Mechanical response and microstructural evolution of fibre-reinforced one-part geopolymer and portland cement concretes

The mechanical and microstructural responses of ordinary Portland cement (OPC) and one-part geopolymer concrete (OPGC) to fibre reinforcement have not been scientifically explored, hence generating a research gap. As more construction industries seek high-performance and ecologically friendly building materials, geopolymer concrete is becoming more popular as an alternative to OPC. Because it does not need liquid activators, a one-part geopolymer system is advantageous, and adding fibres increases its tensile and flexural strength. Despite these benefits, a comprehensive evaluation of its strength performance in comparison to conventional OPC concretes requires more research. Four concrete mixes, which are ordinary Portland cement (OPC), fibre-reinforced ordinary Portland cement (FROPC), one-part geopolymer concrete (OPGC), and fibre-reinforced one-part geopolymer concrete (FROPGC), are examined in this study for their fresh, mechanical, and microstructural characteristics. Workability was assessed using slump tests, and at 7, 14, and 28 days, compressive, flexural, and split tensile strengths were measured. Stiffness, permeability, and internal quality were evaluated using the modulus of elasticity, water absorption, and ultrasonic pulse velocity (UPV), and microstructural examination was conducted using scanning electron microscopy (SEM). According to the findings, geopolymer concretes had better fresh qualities than OPC, with slump that were 20–31% higher. While fibre insertion greatly increased tensile and flexural strengths, it decreased workability. The highest compressive strength (63.78 MPa) was obtained by OPGC, whereas the highest flexural (15.1 MPa) and tensile (9.15 MPa) strengths were attained by FROPGC. Additionally, FROPGC showed the highest modulus of elasticity (44,040 N/mm2), and a refined microstructure with fewer vacancies and well-bonded fibres was shown in FROPC and FROPGC.