Preparation and characterization of a novel alkali-activated magnesite cement. (22nd August 2022)

• Record Type: Journal Article
• Authors: Abdel-Gawwad, Hamdy A.; Tawfik, Taher A.; Sikora, Pawel; Abd Elrahman, Mohamed
• Is Part Of: Construction & building materials. Volume 345(2022)
• Publication Date: 2022-08-22
• Subjects: Magnesium silicate hydrate -- Compressive strength -- Magnesium carbonate -- Microstructure -- Leaching; Building materials -- Periodicals; 624.18
• DOI: 10.1016/j.conbuildmat.2022.128384
• Languages: English
• ISSNs: 0950-0618

Abstract

Highlights: Magnesite was used as a precursor for synthesizing alkali-activated binder. Magnesite was activated by sodium hydroxide, silicate and aluminate. Adding lead glass sludge enhanced the polymerization of magnesium silicate hydrate. Magnesite based binder recorded 28-day compressive strength of 9–53 MPa. The prepared binder showed high efficiency in the stabilization of Pb inside sludge. Abstract: The present paper focuses on synthesizing an alkali-activated binder, in which magnesium carbonate (MC) was the only precursor. MC was individually activated with sodium hydroxide (NaOH), sodium silicate (Na2 SiO3 ) and sodium aluminate (NaAlO2 ). Increasing Na2 O content (as NaOH) up to 10 wt% enhanced the compressive strength slightly. At constant Na2 O content (10 wt%), the sample activated by (Na2 SiO3 ) recorded the highest compressive strength. Although the hardened mixture activated by NaAlO2 showed the higher compressive strength compared to NaOH-activated sample, it still recorded strength lower than Na2 SiO3 -activated-mixture. XRD, TG/DTG, FTIR, and SEM techniques indicated that phase composition depends mainly on the Na2 O source. 29 Si MAS-NMR spectroscopy verified the formation of magnesium silicate hydrate with Q 1, Q 2, and Q 3 silicate connectivity, when MC was activated with Na2 SiO3 . Incorporating lead glass sludge (LGS) as a silicate source, enhances the formation of a cross-like silicate chain (Q 3 ) coinciding with an improvement of the compressive strength and a retardation of Pb-leachability. As proved by 27 Al MAS-NMR, Al inside hydrotalcite phase, formed within NaAlO2 -activated-MC, has six coordination bonds. Activating MC with NaOH produces magnesium hydroxide (Mg(OH)2 ) and thermonatrite Na2 CO3 ·H2 O phases. Owing to the diversity of the hydration products, a wide range of 90-day compressive strengths (9–53 MPa) was recorded. A preliminary result showed that the CO2 -emission generates from optimum mixture containing 30 wt% LGS is lower than resulted from Portland cement manufacturing.