Effect of Na_2SiO_3/Na0H Ratios and NaOH Molarities on Compressive Strength of Fly-Ash-Based Geopolymer

摘要

Carbon dioxide (CO_2) emissions from the production of 1 ton (2204.62 lb) of cement vary between 0.05 and 0.13 tons (110.23 and 286.60 lb). It is important to reduce CO_2 emissions by the greater use of substitutes for portland cement (PC), such as fly ash (FA), clay, and other geo-based materials. This paper studies the processing of geopolymers using FA and alkaline activators. The factors that influence the early-age compressive strength, such as the sodium hydroxide (NaOH) molarity and Na_2SiO_3/NaOH ratios, were studied. Sodium hydroxide and sodium silicate solutions were used as alkaline activators. The geopolymer paste samples were cured at 70℃ (158°F)for 1 day and kept at room temperature until testing (the seventh day). The compressive strength was measured after 7 days. The results show that the geopolymer paste with a combination of an Na_2SiO_3/NaOH ratio of 2.5 and a 12 M NaOH concentration produces the highest compressive strength. The density obtained for geopolymer for PC is in the range of 1760 to 1855 kg/m~3 (0.064 to 0.067 lb/in.~3). The porosity of the geopolymer was in the range of 12.16 to 26.19%, and the water absorption was in the range of 5.03 to 8.13%. The results of scanning electron microscopy (SEM) indicated that the samples with a denser matrix and less unreacted FA contributed to the maximum compressive strength. In the X-ray diffraction (XRD) patterns, the intensity of quartz content at 12 M was highly detected compared to the 6 and 10 M solutions.