Accelerated carbonation of oil-well cement blended with pozzolans and latent hydraulic materials

Abstract

Accelerated carbonation of cement mixtures consisting of class G cement, silica fume, metakaolin, or blast furnace slag was studied by thermogravimetric, X-ray diffraction and Fourier transform infrared analyses for 1 year. Surface parts were fully carbonated during the first 7 days. Polymerization of amorphous hydrates due to their decalcification was observed together with the rising amount of calcium carbonates and reformation of gypsum from ettringite and monosulfate. Decalcification of clinker phases took place fast after the depletion of portlandite. Although portlandite was still present in unblended pastes, because of slower carbonation rate in the surface parts and higher C/S ratio of amorphous hydrates, the carbonation front moved inward during 3 months. Pozzolanic reactions in the samples with 30 mass% of additives depleted portlandite, however, higher amounts of C–(A)–S–H phases with lower C/S ratio, denser microstructure and faster carbonation of surface parts ensured their resistance against carbonation throughout the monitored period.