Effect of calcium carbide residue and superplasticizer dosages on the mechanical and microstructural properties of fly ash based geopolymer composites

• Investigated low-calcium fly ash-based geopolymer mortar using Calcium Carbide Residue (CCR) as binder. • Studied effects of alkaline activator molarity and PCE-based superplasticizer on workability and setting time. • Evaluated uniaxial tensile strength and strain capacity as an alternative to split tensile tests. • Developed optimized mix design to improve flowability and structural performance for sustainable applications. . The role of calcium-rich waste like Calcium carbide residue (CCR) in enhancing the performance of geopolymer remains inadequately explored. This study investigates the structural, mechanical, and microstructural behaviour of low-calcium fly ash (FA)-based geopolymer composites modified with varying CCR contents (0%, 10%, 20%), sodium hydroxide molarities (8M, 10M, 12M), and superplasticizer dosages (0%, 1%, 2%). Results revealed that 10% CCR combined with 2% superplasticizer and 12M NaOH offered optimal performance, achieving a 16.8% increase in compressive strength, a 144.8% rise in tensile strength (3.06 MPa), and a 145.5% improvement in flexural strength (3.83 MPa). Flowability improved by 15% with higher superplasticizer dosage, whereas excessive CCR (20%) adversely affected strength and porosity. Microstructural observations confirmed the synergistic formation of N-A-S-H and C-S-H gels in optimized mixes. These findings highlight CCR’s viability as a sustainable calcium source in geopolymer technology, promoting enhanced mechanical performance and environmental sustainability through industrial waste valorisation. .