Carbonation and Restrained Shrinkage Cracking as Coupled Service-Life Controls in Low-Carbon Building Concrete: A Critical Review

Embodied-CO2 savings in clinker-reduced concrete must be evaluated alongside cover-zone durability and service life. This review examines carbonation and shrinkage/restrained cracking as coupled, rather than independent, controls on atmospheric service life in reinforced concrete buildings. The synthesis links binder route to cover-zone transport and alkalinity buffering and explains how curing, preconditioning, relative humidity (RH), CO2 concentration, exposure geometry, and crack state affect reported carbonation rankings. It develops a two-domain conceptual framework for interpreting the effective carbonation front in cracked cover, with a descriptive crack-amplification index for reporting localized penetration. Practical mitigation is organized around mix-design levers, curing and construction actions, and a three-tier performance-based assessment workflow with a coupled test matrix. The review closes with a reporting checklist and five research gaps. The central conclusion is conditional: clinker-reduced building concrete can meet specified carbonation-performance requirements when curing, RH history, paste volume, and crack connectivity are assessed and managed together.