Mechanical properties of metakaolin and granulated blast-furnace slag-based roller-compacted geopolymer concrete containing 100 % reclaimed asphalt pavement: Optimization and prediction via response surface methodology

Abstract

The growing volume of Reclaimed Asphalt Pavement (RAP) waste, combined with the environmental impact of high cement production, highlights the urgent need for sustainable solutions. Alternative binders and efficient waste utilization offer promising ways to address these challenges. Unlike traditional concrete, which relies on supplementary cementing materials (SCM) to enhance strength, geopolymer concrete uses aluminosilicate sources (AS) to drive the geopolymerization process. This study explores the mechanical properties of roller-compacted geopolymer concrete (RCGC), focusing on the role of metakaolin (MK), both with and without granulated blast furnace slag (GBFS) as an additive AS. Hydrated lime (HL) was chosen as an alkali activator due to its affordability, availability, and its known effect on accelerating the setting process in geopolymer mixtures. The research examines how variations in sodium hydroxide molarity, HL content, and GBFS ratio influence the strength of RCGC. The results showed that increasing HL content had a negative impact on the mechanical properties, while higher concentrations of GBFS and sodium hydroxide (SH) significantly improved compressive, tensile, and flexural strengths. The optimal mix design, identified using response surface methodology (RSM) with a score of 0.96, consisted of 10 M SH, no HL, and 40 % GBFS, achieving a maximum 28-day compressive strength of 15.9 MPa. Distinct failure modes were observed: MK-based RCGC exhibited mortar failure, while mixes containing 100 % GBFS showed aggregate failure, indicating better structural integrity. These findings suggest that RCGC can serve as a sustainable and practical solution for low-volume road applications, offering both enhanced performance and environmental benefits.