LAUSR

In this study, changes in transport properties of low-clinker cements on carbonation are investigated. Cement paste and concrete samples were cast using ordinary Portland cement and four types of blended cement. The samples were exposed to 3 ± 0.2% carbon dioxide concentration, 60 ± 5% relative humidity and 27 ± 2 °C temperature to undergo carbonation. The transport properties of uncarbonated and carbonated samples were assessed by measuring water absorption, rate of water absorption and pore structure characteristics. Elemental mapping using scanning electron microscope was carried out to investigate the changes occurring in the microstructure of cement paste on carbonation. Also, volume change occurring on carbonation of different hydration phases was computed theoretically. Irrespective of the type of blended cement, increase in porosity and restructuring of pores are observed on carbonation. The rate of water absorption in concrete is also found to be increased on carbonation. Decalcification of C–S–H and an outward migration of calcium ions from inner C–S–H and clinker grains are observed in elemental maps on carbonation. The volume change calculations show maximum reduction in solid volume on carbonation of alumina-bearing phases like AFt and AFm. The decalcified C–S–H formed on carbonation of C–S–H is found to be hydrous in nature, and the specific gravities of decalcified C–S–H and alumina gel formed on carbonation are found to lie between 2–2.15 and 2.00–2.30, respectively.