Effect Of NanoSiO₂ On Sulfate Attack Resistance Of Cement-based Materials

Durability of cement-based materials served in sulfate environments is a big concern because of the devastating effects of sulfate attack.Ordinary,replacement of cement with supplementary cementitious materials?SCMs?was well developed to increase the sulfate attack resistivity of cement-based materials.However,the sulfate attack resistivity would depend on the maturity of the compositional and microstructural properties of the cement-based materials.An improperly development of the properties at early ages will even decrease the sulfate attack resistivity.By taking the advantages of nanoSiO₂ on the development of the physiochemical properties of cement-based materials,especially at the early ages,the sulfate attack resistivity of cement-based materials was studied and compared with those of conventional SCMs-added cementitious materials?such as fly ash,ground granulated blast-furnace slag,and silica fume?.Small dosages?1 and 3 wt.%?of NS were added into cementitious materials,and the conventional supplementary cementitious materials?SCMs?,i.e.,silica fume?SF,5 wt.%and10 wt.%?,fly ash?FA,10 wt.%and 30 wt.%?and ground granulated blast-furnace slag?GGBS,10 wt.%and 30 wt.%?at their conventional dosages.Samples were initially standard-cured for 7-and 28-day before curing in 5 wt.%Na₂SO₄solution.It was found that NS effectively improved the early age properties of cement paste/mortar/concrete,thus leading to the enhanced mechanical property of samples undergoing sulfate attack.At the same time,the volume expansion of cement paste/mortar,as well as the cracking and the enlarge of porosity,in the NS-added sample was greatly reduced and the effect was more pronounced in the 28-day initially cured mortar samples.For the C₃S paste/mortar,the strength loss and cracking were significantly reduced with NS-added samples when compared with C and SCMs-added samples.In addition,the addition of NS retarded the procees of sulfate attack on C₃S paste/mortar.Work in this study shows NS's potential of improving the sulfate attack resistivity of cement-based materials.This was consistent with the modification of microstructure and hydration products by NS.It provides a basis research to improve the sulfate resistance of cement-based materials of nano-SiO₂ by this research,and it is expected to combine nano-SiO₂with SCMs to improve the sulfate resistivity of cement-based materials.