Enhanced microstructure and mechanical properties of cementless ultra-high-performance fiber-reinforced alkali-activated concrete with silicon dioxide nanoparticles

• Published in: Construction & building materials 2023-09, Vol.398, p.132514, Article 132514
• Main Authors: Piao, Rongzhen, Oh, Taekgeun, Kim, Gi Woong, Choi, Hong-Joon, Banthia, Nemkumar, Yoo, Doo-Yeol
• Format: Article
• Language: English
• Subjects: Bond performance; Porosity; Silica fume; Silicon dioxide nanoparticles; Tensile performance; Ultra-high-performance fiber-reinforced alkali-activated concrete
• ISSN: 0950-0618; 1879-0526
• DOI: 10.1016/j.conbuildmat.2023.132514

•Nano-SiO2 improves the packing density and generates abundant C-A-S-H gels of UHP-AAC.•Interfacial bond strength and pull-out energy of steel fibers in UHP-AAC are improved by nano-SiO2.•The highest compressive strength 184 MPa and lowest porosity of 7.53% are achieved.•The highest tensile strength and strain energy density of UHP-FRAAC are achieved at 2% nano-SiO2 replacement.•Higher dosages of nano-SiO2, 3% or more, negatively affect the tensile properties of UHP-FRAAC due to its agglomeration. This study investigates the effect of silicon dioxide nanoparticles (nano-SiO2) on the microstructure and mechanical properties of eco-friendly, cementless ultra-high-performance fiber-reinforced alkali-activated concrete (UHP-FRAAC). Various amounts of nano-SiO2 were adopted in a range of 0%-5% of the mass of silica fume (SF). The experimental results showed that the addition of nano-SiO2 improves the packing density of ultra-high-performance alkali-activated concrete (UHP-AAC) and generates abundant calcium (alumino)silicate hydrate (C-(A-)S-H) gels to increase its density. Therefore, the interfacial bond strength and pull-out energy of steel fibers from UHP-AAC could be enhanced. At 2% nano-SiO2 replacement, the compressive strength of UHP-FRAAC was the highest (184.2 MPa), and its total porosity was the lowest, decreasing from 9.72% to 7.53%. The highest equivalent bond strength and strain energy density of UHP-FRAAC occurred at 2% nano-SiO2 replacement, i.e., 10.9 MPa and 72.5 kJ/m3, respectively. The maximum tensile strength of 14.5 MPa was observed at a nano-SiO2 content of 3%. Higher dosages of nano-SiO2, 3% or more, negatively affected the interfacial bond and tensile properties of UHP-FRAAC due to its agglomeration, but still exhibited higher performance than that of the plain UHP-FRAAC up to the dosage of 5%. Therefore, the optimal dosage of nano-SiO2 in UHP-FRAAC was suggested to be 2% by mass of silica fume.