One of the essential tasks for a sustainable future is to reduce harmful emissions into the atmosphere significantly. Cement production is the world's largest industrial carbon pollutant, accounting for 8 % of global emissions. More than 2.2 gigatons of carbon dioxide are emitted into the atmosphere every year. Therefore, reducing the energy intensity of products and reducing the number of harmful emissions in cement production is becoming critical. One of the strategies to reduce cement production emissions is to reduce the share of the most energy-consuming component in cement — clinker. In this case, various activation methods are used for maintaining the same level of cement activity. One of these methods is the impact on the hardening binder with magnetic fields. In the paper presented the results of a study of hydration processes of blast–furnace cement activated by a magnetized ferromagnetic additive. The work established that the introduction of pre–magnetized ferromagnetic dust into blast–furnace cement composition has an activating effect on binder hydration. It shows that activation occurs both in the initial and long periods of hardening. The nature of the mutual influence of the components of the hydration system alite — lime — slag in a modified binder was revealed. The investigation determined that the ferromagnetic additive, intensifying the process of slag hardening, increases the proportion of hydrated slag by 1.5–2 times. It was revealed that the formation of the ettringite framework in the modified binder's gel is completed within one day. It is shown that in the subsequent periods, hydration of aluminates occurs mainly due to the formation of hexahydrate tricalcium aluminate, which excludes destructive processes in the late periods of binder hardening. It has been established that under the action of a ferromagnetic additive, the degree of crystallization of hydro silicates in the modified binder increases.