The Effect of Combining Waste-Derived Pozzolanic and Fibrous Materials with Functional Admixtures on Performance and Corrosion Resistance of Concrete

This study investigates the combined effect of waste-based metakaolin, cellulose fibres and functional waterproofing additive on the physical, mechanical, and durability-related properties of sustainable concrete. A total of 12 concrete mixtures were produced, varying in cellulose fibre content (0–2%), metakaolin waste replacement levels (up to 10% of binder), and functional waterproofing additive content (1%). The experimental program assessed workability, density, compressive and flexural strength, ultrasonic pulse velocity (UPV) and alkali–silica reaction (ASR) resistance. The presence of metakaolin due to high pozzolanic activity (1451 mg/g) and fine particle size enhance the formation of additional C–S–H phases. The incorporation of cellulose fibres (1–2 mm in length) improved crack-bridging ability and structural integrity, while functional waterproofing additive enhanced water tightness. Results demonstrated that the synergistic use of these materials led to improved mechanical performance (flexural strength varies from 4.87 MPa to 6.81 MPa; compressive strength varies from 24.01 MPa to 32.97 MPa) and enhanced notable ASR resistance (decrease in expansion varies from 0.209% to 0.029%). The findings highlight the potential of combining waste-derived pozzolanic and fibrous materials with functional admixtures to develop environmentally friendly and performance-optimized concrete composites.