Durability of concrete pipes subjected to combined steam and carbonation curing

A beneficial use of carbonation as an auxiliary curing regime for concrete pipes was studied in an attempt to reduce steam curing time, improve durability performance and explore the possibility of using concrete pipe to sequester carbon dioxide. Durability performance of the carbonated concretes was characterized by carbon uptake, strength gain, pH, calcium hydroxide content, permeability, sorptivity and sulfate and acid resistance. It was found that initial curing using steam is necessary to facilitate carbonation. Although the contribution of early carbonation to strength gain is not noticeable after initial steam curing, the process is unique in promoting enhanced durability performance of concrete. The early carbonation leads to a reduction in calcium hydroxide near the surface while maintaining a pH above the corrosion threshold value at the core. Carbonated concretes also exhibit improved resistance to sulfate attack, water absorption, and chloride ion penetration. A carbon uptake of 9% by cement mass makes concrete pipe an ideal candidate for carbon dioxide capture and storage.

► Carbonation curing of concrete pipes at early age has the potential to sequester CO2 and improve durability.
► Early carbonation eliminates Ca(OH)2 on concrete surface.
► Early carbonation enhances concrete resistance to sulfate attack, chloride penetration and water absorption.
► pH of concrete can still be retained above the corrosion threshold value after early carbonation.
► The early carbonation curing is suited to precast reinforced concretes.