Liwei Zhang

By Liwei Zhang, Manguang Gan and Quan Xue

This chapter explores the profound impact of CO₂ carbonation on the pore structure of cement and concrete. Carbonation, resulting from the reaction of CO₂ with calcium hydroxide and calcium silicate hydrate in cement, is a complex process that affects the durability and performance of cement-based materials. In this chapter, the changes in pore structure of cement and concrete induced by carbonation are examined. Under low pressure CO₂, cement carbonation leads to the formation of dense carbonation regions. For wellbore cement exposed to high pressure and high concentration of CO₂, a calcite precipitation layer with very low porosity is formed in cement, and two highly porous layers due to dissolution of calcite and cement hydration products are formed at both sides of the calcite precipitation layer. For concrete exposed to atmospheric pressure CO₂, carbonation causes hydration products to form CaCO₃ and precipitate in pores. Different from wellbore cement, no distinct calcite precipitation layer is formed in concrete. However, for concrete exposed to 1 MPa CO₂, excessive accumulation of CaCO₃ eventually leads to expansion and cracking of pores, which causes the compressive strength of concrete to decrease after reaching the peak.

Part of the book: Transport Perspectives for Porous Medium Applications