Long-Term Strength Development of Fly Ash-Based One-Part Alkali-Activated Binders

• Published in: Materials Vol. 14; no. 15; p. 4160
• Main Authors: Haruna, Sani, Mohammed, Bashar S., Wahab, Mohamed Mubarak A., Kankia, Mubarak Usman, Amran, Mugahed, Gora, Abdurra’uf Mukhtar
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 27.07.2021; MDPI
• Subjects: Carbon dioxide; Cement; Compressive strength; Crystallization; Curing; Density; Dosage; Efflorescence; efflorescence formation; Emissions; Field emission microscopy; Flexural strength; Fly ash; Greenhouse gases; Industrial plant emissions; Investigations; long-term strength; Mechanical properties; Microcracks; Microstructural analysis; one-part alkali-activated binders; Pastes; Photomicrographs; Pore size; properties; Raw materials; Sodium; Sodium silicates; Water absorption; Malaysia
• ISSN: 1996-1944; 1996-1944
• DOI: 10.3390/ma14154160

This research aims to study the effect of the dosage of anhydrous sodium metasilicate activator on the long-term properties of fly ash-based one-part alkali-activated binders (OPAAB) cured at ambient conditions. Powdered sodium metasilicate activator was utilized in the range of 8–16% by weight of the fly ash in producing the OPAAB. The properties examined are hardened density, compressive strength, flexural strength, water absorption, efflorescence formation, and microstructural analysis. The experimental result revealed that the binders exhibited excellent long-term strength properties. The compressive strength of the OPAAP is well correlated with its hardened density. The pastes were found to exhibit good soundness characteristics over the long-term. The absorption of water decreases with an increase in the activator dosage from 8–12%, and beyond that, the water absorption relatively remains the same. Field emission scanning electron microscope (FESEM) micrograph revealed uniformly formed solid matrices with the micro-crack present were observed in the samples. The larger pore size promotes the crystallization of the resulting hydrate substances (N, C)-A-S-H gel. The initial dissolution of the OPAAP occurred within the first 30 min. At longer age of curing, mixtures with a higher dosage of powdered activator tend to absorb less water. Strength properties beyond 28 days are considered as the long-term strength.