This study aims to develop a sustainable ambient-cured high-performance geopolymer concrete (HPGC) in conjunction with a geopolymer-specific superplasticizer (SP).
A binary blend of high-calcium fly ash (HCFA) and rice hull ash (RHA) geopolymer system was optimized using a Box-Behnken response surface methodology (RSM). Additionally, a raw rice hull-based superplasticizer (RRH–SP) was developed and optimized for its plasticizing and retarding effects. Slump, compressive strength, flexural strength, direct tensile strength, freeze-thaw resistance and life cycle assessment (LCA) were conducted. A quantitative framework was selected to enable systematic analysis and statistical optimization. Slump and strength regression models were developed and validated. The results were further interpreted using microstructural analyses via SEM and XRD.
The optimized concrete achieved a compressive strength exceeding 60 MPa, characterized by a refined microstructure and desirable fresh properties. The addition of 1.5% RRH–SP increased the slump value by about 110% and the initial setting time by 45% without affecting the compressive strength. The optimized HPGCs provided high frost resistance, with a loss in relative dynamic modulus of elasticity of less than 1%. They also showed an improved tension ductility with post-cracking tensile resistance (strain-hardening behavior). Microstructural analysis confirmed the formation of hybrid calcium-alumino-silicate-hydrate (C-A-S-H) and sodium-alumino-silicate-hydrate (N-A-S-H) gels with minor beneficial crystalline phases. Prediction errors of less than 5% were estimated by employing the suggested regression models.
This research addresses key limitations of calcium-rich geopolymer systems. It provides an efficient synergy between industrial waste (HCFA) and agricultural waste (RHA) to produce sustainable and eco-efficient HPGCs. The developed RRH–SP is efficient in the high alkaline geopolymer environment and provides dual retarding and plasticizing effects. The provided methodology enables overcoming key fresh-state issues, eliminates energy-intensive heat curing and produces superior mechanical and durability performance. This paves the way for the scalable production of HPGC, which can be used for in situ concreting, rapid-setting repair applications and automated construction applications.
