Ceramics-Silikáty 69, (3) 457 - 468 (2025)

This study analyses the effects of pozzolanic waste on the properties and structure of cellulose fibre-modified hardened cement pastes. Twelve cement paste batches were prepared for the tests: one reference batch containing 1% of cellulose fibre, six batches containing 1% of cellulose fibre and 2%-12% of metakaolin waste replacing the cement by weight, and five batches containing 1% of cellulose fibre and 1%-5% of silica fume replacing the cement by weight. The modification of the hardened cement paste with cellulose fibre revealed the better integration of cellulose fibres into the cement paste when part of the cement is replaced with metakaolin rather than silica fume. The density, ultrasonic pulse velocity, compressive and flexural strength of the hardened cement paste samples modified with metakaolin waste are 0.4–1.4% and 12.5% higher than those of the specimens modified with silica fume. Thus, the optimum amount of cement replacement by metakaolin in the hardened cement paste with 1% cellulose fibre is 8%, and the optimum amount of cement replacement by silica fume in the hardened cement paste with 1% cellulose fibre is 2%. This type of cement paste can be used in the production of concrete.