Metakaolin can be considered as a model compound foran aluminosilicate-rich supplementary cementitious material (SCM) because of its composition and highly pozzolanic properties. This work presents a systematic investigation of the hydration of white Portland cement (wPc)–metakaolin (MK) blends cured at different temperatures by 29Si and 27Al MAS NMR with the main focus on the structure and composition of the C-(A)-S-H phase. White Portland cement–MK paste samples with wPc replacement levels of 0, 10, 20, and 30 wt% have been prepared and hydrated for 1–8 weeks at five different temperatures (5, 20, 40, 60, and 80 °C). Information on the degree of reaction for alite, belite, and MK is derived from the 29Si NMR spectra and shows that the hydration of the wPc–MK blends is accelerated with increasing temperature except for the blend with the highest MK level (30 wt%). The AlIV/Si ratio of the C-(A)-S-H phase is found to be independent on the hydration time but increases slightly with curing temperature. On the other hand, a significant increase in the average aluminosilicate chain lengths is observed for blends with increasing temperature, reflecting a decrease in the Ca/Si ratio for the C-(A)-S-H phase. Strätlingite is present in the wPc–MK blends at 20 °C and the fraction of this phase decreases with increasing curing temperature.
