Frost-Resistant Rapid Hardening Concretes

This article presents the results of research conducted to determine the possibility of accelerating strength gain and enhancing the operational reliability of concrete. The study tested the effects of modern modifiers on concrete in order to select the composition of rapid hardening concrete (RHC) with better frost resistance characteristics. A basic composition of RHC grade C 25/30 was developed using traditional concrete calculations. Based on the analysis of previous studies by other authors, two basic modifiers (microsilica and calcium chloride (CaCl₂)) and a chemical additive (a hyperplasticizer based on polycarboxylate esters) were selected. Then, a working hypothesis was adopted to find optimal and effective combinations of these components in the concrete composition. In the course of experiments, the most effective combination of additives for obtaining the best RHC composition was deduced by modeling the average strength values of samples in the early ages of curing. Further, RHC samples were tested for frost resistance in an aggressive environment at the ages of 3, 7, 28, 90, and 180 days to determine operational reliability and durability. The test results showed a real possibility of accelerating concrete hardening by 50% at the age of 2 days and achieving up to 25% strength gain by using both microsilica and calcium chloride (CaCl₂). The best frost resistance indicators were observed in the RHC compositions with microsilica replacing part of the cement. The frost resistance indicators also improved with an increase in the amount of microsilica.