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    Öğe
    Improving the durability of pumice-fly ash based geopolymer concrete with calcium aluminate cement
    (Elsevier, 2022) Karaaslan, Cemal; Yener, Engin; Bagatur, Tamer; Polat, Riza
    This study aims to improve the durability of pumice (70 wt%) and fly ash (30 wt%) based geo-polymer concretes (PGCs) by replacing pumice with calcium aluminate cement (CAC) up to 20 wt % of the total powder binder. In this context, durability characteristics (wetting-drying, freeze-thaw, sulfuric acid, resistance to water-penetration, and abrasion) and microstructure (by performing XRD, FTIR, and SEM-EDS analyses) of PGCs were examined and compared with Portland cement-based concrete (PCC) to control. As a result, CAC substitution of 20% increased the 28-day compressive strength of PGC from 20.0 MPa to 70.0 MPa. The abrasion resistance of PGCs was better than that of PCC, regardless of CAC replacement levels. Since PGC without CAC is highly permeable, wetting-drying cycles, freeze-thaw action, and sulfuric acid attack reduced the strength of this concrete by easily leaching the weakly bound Na cations in the geopolymer matrix and forming -OH and H-O-H type bonds. On the other hand, C-A-S-H type gels formed in PGC with 20% CAC reduced the water penetration depth up to 33 mm by reducing the permeability. In addition, upon 20 wetting-drying and 100 freeze-thaw cycles, compressive strength losses with the CAC replacement level increasing from 0% to 20% decreased from 36.7% to 1.4% and from 43.4% to 4.6%, respectively. Exposure to 5% sulfuric acid solution for 120 days resulted in 0.5% and 16.6% weight loss and 47.4% and 72.6% compressive strength loss in PGCs and PCC, respectively.
  • [ X ]
    Öğe
    Synergic effect of fly ash and calcium aluminate cement on the properties of pumice-based geopolymer mortar
    (Elsevier Sci Ltd, 2022) Karaaslan, Cemal; Yener, Engin; Bagatur, Tamer; Polat, Riza; Gul, Rustem; Alma, Mehmet Hakki
    This paper reveals the synergic effect of fly ash (FA) and calcium aluminate cement (CAC) on the properties of pumice-based geopolymer mortars. Geopolymer mortar samples produced by replacing 0, 10, 20, and 30% of the pumice with FA and/or CAC are cured at ambient temperature, and 60C degrees. Physical properties, compressive strength (7, 28, and 90-days), durability, and microstructure of these samples are investigated in this study. While CAC and heat curing greatly reduce the setting time, FA has a limited effect on the setting time. However, both FA and CAC significantly increase the workability of the mortar mix. By replacing the optimum amount of the pumice with FA and CAC, the 7-day compressive strength of heat-cured geopolymer mortars can achieve 68.0 MPa. On the other hand, CAC significantly increases the compressive strength of the geopolymer mortars and their resistance to the wetting-drying and seawater. In addition, the FA has a limited effect on the enhancement of the mechanical properties and durability of the geopolymer mortars. Efflorescence is slightly reduced by FA and CAC additives, however, is greatly reduced by heat curing. The SEM/EDS show that CAC creates C-A-S-H gel and together with FA they reduce cracks and voids in the geopolymer matrix. The findings reveal that the properties of both fresh and hardened geopolymer mortars can be improved by replacing pumice with a suitable amount of FA and CAC.
  • Küçük Resim
    Öğe
    Uçucu kül ve kalsiyum alüminat çimentosu katkılı pomza esaslı geopolimer harçların sülfürik asit direnci
    (Iğdır Üniversitesi Fen Bilimleri Enstitüsü, 2022) Karaaslan, Cemal; Yener, Engin; Bağatur, Tamer; Polat, Rıza; Gül, Rüstem
    Bu çalışmada, uçucu kül ve/veya kalsiyum alüminat çimentosu ağırlıkça toplam toz bağlayıcının %10, 20 ve 30’u kadar pomza ile ikame edilerek pomza esaslı geopolimer (PGP) harçlar üretilmiştir. Ortam sıcaklığı ve 60 °C’de kür edilen bu harçlar, 28. günde %5 derişime sahip sülfürik asit (H2SO4) çözeltisine konularak 120 gün bekletilmiştir. PGP numunelerde sülfürik asit etkisiyle oluşan görsel değişim, ağırlık kaybı ve kalan basınç dayanımı, 60 ve 120. günde ölçülmüş ve Portland Çimentosu esaslı referans harçla kıyaslanmıştır. Çalışma, referans numunelerinin sülfürik asit ortamında çözünerek 60 günün sonunda %25.6 ağırlık kaybı yaşadığını buna karşılık %20 ve 30 oranında kalsiyum alüminat çimentosu içeren karışımların ortam sıcaklığında kür edilmiş numuneleri hariç PGP harçlarda (görsel açıdan) bir çözünme olmadığını göstermiştir. Ayrıca ortam sıcaklığı ve 60 °C’de kür edilen PGP numunelerin 120 günün sonunda sırasıyla en fazla %6.5 ve 4.1 ağırlık kaybına uğradıkları tespit edilmiştir. PGP harçlar, sülfürik asit çözeltisinde 120 günün sonunda %70’e varan basınç dayanım kayıpları yaşamıştır. Ancak yeterli miktarda uçucu kül ve kalsiyum alüminat çimentosu ikamesi ile PGP harçların basınç dayanımı önemli derecede arttığı gibi sülfürik asit direnci de iyileşmiştir.