Strength enhancement - carbon emission reduction - autogenous shrinkage mitigation of cement-slag-limestone ultra-high-performance concrete by using natural wollastonite

초록

Cement-slag-limestone (CSL) concrete is a novel ternary cementitious system, but its application in ultra-high-performance concrete (UHPC) remains relatively unexplored, particularly with respect to autogenous shrinkage. This study systematically evaluated the effects of wollastonite at different replacement levels (0 %, 5 %, 10 %, and 15 %) on the micro- and macroscale properties of CSL-UHPC. The experimental results indicate the incorporation of wollastonite in the CSLUHPC system results in low autogenous shrinkage, high mechanical performance, enhanced durability, and reduced CO2 emissions. Wollastonite significantly accelerates early hydration reactions (0-24 h), increasing hydration rates and heat release peaks; however, higher dosages (>= 10 %) reduce the cumulative heat release due to the dilution effect. In addition, wollastonite effectively mitigated autogenous shrinkage, achieving a maximum reduction of 80.9 % at 7 days through the synergistic effects of localized stress relief and an increased effective water-to-binder ratio. In terms of mechanical properties, the "microrebar effect" of wollastonite significantly enhances both compressive and flexural strengths, with the 10 % replacement level resulting in the highest mechanical performance. Durability analysis demonstrated that wollastonite improved the pore structure and significantly increased the electrical resistivity. Microstructural analysis further confirmed that wollastonite enhances the pozzolanic reaction of slag and the synergistic interaction between slag and limestone, reduces CH formation, and increases the carboaluminate content, leading to a denser microstructure. In conclusion, wollastonite significantly improves autogenous shrinkage, mechanical properties, and durability in CSL-UHPC by regulating hydration reactions, enhancing internal restraint, and optimizing the microstructure. This study provides a crucial theoretical foundation for the application of wollastonite in ultrahigh-performance concrete.

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