Résumé
This study evaluates semi-refined SR-(κ)-carrageenan extracted from Kappaphycus alvarezii as a viscosity-modifying admixture (VMA) for cement pastes (w/c = 0.43). Extraction parameters, KOH concentration (6 to 12%), temperature (104-176°F; 40-80°C), and residence time (1 to 3 hours), were varied, and the resulting materials were assessed for modified-Bingham rheology (yield stress and plastic viscosity), viscoelastic properties (storage modulus and critical shear strain), structural build-up kinetics (build-up index), forced bleeding, hydration induction period, and early compressive strength. SR-(κ)-carrageenan produced under a low-severity operating point (6 % KOH, 104°F; 40°C, 1 h) and dosed at 4% (by mass of water) increased yield stress from 0.21 (10) to 0.42 (20) lb/ft2 (Pa) and plastic viscosity from 0.42 (0.63) to 0.73 (1.18) lb/ft-s (Pa.s). It enhanced early-age rigidity and build-up from 9.29 (445) to 22.03 (1055) lb/ft2.s-3/2 (Pa/s3/2) and reduced forced bleeding relative to the reference. The induction period increased moderately (from 1.4 to 2 hours), and no early-age strength penalty was observed at 1 and 7 days. Compared with pure R-(κ)-carrageenan, SR-(κ)-carrageenan maintained (κ)-carrageenan rheology and structural build-up kinetics while producing a smaller induction- time shift in this paste class. Within the tested matrix, dosages, and protocols, the test results support SR-(κ)-carrageenan as a cement-grade VMA candidate produced via PES/ATC-aligned unit operations.