Effect of Sodium Hexafluorosilicate Addition on the Properties of Metakaolin Based Geopolymers Cured at Ambient Temperature

• Published in: SILICON Vol. 13; no. 5; pp. 1441 - 1451
• Main Authors: Haddaji, Younesse, Majdoubi, Hicham, Mansouri, Said, Tamraoui, Youssef, Boulif, Rachid, Oumam, Mina, Hannache, Hassan
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01.05.2021; Springer Nature B.V
• Subjects: Aluminum; Ambient temperature; Bonding strength; Chemistry; Chemistry and Materials Science; Compressive strength; Efflorescence; Environmental Chemistry; Fourier transforms; Geopolymers; Infrared analysis; Inorganic Chemistry; Lasers; Materials Science; Mechanical properties; Metakaolin; Microstructure; Optical Devices; Optics; Original Paper; Photonics; Polymer Sciences; Raw materials; Room temperature; Silicon dioxide; Sodium; Sodium silicates; Thermal analysis; Metakaolin; SiF; Geopolymer; Na; Compressive strength; X-Ray diffraction; Microstructure
• ISSN: 1876-990X; 1876-9918
• DOI: 10.1007/s12633-020-00536-9

In this investigation, the effect of sodium hexafluorosilicate addition on the mechanical and microstructural properties of metakaolin-based geopolymers cured at ambient temperature was evaluated. The geopolymers were manufactured using metakaolin as a raw material with Sodium hexafluorosilicate Na 2 SiF 6 powder as an additive, and a mixture composed of NaOH, KOH, and sodium silicate together as an activating solution. The amount of Na 2 SiF 6 ranged from 1 to 5%, a (SiO 2 / (Na 2 O + K 2 O)) modulus of 1.3 and a Si/Al ratio varied between 1.60 and 1.70. Geopolymer specimens cured at room temperature under air for 28 days were characterized, using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermal analysis (ATG-DTG), scanning electron microscopy (SEM), and compressive tests to assess the microstructure-compressive strength dependency. The findings indicate that the addition of 2% Na 2 SiF 6 improves the compressive strength by 28%, but beyond this value, the resistance progressively decreases, this observation was explained by the fact that this additive rises the Si/Al ratio, which led to an increase in the amount of strong Si-O-Si bonds. The reduced RC has been related to the excess amount of Na in the blend that promotes the formation of efflorescence, leading to crack formation, which negatively affects the mechanical properties.