Influence of silica fume and lime on belite-rich cement paste subjected to atmospheric and autoclave CO 2 curing regime

The study investigates the effects of using silica fume (SF) and hydrated lime as secondary and tertiary binders in belite-rich cement (BRC) paste. Atmospheric and autoclave CO 2 curing, and water curing were adopted to attain hydrated and carbonated phases. Atmospheric and autoclave CO 2 curing led to significantly higher compressive strength than water curing, with atmospheric CO 2 curing displaying higher or comparable strength to that of autoclave CO 2 curing. At 28 days, for control mixes, while water-cured samples displayed a compressive strength of 12.82 MPa, atmospheric and autoclave-cured samples exhibited compressive strengths of 39.99 MPa and 36.48 MPa, respectively. Atmospheric CO 2 curing at ambient temperature and pressure levels outperformed autoclave curing at high temperatures and pressures. TG/DTG results displayed distinct and high peaks of calcium carbonate for the atmospheric- and autoclave-CO 2 -cured samples, whereas peaks of portlandite were observed for the water-cured samples. Vaterite and calcite were the major polymorphs of calcium carbonate in the atmospheric CO 2 -cured samples, whereas aragonite and calcite were predominant when autoclave curing was used. Regardless of the curing regime, partial replacement of 5 % cement by SF led to the highest compressive strength. At 28 days, while for water curing, lower lime replacement and higher SF replacement levels increased the compressive strength by 78.31 %, for CO 2 curing, an equal proportion of lime and SF increased the strength by 11.24 % and 24.01 % for atmospheric and autoclave curing, respectively.