The effect of size and replacement content of nanosilica on strength development of cement treated residual soil

•Strength development of the treated residual soil were improved by nano silica.•Compressive strength of the soil increased under effect of nano silica.•CEC and ER of treated soil increased when nano silica was added.•C-S-H gel of cement treated soil increased when nano silica was added. In this study, effects of size and replacement content of nanosilica on physical, chemical, and microstructural characteristics of cemented residual soil were investigated. Accordingly, UCS and electrical resistivity tests were conducted on cemented specimens with replacement contents of 0.2%–1% nanosilica of 15 and 80nm at 7, 14 and 28days. XRD, Zeta potential, CEC, FTIR, and SEM tests were performed to identify chemical and microstructural changes over time. The results showed that smaller size nanosilica had an accelerated influence on samples while nanosilica of larger size was more effective at ages after 14days of curing.