Development of Geopolymer Paste Mixture Made from Low-Calcium Fly Ash using Sodium Silicate-Sodium Hydroxide-Potassium Hydroxide Combination as Activator

Author : Caguisa, JC Faith Mae Agrabio
Major Adviser : Laurio, Michael Vincent O.
Committee Members : Alfafara, Catalino G.; Borines, Myra G.; De Castro, Leandro T. 
Year : 2017
Month : June
Type : Thesis
Degree: BS
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This study focused on the development of low calcium fly ash based geopolymer paste using Na₂SiO₃, NaOH, and KOH as activators. The proportions of class F fly ash, Na₂SiO₃ (silicate modulus of 2.2), 10 M NaOH, and 10 M KOH were the parameters varied while compressive strength and area factor were the response measured. Prior to compressive strength test, samples were subjected to pre-curing for 24 hours, thermal curing at 60 °C for 24 hours, and ambient curing for seven days. Based from ANOVA results, the proportion of NaOH, Na₂SiO₃ and KOH were the significant main effects for compressive strength and workability. The blending effect on compressive strength of fly ash-NaOH and Na₂SiO₃-KOH were positive. High compressive strength were observed on region with low NaOH, low fly ash, and high Na₂SiO₃ proportion and on region with low NaOH, intermediate Na₂SiO₃, and intermediate KOH proportion. From the results of numerical optimization, it was the proportion 0.769 fly ash, 0.231 NaOH and no sodium silicate and KOH solution that was selected as the optimum proportion for desirable compressive strength. For geopolymer paste activated with both NaOH and KOH, it was the geopolymer paste mixture with proportion 0.71 fly ash, 0.045 NaOH, 0.2 Na₂SiO₃ and 0.045 KOH that yielded the highest average compressive strength. Results of SEM analysis showed that high compressive strength can be attributed to compact microstructure and low proportion of unreacted raw materials while results of FTIR analysis confirmed the presence of Si-O-Si bond, an indicator that geopolymerisation occurred in the samples.

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