Effect of AlF₃ production waste on the processes of hydration and hardening of the alkali-activated Portland cement with sodium silicate hydrate

Generally, the early strength of hardened Portland cement paste is controlled, by changing the mineral composition of clinker and grinding fineness. By using clinker (calcium silicates) and liquid glass (sodium silicate) together, these materials have high degree of coagulation and rapid hardening. For this reason, it is important to regulate the setting times. One solution of this problem is the use of chemical admixtures. In this research, the admixture made from liquid glass and AlF₃ production waste was suggested (the waste from phosphates fertilizers production). The cement system "Portland cement clinker–sodium silicate hydrate–AlF₃ production waste" was characterized by X-ray diffraction, differential scanning calorimetry, measurements of hydration temperature and the compressive strength of hardened cement paste specimens. The microstructure of hardened cement pastes was evaluated by scanning electron microscopy. Reference specimens were made from pure Portland cement clinker. A possibility to regulate hydration rates both at the early stage of hardening and at the later ones by addition of this admixture was demonstrated. The effect of AlF₃ production waste was described. By using this admixture, the hydration temperature increased, the hydration process delayed, and compressive strength of hardened Portland cement clinker paste samples increased, especially at later ages. This gave the opportunity for composition: clinker–liquid glass–AlF₃ production waste to create slowly curing cement; which is suitable for long transportation and for massive constructions.