Ceramics-Silikáty 65, (3) 273 - 280 (2021)

This study investigates the effect of the amount (from 0.6 % to 1.4 %) of crystallizing admixture (CA) on the shrinkage, density, porosity and mechanical properties of concrete specimens. A higher content of CA increased the total porosity of concrete from 10.6 % to 11.15 %. In contrast to the specimens containing 0.8- 1.0% of CA, the lowest amount of closed pores and highest total porosity was observed in the specimens containing 1.2 %-1.4 % of the CA. Compared to the control specimen, concrete specimens containing 1.4 % of CA showed a 5.4 % decrease in flexural strength and a 13.6 % decrease in compressive strength after 28 days of curing. The specimens containing 0.9 %-1.0 % of CA demonstrated the lowest shrinkage in the period of 190 days. The shrinkage of these specimens reduced 4.8 %-4.9 % compared to the control specimen. Higher content of CA had an opposite effect on the shrinkage, a short-term expansion of specimens was observed after 28-56 days. Taking into account all the properties of the concrete specimen, the optimum amount of CA, which could prevent cracks in the structures is 1.0% of the cement mass.