Fabrication, microstructural and mechanical characterization of Luffa Cylindrical Fibre - Reinforced geopolymer composite

Abstract This study reports on the preparation, microstructure, density and mechanical properties of new geopolymer composites (LG-composite) that are unidirectionally and randomly reinforced with 10 vol% natural Luffa Cylindical fibres (LCF). The geopolymer matrix was synthesized from metakaolin activated with sodium silicate and sodium hydroxide solutions. A greater amount of geopolymer gel was formed after introducing the LCF into the geopolymer matrix. As a result of the strong alkali setting reactions (geopolymerization), the hemicelluloses and lignin present in the LCF were extracted, leaving a rough LCF surface. In this way the hydrophobicity of the rough LCF increased and helped strengthen the bonding between fibre and geopolymer matrix. Two main morphological types of crystalline objects were observed in the LG-composite due to the incorporation of the extracted constituents of LCF: fibre-like crystals, or whiskers, and fine crystals of cubic shape. These crystals assist in crack healing while increasing the tensile strength and toughness of the composite. In terms of mechanical properties, it is found that by introducing LCF as reinforcement, the compressive and flexural strengths of the end geopolymeric products respectively increase from 13 MP and 3.4 MPa up to 31 MPa and 14.2 MPa. The LCF-reinforced geopolymer composite exhibited ductile-like failure with a strain hardening Modulus of 72 MPa, unlike the brittle matrix. In addition, the bulk density decreases from 1.5 g/cm3 to 1.38 g/cm3. A preliminary aging study has demonstrated that the LG-composite shows no significant deterioration in mechanical performance over a duration of 20 months.