Next-generation ultra high performance geopolymer concrete: Optimizing calcium aluminate cement clinker and nano rice husk ash for mechanical strength, durability and thermal resistance

The high demand for sustainable and durable construction materials has exposed the limitations of traditional Portland cement and standard geopolymer concrete, particularly in high-performance structural applications. Conventional geopolymer concrete formulations often fall short in meeting the stringent requirements for mechanical strength, thermal stability, and chemical resistance. To address these challenges, this research explores the use of calcium aluminate cement (CAC) clinker and nano rice husk ash (NRHA) in developing ultra-high-performance geopolymer concrete (UHPGC). Four groups of UHPGC mixtures were prepared by varying the CAC clinker content (0 %, 25 %, 50 %, and 75 %) as a partial sand replacement and NRHA (0 %, 1 %, 2 %, and 3 %) as a replacement for ground granulated blast furnace slag (GBFS). The physical, mechanical, and durability properties of the mixes were systematically evaluated. Results demonstrated that the incorporation of CAC clinker and NRHA significantly improved the compressive, splitting tensile, and flexural strengths. The optimal mix, designated as G3 (50 % clinker, 50 % sand, and 2 % NRHA), achieved a compressive strength of 157 MPa at 91 days, a splitting tensile strength of 11.2 MPa, and a flexural strength of 17.5 MPa at 28 days. Durability tests conducted under elevated temperatures and chemical exposures (including chloride, sulfate, and nitrate solutions) confirmed the enhanced performance of the optimized mix. G3 retained 48–53 % of its residual compressive strength at 800 °C and showed high resistance to sulfate and nitrate attack. G4 (75 % clinker, 3 % NRHA) exhibited superior resistance to chloride penetration. Microstructural analysis revealed the formation of dense C-A-S-H and N-A-S-H gels, which contributed to the improved performance. Overall, this study demonstrates the potential of CAC clinkers and NRHA to produce sustainable, high-performance geopolymer concretes suitable for demanding construction environments.