Integrated Performance Assessment of Sustainable One-Part Geopolymer Seawater Sea-Sand Concrete Reinforced with Hybrid Polypropylene Fibers

Freshwater and natural river sand scarcity, together with Portland cement’s environmental burden, highlights the need for resource-efficient concrete systems. However, the combined use of seawater sea-sand (SWSS), one-part geopolymer concrete (OGPC), and hybrid polypropylene (HPP) fibers remains insufficiently investigated under multiple exposures. This study presents an experimental assessment of SWSS-based OGPC reinforced with HPP fibers, conventional Portland cement concrete (PCC) and two-part geopolymer concrete (TGPC) as reference systems. Eleven mixtures were investigated by varying fly ash (FA)/ground granulated blast furnace slag (GGBFS) binder composition and HPP fiber content, covering mechanical, transport, sulfate, and thermal performance up to 800 °C. SEM and EDX analyses were conducted before and after sulfate exposure to assess sulfate-related microstructural changes. An integrated multi-objective performance grading (MOPG) framework was used to identify balanced mechanical–durability performance. The results showed that binder composition was the dominant factor governing performance. Increasing the GGBFS fraction from 25% to 75% increased the 28-day compressive strength from 40 to 63 MPa, while the GGBFS-rich formulation reached 67 MPa at 120 days. The OGPC exhibited superior integrated performance compared with the corresponding TGPC. Water penetration and absorption decreased by 55% and 41.7%, respectively, compared with PCC. HPP fibers enhanced tensile-related performance, with 1% HPP increasing splitting tensile, flexural, and bond strengths by 16.7%, 110.5%, and 50%, respectively, while reducing compressive strength and elastic modulus by 25% and 13.1%, respectively. At 800 °C, geopolymer mixtures achieved higher strength retention than PCC, reaching 75% compared with 28.9%, while 0.5% HPP achieved 80% retention. SEM/EDX observations supported sulfate resistance through evidence of matrix stability and microstructural changes. The highest MOPG of 0.66 was achieved by the 50/50 FA/GGBFS system with 1% HPP. Sustainability assessment showed reductions of 78% in CO2 and 69% in embodied energy per unit 28-day compressive strength, with MOPG-normalized reductions of 89% and 85%, respectively. The proposed OGPC incorporating SWSS and HPP fibers demonstrates promising performance, indicating its potential for sustainable concrete applications in environments where freshwater and natural river sand are constrained and resistance to aggressive exposure is required.