Cryogenic cooling using liquid nitrogen in production of massive concrete: temperature profile, setting time and compressive strength

Abstract

Various cooling methods of concrete mixtures are used in mass concrete structures to reduce concrete's thermal cracking and enhance the structures’ integrity. In concrete production, mixing cement with water is associated with hydration heat generation, which may cause concrete mixes to dry out and crack. The experimental work aims to evaluate the effects of using liquid nitrogen (LN) in cooling mortar mixes and concrete. LN was used in doses of 0, 25, 50, 75, and 100% by water volume to either cool the mixing water at T = 4 °C or to inject it into concrete mixtures directly. The proportions of concrete mixtures were based on ACI PRC-207.1-21 for mass concrete. Measurements of the mortars’ initial and final setting times and temperatures indicated that more LN% delayed the hardening process, so the peak hardening rates occurred later, exhibiting a slowdown of the cement hydration. LN cooling enhances the mortar and concrete cubes’ compressive strength when VLN/Vwater≤1. However, concrete compressive strength decreased due to the appearance of ice lenses that turn into voids when VLN/Vwater>1. Cooling concrete with chilled water (at T = 4°C) showed a 30% increase in the mortar cubes’ compressive strength and a maximum of 16.45% when injecting LN into the mixes. The concrete compressive strength increased by 34.51% and 12.97% when mixed with cooled water and injected LN into the mixtures, respectively. The slower cooling process promoted better cement hydration in the chilled water method compared to the injection of LN into the concrete mixture.