Low-Carbon Cementitious and Alkali-Activated Materials for Roadbed Stabilization: A Review from Microstructural Mechanisms to Engineering Adoption

Abstract

Problematic subgrade soils degrade pavement performance, while conventional cement/lime stabilizers generate excessive carbon emissions. Unlike earlier reviews that focus on single-material systems—such as industrial by-products, alkali-activated binders for expansive soils, or geopolymers for pavement applications—an integrated framework spanning reaction mechanisms, microstructural evolution, engineering parameterization, and life-cycle validation is proposed The work offers three distinctive contributions: (i) a four-level evidence chain hierarchy (strength → microstructure → durability → leaching/LCA) to grade research completeness; (ii) repositioning resilient modulus, permanent deformation, and pore-connectivity evolution as core engineering outputs bridging material design and structural response; and (iii) a comparative assessment of alkali-activated geopolymers, low-clinker calcium-based composites, and multi-scale reinforcement strategies under consistent durability and environmental boundaries. Quantitative synthesis reveals the following: strength retention after 12 wet–dry/freeze–thaw cycles ranges from 60% to 85%; resilient modulus improvements over untreated soils reach 30%–120%, yet stress-dependent characterization remains essential; leaching concentrations of hazardous elements (Cr, Ba, Pb) can increase by 50%–200% after durability cycling if pore connectivity rebounds. Life-cycle carbon comparisons are boundary-sensitive—geopolymer advantages shrink from 60% to ≤20% when activator transport and pre-treatment are included. We conclude that the primary barrier to engineering adoption is not the absence of high-strength formulations, but the lack of extrapolatable design parameters and closed-loop evidence chains. A decision-support framework incorporating durability retention, leaching safety, carbon footprint, and field validation is proposed to guide robust design and industrial scaling. Critically, the review identifies that engineering adoption is constrained not by the absence of high-strength formulations, but by the lack of standardized construction protocols, quality control procedures, and long-term field performance data—gaps that must be addressed through coordinated field-scale demonstration projects.