This paper explores the development of sustainable alkali-activated ultra-high performance concrete (AA-UHCP) with decreased slag content by the combined usage of metakaolin, limestone powder, and calcium hydroxide.
The simplex centroid design method is employed as a mix design method, and the effect of binder composition on macro properties and microstructure is characterized. The results indicate that limestone powder serves as a physical filler, enhances the hydration efficiency of precursors by providing nucleation sites, promotes the development of the AFm-CO3 phase, and increases the mean chain length. The incorporation of metakaolin introduces reactive aluminum, facilitating the binding of alkali metal ions to generate a strongly polymerized C-(N)-A-S-H gel and zeolite phase, thus enhancing pore structure. Simultaneously, this significantly mitigates drying shrinkage, resulting in a maximum 73.2 % reduction. The incorporation of calcium hydroxide promotes the pozzolanic reaction. The combined action of the three binders significantly enhances the development of hydration products and the improvement of macro characteristics in a low slag content system. Mixture with 50 % slag replacement attains remarkable sustainability with a compressive strength over 110 MPa, a flexural
strength surpassing 10.0 MPa, and a chloride diffusion coefficient of 0.223 × 10− 12 m²/s. The developed AA-UHPC fulfills the criteria for high performance and sustainability, offering technical guidance for the future advancement of low-carbon AA-UHPC |
