The role of kaolinite clay in the evolution of the structure and properties of slag-alkali cements

Slag-alkali cements are environmentally friendly, as they use industrial waste for their production. One of the perspective areas of control of the properties of slag cements is the introduction of complex modifying additives, which include clays of different composition and energy state. The use of such additives opens the possibility not only to control the physical and mechanical properties of cements, but also to provide them with the desired decorative effect. Previous studies have shown that the introduction of slag cement up to 15% by weight of kaolinite clay provides a cement with a whiteness factor of ≥70%. The role of kaolinite clay in the evolution of the structure and properties of white slag cement is investigated. It is shown that the introduction of kaolinite clay in the amount of 5…10% by weight increases the water consumption from 23% to 24%, reduces the time of onset of hardening from 48 minutes. up to 45 minutes, slows down the set of strength in the initial curing period and activity at 28 days of age from 56,7 to 50,4 MPa. But with an increase in the amount of clay to 20% by weight, the time of onset of hardening increases to 51 minutes. The introduction of clay up to 20% also helps to reduce heat dissipation from 84,2 J/g to 40 J/g. The amount of introduced clay significantly affects the strength of cement, which with increasing its amount to 15% by weight decreases at 28 days of age from 56,7 MPa to 49 MPa, but after 90 days it exceeds the control strength without additives and is 67,5 MPa. The study of structural processes showed that the introduction of kaolinite clay in the composition of slag-alkaline cement intensifies the binding of free alkalis in zeolite-like hydrated neoplasms such as analcim and hydronepheline. To intensify the processes of structure formation, especially in the initial stages, the efficiency of the introduction of alkali cements up to 2% by weight of Portland cement has been demonstrated.