Nano-cellulose and biochar reinforced fly ash–ggbs based geopolymer concrete: a sustainable pathway to enhanced strength and durability

ABSTRACT This research aims to explore the mechanical and durability properties of geopolymer concrete (GPC) with varying content of fly ash, Ground Granulated Blast Furnace Slag (GGBS), biochar, and nano-cellulose fibres under different curing conditions. GPC, compared to traditional concrete, showed superior strength properties, particularly in mixture containing optimized GGBS and biochar. The maximum 28 day compressive strength of 61.12 MPa was recorded in the mixture containing 22% fly ash, 72% GGBS, 6% biochar, and 0.6% nano-cellulose fibres. The mixture also exhibited good workability and enhanced tensile and flexural strengths. Tests of durability such as Rapid Chloride Permeability Test (RCPT), acid and sulphate resistance, and carbonation depth indicated that additions of biochar and nano-fibres greatly alleviated permeability and strength loss. Nano-cellulose fibres have also improved matrix compaction, minimizing carbonation depth and enhancing durability in aggressive exposures. ANOVA has ensured that there were significant workability and compressive strength differences, whereas RCPT differences were statistically insignificant, indicating time-dependent variability in chloride resistance. In general, the incorporation of biochar and nano-cellulose fibres into GGBS rich GPC enhances mechanical strength and durability, justifying its viability as a green replacement for ordinary Portland cement (OPC) for long-term infrastructure construction under extreme environmental conditions.