A comparative review and parametric carbon footprint framework for soil stabilization binders in road earthworks

Abstract Road infrastructure accounts for a substantial share of global material stocks and embodied greenhouse gas emissions, yet the environmental optimisation of subgrade soil stabilisation – a ubiquitous earthworks practice – has received limited systematic attention. This review assesses the life-cycle evidence available for the principal soil-stabilisation binders: lime, Portland cement, Hydraulic Road Binders (HRB, EN 13282), supplementary cementitious materials, geopolymers, and bio-binders. A documented and reproducible search protocol is reported in full, and every value carried into the quantitative synthesis was re-checked against its primary publication. That verification is the review’s principal finding: of thirty study rows assembled from the standard secondary literature, only three carried a value that could be located in the cited source, while thirteen had to be withdrawn because the value was absent, the cited work contained no carbon data, or the study assessed concrete or cement manufacture rather than soil stabilisation. Published cross-binder rankings, including ranked class ranges of the kind this literature routinely reports, are therefore not currently supportable. What the verified evidence does support is reported instead: a single study comparing binder systems on the same soil under the same boundary (182.2 versus 32.5 kg CO 2 -eq/m 3 ), and declared emission factors for binders covered by environmental product declarations. Contrary to a widely repeated claim, Hydraulic Road Binders are not an evidence vacuum but an evidence asymmetry: no peer-reviewed life-cycle assessment was retrieved in six languages, yet current declarations span 173–852 kg CO 2 -eq per tonne across the EN 13282 composition range. A parametric model built only from traceable factors, with Monte Carlo propagation of parameter uncertainty, shows that accounting convention moves results more than binder composition does – within one declaration, allocation changes the GGBS factor by a factor of 5.5 – and that no confident ordering exists at the low-GWP end, although lime and Portland cement are robustly the highest-impact options. Recommendations are given for functional-unit standardisation, allocation-rule harmonisation, and the primary soil-stabilisation assessments the field currently lacks.