Toughness enhancement of geopolymer stabilized laterites using para rubber latex for sustainable base and subbase applications

This study investigated the mechanical performance, toughness behavior, failure characteristics, and microstructure of geopolymer-stabilized laterites modified with modified natural rubber latex (MNRL) for application in pavement base and subbase layers. Class C fly ash was used as the primary binder, with MNRL added at a weight% of 0–10% of the dry soil. Unconfined compressive strength ( q u ), indirect tensile strength ( q t ), and flexural strength ( q f ) were evaluated, alongside brittleness index (BI), improvement toughness ratio (ITR), and scanning electron microscopy (SEM). The results showed that while the addition of MNRL reduced peak q u by 20–60%, most mixtures still satisfied subbase ( q u > 0.70 MPa) and base ( q u > 1.75 MPa) strength criteria. MNRL significantly decreased BI (from 1.00 to as low as 0.03) and increased ITR (up to 6.28), indicating a transition from brittle to ductile failure. SEM analysis confirmed the formation of elastic polymer films that bridge fly ash and soil particles, thereby enhancing matrix cohesion and reducing porosity. The optimal mixture containing 25–30% fly ash and 5–7% MNRL achieved q u values of 1.83–2.64 MPa with improved ductility. The findings confirmed that MNRL effectively enhanced toughness and fracture resistance, making it a promising sustainable additive for laterite stabilization in tropical pavement infrastructure.