Comparison study on the sulfate attack resistivity of cement-based materials modified with nanoSiO2 and normal SCMs: Pore structure and phase composition

Magnesium Sulfate Attack Resistance of SCM-Modified Cement-Based Materials

“…All the specimens showed expansion at 180 days of immersion. The NSblended specimens showed greater expansion due to the ultrahigh activity of nano-silica [24,25] and the higher crystallisation pressure within the denser structure [25]. The GGBS was slightly more reactive than the FA in Figure 2.…”

“…The strength of the SF-blended specimens showed a decreasing trend at 180 days due to the insufficient dispersion of the silica fume and agglomeration within the hydration system, and the erosion process caused the disintegration of the agglomerated silica fume and a decrease in the strength, as can be seen in Figure 4. The specimens blended with GGBS also showed a reduction in b) SEM image of the SF-added samples a) X-CT images of the SF-added samples strength at 180 days, due to the weak interface bonding between the unhydrated GGBS and hydrated products, as well as the crystallisation pressure of the erosion pro-ducts [25]. The SEM images and EDS results in Figure 5 show the ettringite and gypsum are formed after the sulfate attack.…”

“…When the amount of sulfate attack products continued to increase, these products filled the pores enhancing the strength, and the sulfate attack products reached a certain level of damage again. The SF-blended specimens showed a gradual decrease in the flexural strength because the agglomerated SF particles tended to depolymerise under erosion [25], to aggravate the extension of the cracks and the defects and then to make the flexural strength decrease. The strength of the FA-blended specimens showed a continuous increase because the FA reaction activity was low and the structure was loose, which provided a larger space for the generation of sulfate products.…”

“…The strength of the FA-blended specimens showed a continuous increase because the FA reaction activity was low and the structure was loose, which provided a larger space for the generation of sulfate products. Therefore, the magnesium sulfate attack products during the curing had enough space to grow and the resulting crystallisation pressure was not enough to destroy the matrix, but the filling played a strengthening role [25].…”

“…In recent years, some researchers have shown that nano silica (NS) has a very high pozzolanic reactivity which will significantly improve the microstructure and performan-ce of cement-based materials at the very early ages even at small dosages [18][19][20][21][22]. The results showed that NS can effectively improve the performance of cement-based materials even after a short initial curing time [23][24][25], which hinted at its potential of being used to improve the sulfate attack resistivity of cementitious materials.…”