STRUCTURING ROLE OF MICROCALCITE IN 3D PRINTABLE CEMENT COMPOSITIONS

The article deals with the current problem of structure formation and hardening of for 3D printable mixtures. The objects of the research are the hardening systems “cement - microcalcite - modifying additives”. Cement and microcalcite, as the main com-ponents of hardening systems, were characterized by similar dimensional and geometric features. The mass ratio of binder and filler was constant in the composition of mixtures, but the modifier type was varied. Complex additives based on nanoparticles Al2O3·SiO2, SiO2, potassium pyrophosphate were used as modifiers. X-ray method was applied to study the phase composition and microstructure of hydration products. The hardening kinetics of cement systems was evaluated according to the compression tests of samples at the age of 1, 3, 7, 14, 28, 60 and 90 days. It has been stated that the use of modifying additives with Al2O3·SiO2, SiO2 nanoparticles is effective, as they make microcalcite involved in the structure formation of hardening systems. Also, the bal-ance between hydration products in the structure is shifted towards an increase in the content of CSH-phases with the value of C/S=0.5. The highest values of compressive strength both at the initial stage of hardening (Rc = 25 MPa in 1 day) and in the long term are typical for cement systems with microcalcite modified by the additive based on nanoparticles Al2O3·SiO2 (Rc = 58 MPa in 90 days). Systems with SiO2 and potassium pyrophosphate-based modifiers are characterized by low strength at the initial stage of hardening (Rc = 2 - 10 MPa in 1 day); its values are similar in a long-term period (Rc = 40 - 45 MPa).