Performance of alkali-activated UHPC reinforced with PET micro fibers and a bio-based retarder

This study explores the combined use of waste polyethylene terephthalate (PET) microfibers and sucrose, a bio-based retarder, to improve the performance and sustainability of alkali-activated ultra-high-performance concrete (AAC-UHPC). The binder system was produced with ground granulated blast furnace slag and silica fume, activated by sodium hydroxide, sodium silicate solutions and blended with quartz powder and natural sand. From twelve trial mixtures, an optimal baseline matrix was identified and further modified with sucrose to extend the setting time. This adjustment enabled proper dispersion of PET fibers and stronger fiber–matrix interaction, as confirmed by microstructural analysis. The addition of 2 vol% of 12-mm PET fibers enhanced tensile strength by 48% and flexural strength by 153% compared with the control, while also reducing sorptivity and improving sulfate resistance. The optimized mixture reached a 7-day compressive strength of 135 MPa and achieved a 27.5% reduction in CO 2 emissions and a 10.3% decrease in cost per unit strength compared with conventional cement-based UHPC. These findings demonstrate a practical pathway for producing eco-efficient, high-performance concrete by combining controlled retardation with waste-derived fibers, contributing to circular economy practices and sustainable infrastructure development.