Waste to worth: Fruit peel-derived retarder as a sustainable admixture in hazardous waste-based concrete systems

The production of ordinary Portland cement (OPC), a key component of concrete, contributes significantly to global CO₂ emissions, prompting a shift towards sustainable construction practices. Fly ash, a byproduct of coal combustion, is a widely accepted supplementary cementitious material (SCM), but its underutilization in India raises serious environmental and regulatory concerns. Concurrently, the concrete industry heavily depends on chemical admixtures like sodium gluconate (SG), most of which are imported, particularly from China - posing supply chain vulnerabilities. This study addresses both challenges by synthesizing gluconic acid (GA), the parent compound of SG, from fruit peel waste and evaluating its efficacy as a bio-based retarder in fly ash concrete systems. Experimental work involved replacing cement with fly ash at levels ranging from 10 % to 50 %, and incorporating GA as a retarder. The experimental mixes exhibited improved workability with slump retention up to 180 min and maintained compressive strength, with the 30 % replacement mix (FA30GA) showing optimal performance. Durability properties were enhanced, and microstructural analyses via SEM confirmed the formation of denser matrices. TCLP results verified the environmental safety of the formulations. From a sustainability perspective, the FA30GA mix demonstrated a 41.47 % cost reduction and considerable decreases in CO (42 %), NOₓ (32.56 %), and SO₂ (33 %) emissions. Life cycle assessment (LCA) and cost analysis affirmed the economic and environmental benefits of the approach. This work offers a dual solution: it promotes high-volume fly ash utilization in compliance with India's Ministry of Environment guidelines, and it provides an indigenous, waste-derived alternative to imported chemical admixtures, contributing to circular economy principles and the vision of Atmanirbhar Bharat.