Contact strength of C-S-H cement phase with additives

The study of the contact-condensation properties of building materials is based on the possibility of forming a durable water-resistant artificial stone by a convergence of particulates, for example, in the pressing process. It allows to obtain in the shortest time possible a durable material based on waste and by-products of the industry, for example, nepheline sludge, con-crete scrap, the main phase of which are hydrated silicate minerals – C-S-H cement phase. Structural-chemical and thermody-namic analyzes of the structure of C-S-H phase nanoparticles show that for the formation of silicon-oxygen chains on the portlandite surfaces of these particles, a combination of silicon-oxygen diortho groups with bridging alumina-oxygen tetrahe-dra is advantageous. That is why it is advisable to study the contact hardening of the C-S-H phase with various additives including calcium aluminates. The directional formation of silicon -alumo-oxygen chains and the modification of the basicity of the C-S-H phase due to the use of aluminate and silicate additives is a scientific novelty of the work. The contact harden-ing of the C-S-H cement phase with additions of portlandite, nano-silica, and nano-alumina was carried out in this work. The C-S-H cement phase was synthesized from calcium oxide, silica, and water at a temperature of no higher than 100 °C. The experimental part contains a study of the dependences of the compressive strength of a stone from C-S-H on the type of addi-tives, hardening time and pressing pressure. It is shown that the addition of high-alumina slag significantly increases the compressive strength of the pressed stone, which is provided by the formation of contact-active C-S-H and alumina gel Al(OH)3.