregates in Mortar Production

  Gülmez, Nihan

  Sustainable waste management is becoming more and more important in the construction industry due to increasing waste costs as well as environmental effects. As a result of increasing level of wastes and environmental damage, the use of these wastes has become the focus for beneficial construction activities and sustainable industrial applications. This study presents experimental results on the effect of industrial wastes on the performance of cementitious mixtures. The scope of this study, therefore, was to assess the effect of waste aluminium on physical and mechanical properties of cement based mixtures prepared in different compositions. Consistency, bulk density, porosity, absorption, flexural and compressive strength tests were carried out on mixtures produced by using waste aluminium aggregates in different percentages instead of fine aggregate. Results showed that mixtures prepared with 4% aluminium aggregates had the highest water absorption and porosity. With the addition of %1 lathe waste, it was observed that the flexural behavior of mortar was maximum and the optimum percentage for flexural strength was noted. In addition, when mixtures produced with the same percentage of aluminium were compared, the amount of binder played a significant role on both compressive and flexural strength. Results have shown that to incorporate aluminium into mixtures can be a suitable solution for recycling in industrial applications.

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  AtıfOpenAlex5

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• MakaleYalnız künye2021Scopus SJRQ1/r/munzur/3030
  Performance of marble powder on cementitious composites including waste steel chips as an additive

  Gülmez, Nihan

  The reuse of industrial waste materials in cement-based composites contributed to preventing increasing environmental problems and reducing production costs. This article examined the effectiveness of using recycled steel chips (Ast) from metal industry waste and waste marble powder (BMP) instead of cement and the possibility of obtaining eco-efficient specimen. While steel chips included in mortars as additives decreased workability, marble powder increased it. An increment in the level of substitution of steel chips resulted in a subsequent increase in water absorption percentages and apparent porosities of mortars. Maximum flexural strength was obtained in 2% steel chips-10% marble powder in waste system.

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  AtıfScopus16·WoS15·OpenAlex21

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