Abstract
Effect of sulfate solution on the geopolymer formed from electric arc furnace slag (EAF) along with water cooled slag and cement kiln dust was studied. Activation was carried up on usage of 25% CKD as it bears high alkali content that can initiate and propagate the polymerization process. The formed geopolymer products were immersed in 5% MgSO4 solution to determine the stability up on sulfate attack. FTIR, XRD, SEM, compressive strength and water absorption were utilized to examine the resulted geopolymer product under sulfate attack. Results showed that, the compressive strength of geopolymer specimens increase with EAF slag up to 50% then decrease with further slag increase, possessing stability up 12 months and giving an increased compressive strength than the control mix that has not EAFS by 6.53%, 14.72%, 47.44% and -4.89 % after immersing ages of 3 months and 2.26, 14.26, 43.97 and 19.98 % after immersing age of 12 months for replacement by 10, 25, 50 and 75% of EAFS, respectively. Data elucidated a good stability and resistance of mix containing slag substitution by 50 % EAF and 25 % GGBFS and results in further enhancement in both mechanical and microstructural characteristics than the non-immersed samples (28days).
Highlights
Geopolymers are inorganic polymers, induced by alkalis for dissolution of aluminosilicate precursors where the resultant structure constituted of alternating SiO4 and AlO4 tetrahedra chains and connected by a shared oxygen atom and balanced by cations. Feret (1939) and Purdon (1940) were the first to study alkali-activation, during the 1940s, using ground granulated blast furnace slag (GGBFS) as precursor material
The main target of this paper is to demonstrate the durability issue upon immersion in 5 % MgSO4 up to one year of electric arc furnace slag geopolymer composites activated by cement kiln dust instead of regular activator, where there is a shortage in the studies of this point
The pattern illustrate a an amorphous band in the region of 6° to 10° 2θ for aluminosilicate gel and small band in the region of 17° to 35° 2θ which characterize the glassy phase of the geopolymer constituents. These two regions are considered as vital keys in geopolymer characterization, where any increase in these regions will be reflected on the performance and efficiency of the resulting geopolymer gel. It can be noticed a decrease in the intensity of CSH band up to 3 months, an increase in the broadness and intensity of CSH with the increase in immersion time up to 12 months as indicated from the increased broadness at 29.4° as a result of increased matrix alkalinity due to the hydration progress as well as an increased geopolymerization reaction and the interaction of freely dissolved silica with free lime in Cement kiln dust (CKD) and free dissolved calcium species within the matrix forming CSH, which accumulate in the open pores and transformed into crystalline form at the later curing ages
Summary
Geopolymers are inorganic polymers, induced by alkalis for dissolution of aluminosilicate precursors where the resultant structure constituted of alternating SiO4 and AlO4 tetrahedra chains and connected by a shared oxygen atom and balanced by cations. Feret (1939) and Purdon (1940) were the first to study alkali-activation, during the 1940s, using ground granulated blast furnace slag (GGBFS) as precursor material. Feret (1939) and Purdon (1940) were the first to study alkali-activation, during the 1940s, using ground granulated blast furnace slag (GGBFS) as precursor material. Their first attempt utilized cement as alkali activator and the second employed as NaOH solution. Bakharev et al (1999) reported that the C–S–H structure formed in the presence of high concentrations of NaOH was less dense than the normal C–S–H structure resulting from hydration of Portland cement. It is possible to form structures in which the sodium is incorporated into the structure of the hydrated silicate gel (NC-S-H)
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