Development of an Original Fibre-Reinforced Geopolymer Concrete Mix Design Framework for Tropical Infrastructure in Nigeria

Geopolymer concrete, produced using industrial by-product binders such as fly ash and ground granulated blast furnace slag instead of Portland cement, offers significant CO2 emission reductions of 40 to 80 percent relative to conventional concrete, and its optimisation for tropical infrastructure conditions in Nigeria represents both a scientific and sustainability contribution. This study develops an original mix design framework for fibre-reinforced geopolymer concrete (FRGPC) calibrated for Nigerian tropical conditions, using locally available industrial by-products and natural fibres. An experimental programme investigated 144 mix combinations varying fly ash-to-slag ratio, sodium hydroxide molarity (6 to 14 M), sodium silicate-to-sodium hydroxide ratio (1.0 to 2.5), steel and sisal fibre contents (0 to 1.5 percent by volume), and curing temperature (ambient 28 to 45 degrees Celsius reflecting Nigerian conditions). Fresh properties (workability by flow table), mechanical properties (compressive strength, split tensile strength, flexural strength), and durability indicators (water absorption, chloride diffusion, and rapid chloride penetration test) were measured at 7 and 28 days. Original constitutive models relating mix composition to strength and durability are developed using response surface methodology and artificial neural network regression. The optimised FRGPC achieves 56.4 N/mm2 compressive strength at 28 days (ambient tropical curing) with 0.8 percent sisal fibre content, meeting requirements for structural concrete applications. Carbon footprint analysis confirms 61 percent GWP reduction versus equivalent Portland cement concrete. The mix design framework is validated through scale-up trials and proposed as a standard for sustainable construction in Nigeria.

Keywords: geopolymer concrete, fibre reinforcement, mix design, tropical infrastructure, sustainable concrete