Investigation on effect of nanosilica dispersion on the properties and microstructures of fly ash-based geopolymer composite.

• Sonication is more efficient than manual stirring for the dispersion of nanoparticles. • Better dispersed nanoparticles can bring additional benefits to the strength of geopolymer. • Nanosilica particles accelerate the reaction at the early stage, especially with better dispersion. • Nanosilica increases micro elastic modulus of gel by 15.18% and 29.93% for different samples. • Dispersion can make the particles play a better filling effect and have a more uniform distribution. Nanosilica-geopolymer composites with different dispersion levels of nanoparticles were investigated on the physical properties and gel properties. The results indicated that compared with the nanosilica-geopolymer composites without ultrasonic dispersion, the 20 and 120 min of sonication brought 3.88% and 13.59% of additional strength enhancement, respectively. For the micromechanical properties of N-A-S-H gel, the better dispersed samples exhibited higher elastic modulus. In comparison to the reference sample, the elastic modulus was increased by 15.18% and 29.93% respectively for samples with 20 and 120 min of sonication. The better dispersed nanoparticles exhibited smaller sizes and increased the physical filling effect which could result in densified microstructures, better bonding behaviors and the both improved micro and macro mechanical properties. [ABSTRACT FROM AUTHOR]