| Abstrakt: |
Abstract: The investigations of the effect of the Ca(NO3)2 dosage at different initial curing temperatures on the Portland cement hydration process and the physical and mechanical properties of Portland cement are presented in the paper. The results show that the Ca(NO3)2 admixture shortens the induction period of the hydration of the cement paste and reduces the maximal hydration temperature of the cement paste. The setting time of the cement paste with Ca(NO3)2 is about 1 hour shorter for 1% of Ca(NO3)2 in the cement paste. At 0 °C and 5 °C, the accelerating effect of the Ca(NO3)2 admixture is the most pronounced. At lower temperatures (-5 °C, -10 °C), only 3 % of the Ca(NO3)2 admixture can shorten the initial setting time by about 40 %. The most effective application of Ca(NO3)2 is achieved at -5 °C. For the 2 day-specimens cured at the lower initial temperatures (-5 °C, -10 °C), the higher Ca(NO3)2 dosages (2-3%) significantly improve the standard strength values of the concrete. |
