Investigating the Effects of Liquid Nitrogen on Concrete Properties in Hot Weather Concreting

Concrete structures are always affected by environmental conditions, and hot weather condition during mixing and casting impressively affect the performance of concrete. Concrete producers have been using different methods of reducing the temperature of concrete such as liquid nitrogen through direct injection of it into the drums of concrete trucks. Liquid nitrogen with having temperature of -196°C provide accurate temperature control and is not limited by the water-cement ratio as in the case of chilled water or ice. The purpose of this research was to investigate the effects of liquid nitrogen on concrete properties such as slump, setting time, compressive strength, tensile strength and flexural strength with two different curing methods. In this research, three mixtures were prepared: control, hot and LN-cooled. The temperature in control mixture was considered to be 27°C. Hot mixture which was made from materials stored for 72 hours at the desired temperature (50°C) to simulate hot weather condition, and the temperature in this mixture was obtained 40°C. The process in preparation of the LN-cooled mixture was the same with the hot mixture with the difference that, the temperature of the LN-cooled mixture was lowered to the control mixture (27°C). The results indicate that the liquid nitrogen improved the properties of concrete in hot weather and additionally the results show that the properties of concrete are relatively unaffected when cooled with liquid nitrogen to room temperature. Finally based on findings in this research, liquid nitrogen is an appropriate option in hot weather concreting.