This paper discusses the utilization of ternary binders of granulated blast furnace slag (GGBS), limestone powder (LP), and metakaolin (MK) for the production of alkali-activated ultra-high-performance concrete (AA-UHPC). The micro-structural characteristics of this binding system are identified by X-ray diffraction (XRD), thermogravimetric analysis (TG-DTG), and nuclear magnetic resonance (29Si NMR), and some important durability issues such as drying and chemical shrinkage, chloride binding capacity, and carbonation are evaluated. The results show that mixtures with a low slag content of 50% can still achieve ideal mechanical properties of more than 110 MPa at 28 days, combined with favorable microscopic characteristics, featuring an increased mean chain length of 13.08 and a higher hydration product ratio of 84.37%, thereby demonstrating the feasibility of producing AA-UHPC with significantly reduced slag content. The synergistic inclusion of slag and metakaolin enhances long-term performance through the formation of C-A-S-H and N-A-S-H gels, producing a densified and compacted microstructure with superior durability properties. In the ternary blended system, metakaolin promotes the formation of additional aluminosilicate gels, increasing the mean chain length of reacted gels and overall reactivity, while limestone powder act as filler and nucleation sites to promote the formation of reaction products and extend their chain length. The ternary blended binders can show significantly improved shrinkage behavior, chloride binding capacity, and carbonation resistance due to metakaolin and limestone induced phase modifications. The findings demonstrate that when properly designed, a ternary blended AA-UHPC with further reduced slag content can be achieved with modified microstructure and acceptable balances among mechanical properties, and durability issues. |
