This study aimed to monitor the effect of temperature and the addition of nanosilica on the nanostructure of the CSH gel forming during tricalcium silicate (C3S) hydration. Two types of paste were prepared from a synthesized T1 C3S. The first consisted of a blend of deionized water and C3S at a water/solid ratio of 0.425. In the second, a 90wt% C3S+10wt% of nanosilica blend was mixed with water at a water/solid ratio of 0.7. The pastes were stored in closed containers at 100% RH and 25 degrees C, 40 degrees C, or 65 degrees C. The hydration reaction was detained after 1, 14, 28, or 62 d with acetone, and then pastes were studied by 29Si magic angle spinning nuclear magnetic resonance (29Si MAS NMR).The main conclusion was that adding nSA expedites C3S hydration at any age or temperature and modifies the structure of the CSH gel formed, two types of CSH gel appear. At 25 degrees C and 40 degrees C, more orderly, longer chain gels are initially (1d) obtained as a result of the pozzolanic reaction between nSA and portlandite (CH) (CSHII gel formation). Subsequently, ongoing C3S hydration and the concomitant flow of dimers shorten the mean chain length in the gel.