Mechanical properties and durability of geopolymer concrete based on fly ash and coal gangue under different dosage and particle size of nano silica

Abstract

In order to test the engineering applicability of mixed base geopolymer concrete and analyze the modification effect of nano additive systematically, nano silica (NS) was used to reinforce fly ash and coal gangue based geopolymer concrete (FACGGC). The mechanical properties and environmental suitability of the specimens were tested to analyze the effects of different dosing amounts (0–1.5 wt%) and particle sizes (20 and 100 nm) of nano silica on FACGGC. The results showed that the appropriate amount of NS could significantly improve the performance of FACGGC, excessive NS had significant negative impact. For different performance tests, the optimal dosage of NS was different. Under the same dosage, the effect of smaller particle size NS (20 nm) on the mechanical properties and water absorption of NS-FACGGC was better than larger particle size NS (100 nm), while the effect of larger particle size NS on resistance to sulfate attack was better. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and image analysis showed that NS with smaller particle sizes had a higher filling effect and were more likely to serve as nucleation sites, but when NS was over doped, the agglomeration effect of NS with smaller particle sizes was more significant.