Journal of Materials Research and Technology (May 2025)
Enhancing mechanical strength and reducing drying shrinkage in high-volume fly ash mortar: Synergistic effects of steel fibers and nano-SiO2
Abstract
This study investigated the effects of steel fibers and nano-silica dioxide (nano-SiO2) on the fluidity, capillary water absorption, mechanical properties, and drying shrinkage of mortar when 50 % of the cement was replaced by fly ash. The mechanisms by which steel fibers and nano-SiO2 influence high-volume fly ash mortar were discussed based on macroscopic tests and microscopic structural analysis. The results show that while nano-SiO2 and steel fibers had negligible effects on the fluidity of fly ash mortar, they significantly enhanced its mechanical properties. When the steel fiber content was 1.0 % and the nano-SiO2 content was 2.0 %, the modified mortar exhibited increases in flexural and compressive strength by 86.4 % and 53.7 %, respectively, compared to the unmodified mortar at 28 days of age. Additionally, the incorporation of nano-SiO2 and steel fibers significantly reduced the capillary water absorption and drying shrinkage of the mortar. The capillary absorption rate of the 1.0 % steel fibers and 2.5 % nano-SiO2 composite mortar decreases 67.8 % compared to the fly ash mortar. At 90 days of age, the drying shrinkage of the modified mortar containing 1.0 % steel fibers and 2.5 % nano-SiO2 was reduced by 44.4 % compared to the unmodified mortar. Microstructural characterization through scanning electron microscopy (SEM) and X-ray diffraction (XRD) demonstrated that nano-SiO2 incorporation enhanced the hydration of both fly ash and cement, leading to a significant reduction in unhydrated fly ash particles. Furthermore, mercury intrusion porosimetry (MIP) tests demonstrated that the addition of nano-SiO2 and steel fibers markedly decreased the average and median pore sizes in the mortar, resulting in a more optimized pore structure distribution.
