Surfactant-free synthesis of highly monodispersed in situ grown nano-silica on modified fly ash and its impact on the properties of cement pastes

This paper introduces a novel approach to synthesize highly mono-dispersed in situ grown NS (INS) on Fly Ash (FA). The uniform particle size (41 +/- 3.5 nm) and mitigation of the agglomerations tendency of INS were accomplished without any surfactant by utilizing the surface properties of acid-treated FA. INS's growth and adsorption mechanisms were proposed by employing the findings of FTIR and zeta potential investigations. SEM and TEM were used to evaluate the structure and INS dispersion. The impacts of synthesized INS and commercial NS (CNS) on cement pastes' cementitious properties were comparatively investigated using equal dosages of INS & CNS (0.5%, 1.0%, 1.5%). The experimental results revealed that even the highest dosage (1.5%) of INS exhibited better fluidity and rheological behavior than the lowest dosage (0.5%) of CNS in cement pastes. Moreover, compared to CNS, excellent dispersion of INS engendered prominent hydration kinetics of cement pastes and showed more efficient early and long-term strength development. QXRD cement pastes' findings further endorsed INS's prominence over CNS by indicating a significant increase in amorphous content and a notable reduction in CH content. Furthermore, INS refined the pores in the hardened cement pastes efficiently by decreasing the porosity more remarkably.