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    Antimicrobial Activity of Eco-Friendly Fly-Ash-Based Geopolymer Mortar
    (MDPI, 2025) Iyigundogdu, Zeynep; Urunveren, Husamettin; Beycioglu, Ahmet; Ibadov, Nabi
    As cement production causes large amounts of CO2 emissions and is not sustainable, there is a growing worldwide interest in developing cleaner construction materials by reducing carbon emissions and reusing existing industrial waste. Also, antimicrobially active construction materials are gaining attention due to enhancing structural longevity. By preventing microbial growth, these materials help to improve indoor air quality and occupant health. Geopolymer mortars/concretes (GPM/GPC) with high mechanical, physical and durability properties are considered as an eco-friendly alternative to ordinary Portland cement (OPC) mortars/concretes. In this study, the composition, microstructural, mechanical and antimicrobial properties of geopolymers produced at different curing temperatures (60, 80, 100 and 120 degrees C) were investigated. Low-lime fly ash was used as binder and sodium silicate and sodium hydroxide were used as the alkaline solution in geopolymer production. Although X-ray fluorescence (XRF) results showed an increase in geopolymerization products with increasing temperature, SEM analysis showed that the crack formation that occurs in the microstructure of geopolymers cured above 100 degrees C leads to decreased mechanical properties. The strength and antimicrobial performance test results for geopolymer mortars showed that the optimum temperature was 100 degrees C, and the highest compressive strength (48.41 MPa) was reached at this temperature. A decrease in strength was observed due to cracks occurring in the microstructure at higher temperatures. The agar diffusion method was used to determine the antimicrobial activity of GPMs against four bacteria and one fungus species. The antimicrobial activity test results showed that the samples subjected to thermal curing at 100 degrees C formed the highest inhibition zones (38.94-49.24 mm). Furthermore, the alkalinity of the components/mixtures has a direct relationship with antimicrobial activity. As a result, GPMs with superior antimicrobial and mechanical properties can be considered as promising building materials, especially for construction applications where hygiene is a priority and for structures that are likely to be exposed to microbial corrosion.
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    Bond Performance of GFRP Bars in Glass and Basalt Fiber-Reinforced Geopolymer Concrete Under Hinged Beam Tests
    (MDPI, 2025) Erturkmen, Duygu; Urunveren, Husamettin; Beycioglu, Ahmet; Ibadov, Nabi; Aruntas, Hueseyin Yilmaz; Garbacz, Andrzej
    In recent years, researchers have focused on the usability of fiber-reinforced polymer (FRP) bars due to their lightweight, corrosion-resistant, and eco-friendly characteristics. Geopolymers, as low-carbon alternatives to traditional binders, aim to reduce CO2 emissions in concrete production. The bond strength between FRP bars and concrete is critical for the load-bearing capacity and deformation characteristics of reinforced elements. The objectives of this work are to investigate the bond performance of GFRP bars in chopped glass and basalt fiber-added geopolymer concrete using hinged beam tests. Since the hinged beam test accurately represents the behavior of real bending elements, this test method was selected as a main bonding test. Initially, three geopolymer mixtures with Ms modulus values of 1.2, 1.3, and 1.4 were prepared and tested. The mixture with a modulus of 1.2 Ms, achieving a compressive strength of 56.53 MPa, a flexural strength of 3.54 MPa, and a flow diameter of 57 cm, was chosen for beam production due to its optimal workability and strength. After mechanical and workability tests, SEM analysis was performed to evaluate its internal structure. For evaluating the bond performance of GFRP bars, 12 geopolymer beam specimens were prepared, incorporating varying fiber types (chopped glass fiber or basalt fiber) and embedment lengths (5 & Oslash; or 20 & Oslash;). Hinged beam tests revealed that the bond strengths of glass and basalt fiber-added mixtures were up to 49% and 37% higher than that of the control geopolymer concrete, respectively. It was concluded that incorporating fibers positively influenced the bond between geopolymer concrete and GFRP bars, with glass fibers proving more effective than basalt fibers. These findings enhance the understanding of bond mechanisms between GFRP bars and geopolymer concrete, emphasizing their potential for sustainable and durable construction in both industrial and scientific applications.