Effects of Liquid Nitrogen Cooling on Fresh Concrete Properties

This paper will discuss how, in hot weather, it is a common practice to cool concrete - particularly for mass concrete applications - to prevent thermal cracking and durability problems. An increasingly popular method of cooling is through direct injection of liquid nitrogen (LN2) into the drums of concrete trucks. During an investigation of the effects of LN2 on concrete properties, it was observed that the practice has unexpected impacts on concrete slump and setting time. While it is known that increasing temperature decreases slump for concrete with given mixture proportions, it is surprising that concrete cooled with LN2 has low slump similar to that of a hot mixture, a phenomenon that is not affected by the time at which the concrete is cooled. The initial setting time, however, is actually longer than predicted when there is a significant delay in LN2 cooling.