Impact of calcium aluminate cement and calcium sulfate on gel C-A-S-H formation during the Portland cement hydration

This study examines how calcium aluminate cement (CAC) and calcium sulfate influence the hydration and gel structure of Portland cement (PC). A binary PC/CAC (85/15) mix was compared with ternary systems containing 3% and 5% calcium sulfate under two curing conditions. FTIR and 29Si NMR analyses showed that CAC promotes aluminum incorporation into the C-S-H gel, leading to a more homogeneous C-A-S-H structure. Water curing further enhanced this integration, with increased Q² and reduced Q¹ signals. Calcium sulfate addition mitigated the silicate hydration delay caused by CAC and promoted longer silicate chains and higher Al(IV)/Si ratios. Overall, CAC enhances aluminum incorporation, while calcium sulfate improves silicate polymerization, resulting in a more uniform and well-structured C-A-S-H gel.