Synergistic influence of eco-friendly treatment and fly ash on water absorption morphology and hardness of grewia optiva <i>/</i> basalt fiber hybrid polyester composites

The present study investigates composites reinforced with treated Grewia optiva (GO), basalt (BA) fibers both chopped into 3 mm length and fly ash (FA) fillers in an unsaturated polyester resin (UPR) matrix. GO fibers were treated with a 5 wt.% mild alkaline sodium bicarbonate (NaHCO 3 ) solution. BA and FA are set from 5 to 10 wt.%, and treated-GO fiber loading is varied between 5 and 15 wt.%. Experimental (1.20-1.36 g/cm 3 ) and theoretical (1.22-1.41 g/cm 3 ) density of composites have substantial degree of agreement with minimum (1.63%) voids fraction for C15/5-5 hybrid composite, remarking adequate association and enhance interface bonding. Diffusion pattern occurs in three phases of water absorption equilibrium between the ranges from 1.23 to 2.23%. Higher swelling and micro-porosity are observed as the concentration of treated-GO fiber increase in the composite. The maximum shore D hardness (39.2 HD) was achieved in C15/5-5 hybrid composite due to higher stiffness. The diffusion coefficient (2.003×10 −6 -2.335×10 −6 mm 2 /s) has enhanced with the increment of fibers and FA, professed for better barrier characteristics. Comprehensive the present study revealed that the treated natural fiber, and inorganics filler reinforcement developed long-lasting, weight suitability, eco-friendly, and resistant against water absorption hybrid composite for constructive engineering in the Uttarakhand landslide-prone level areas.