Ceramics-Silikáty

This study evaluates the synergistic effect of cellulose fibres (CF), metakaolin waste (MW), and crystallizing additive (CA) on the mechanical performance, microstructure, and freeze-thaw durability of concrete. Metakaolin waste was used as a partial cement replacement, while cellulose fibres and a crystallizing additive served as functional modifiers to enhance structural integrity. Five concrete mixtures with a constant water-to-cement ratio of 0.3 were cured for 28 days, and their physical and mechanical properties were evaluated by density, ultrasonic pulse velocity, compressive, and flexural strength tests before and after 56 freeze-thaw cycles. Durability was evaluated based on absorption, porosity measurements, and surface mass loss after freeze-thaw durability tests. Microstructural analyses using SEM explained the observed macroscopic behaviour. The results demonstrate that the combined incorporation of CF, MW, and CA leads to a denser cement matrix, reducing structural damage under cyclic freeze-thaw cycling. The crystallizing additive increased density and UPV values, indicating improved internal density, while the fibre-metakaolin system modified pore structure and crack-resistance behavior. The findings confirm the potential of metakaolin waste use in fibre-reinforced concrete and highlight the combined effect of waste-based pozzolanic material, fibres, and crystallization processes in improving durability.