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    Effect of waste COVID-19 face masks on self-compacting high-strength mortars exposed to elevated temperature
    (Elsevier, 2023) Durmus, Goekhan; Celik, Damla Nur; Demircan, Rueya Kilic; Kaplan, Goekhan
    During the pandemic, it becomes customary to wear a disposable surgical (face) mask (SM) to guard against coronavirus illness 19 (COVID-19). However, because existing disposal procedures (i.e., incinera-tion and reclamation) emit hazardous substances, vast generations of contaminated surgical masks pose an environmental risk. Therefore, many studies are currently being carried out worldwide to dispose of SM. The easiest and cheapest of these methods is the disposal of SMs in cement-based composites. This study cut waste SMs to macro size and used them in cement-based composites such as polypropylene fiber. The elevated temperature resistance of cement-based composites decreases as their compressive strength rises. Low-melting materials like polypropylene fiber are utilized to improve the high -temperature resistance of cement-based composites. Therefore, SM with a low melting temperature was used in the design of the mixtures. SM was added to the mix at rates of 0.3, 0.5, 0.8, and 1 by weight of cement. As the SM ratio increased, the workability of the mixtures decreased. Water absorption and apparent porosity increased as SM reduced the workability of composites. The mixes' 28-day compres-sive strength ranges from 36.6 to 79.4 MPa. It was observed that flexural strength raised in some mix-tures when SM was used. In the mixes using 0.5 % SM, about 40 MPa compressive strength was obtained after 800 degrees C. Additionally, SEM images showed that SM changed into microfibre during mixing. As a result, it has been determined that SM can be used at low rates to increase the elevated temperature resistance of cement-based composites. (c) 2022 THE AUTHORS. Published by Elsevier BV on behalf of Faculty of Engineering, Ain Shams Uni-versity. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
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    High temperature resistant restoration mortar with fly ash and GGBFS
    (Taylor & Francis Ltd, 2022) Demircan, Ruya Kilic; Kaplan, Gokhan; Celik, Damla Nur
    Nowadays, the development of sustainable building materials is of loom large in for the preserve resources and reducing CO2 emission and environmental pollution effects. Exposure to fire or other high temperatures of mortars produced with calcium-based binders (cement or hydraulic lime) adversely affects their mechanical properties. In addition, the effect of high temperature may cause a change in the pore structures, causing cracking and spalling. Protecting the integrity of historical buildings exposed to high temperatures is important for cultural sustainability. In this study, natural hydraulic lime (NHL) used as a binder in mortars was replaced with 15, 30 and 60% fly ash (FA) and granulated blast furnace slag (GBFS). In the mixtures, 1.5% (by volume) polypropylene fiber (PF) was also used. Test results reveal that while the mortars' workability increased as the FA and GBFS content increased, PF decreased the flow diameters of the mortars. It has been determined that the paste content affects the porosity and water absorption rates of mortars. With the addition of FA content, paste content increased and porosity reduced. Compressive strength over 10 MPa was obtained by using 30% FA in 90-day lime mortars. As the addition of GBFS, the compressive and flexural strength were negatively affected. PF has reduced the porosity and water penetration depth of the mortars thanks to its micro filler effect. FA-based mixtures were more resistant to high temperatures than GBFS-based mixtures. Compressive strength was measured between 4.3 and 8.6 MPa after 600 degrees C temperature in FA-based mixtures. In fibrous mixtures, increment of mass loss was more with high temperature. C-S-H gels were observed in XRD and SEM analyzes of mortars exposed to high temperatures. PF was observed in stereomicroscope images of mixtures exposed to 200 degrees C. Since the porosity of the mortars is relatively high (19.7%-30.8%), the PF in the mixtures exposed to 200 degrees C did not melt completely but was damaged. As a result, it would be more appropriate to use 30% of FA and 15% of GBFS in NHL mortars.
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    Innovative solutions on ductility and bearing capacity: Strengthening flexural performance of reinforced concrete beams with recycled face mask fibers
    (Elsevier Sci Ltd, 2025) Ozdemir, Anil; Bozyigit, Baran; Demircan, Ruya Kilic; Mercimek, Omer; Celik, Damla Nur; Akkaya, Sercan Tuna; Kaplan, Gokhan
    This study investigates the effects of fibers derived from disposable face masks on the flexural performance of reinforced concrete (RC) beams during the COVID-19 pandemic. Mask fibers were compared with commonly used synthetic fibers such as glass, basalt and polypropylene to evaluate structural elements' bearing capacity, ductility and energy absorption capacities. In the experimental study, five different BA beams were investigated by applying a four-point bending test, and the experimental test results were verified using finite element analysis (FEA) with ABAQUS software. The test results show that the fibers obtained from the mask increase the bearing capacity by 6 %, improve the ductile behavior of the beams, and increase the energy absorption capacity up to 80 % after the load-carrying capacity reaches its maximum. An increase of up to 40 % in energy absorption capacity was observed. This demonstrates that mask fibers enable reinforced concrete beams to absorb more energy under deformation. It was also found that the fibers obtained from the mask exhibited similar performance with polypropylene fibers. Still, the effect of glass and basalt fibers on the bearing capacity was higher. The study results show that mask waste can be used in reinforced concrete elements as a sustainable and innovative building material. Both experimental and finite element results prove that mask fibers improve the flexural performance of reinforced concrete beams and contribute to environmental sustainability. Reusing mask waste in the construction industry has significant environmental and economic potential.
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    The effect of animal and synthetic fibers on the physico-mechanical durability and microstructure properties of natural hydraulic lime-based mortars
    (Elsevier, 2023) Demircan, Ruya Kilic; Tayeh, Bassam A.; Celik, Damla Nur; Kaplan, Gokhan; Tobbala, Dina E.
    This paper aims to study the effect of adding horsehair (HH), polypropylene (PF), carbon (CF), basalt (BF) and glass fibers (GF) on the physico-mechanical durability and microstructure properties of natural hydraulic lime-based mortars (NHL). The studied fibers were added to the mixture at 0.3 %, 0.6 %, and 1.2 % by weight of NHL and compared with plain NHL mortar. The workability (flow diameter test), physical (dry bulk density and water absorption), compressive strength (f(c)) and flexural strength (f(f)) (at 7 and 28 days) were tested. The durability was tested by water penetration depth (Wd), NaCl and Na2SO4 salt crystallization and exposure to the wetting-drying (W-D) cycles in Na2SO4, as proved by XRD. Scanning electron microscopy (SEM) of samples after 28 days of curing. From the results, it can be concluded that HH3 (0.3 % fiber) has the highest dry density (1794 kg/m(3)), fc and f(f) at 28-days (13.3 and 4.2 MPa), and resistance of all salt crystallization tested, smallest water absorption percentage (16.2 %), and water penetration depth (38.23 mm) of all mortars. On the other hand, it can be noted that adding synthetic types of fibers reduced the dry density and increased water absorption. The XRD explained that immersion or exposure to (W-D) cycles of Na2SO4 has a worse effect on hydration than NaCl exposure. The SEM shows that fiber-filled lime mortar's mechanical properties and durability are improved through the conductive network, especially HH, which had a large diameter with a rough surface and indicated a sufficient level of adhesion with the matrix.
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    The engineering properties of high strength mortars incorporating juniper seed ash calcined at different temperatures: Comparison with other SCMs
    (Elsevier, 2023) Celik, Damla Nur; Demircan, Rueya Kilic; Shi, Jinyan; Kaplan, Gokhan; Durmus, Gokhan
    The juniper tree is widely distributed in Europe, but its fruit (juniper seed ash, JSA) is not well utilized, and most of it is naturally degraded. This study provides an efficient way to recycle JSA by calcining it at different temperatures (350 and 500 degrees C) to obtain supplementary cementitious materials (SCMs). The feasibility of using JSA to modify mortar is discussed from technical, economic and environmental aspects, and it is compared with conventional SCMs. The results show that the incorporation of JSA significantly improves the flowability of the mixture and reduces the unit weight of the hardened sample compared to conventional SCMs. However, JSAmodified mortars exhibit higher apparent porosity and water absorption due to the low pozzolanic reactivity and high porosity of JSA, but JSA outperforms RHA for high-content (12.5%-17.5%) SCM-modified mortars. The incorporation of a small amount (7.5%) of JSA reduces the compressive strength of the mortar, but the compressive strength of the mortar mixed with JSA-350 calcined at 350 degrees C is slightly higher than or similar to that of the traditional SCM-modified mortar. Since the flexural strength is more sensitive to the microstructure, the incorporation of JSA makes it significantly lower. In addition, the low reactivity and high porosity of JSA also lead to an increase in the 91-d capillary water absorption and a decrease in the electrical resistivity of the mortar samples. Meanwhile, the pozzolanic reaction of traditional SCM consumes Ca2+ ions and OH- to increase the electrical resistance of the mortar, while the alkalinity of JSA increases the content of OH and reduces the electrical resistance of the mortar. In addition, using JSA to modify high-strength mortar also reduces its cost and carbon footprint, which indicates that recycling juniper seeds in high-strength mortar is a sustainable strategy.