Comparative Performance of Polyethylene- and Carbon Fiber-Reinforced Slag/Fly Ash Blended Geopolymer Concrete

Fiber reinforcement of geopolymer concrete is well established, but selection of a fiber system depends on several performance requirements. This study examines whether polyethylene (PE) and carbon fiber systems retain the same ranking across fresh, mechanical, water-absorption, and impact–abrasion responses in an ambient-cured slag–fly ash concrete. The binder contained equal masses of slag and fly ash and was activated with sodium silicate and 12 M sodium hydroxide solutions. Both fibers had a nominal length of 6 mm. PE was incorporated at 0.25–1.25% by nominal volume, whereas carbon fiber was limited to 1.00% because of workability loss. At matched contents of 0.25–1.00%, carbon mixtures had 17–79% higher flexural-strength means than PE mixtures, accompanied by 46–71% lower slump, 14–49% lower elastic-modulus means, and 9–15% higher mass-based absorption after immersion. Carbon mixtures had lower final impact–abrasion mass loss than PE mixtures at 0.25–0.50%, but higher loss at 0.75–1.00%. Within the carbon series, increasing content from 0.50% to 0.75% increased flexural strength from 6.0 to 7.7 MPa while final abrasion mass loss increased from 50% to 90%. PE0.25 had the largest measured compressive-strength means. The principal contribution is the quantification of response-dependent rankings and their consequences for selecting a fiber system or dosage from a single strength result.