The durability of concrete produced using CO2 as an admixture

Abstract

Carbon dioxide has been investigated as a beneficial admixture to freshly mixing concrete. The reaction between the CO2 and the hydrating cement forms finely distributed calcium carbonate reaction products. The carbon dioxide can be incorporated into conventional ready mixed concrete production through a simple gas system retrofit. A comprehensive durability evaluation of carbon dioxide treated concrete was conducted. The effect of the carbon dioxide in the fresh state was assessed in terms of slump, air content, plastic density, heat of hydration and time of time. Hardened state tests included compressive strength, freeze-thaw durability (ASTM C666), linear shrinkage, rapid chloride permeability (ASTM C1202), and deicer salt scaling. Comparisons were made between a reference concrete batch, a batch that contained a conventional accelerating admixture, and a batch subjected to the carbon dioxide addition. The concrete to carbon dioxide was found to reduce the time to initial and final set by over 20%. The CO2-treated concrete had a 14% higher compressive strength than the control at one day and 10% higher strength at 3 days. Later strengths were equivalent. Durability was general unchanged although salt scaling was reduced. The carbon dioxide could be a viable non-chloride accelerator.