This research evaluates the hydration kinetics of micron- and submicron-sized fly ash blended cementitious mortar exposed to four different curing temperature conditions (i.e., −4°C, 0°C, 27°C, and 60°C) by quantifying the chief hydration phases, including portlandite (CH) and water linking to hydration products (WH) such as C-S-H, AFt, AFm, C-A-S-H (WH) through Thermogravimetric-derivative thermogravimetric (TG-DTG) analysis. The study also portrays associated quantitative variation in hydrated phase composition due to the deleterious action of chloride ion (Cl⁻) and Friedel’s salt (Fs, Ca₂Al(OH)₆(Cl, OH)·2H₂O) formation at the characteristic temperature boundary of 230–380°C. The hydration products and chloride-induced phases coupling to functional groups were qualitatively evaluated by means of the Fourier-transform infrared spectroscopy (FTIR) technique. Binary and ternary blended mixes proportioned using the modified Andreasen and Andersen model outperformed the control mix at ambient (27°C) as well as at high-temperature (60°C) curing and exhibited contrasting behavior at freezing (0°C) and subzero (−4°C) curing conditions, regardless of curing ages. Quantified WH% and CH% exhibited enhanced hydration kinetics in multiblended cementitious mixes cured at 27°C (WH: 10–15 %, and CH: 4–9 %) and 60°C (WH: 11–14.5 % and CH: 11–4.5 %), the same showed impeded reactivity when cured at −4°C (WH: 6.5–9 %, and CH: 4–8 %), and 0°C (WH: 7–9.5 % and CH: 4–8.5 %). FTIR spectra revealed a shift in the major Si-O-T band toward a higher wavenumber for the ternary blended mix at ambient and high-temperature curing conditions. Further, the concentration of total chloride (Cl⁻) content is found to be extremely high at the specimen surface for all mixes under subzero curing temperature conditions, i.e., in the range of 0.95–1.38 %. The rate of formation of Fs (Ca₂Al(OH)₆(Cl, OH)·2H₂O) concerning curing temperature conditions is seen to be in the order of −4°C < 0°C < 27°C < 60°C.