Recycled Aggregates and Industrial By‑products in Green Concrete

Abstract

            Global concrete production reaches 30 billion tonnes annually, with cement manufacturing (4.0 Gt/yr) emitting ~0.9 t CO₂ per tonne of cement. Construction accounts for ~40% of world energy use and ~35% of greenhouse gases. Concurrently, vast waste streams—~1 Gt/yr fly ash, 0.27–0.32 Gt/yr blast furnace slag, and 3 Gt/yr construction/demolition waste (CDW)—necessitate sustainable solutions. Green concrete addresses these challenges by replacing virgin materials with wastes: recycled concrete aggregates from CDW substitute natural aggregates, and supplementary cementitious materials (fly ash, slag, silica fume, metakaolin) replace part of the cement. This review synthesizes current knowledge on recycled aggregates (sources, properties, concrete performance) and SCMs, examining mechanical strength, durability, environmental/economic benefits, and future challenges. Comprehensive tables compare key findings. With careful mix design, high-volume waste replacements achieve required performance while delivering substantial sustainability gains.