Synergetic effect of C-S-H seeds and SAP on LC3 UHPC: Microstructure evolution, compressive strength and autogenous shrinkage

Enhancing the early strength of limestone calcined clay cement (LC³) ultra-high-performance concrete (UHPC) and addressing the research gap in its autogenous shrinkage are critical for reducing carbon emissions and improving UHPC durability. This study accelerates early hydration by incorporating calcium silicate hydrate (C-S-H) seeds and mitigates autogenous shrinkage by using superabsorbent polymers (SAP) as internal curing agents. The results indicated that C-S-H seeds significantly enhanced the early hydration rate of the cement matrix. The combined use of C-S-H seeds and internal curing not only improved early strength but also effectively reduced autogenous shrinkage while maintaining high strength at later stages. The inclusion of C-S-H seeds and internal curing increased the 1d compressive strength of LC³ UHPC by 113.2 % compared to the reference group. At 28d, compressive strength was 13.2 % higher than that of samples containing only C-S-H seeds. Furthermore, the 7d autogenous shrinkage was reduced by 47.1 % relative to the reference group. The optimized LC³ UHPC achieved a GWP intensity of 5.16 kg CO₂ eq/(MPa·m³), lower than that of conventional UHPC. This study offers valuable insights for designing sustainable UHPC.