Heat exchange of concrete mixture with the surroundings
was found during sample exposure to the direct
sunlight at air temperature of 22.2 °C. The sun rays caused
increasing temperature of the internal environment by 5°C.
Duration of temperature exchange between the surroundings
and sample lasted 4 hours. Creating a solid structure at
higher temperatures was observed at evolution of hydration
heat. The extreme was found in used concrete mixture
placed in direct sunlight during the measurement. When
the ambient air temperature was 22.2 °C after 12 hours
extreme of 10 kJ/kg occurred (see Fig. 12.).