Perspective Chapter: Pore Structure Evolution of Cement and Concrete Induced by CO2 Carbonation

Abstract

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.