This paper is concerned with changes in the phase structure of cement paste modified by complex antifreeze agents based on sodium formate, calcium chloride and S-3 superplasticizer. Complex modifiers were developed for cement-crushed mixtures hardening at low temperatures (down to –15.0 °C) used in pavement structures. In countries where construction and operation of highways occur at low air temperatures (below 0 °C), it is promising to use the method of modifying cement-crushed mixtures with complex antifreeze agents. The structural studies of cement paste with these additives are poorly described in scientific literature. Therefore, the aim of this work was to consider the impact of complex antifreeze agents in cement paste on the peculiarities of phase structure formation and the relationship between the structure and the properties of the obtained materials. The cement paste was tested for compressive strength using the standard technique; then after preparation, the samples were tested by X-ray, differential thermal and thermogravimetric analyses. It was established that the modification provides the possibility to increase the content of the crystalline phase compared with the amorphous one in the form of new formations (portlandite and dicalcium hydrosilicates). The developed complex modifiers contribute to activation of hydration processes in cement paste, which is confirmed by the level of the hydration degree up to 0.6 and the integral value of weight loss up to 20.5 %. The relationships between the increase in the compressive strength of cement paste and the increase in the hydration degree of calcium silicates and the integral value of weight loss were established. It was shown that the combined use of components of the complex three-component additive provided synergism of processes of structure formation and, as a consequence, an increase in the strength of cement paste. The use of the developed compositions of antifreeze agents in the technology of construction of cement-crushed bases at subzero temperatures (up to –15 °C) prolongs the road construction season and improves the operational indicators of road pavement materials.