New insights on rheology, durability and mechanical and thermal properties of polyester and steel fiber-reinforced self-compacting concretes

Self-compacting concrete improves fresh-state fluidity while maintaining mechanical properties, and presents an increasing research interest in fiber incorporation. However, the effects of fibers on rheological behavior and durability remain insufficiently studied in existing literature. This study provides new insights on the effect of polyester and steel fibers on the rheological, mechanical, durability, microstructural, and thermal properties of SCC. Nine different mixtures were studied: one reference SCC (without fibers), four SCC incorporating steel fibers, and four other mixtures incorporating polyester fibers. The four percentages studied for each fiber type were 0.25%, 0.5%, 0.75%, and 1%. The results showed that whatever their type, adding fibers reduces workability while improving compressive strength of SCC. Incorporating 1% of steel fibers increased flexural strength of SCC by 97%, whereas polyester fibers had no significant effect. In terms of durability, adding fibers increased SCC porosity but reduced its sorptivity. For instance, adding 1% of polyester fibers increased porosity by 9.5% whilst reducing sorptivity of SCC by 23% compared to the reference one. Polyester fibers also improved SCC thermal conductivity, whereas steel fibers had an inverse effect. An inverse proportionality between plastic viscosity and sorptivity was identified, highlighting the importance of plastic viscosity in influencing the transport properties of hardened SCC. Based on these findings, it is recommended that careful attention should be taken on the change of both rheological and transport properties when incorporating a given percentage of fibers into SCC.