Mineralogy of tricalcium aluminate hydration with silica nanoparticles

•n-SiO2 promote the formation of siliceous-hydrogarnet along with C-S-H and C-A-S-H.•n-SiO2 suppress the formation of h-AFm phases that could be responsible for higher durability.•More polymerized C-S-H was observed with n-SiO2. Formation of siliceous-hydrogarnet (Si-hydrogarnet) and stability of katoite (C3AH6) in tricalcium aluminate (C3A) system in presence of silica nanoparticles (n-SiO2) have been examined in the present study. C3A hydration in presence of n-SiO2 upto 24 h show retardation in hydration due to the surface coverage of C3A grain through calcium-silicate-hydrate (C-S-H)/calcium-alumino-silicate-hydrate (C-A-S-H) (previous study). However, in the present investigation, hydration was studied upto 10 days using QXRD, TGA, FTIR, FESEM, EDS and Mapping and 29Si NMR techniques. QXRD results show that in case of control samples, the katoite content increases from 61 to 73%, while in n-SiO2 incorporated C3A samples, it decreases from 28 to 15% as the hydration proceeds showing katoite phase destabilization in presence of n-SiO2. Further, FTIR results show symmetric stretching vibration of Si-O-Si at ∼784 cm−1 and ∼818 cm−1, while asymmetric stretching vibration of Si–O–Si/Si-O-Al at ∼1028 cm−1 indicating the formation of C-S-H/C-A-S-H and Si-hydrogarnet in presence of n-SiO2. In 29Si NMR results, Q2u peak at −89 ppm confirm the formation of Si-hydrogarnet at 10 days of hydration. The present study is important from performance and durability point of view as formation of C-A-S-H and Si-hydrogarnet can act as an aluminum reservoir, which may prevent severe chloride and sulphate attack.