Compressive Strength and Microstructure of Carbide Slag and Alkali-Activated Blast Furnace Slag Pastes in China

• Published in: Buildings (Basel) Vol. 14; no. 6; p. 1681
• Main Authors: Li, Zhixin, Xu, Kaidong, Sun, Nan, Wang, Jina, Xue, Kaiwang, Xu, Longyun, Ren, Yi, Yan, Zhenzhou, Sima, Tongbao
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01.06.2024
• Subjects: Alkalinity; blast furnace slag; Blast furnace slags; Calcium silicate hydrate; Calorimetry; carbide slag and alkali activation; Carbides; Carbon; Carbon dioxide; Carbon dioxide emissions; Caustic soda; Cement; Cement hydration; Cement industry; Compressive strength; Construction; Curing; Differential scanning calorimetry; Diffraction; Dosage; Ettringite; Fourier transforms; Industrial wastes; Infrared analysis; Infrared spectroscopy; Microstructure; Morphology; Particle size; Pastes; Portland cement; Portland cements; Scanning electron microscopy; Slag; Sodium; Sodium hydroxide; Thermogravimetric analysis; X-ray diffraction; X-rays; China
• DOI: 10.3390/buildings14061681
• ISSN: 2075-5309

The alkali-activated blast furnace slag is attracting significant attention in replacing Portland cement due to several characteristics similar to cement hydration. However, there are a few practical problems with commercial alkali activators, such as the fast setting time, relatively high costs, and significant CO[sub.2] emissions during preparation. Thus, discovering industrial residues possessing inherent alkalinity are urgent. This study proposes the use of carbide slag at levels of 0%, 5%, 10%, 15%, 20%, and 30% and alkali at levels of 1%, 2%, 3%, 4%, 5%, 6%, 8%, and 10% activated blast furnace slag. The compressive strength and microstructure of carbide slag and alkali-activated blast furnace slag (CAB) pastes were examined using X-ray diffraction analysis (XRD), Differential Scanning Calorimetry/Thermogravimetric Analysis (DSC/TG), Fourier transform infrared spectroscopy (FTIR) and Scanning electron microscopy (SEM). The results revealed that the addition of carbide slag produced more hydrotalcite-like phase as well as decreased the content of ettringite (AFt) and the calcium–silicate–hydrate (C-S-H) gel, which decreased the compressive strength of the CAB pastes. At the age of 28 days, when the dosage was 5%, 10%, 15%, 20%, and 30%, the compressive strength of CAB mixes decreased by 2.1%, 7.1%, 9.2%, 9.8%, and 28.1%, respectively. The addition of NaOH promoted the formation of AFt, and there was an optimum level of NaOH corresponding to the high compressive strength of paste. At the age of 3 days and 7 days, the compressive strength reached its maximum at the dosage of 6% NaOH, which was 24.8 MPa and 36.3 MPa, respectively. However, at the ages of 14 days and 28 days, the compressive strength increased as the dosage of NaOH increased to 5%, which was 43.3 MPa and 44.5 MPa, respectively. The water curing could both enhance the early and later strength, the compressive strength of 23.3 MPa was gained at 3 days, and this increased by 16.3%, 24.0% and 36.9% at 7 days, 14 days and 28 days, respectively. Therefore, water curing was suitable for the strength development of CAB pastes.