The effect of sodium hydroxide (SH) concentration and sodium silicate (SS) content in alkali activator on mechanical properties and wet-dry resistance of fly ash added pumice based geopolymer paste were investigated. In the study, the concentration of SH was used as 8, 10, 12 and 14 molar, while the weight ratio of SS to SH was used as 0, 1, 2 and 3. While the density of geopolymer paste samples increased significantly with the increase of SH molarity in mixtures with low SS content, it was less affected by SH molarity in mixtures with high SS content. For all SH molarity values, the compressive strength of the geopolymer paste samples increased with the increase of the SS/SH ratio, while a slight decrease was observed with the SS/SH ratio increasing from 2 to 3. However, with the increase of the SH molarity, the compressive strength of the samples was less affected by the SS content. As large cracks or splits occur in paste samples activated only with SH under the effect of wet-dry, their compressive strength could not be measured. The wet-dry performance of the paste samples activated with SS + SH was not affected much by the SH molarity and the SS/SH ratio and were close to each other. When looking at the microstructure studies, FTIR analyzes show that SS content provides a better geopolymerization, and SEM images show that micro-cracks relatively decrease with SS content.

The effects of curing regimes varying combinations of temperatures (ambient, 60 °C, 75 °C, 90 °C, 105 °C) and durations (4h, 8h, 24h, 48h, 96h, 168h) on the performance of fly ash added pumice based geopolymer pastes were investigated in this study. The precursor raw material consists of 70% pumice dust and 30% fly ash (FA). Alkali activator was prepared by mixing 10M sodium hydroxide (SH) solution and liquid sodium silicate (SS) in the ratio of SS/SH=2. Activator to precursor ratio was fixed as 0.45. Compressive strengths were determined at the 28 days of age as well as after exposure 5 wetting-drying (w-d) cycles. In addition, Fourier Transform Infrared Spectroscopy (FTIR) tests were conducted on the fresh and hardened geopolymer pastes in order to examine the effect of curing conditions to the structural changes and reaction products. The results show that in the case of 60 °C and 75 °C, the strength of the w-d conditioned samples increased steadily as the curing time increased. However, longer curing times of more than 24 hours are not beneficial for high curing temperatures (90 °C and 105 °C). The maximum strength after the w-d cycles is obtained for the curing conditions of 60°C/168h (74.4 MPa). Also, FTIR analysis confirmed that the hardened geopolymer paste transformed into a more coordinated structure and soluble carbonate compounds were reduced at 60 °C and 168 hours curing condition.

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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