During Florida summers, the concrete temperature drops in some Florida Rock Industries ready mix trucks. The workers are using a liquid nitrogen (LIN) cooling process. When they complete the 1,300-foot Dame Point Bridge in Jacksonville, Florida about 80,000 cubic yards of the concrete in it will have been cooled by liquid nitrogen.
WHY USE LIQUID NITROGEN?
In bridge piers, concrete placed at high temperatures is likely to develop cracks caused by surface concrete cooling and contracting faster than the interior concrete. Liquid nitrogen allows temperature reductions that can't be achieved using chilled water, slush, or ice. With the liquid nitrogen cooling equipment, concrete is cooled to an exact predetermined temperature without altering the water-cement ratio. To cool the concrete, a LIN injection lance pokes into the back of a truck mixer like a huge mosquito and sprays the concrete with negative 320 degree Fahrenheit liquid nitrogen. The length of spraying time, preset at a control station, determines how much the concrete temperature is lowered.