Directed synthesis of alkaline aluminosilicate minerals in a geocement matrix

Geocements were created in accordance with a hypothesis put forward by Prof. V. Glukhovsky that the structure formation processes in the alkaline aluminosilicate binders corresponded to geological transformations of aluminosilicate minerals taking place in nature. At low temperatures, a type of hydration products depends on curing conditions and mix composition. An autoclave curing allows for an intensive synthesis of a well-crystallized zeolite structure, whereas other types of curing result in the formation of an amorphous structure with crystalline inclusions represented mainly by hydroxysodalite. On the contrary to this, after curing at high temperatures, a formation of nepheline, albite or α-cristobalite depends exclusively on the firing temperature and initial geocement composition. Mechanical strength of the geocements may reach 88.5 MPa after low temperature curing and 88.7 MPa after firing at 800 °C. Optimal thermo-mechanical properties of the metakaolin- and fly ash-based geocements may be reached in compositions with a microstructure represented by an average amount of thermostable zeolites, since just these phases are characterized by a smooth dehydration and subsequent re-crystallization into stable anhydrous alkaline aluminosilicates without destruction of a framework. Directed regulation of structure formation at low temperatures is a key question in obtaining a wide range of special materials such as acid-resistant, high-strength, quick hardening, with low leach rates, high adhesion, etc. At the same time, a structure formation at high temperatures is important with regard to creation of heat- and fire-resistant composite materials. Synthesis of analogies to natural aluminosilicate minerals ensures also high durability.